Headwater streams are critical for global biogeochemical cycles, transporting and retaining large amounts of carbon (C), nitrogen (N) and phosphorus (P). However, global element fluxes within headwater fluvial networks remain poorly constrained, partially due to the extreme spatial variability in water chemistry. Here, we assessed how confluences shape C, N and P concentrations and major biogeochemical fluxes along Mediterranean fluvial networks. We hypothesized that confluences act as biogeochemical hotspots because lateral inflows can supply limiting resources to the receiving streams. To test this hypothesis, we conducted synoptic surveys in fall 2024 across three Mediterranean headwater fluvial networks within the Tordera basin (Catalonia). We measured organic and inorganic C, N and P concentrations every 50 meters along the mainstem as well as in major lateral inflows, including permanent tributaries, intermittent tributaries and preferential groundwater flowpaths. Further, we performed laboratory incubations to assess changes in heterotrophic activity, C degradation and nutrient uptake between sites located upstream and downstream of major confluences. Preliminary results show that C:N:P ratios varied across streams (from 483:2:1 to 818:58:1), suggesting that stream biota was limited by either N, P or both. Further, confluences shaped element concentrations along the mainstem by either diluting element concentrations (mixing effect) or delivering limiting nutrients that enhanced biogeochemical activity (reactor effect). Overall, these findings underscore the role of confluences as biogeochemical hotspots and highlight their importance for regulating water chemistry and element fluxes within stream networks.
How to cite: Lupon, A., Peñarroya, X., Jativa, C., Xinyue, Z., Martí, E., Catalán, N., Rodellas, V., Bernal, S., Rocher-Ros, G., Poblador, S., Merbt, S., and Olid, C.: Confluences act as biogeochemical hot spots in Mediterranean stream networks, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8520, https://doi.org/10.5194/egusphere-egu25-8520, 2025.
High-frequency nitrate-N () data are increasingly available, while accurate assessments of the importance of in-stream retention processes is deviating stream orders are still unclear. In this presentation we hypothesize that similar diurnal nitrate uptake pattern exists in different stream orders and that these patterns can reveal insights into the dominance of uptake processes across stream scales. To test this assumption continuous 15-min estimates of retention was derived in a 1st stream and a 6th-order reach of the lower Bode River network (27.4 km, central Germany) using a one station method for the 1st order agricultural headwater stream and a two-station approach for the 6th order stream applying a data fusion framework capturing river hydraulics and their impacts on solute signal propagation through river hydrodynamic modelling (Yang et al. 2023). This methodological setting was used for long-term sensor monitoring data from 2015-2023 capturing highly deviating hydrological (normal and drought) and stream morphological conditions. The unique retention estimates revealed very similar characteristic diurnal variation of retention pattern. Three very similar clusters of diel uptake patterns were identified in both streams, potentially representing changes in dominant autotrophic and heterotrophic retention processes. While the dominating N-uptake clusters were similar in both systems, their seasonal occurrence showed significant differences between the two streams. For example, clusters reflecting assimilatory N-uptake dominated in the 1st order stream in all years and seasons. In the 6th order reach autotrophy-characterized clusters mostly occurred during early seasons, which are then followed by a shift to heterotrophic-dominated uptake pattern during summer- autumn low-flow periods. In addition, dominance of autotrophic retention extended more widely across seasons during the drought years. In contrast, the 1st order stream showed relevance of both autotrophic and heterotrophic uptake even in the winter month due to the stimulation by elevated spring water temperature. The analysis of characteristic uptake clusters and the suggested framework can be flexibly transferred across sites and scales, thereby complementing high-frequency monitoring to identify in-stream uptake processes and to inform river management.
Reference
Yang, X., Zhang, X., Graeber, D., Hensley, R., Jarvie, H., Lorke, A., Borchardt, D., Lif, Q., Rode, M. (2023) Large-stream nitrate retention patterns shift during droughts: Seasonal to sub-daily insights from high-frequency data-model fusion. Water Research, 243, 120347.
How to cite: Rode, M., Yang, X., Zhang, X., and Shawon, S.: Similar pattern of diurnal nitrate retention in different stream orders: seasonal to sub-daily insights from high-frequency data, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8876, https://doi.org/10.5194/egusphere-egu25-8876, 2025.
Over the past two decades, there has been a notable advancement in the development of high-frequency measuring equipment for the monitoring of biophysical and chemical parameters in surface water. Optical probes, especially fluorescence probes, are of particular importance in the integration of high-frequency measurements into environmental monitoring. The joint development of the Fluocopée® probe by LEESU and SIAAP represents a further contribution to this dynamic. This innovative fluorescence probe is capable of monitoring temporal evolution of 25 fluorophores in situ at high frequency (every 15 minutes), thereby enabling the characterization of dissolved organic matter (DOM). The extensive range of fluorophores monitored by the Fluocopée® probe facilitates the monitoring of water quality and the investigation of the biogeochemical processes linked to DOM in aquatic environments. Furthermore, its sensitivity is compatible with the levels of OM concentration observed in continental aquatic environments.
Since October 2023, several Fluocopée® probes have been implemented on the river Seine and its two main tributaries (the Marne and Oise rivers) at six sites upstream and downstream of the Paris conurbation (see Figure 1). This allows us to assess the spatial variability of organic matter in the river Seine across the Paris conurbation at a high temporal frequency and provides a valuable opportunity to enhance our comprehension of the organic matter biogeochemical dynamics in the river Seine as well as to assess the impact of urban pressures. The installation of Fluocopée® probes at sites already equipped (as part of the MeSeine monitoring system or drinking water treatment plants intakes) with numerous measuring devices has been shown to facilitate the interpretation of fluorescence data by providing supplementary information from the chronicles of other physicochemical parameters (pH, turbidity, dissolved O2, TSS, Abs254nm, fecal indicator bacteria etc.).
Furthermore, proxies for determining dissolved organic carbon (DOC) and its biodegradable fraction on the basis of fluorescence measurements have been developed in our laboratory. The development of these models was achieved by identifying the most suitable existing correlation between these physiochemical parameters and fluorescence measurements using various statistical algorithms (e.g., multilinear regressions, partial least squares regressions, machine learning algorithms, etc.). Used in association with Fluocopée®, these proxies provide estimation of these parameters at high frequency in addition to fluorescence measurements.
The fluorescence, DOC and biodegradable DOC concentration measurements acquired at high frequency over a year using our monitoring system will be presented and discussed. The influence of the hydroclimatic situation and the impact of urban pressures on the organic matter dynamics in the Seine across Paris Conurbation will be assessed. Additionally, it will provide a detailed account of the methodology employed to process these data sets, from the initial acquisition of raw data to its subsequent validation.
Figure 1 : Implantation of Fluocopée® probes
How to cite: Raoult, A., Goffin, A., Raymond, V., Desbourdes, F., Yilmaz, M., Krimou, R., Mougin, J., Guérin-Rechdaoui, S., Rocher, V., Thibert, S., and Varrault, G.: Fluocopée® probe deployment in the Seine river (France): Towards high-frequency in situ monitoring of aquatic environments using fluorescence spectrometry, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17878, https://doi.org/10.5194/egusphere-egu25-17878, 2025.
Heterotrophic bacteria can contribute to improve stream water quality by taking up nitrate (NO3-) from the water column, although microbial demand for this nutrient is usually lower than for other inorganic nitrogen (N) forms, such as ammonium. Heterotrophic NO3- uptake has been related to the availability of dissolved organic carbon (DOC) relative to nutrients (i.e., DOC:nutrients ratios). Yet, how dissolved organic matter (DOM) composition and specific microbial assemblages influence NO3- uptake remains poorly understood. We conducted laboratory incubations to investigate heterotrophic NO3- uptake kinetics in 9 Mediterranean freshwater ecosystems, primarily headwater streams, exhibiting wide variation in DOC:NO3 ratios (from 1.5 to 750). Moreover, we characterized DOM composition using spectroscopic indexes and its degradation via a Reactivity Continuum model approach. Microbial community composition and functioning were assessed by analysing extracellular enzymatic activities and the potential abundance of N-cycling genes. Our results revealed that NO3- uptake rates (kNO3) were positively related with DOC:NO3 ratios (r2 = 0.4) and to NO3:SRP ratios as well (r2 = 0.6). Furthermore, kNO3 was negatively correlated to the humification index (r2= 0.7), suggesting that a higher proportion of humic-like compounds slow down heterotrophic NO3- uptake. A partial least squares regression model (PLS) pinpointed that DOC and nutrient stoichiometry, DOM composition and reactivity, and microbial composition and activity collectively contributed to explain the variability in kNO3 observed across treatments. Our findings suggest that heterotrophic NO3- uptake may show significant responsiveness to shifts towards more labile DOM sources and nutrient imbalances induced by global change.
How to cite: Peñarroya, X., Catalán, N., Freixa, A., Lupon, A., Triadó-Margarit, X., Martí, E., Soler, M., O. Casamayor, E., and Bernal, S.: Organic matter composition and water stoichiometry are main drivers of heterotrophic nitrate uptake in Mediterranean headwater streams., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4249, https://doi.org/10.5194/egusphere-egu25-4249, 2025.
Sediment phosphorus release, also referred to as internal loading, typically delays the response of eutrophic waters to reductions in external nutrient inputs. Internal loading is particularly relevant in shallow waterbodies like floodplain lakes with high sediment-to-water ratios. Traditionally, sediment phosphorus release has largely been explained by the biogeochemical interactions of iron, phosphorus, and oxygen. However, in sediments with a limited availability of iron but high organic content, the direct release of phosphorus from microbial mineralisation is the major mechanism behind internal loading. This is particularly the case in floodplains where benthic microbial functional diversity and corresponding activity play a pivotal role in sediment phosphorus release. Lateral hydrological connectivity further modulates sediment nutrient fluxes and microbial processes by altering biogeochemical conditions. Although the importance of microbe-organic matter interactions for phosphorus dynamics has been recognised, they are often not considered when assessing sediment phosphorus release.
Here, we analyse the trajectory of potential sediment phosphorus release as well as dissolved carbon and nitrogen concentrations along a river-floodplain gradient of the River Elbe (Germany) from April to September 2024. Specifically, we link the dynamics of nutrients to dissolved organic matter quality and quantity, extracellular enzyme release, metabolic carbon diversity and further sediment biogeochemical parameters. Our findings reveal a general decrease in dissolved phosphorus concentrations from the river to the floodplain backwaters. However, in the periodically disconnected waterbody, we observed unexpectedly high soluble reactive phosphorus concentrations (~0.5 mg L⁻¹) following hydrological isolation, coinciding with elevated benthic extracellular phosphatase and β-glucosidase activity. Further linkages between the prevalent dissolved organic matter components, microbial mineralisation and microbial functional diversity were analysed and will be presented. Our results contribute to the mechanistic understanding of how microbial mineralisation processes modulated by hydrological connectivity shape sediment phosphorus release in river-floodplain systems.
How to cite: Meyer, M., Koschorreck, M., Weitere, M., Graeber, D., Kneis, D., and Perujo, N.: Microbial control of sediment phosphorus release along a river-floodplain gradient, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13396, https://doi.org/10.5194/egusphere-egu25-13396, 2025.
Subalpine lakes are highly sensitive ecosystems that respond rapidly to variations in temperature, precipitation, and hydrological inputs triggered by climate change. These lakes are typically oligotrophic, and the availability of nutrients is highly dependent on nutrient loads with rainfall and runoff and further controlled by in-catchment processes. Altered precipitation patterns, rising (water) temperatures, and ice- and snow-free winters can significantly impact these ecosystems' water balance, stratification, and nutrient dynamics. Understanding these processes is critical, as small environmental changes can affect their biogeochemical cycles and biological communities. Although the effects of warming on subalpine lakes are recognized, the magnitude by which climate change impacts the water balance and nutrient dynamics in these ecosystems remains uncertain. Moreover, subalpine lakes, as part of the headwater catchment, impact water and nutrient availability downstream. In this context, water stable isotopes provide essential insights into the hydrological processes, helping to understand the water balance and mixing processes of lakes. Long-term data from subalpine Lake Lunz, Austria, indicate a decrease in nitrate concentrations (N−NO3−) during the past decade. This study investigates the spatiotemporal patterns of N−NO3− and stable water isotopes (δ18O−H2O and δ2H−H2O) during two hydrometeorological cycles. Samples were collected monthly from the inflow, outflow, epi-, meta-, and hypolimnion of the lake. Preliminary results showed that precipitation and snowmelt during spring significantly influenced lake water levels and nitrate inputs. Stable water isotope analyses revealed seasonal isotopic stratification, with higher values of δ18O−H2O in the epilimnion during summer following an isotopically enriched signal from the catchment. The hypolimnion exhibited stable isotopic values of water with minimal variation, suggesting limited vertical mixing. Nitrate concentrations in the inflow and the epilimnion were higher in winter and spring, coinciding with depleted isotopic values from the water molecule and suggesting snow melt as an essential source of N−NO3−. On the other hand, the hypolimnion showed increased nitrate concentrations as stratification persisted and dissolved oxygen levels declined, possibly due to remineralization of organic matter from the thick layer of fine sediment at the bottom of the lake. These findings indicate the need to study the sensitivity of lake nutrient dynamics to variations in hydrological inputs during climate change.
How to cite: Machado, D. V., Harjung, A., Vystavna, Y., Terzer-Wassmuth, S., Kainz, M. J., and Wassenaar, L.: Changing precipitation patterns affect nitrate input to and subsequent cycling in a subalpine lake, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16543, https://doi.org/10.5194/egusphere-egu25-16543, 2025.
The exchange of gas across the interface between rivers and the atmosphere is a key control of oxygen and carbon fluxes (in the form of carbon dioxide and/or methane) in rivers and streams. The intensity of gas exchange is measured by the gas transfer velocity, k, a parameter expressing the efficiency of sub-surface mixing driven by turbulence in water. Scaled experiments and theoretical analysis both suggest a significant shift in the drivers of k depending on the relative submergence, i.e., the ratio between water depth H and the characteristic bed roughness scale, D: In high-submergence (deep) rivers, turbulent mixing is dominated by viscous forces, while in low-submergence (shallow) rivers by form drag due to protruding bed roughness elements. However, the bed roughness scale is not usually reported in field gas transfer datasets and the effects of submergence are neglected by existing models.
We conducted a meta-analysis of the largest known dataset of gas transfer velocity and hydraulic flow parameters to investigate the potential role of submergence on gas transfer in the field, estimating the relative submergence according to the observed flow resistance through an established semi-empirical variable-power relation. Then, we used the same model to partition the gas transfer velocity into its friction (high submergence) and macro-roughness (low submergence) constituents. The results indicate that 93% of data was recorded in low-submergence streams and rivers (partition coefficient > 0.5). Such skewness in the data distribution is explained by the difficulty in measuring the gas transfer velocity in large rivers using existing methods. Due to the different physical mechanisms governing gas exchange, widely used semi-empirical models calibrated in shallow rivers may overestimate k in deep rivers. Since large rivers contribute around 50% of global riverine CO2 emissions, the impact on global emissions uncertainties may be significant. Ultimately, our results highlight the urgent need for improved measurement approaches to characterise the gas transfer velocities in large rivers, and the importance of introducing systematic quantitative riverbed surveying into gas exchange measurement protocols.
How to cite: Dolcetti, G. and Siviglia, A.: Predictions of riverine gas exchange rates may be biased towards low-submergence rivers, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6612, https://doi.org/10.5194/egusphere-egu25-6612, 2025.
Global atmospheric methane (CH4) emissions have risen significantly, tripling in atmospheric concentrations since preindustrial times. Wetlands, as the largest natural source of CH4 emissions, contribute significantly to the global CH4 budget. However, quantifying wetland CH4 emissions remains highly uncertain due to the complex interplay of hydrological and biogeochemical processes. In this study, we develop a random forest (RF) and SHapley Additive exPlanations (SHAP) framework to identify the main predictors of CH4 emissions across different climate zones and on a global scale. We used monthly global environmental variables and CH4 flux emissions from FLUXNET-CH4 dataset, incorporating 39 wetland sites over the globe. These sites are classified into tropical, temperate, and boreal regions by latitude. Key variables considered in the analysis included mineral-associated organic carbon, soil organic carbon, soil moisture, and canopy height. Our findings reveal that air temperature and latent heat are the most important predictors of CH4 at both global and regional scale. Regionally, tropical wetlands are primarily influenced by canopy height, water table level and soil organic carbon while soil temperature emerges as the dominant driver in temperate and boreal wetlands. Furthermore, we analyze the similarities and differences in CH4 predictors across climate zones to improve our understanding of regional and global wetlands CH4 dynamics. Understanding the main predictors of CH4 emissions across wetland regions is essential for improving CH4 budget accuracy on both regional and global scales.
How to cite: Rivas Pozo, E. and Kim, Y.: Identifying the main drivers of methane flux in wetlands using machine learning and FLUXNET data across climate zones, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15443, https://doi.org/10.5194/egusphere-egu25-15443, 2025.
Urban stormwater ponds (SWPs) are a common runoff control measure that can also have beneficial outcomes for water quality. However, pond emissions of greenhouse gases (GHGs), such as carbon dioxide (CO2) and methane (CH4), raise questions about the climate impact of SWPs. Here, we establish whole-system annual carbon budgets for two SWPs in the City of Kitchener, Ontario, Canada, to compare the open water CO2 and CH4 effluxes to other input and output fluxes of carbon. These include the fluxes of particulate and dissolved inorganic and organic carbon at the inlet and outlet points of the pond, plus those associated with the sediments accumulating in the ponds. In both SWPs, the open-water effluxes of CO2 and CH4 are small compared to the inflow, outflow, and burial carbon fluxes. The SWP sediment budgets further imply that a large fraction of the sediment accumulating in the ponds is supplied by erosion of the embankment. The accompanying delivery of soil organic matter, together with direct litter and organic detritus inputs from the vegetation surrounding the pond, serves as an important source of the open-water CO2 and CH4 emissions. The latter are therefore largely derived from atmospheric CO2 fixed by the ponds’ littoral and embankment vegetation. Consequently, although the SWPs open waters emit CO2 and CH4, the entire SWP engineered systems, including the embankment, act as net CO2 sinks. Overall, our results point to the potential to design and manage SWPs for enhanced climate change mitigation.
How to cite: Slowinski, S., Zhou, D., Radosavljevic, J., Bova, C., Weatherson, H., Sabur, M. A., Zhou, B., Rezanezhad, F., and Van Cappellen, P.: On why the embankment matters when assessing greenhouse gas emissions from urban stormwater ponds, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14627, https://doi.org/10.5194/egusphere-egu25-14627, 2025.
The Land-Ocean Aquatic Continuum (LOAC) plays a pivotal role in the transfer and transformation of carbon and nutrients from terrestrial systems to coastal waters, critically influencing coastal eutrophication resulting from excessive nitrogen (N) and phosphorus (P) loads from rivers compared to Silica (Si). Indeed, both agricultural practices on land and biogeochemical processes in and near streams as well as within estuaries control the eventual export of carbon and nutrients into the coastal sea. To address the complex interplay of biogeochemical processes that govern these transfers, an integrated modeling approach combining agricultural practices (GRAFS, an agri-food system model), river network and wetland processes (pyNuts-Riverstrahler modelling framework), and estuarine dynamics (C-GEM model) was applied across metropolitan France over the 2014–2019 period. The estuarine dynamics were modelled only where relevant, on 40 macro-tidal estuaries along the French Atlantic coast. This comprehensive framework explicitly quantifies the cascading fluxes of Dissolved Organic Carbon (DOC), and different forms of N, P and Si from headwaters to estuarine outlets. In addition, three different scenarios of agricultural practices modulating N diffuse inputs were designed and applied ranging from ‘business as usual’ to a switch towards ‘agroecology’. The modeling chain described above was applied to all watersheds larger than 300 km2 (n = 80) using reference conditions representative of the 2014-2019 period and validated by an extensive riverine database of 392,870 measurements from 929 stations.
This integrated approach allows quantifying potential excess in nutrient export into the coastal seas compared to Redfield ratios between N, P and Si. Our simulations reveal that even under the most optimistic trajectories of nutrient reduction from agricultural practices, some coastal regions such as those flowing into the Celtic Sea will still experience nutrients exports above admissible values, despite in and near streams processes in rivers and estuaries typically removing 20-60% of the nutrient inputs from the land. Our results thus highlight the need for an integrated approach of nutrient management strategies encompassing terrestrial ecosystems, inland and coastal waters. Such an approach is needed to evaluate how these management strategies can help achieve sustainable water quality thresholds across the interconnected aquatic ecosystems of the LOAC.
How to cite: Laruelle, G. G., Casquin, A., Thieu, V., Silvestre, M., Capet, A., and Regnier, P.: Towards sustainable nutrient management along the Land-Sea continuum, an integrated modeling perspective, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13368, https://doi.org/10.5194/egusphere-egu25-13368, 2025.
Stormwater ponds (SWPs) are a common stormwater management technology in new urban developments and have been suggested to be significant sources of the greenhouse gases (GHGs) carbon dioxide (CO2) and methane (CH4). However, they also sequester organic carbon and reduce the surface runoff of nutrients, hence, altering nutrient limitation patterns, trophic conditions, and GHG exchanges. Although numerous studies have focused on estimating open water GHG emissions in artificial ponds, there are limited studies that evaluate net carbon budgets of urban SWP systems comprehensively. In this study, we assessed the relative contributions of the littoral vegetation and open water GHG fluxes to the carbon budgets in two SWPs located in the City of Kitchener, Ontario, Canada. CO2 and CH4 fluxes were measured in the forebay and main basin of two SWPs draining catchments with two different catchment land use (residential versus industrial). Using vegetation and floating chambers, CO2 and CH4 fluxes were measured bi-weekly across all seasons, capturing Net Ecosystem Exchange (NEE), Ecosystem Respiration (ER), and Gross Ecosystem Production (GEP) from both bank and submerged vegetation, plus the diffusive and ebullitive fluxes from the open water surface. Additionally, key parameters, including photosynthetically active radiation (PAR), air and soil temperature, water pH, conductivity, and dissolved gas concentrations, were also measured. We observed significant differences in the fluxes between the littoral vegetation and open water surfaces. Carbon gas emissions from the open water surface were dominated by ebullitive CH₄ fluxes, with the open water acting as a net carbon source. Ebullition events occurred more frequently and with greater intensity in the forebay areas of the SWPs, contributing the most to open water carbon emissions. In contrast, carbon gas emissions from the vegetation were largely driven by photosynthesis and soil respiration, with the vegetated littoral zone functioning as a net CO2 sink. Different vegetation types exhibited varied responses to meteorological conditions, but all showed clear seasonal trends, with higher gas fluxes in summer due to increased biological activity, and minimal fluxes during the frozen season. Unlike vegetation, open water fluxes did not display a distinct seasonal trend; instead, they were primarily influenced by precipitation events and inflow runoff. The forebay of the industrial pond received higher carbon inputs from contaminated stormwater runoff, leading to greater sediment accumulation and elevated GHG fluxes, with frequent and high-intensity CH4 ebullition events being a notable feature. Our findings highlight the critical influence of land use, hydrological events, and seasonal cycles on the carbon balance of SWPs and their potential role in urban carbon cycling.
How to cite: Zhou, D., Rezanezhad, F., Slowinski, S., Radosavljevic, J., and Van Cappellen, P.: The Role of Littoral Vegetation and Open Water Greenhouse Gas Fluxes on the Carbon Budget of Urban Stormwater Ponds, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13098, https://doi.org/10.5194/egusphere-egu25-13098, 2025.
Despite far-reaching legal regulations and extensive management measures, nitrogen and phosphorus are still elevated in many river systems causing the degradation of ecosystems and the failure to achieve good ecological status following the EU-WFD. Our study analyzes the long-term change in nitrogen surpluses, and quantifies the denitrification rates as well as the residence time in soil and groundwater. The goal is to assess the effect and the time lag of management measures and to evaluate the achievability of environmental goals, e.g. EU-WFD or EU-MSFD.
The calculations were carried out with a completely revised version of the widely applied nutrient emission model “MONERIS” with a resolution of 1 km x 1 km on a monthly basis from 2003 to 2020 for all German rivers including their hydrologically connected catchment areas in neighboring countries. The runoff and residence times were modeled using an integrated precipitation-runoff model and the retention processes in soil and groundwater were calculated via a coupled three-layer denitrification module, based on soil characteristics such as pH, soil texture, soil temperature, leakage water concentration. The effect of oxygen-reduced conditions in soils is represented by the water saturation.
The residence time in the soil ranges usually between a few days and a month, with local peaks of up to several months. The residence time in groundwater shows strong spatial variations. It ranges between less than 5 years and more than 100 years, however, for the N-balance history, a maximum of 50 years was taken into account. Although longer residence times generally lead to higher total denitrification, the rates are strongly controlled by local site characteristics such as pH value, N leachate concentration and soil texture.
Due to the highly variable denitrification rates (< 1 – 92 kg/ha/yr, mean 44.1 kg/ha/yr), nitrogen emissions vary despite resulting from similar N surpluses. However, the proportions of the emission pathways surface runoff, interflow, and groundwater determined both the total emissions due to different denitrification rates as well as the resulting average lag time between fertilizer application and nutrients entering a surface water. Locally, the total residence time as mean over all pathways is determined by the proportions of runoff components and the respective residence times involved. Whereas areas with a high proportion of direct runoff and sealed urban areas react within months or even days, the lag time in surface waters results as a runoff-weighted average of local residence time in its upstream reaches.
The management to reach environmental quality goals and the need to rapidly reduce N surpluses and N concentrations in surface waters require comprehensible links between reduction measures and their effects on concentrations in surface waters. Our results indicate that the efficiency of measures to reduce nutrient concentrations in surface waters should not be assessed solely on the basis of the quantitative reduction potential, but also taking into account the time component. This also opens up the possibility of achieving a higher level of acceptance among the public and politicians if the time delays are known and considered during implementation.
How to cite: Venohr, M. and Oprei, A.: Implications of nitrogen legacy on the effectiveness of management measures in central European river catchments, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21186, https://doi.org/10.5194/egusphere-egu25-21186, 2025.
Draining land from excess water is a common practice in forestry to accelerate tree growth, but it has significant environmental implications, particularly in the case of peatland forests. Drainage exposes nutrient-rich peat soils to oxygen, triggering peat decomposition and mineralization, which leads to increased CO2 emissions from the soil and the leaching of solids, organic matter, and nutrients to water. While accelerated tree growth may partially offset CO2emissions, unmanaged drainage ditches are possible hotspots for greenhouse gas (GHG) emissions.
This preliminary study monitors water quality and quantity, and GHG emissions in unmanaged ditches of four sub-catchments of a 507.6 ha peatland forest drainage system in western Estonia. Ditch reconstruction works will be done in the summer of 2025. To mitigate the negative impacts, ecological water protection measures - sedimentation ponds and hybrid systems combining ponds with treatment wetlands, are used. From July 2022, once per month, water temperature, dissolved oxygen content, electrical conductivity, pH, redox potential, and turbidity are measured onsite from ditches entering mitigation measures. From grab samples total suspended solids (TSS), total inorganic carbon, total organic carbon (TOC), dissolved organic carbon, total phosphorus (TP), phosphate-phosphorus, total nitrogen (TN), nitrite-nitrogen, nitrate-nitrogen, ammonium, sulfate, magnesium, calcium, chlorides, and total iron are analyzed in the laboratory. Flow rates monitored from the outflows of mitigation measures with V-weirs combined with automated water level loggers are the basis for the estimation of potential sediment and nutrient loads. From April 2023, monthly CH4 and CO2 fluxes were measured on four 0.6 km sections of unmanaged ditches entering mitigation measures with a floating chamber and portable LI-7810 trace gas analyzer. In addition, an extensive random mapping of GHG emissions from unmanaged ditches of the whole drainage system was conducted in May 2024.
The median concentration (range presented in parenthesis) of TSS 10.0 (2.0-200), TOC 53.0 (28-81), TP was 0.032 (0.012-0.281), and TN 2.70 (0.78-14.0) mg L-1 are indicating that the studied ditches are a source of diffused water pollution, foremost for phosphorus.
The median CH4 and CO2 flux emissions from unmanaged ditches entering mitigation measures were 0.30 (0.01-69.39) mg CH4-C m-2h-1 and 31.02 (0.39-644.38) mg CO2-C m-2h-1, respectively. The mapping resulted with median CH4 and CO2emissions of 1.40 (0.06-70.25, n=33) mg CH4-C m-2h-1 and 30.30 (-64.46-100.14, n=23) mg CO2-C m-2h-1. GHG emissions from unmanaged ditches show high seasonal variability, high emissions in summer, and relatively low mean emissions during autumn and spring.
The performed monitoring gives unique information about the water quality and quantity, and GHG emissions in unmanaged ditches. This background data is the main input for evaluating the impact of reconstruction works of peatland forest ditches and the performance of mitigation measures.
How to cite: Sarjas, J., Kõiv-Vainik, M., Yildiz, K., Okiti, I., Tamm, I., Pindus, M., and Kasak, K.: Water quality and greenhouse gas emissions from degraded forest drainage ditches on peat soil , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13121, https://doi.org/10.5194/egusphere-egu25-13121, 2025.
Protecting wetlands from various human activities requires a deep understanding of their aquatic limnology. This calls for continuous monitoring, which generates extensive and complex datasets. By applying statistical analyses and modelling techniques, these datasets can be effectively interpreted to uncover, define, and gain critical insights into the functions and processes that drive aquatic ecosystems. The present study aims to integrate water quality, sedimentology, aquatic toxicology and modelling techniques to present a detailed and comprehensive assessment of different components of Deepor Beel's (a Ramsar site) ecosystem. Deepor Beel is situated on the banks of the Brahmaputra River in the northeastern region of India and holds immense significance to the city of Guwahati. Originally spanning across more than 40 sq. km area, rampant encroachment and anthropogenic disturbances have not only degraded the wetland ecosystem but also reduced its effective area to now a meagre four sq. km. Large-scale eutrophication due to the discharge of untreated municipal wastewater has played a significant role in the wetland's deterioration. Although several restoration measures were undertaken in the past, they could have been more effective as they lacked prognosis. Hence, we carried out systematic monitoring (the first such extensive monitoring was undertaken) of four components of Deepor Beel's ecosystem, i.e., water, sediment, fish, and aquatic weeds, to understand the governing factors responsible for the wetland's deterioration. We employed different multivariate statistical techniques to understand the sampling site's characterization and behaviour under various environmental and climatic stresses and identify and quantify latent pollution sources contributing to wetland pollution. In addition, a novel water quality index was developed employing Shannon Entropy, which encompasses all essential variables for a comprehensive understanding of the wetland's water quality. We assessed sediment contamination from heavy metals—including chromium (Cr), cadmium (Cd), iron (Fe), manganese (Mn), copper (Cu), lead (Pb), and mercury (Hg)—and conducted fractionation studies, revealing important insights into how these metals interact within the ecosystem. Fish samples from three indigenous species that are locally consumed were collected, and we analyzed the bioaccumulation of heavy metals in various tissues and organs. Our findings indicated significant amounts of heavy metals in the fish organs, making their consumption potentially carcinogenic for humans. Finally, a eutrophication-based ecological model was developed to understand the nutrient dynamics within the wetland. The model was calibrated, and sensitivity analyses were performed and validated using the dataset generated through the laboratory analyses. The model was then simulated for two scenarios: 1) harvesting of aquatic weeds reflecting the current practices, and 2) establishing a treatment unit handling the nitrogen and phosphorus loadings. The results demonstrated that treating the inflow is a more sustainable approach to reducing eutrophication, and this strategy should be implemented promptly. Given the gravity of the situation for Deepor Beel, the findings of this study are significant and call for immediate attention and action.
How to cite: Dash, S. and Gupta, P.: Understanding the governing dynamics and trade-offs between heavy metals and nutrients in heavily contaminated wetlands, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-656, https://doi.org/10.5194/egusphere-egu25-656, 2025.
River damming has altered riverine biogeochemical cycles, yet we still lack a mechanistic understanding of how modified hydrodynamic conditions reshape mainstream-tributary ecosystems, particularly the coupling between physicochemistry processes and phytoplankton functional groups in channel-type reservoirs. Here, through high-frequency sampling and multidimensional analysis of the Xiangjiaba Reservoir in the upper Yangtze River, China, we explored spatial heterogeneity of tributary ecosystems and its underlying mechanisms. Distinct spatial patterns emerged - while maintaining strong connectivity between mainstream and tributaries (connectivity index: 0.85), the inter-tributary connectivity remained notably weak (0.26-0.34). Intriguingly, adjacent tributaries (Xining and Zhongdu Rivers) developed markedly different ecological characteristics, whereas geographically distant tributaries (Zhongdu and Dawenxi Rivers) displayed unexpected ecological convergence, challenging conventional spatial distance-ecological similarity paradigms. This spatial heterogeneity was reflected in both biogeochemical processes and phytoplankton functional groups: restricted water exchange in tributaries may promote nutrient accumulation (TN: 1.35-1.45 mg/L), leading to distinct shifts in functional group composition (ρ = 0.574, p < 0.001). We identified a critical threshold in relative water column stability (RWCS = 5.111/m) beyond which bloom-forming functional groups became dominant. Temporal analysis revealed synchronized patterns where tributary algal biomass peaked when system connectivity reached its minimum (0.30) in May, highlighting the cascading effects from hydrodynamics to ecosystem functions. These findings provide fresh perspectives on tributary ecosystem heterogeneity in regulated rivers, with important implications for reservoir management under global change.
How to cite: Wang, X. and Sun, J.: Spatial heterogeneity of tributary ecosystems in a channel-type reservoir: Linking physicochemistry to phytoplankton functional groups, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14379, https://doi.org/10.5194/egusphere-egu25-14379, 2025.
Brazil has 1,320 hydroelectric plants in operation, distributed throughout its territory. The construction of dams for water storage and energy generation causes significant changes in sediment transport and hydrological dynamics, affecting the biogeochemical cycle of various elements. In the Southeast region, the Paraíba do Sul River Basin (PSR) accounts for approximately 6% of these plants, making it a strategic area for studying the environmental impacts associated with reservoirs. To assess the impacts on physicochemical and elemental dynamics (i.e., Dissolved Oxygen “dO2”, pH, turbidity, dissolved Fe, and total Mn), this study analyzed three years (2021–2023) of water quality monitoring data along the main course of the river, covering four dams with different operational systems (Santa Branca and Funil: storage; Lavrinhas and Anta: run-of-river). The dO2 median concentration increased downstream, while turbidity, d-Fe, and t-Mn showed a decreasing trend. On the other hand, pH levels remained relatively stable, with little variation. However, near the dams, a decrease in dO2, pH, turbidity, and d-Fe concentrations was observed immediately downstream of the Santa Branca and Funil dams. Conversely, the Lavrinhas and Anta dams showed little or no influence on these variables. The upper region of the PSR is characterized by intense industrialization, which contributes to the deterioration of water quality variables in this section of the river. The reservoirs in the basin exhibit distinct dynamics, influencing the levels of these variables in different ways. Santa Branca and Funil are larger storage reservoirs with depths ranging from 20 to 40 meters, where intermediate and deep layers have distinct characteristics from surface waters, promoting hydrogeochemical changes at certain times of the year. These waters are generally more acidic and less oxygenated due to the decomposition of organic matter and the respiration of organisms. Additionally, these reservoirs promote particle deposition, contributing to reduced turbidity downstream. These conditions favor the release Fe and Mn from bottom sediments, increasing their dissolved concentrations in the water column. The availability of Fe and Mn, as well as other nutrients, increases the growth of macrophytes and phytoplankton productivity, generating large areas of eutrophication. This process reduces the dissolved fraction of these elements and consequently increases the particulate fraction. On the other hand, Lavrinhas and Anta are run-of-river reservoirs with shallower depths and little to no stratification in the water column, resulting in less significant changes in parameters downstream. However, even in run-of-river reservoirs, depth can influence variable dynamics. This is evident in the case of Anta, which showed an influence on Fe and Mn levels, highlighting that even smaller run-of-river reservoirs can impact the cycles of these elements. In conclusion, long-term studies on these reservoirs are essential, since over the years we have been reporting high concentrations of cyanobacteria with the potential to produce toxins, which has led to interruptions in water supply to the population.
How to cite: Sartori, É., Lacerda, D., dos Santos Vergilio, C., and Eduardo de Rezende, C.: Changes in spatial dissolved Fe and total Mn in a tropical river in Brazil: Influence of reservoirs with different operational dynamics, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11080, https://doi.org/10.5194/egusphere-egu25-11080, 2025.
Stream metabolism is a fundamental ecosystem function that includes gross primary productivity (GPP) and ecosystem respiration (ER). These processes measure the energy supply and consumption in the aquatic system and are the basis for the green and brown food webs. Because of their sensitivity to environmental stressors, they are important in aquatic ecosystem management as functional indicators of the ecosystem’s health. They also have the benefit of being an integrative indicator of ecosystem change since they are influenced by multiple factors at different scales. Although the drivers of metabolism in river systems are known, there is great variation in the factors controlling stream metabolism within and between individual river systems due to natural and anthropogenic drivers. Additionally, limiting factors can vary from one system to another, leading to distinct metabolic regimes.
In Uganda's mountainous regions, the interaction between natural factors such as elevation and human-induced disturbances, including deforestation, agriculture and urbanization can cause metabolic patterns to deviate from those predicted for headwater streams. Understanding the drivers of stream metabolism in these anthropogenically impacted ecosystems is therefore crucial for their sustainable management. Considering the increased impact of anthropogenic activities on headwater streams and the general lack of understanding of the drivers of metabolism in these systems, this study examined the drivers of metabolism in anthropogenically disturbed headwater montane streams in western Uganda.
Over 7 months, metabolism and its hypothesised drivers were measured in 11 tropical stream reaches at high elevation. Stepwise regression was used to build models to understand the factors influencing GPP and ER at catchment and local scales. At large scales, stream order, catchment area, and percentage of agriculture and forest cover influenced GPP, while stream order, elevation and the percentage of urban land use influenced ER. Structural equation modelling showed that catchment factors influenced GPP through effects on local drivers such as stream width, ammonia and phosphorous concentrations in sediments, turbidity and canopy cover. On the other hand, the catchment drivers controlled ER through influence on discharge, temperature, phosphorus, and ammonia. Our results suggest that metabolism in mountainous streams is not only affected by anthropogenic activities, but elevation also plays an important role for the observed patterns. The high elevation and steep slopes initiate further sediment-related processes, erosion and sedimentation, influencing metabolism.
How to cite: Nansumbi, F., Weigelhofer, G., Odong, R., and Hein, T.: Drivers of stream metabolism in anthropogenically disturbed mountainous streams of Uganda. , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7457, https://doi.org/10.5194/egusphere-egu25-7457, 2025.
Phosphorus (P) transfer indices (Mobilisation index and Delivery index) were recently introduced to facilitate a standardized, systematic and objective method to evaluate P transfer and impact risks at the catchment scale. The method was developed from high-frequency hydro-chemo-metric data using ratios of high and low percentiles of P concentrations and mass loads. Using a large dataset from 23 catchments in North-western Europe, we present a pooled catchment approach to establish a relationship between the Mobilisation and Delivery indices with the catchments’ baseflow and flashiness indices with the objective to identify catchment P impact risk typologies. While hydrology largely controls P transfer, the deviation from this hydrological relationship highlighted the presence of other influences, such as intrinsic P retention and point source or legacy P controls. The method distinguishes the type of dominating mobilisation and delivery risk (runoff, point source and/or legacy P) and of intrinsic retention (poor solubility and/or poor hydrological connectivity).
The P mobilisation in 12 of the catchments was dominated by hydrological controls. Five other catchments, with large flat areas, high water storage capacity and/or with a high P sorption capacity, had a potential to retain 39% - 68% of reactive P (RP) corresponding to an annual retention of 0.02 - 0.32 kg RP/ha. The highest intrinsic P retention was in a karstic limestone spring contribution zone rich in calcium. Finally, six of the catchments manifested a varying degree of point source influences, which elevated the RP mobilisation by 16% -77% and corresponded to an annual loss of 0.02 – 0.12 kg RP/ha. While hydrological controls dominated P delivery in all catchments, two catchments manifested a P delivery reduced by 72% and 76% due to poor hydrological connectivity (0.02 and 0.12 kg RP/ha per year). Eight catchments had a higher Delivery index in relation to the Mobilisation index, and these catchments were those with above average hydrological flashiness. We propose that these catchments are, to a varying degree, influenced by legacy P (river scouring and/or resuspension of P). This highlights that mobilisation risk could be independent from delivery risk owing to the hydrological connectivity of the landscape.
The proposed approach can guide P pollution management by identifying and quantifying the underlying dominant impact risks within catchments. Identifying catchment typologies based on P risk classes can be further useful for scaling up and for understanding the additional pressures caused by climate and land use changes.
How to cite: Mellander, P.-E., Jordan, P., Cassidy, R., Ezzati, G., Ortega, J., Stutter, M., Bieroza, M., Dupas, R., Collins, A., Adams, R., Hiscock, K., Cooper, R., and Haygarth, P.: A new approach for identifying catchment typologies based on phosphorus impact risks, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10803, https://doi.org/10.5194/egusphere-egu25-10803, 2025.
Benthic foraminifera are a group of protists that inhabit a diverse range of habitats from salt marsh meadows to the deepest sea. Recently, benthic foraminifera have been shown to intracellularly accumulate phosphate. Intracellular phosphate concentrations can be 100-1000 times higher than in the surrounding water. Phosphate is an important macronutrient in marine ecosystems and widely used as an industrial fertilizer, which is potentially leaked to the ocean. We show that phosphate storage in foraminifera is widespread and occurs in diverse environments such as tidal flats, hypoxic fjord basins, oxygen minimum zones and the Mid-Atlantic Ridge. The highest intracellular phosphate concentrations have been found in cells of the species Ammonia confertitesta from the German Wadden Sea. The total amount of intracellular phosphate stored in A. confertitesta in the Wadden Sea during a bloom is as high as ~5% of the annual consumption of phosphorus (P)-fertilizer in Germany. More detailed budget calculations for the Southern North Sea and the Peruvian oxygen minimum zone indicate that benthic foraminifera may buffer riverine P runoff for ~37 days at the Southern North Sea and ~21 days at the Peruvian margin. This indicates that these organisms are likely relevant for marine P-cycling. They potentially buffer anthropogenic eutrophication in coastal environments.
The intracellular phosphate storage seems to have diverse functions. Coupled TEM-EDS and cryo-SEM-EDS was used to map the intracellular phosphorous distribution in cells of the species Ammonia veneta and Bolivina spissa. Phosphorous accumulations were associated with round vesicles, possibly acidocalcisomes that are typically used to store polyphosphates in eukaryotic cells. The metabolic functions of these organelles can range from regulation of osmotic pressure and intracellular pH to calcium and energy storage. Foraminifera encode the genes required for both a polyphosphate, as well as a creatine phosphate metabolism. Creatine phosphate and polyphosphates are good energy carriers that can generate energy, when electron acceptors are depleted. Thus, storage of energetic P-compounds, such as creatine phosphate and polyphosphate, is likely also an adaptation of foraminifera to O2 depletion.
How to cite: Glock, N. and the Foram Phosphate Team: Widespread occurrence of phosphate storage in foraminifera might buffer anthropogenic eutrophication in coastal environments , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16170, https://doi.org/10.5194/egusphere-egu25-16170, 2025.
Seagrasses are marine plants that play a crucial role in climate change mitigation through carbon sequestration. This process relies heavily on nutrients, e.g., phosphorus (P), which is often limiting in marine environments. However, the complex dynamics between seagrasses and P reservoirs remain poorly understood. Moreover, seagrasses are rapidly disappearing worldwide at alarming rates, making it crucial to study their impact on the marine P cycle, particularly in light of their decline. Here, we investigate P speciation in seagrass-influenced sediments, bioavailability, and transformations during seagrasses decomposition. The P distribution within the plant exhibits correlation with elongation as the young leaves contain more P than the old leaves, indicating the plant’s P allocation efficiency. This is further explored in decomposition experiments which reveal that aboveground biomass releases more P than belowground biomass. These findings underscore the critical influence of seagrass on P dynamics amid global seagrass decline.
How to cite: Soto, N., Antler, G., and Gross, A.: The Impact of Seagrasses Disappearance on the Marine Phosphorus Cycle, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10171, https://doi.org/10.5194/egusphere-egu25-10171, 2025.
Ammonia is one of the dominant foraminiferal species in the intertidal zone and the late Quaternary delta stratigraphy, which has been popularly used as a key micropaleontological indicator for the past environment. However, its classification has been battled since 19th century. The development of molecular analysis has shed a new light on the taxonomy and phylogeny of foraminifers over the last several decades.
Ammonia confertitesta Zheng 1978, taxonomically erected and adopted in the microfossil study for the Shangdong peninsula, China, is the most dominant species in the surface sediments of shallow water of the Yellow Sea. This species was reported recently in the European ocean environment (harbor), regarding as a non-indigenous species. Ammonia aomoriensis (Asano, 1951) has also been adopted in some recent publications. For a better understanding of its taxonomy and distribution, in this study, living Ammonia specimens were collected from the muddy sediments at the Haimen inter-tidal zone of the southwestern Yellow Sea, and performed molecular analyses on their SSU rDNA sequences.
A large number of the inter- and intra-specific SSU rDNA sequences were obtained for Ammonia confertitesta specimens of the southwestern Yellow Sea. These sequences were conducted phylogenetic analysis together with other related Ammonia sequences from the GenBank.
The phylogenetic tree shows that Ammonia catesbyana (d'Orbigny, 1839), Ammonia aomoriensis (Asano,1951), Ammonia confertitesta Zheng 1978 and Ammonia sp. T6 (Hayward et al. 2004) form one distinct group (Clade A), and suggests that A. confertitesta, A. catesbyana and A. aomoriensis be synonymous. Ammonia catesbyana, was first reported and described from the shallow waters off Cuba (D'Orbigny, 1839). Therefore, instead of others, we propose that Ammonia catesbyana (D'Orbigny, 1839) be a valid nomination for the distinct group; and the worldwide distribution of Ammonia catesbyana implies that Ammonia confertitesta Zheng 1978 in Europe is probably not a non-indigenous species from the East Asia marine waters.
This work is supported by the CAS Strategic Priority Project (XDB XDB26000000) and the National Natural Science Foundation of China (Grants 41776073).
How to cite: Li, B. and Zhang, K.: Taxonomy of Ammonia catesbyana (d'Orbigny, 1839) revisited: evidence on the intraspecific DNA sequences from the intertidal sediments of the southwestern Yellow Sea, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2972, https://doi.org/10.5194/egusphere-egu25-2972, 2025.
The rapid advancement of computational power has facilitated the widespread adoption of deep learning, a subset of artificial intelligence (AI), in various fields. Automated microfossil classification using AI is increasingly explored as a solution to reduce labor and address the declining availability of skilled personnel. However, practical implementation in research remains limited due to challenges such as the need for extensive training datasets and the lack of advanced equipment like automated microscopes. To address these issues, we implemented deep learning as a function to automatically classify microfossils on a virtual slide scanner that can process up to 360 microscope slides continuously. This study applied the system to sediment core DCR-1PC from the Indian Ocean sector of the Southern Ocean to obtain high-resolution records of the radiolarian analysis.
How to cite: Itaki, T., Miyakawa, A., Mimura, K., and Ikehara, M.: A High-Throughput Automated Microfossil Classification System Using Deep Learning, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8073, https://doi.org/10.5194/egusphere-egu25-8073, 2025.
Natural habitats consist of a large variety and variability of environmental factors. Reproduction in laboratory cultures is thus a highly effective way to pinpoint and quantify the impact of a specific environmental factor on a species which is hardly possible in natural environments.
The most common ostracod species in European marginal marine environments is Cyprideis torosa (Jones, 1850). It is a morphologically variable species but laboratory reproduction experiments of C. torosa are scarce and thus reducing an undisputed use of its morphological variability as a paleo-environmental proxy.
Although it is usually intended to use ostracod valves as paleo-thermometer, the nature of the impact of temperature on ostracods and on their morphology remains questionable. We aim to test whether temperature plays a significant role influencing the morphological characteristics of C. torosa in different salinities. In addition, laboratory cultures are a great opportunity to better understand the life cycle of ostracods, their reproduction times and juvenile numbers.
We collected samples from Marano Lagoon (Italy) at salinity levels of 7.2, 17.2 and 29.6 psu. For our experimental setup, we transferred boiled (= sterile) sediment (<150µm) from each of the newly established cultures in five crystallizing dishes, added lagoon water from each sampling location, and added 8 male and 12 female adult specimens of C. torosa. We placed one dish per salinity level in incubators at fixed 15, 20, 30 or 35°C and one outdoors. After finding at least 10 hatched juveniles, adult specimens were removed and remaining juveniles were raised to adulthood. Subsequently, we continued to check the abundance of juveniles and remove newly grown adults from the culture in monthly sievings. The morphological characteristics of the original and new adults were mutually compared.
The first results of our cultivation experiment suggest a rather stable reproduction rate at constant temperatures and salinities. The reproductive activity of C. torosa is highest in the lower saline cultures at 20 and 30°C and decreases with higher salinities as well as extreme low and high temperatures. First morphometric results indicate a phenotypic salinity-temperature modification of its size, ornamentation and shape.
How to cite: Berndt, C., Nagy, M., Berger, I., Melis, R., and Salvi, G.: Reproduction and morphological variability of Cyprideis torosa under different water temperatures and salinities in laboratory cultures, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9893, https://doi.org/10.5194/egusphere-egu25-9893, 2025.
Current rising temperatures in the oceans change marine habitats and faunal compositions as well as physiological and metabolic processes in marine organisms. While thermal stress is potentially threatening existing benthic communities it can be advantageous for invasive species that are better adapted to high temperatures. One such example of a successfully expanding species is the symbiont-bearing large benthic foraminifera Amphistegina lobifera Larsen, 1976 originating from the Red Sea, that has spread throughout the coastal ecosystems of the eastern Mediterranean. Studies on A. lobifera have shown its high tolerance to increasing temperature with regards to survivorship and photochemistry in temperature ranges from 24 °C to 36 °C. Interestingly, little is known about the species’ actual metabolic and photosynthetic activity with respect to oxygen consumption and production under different temperatures, especially towards the lower boundaries of its optimal environment. This study addresses this gap with a quantitative assessment of A. lobifera’s respiration rates that also allows for better comparison with other species and environmental factors. Amphistegina lobifera was permanently cultivated in the laboratory at University of Vienna in artificial seawater (ASW) at 24 °C and 38 psu with a day:night light cycle of 8:16 hours and ~ 10 µmol photons/m²/s light intensity. A non-invasive method was used to analyse oxygen respiration rates. The method involved placing an Oxygen Sensor Spot in a small, 2 ml airtight glass vial filled with ASW alongside the foraminifera. Oxygen concentrations under dark and light conditions (~ 30 µmol photons/m²/s) at different temperatures (16 °C, 20 °C, 24 °C, 28 °C, 32 °C, 36 °C) were recorded. Seventeen cleaned, living specimens were measured in triplicate after a 24-hour acclimation period. Respiration rates, normalized for biovolume (µm³), ranged from 3.73 × 10⁻⁹ nmol O₂/µm³/h at 16 °C to 2.83 × 10⁻⁸ nmol O₂/µm³/h at 32 °C under dark conditions. Oxygen production under light conditions consistently exceeded consumption. Gross photosynthesis was lowest at 36 °C (1.45 × 10⁻⁹ nmol O₂/µm³/h) compared to the overall mean of 4.06 × 10⁻⁸ nmol O₂/µm³/h. These results will give further insights into the ecological impacts and the contribution to biogeochemical cycles of A. lobifera in future ocean environments. Furthermore, the method provides a robust approach for comparing respiration rates across species and isolating the effects of specific environmental factors on metabolic rates.
How to cite: Palme, T. and Nagy, M.: Quantifying respiration and photosynthesis rates in Amphistegina lobifera at different temperatures, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10216, https://doi.org/10.5194/egusphere-egu25-10216, 2025.
Rising sea levels and intensifying storms, as a consequence of a changing climate, impact our coastal ecosystems. This impact is exacerbated by human-induced pressures which include: organic and contaminant pollution by agricultural activities, industry, urban sewage, and traffic threatening ecosystems and its services, and increasing human populations.
Within the two studied regions of Ghana and South Africa there is a paucity of effective water quality monitoring data, management, and strategies. With the changing climate and rising water demands, it is critical to maintain and restore water bodies to ensure their sustainable future. To achieve this objective, one of the methods is to apply bioindicators. Today, there is a growing global interest in using bioindicators for water quality monitoring, which can provide valuable insights into environmental conditions by analyzing the abundance, and species and population composition of bioindicator populations. Bioindicators provide an integrated and sensitive approach to environmental monitoring by capturing the cumulative effects of contaminants over time, and by revealing indirect biotic effects and bioaccumulation that may be missed by traditional chemical and physical measurements.
We present the first comprehensive investigation of marginal marine Ostracoda and Foraminifera in Ghana, shedding light on their ecology and distribution in western Africa. Elevated Foraminiferal Abnormality Index (FAI) values correlate with high heavy metal concentrations and variable salinity, suggesting pollution-induced abnormalities. Certain taxa, such as Quinqueloculina sp., Ammonia sp., and Cyprideis remanei dominate in contaminated areas, due to their tolerance to various pollutants. This study reveals a positive correlation between organic matter content and faunal diversity, contrary to typical pollution-diversity trends, likely influenced by salinity and allochthonous inputs. Heavy metal concentrations exceed thresholds near settlements, indicating significant anthropogenic pollution. Despite the pollution, higher diversity is observed, particularly in sites with marine-like salinity, suggesting complex responses to mixed effects to salinity or hydrographical effects and heavy metals.
Furthermore, we conducted a study on the uMlalazi river, South Africa, where, despite previous assumptions regarding the river’s pristine condition, we found high pollution, emphasizing the need for a continuous monitoring strategy. For assessing pollution and ecological health, we focused on Foraminifera and Ostracoda. We identified 17 ostracod species and 19 foraminifer species. Three distinct assemblages correlated with varying salinity and Pollution Load Index (PLI) levels. Our findings support the common trend of reduced species diversity with increased pollution. FAI correlated with PLI, showing that malformations where predominantly anthropogenically driven. Geochemical analysis indicated significant anthropogenic pressure, with elevated concentrations of heavy metals, sulphur, and microplastics from human induced activities such as sugarcane farming, urban sewages, fish farming and unknown sources.
Our studies emphasize the potential of Ostracoda and Foraminifera as indicators of environmental pressure and stresses, and a call for a more complete datasets to establish clearer correlations between meiofaunal associations and pollution effects.
How to cite: Schmitz, O., Alivernini, M., Akita, L. G., Finch, J., Hill, T., Haberzettl, T., and Frenzel, P.: Ostracoda and Foraminifera as indicators of anthropogenic impacts – case studies from Sub-Saharan Africa, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20020, https://doi.org/10.5194/egusphere-egu25-20020, 2025.
Using extensive datasets of benthic foraminiferal occurrences, we investigate spatial patterns of species diversity across the Arabian Gulf and assess how environmental gradients influence these distributions through species distribution modeling approaches. We evaluate the effectiveness of stacked species distribution models in predicting foraminiferal diversity patterns and identifying potential diversity hotspots across the Arabian Gulf basin. We compiled a comprehensive dataset of benthic foraminiferal occurrences from published literature and public databases, encompassing more than 492 species from nine orders. Using an ensemble of species distribution models, we predict the spatial patterns of individual species and stack these predictions to estimate foraminiferal species richness across the basin. We validated model predictions using independent datasets and assessed the relative importance of environmental variables. Our stacked species distribution models showed high performance (mean AUC > 0.94, TSS > 0.8, Kappa > 0.82), revealing a clear north-south gradient in foraminiferal species richness. The highest diversity was observed in the northern part of the Gulf, contrasting with typical latitudinal diversity gradients. Bathymetry and dissolved oxygen emerged as primary drivers of foraminiferal distributions (10.50% and 8.55% contribution respectively), followed by iron concentration and salinity. The eastern part of the Gulf displayed higher diversity compared to the western regions, likely reflecting the influence of the counterclockwise circulation pattern. Our study provides the first basin-wide assessment of benthic foraminiferal diversity in the Arabian Gulf, revealing complex spatial patterns and environmental relationships. The models' ability to delineate species-specific niches and environmental gradients enables efficient prediction of species responses to climate-driven changes. This approach establishes a robust baseline for monitoring ecosystem shifts and offers valuable insights for both paleoenvironmental reconstructions and future targeted studies in this extreme marine environment.
How to cite: Amao, A., Al-Ramadan, K., Kaminski, M., and Frontalini, F.: Modeling Benthic Foraminiferal Diversity in the Arabian Gulf: Species Distribution and Environmental Controls in a Basin-Wide Assessment, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20615, https://doi.org/10.5194/egusphere-egu25-20615, 2025.
Posters on site: Fri, 2 May, 08:30–10:15 | Hall X1
Shallow hypersaline playas are flat endorheic basins that form a salt crust at the top sediment layer. They are episodically flooded after intense rainfall events. After flooding, if precipitation does not persist, evaporation causes the water to recede, and salinity can increase up to 35–45%. Ultimately, the system dries up and evaporites like eugsterite (Na4Ca(SO4)3·2H2O), blödite (Na2Mg(SO4)2·4H2O), halite (NaCl) and gypsum (CaSO4·2H2O) can precipitate forming a rigid crust layer.
The present study focuses on measuring the exchange of CO2 between the upper sediments and the atmosphere at “La Muerte” playa-lake in the Monegros region (Aragon, Northeast Spain). Its main characteristic is the presence of a benthic organicmineral film dominated by cyanobacteria which uniformly covers the basin after rain events. As the water body evaporates, the biofilm contracts, while precipitated minerals replace organics and partially cement pore spaces, forming a rigid, salt crust–biofilm assemblage up to 1 cm thick. The two main objectives of the present study are:
- To estimate the net CO2 exchanges under wet and dry conditions and therefore to verify the impact of water availability in modulating the magnitude and sign of CO2 fluxes
- To investigate the significance of the upper organomineral crust on modulating the CO2
To accomplish these objectives this study relies on field in-situ short-term incubations complemented by additional ex-situ laboratory estimates. Main preliminary outputs are:
- Net CO2 emission typically predominated over net consumption.
- Net CO2 emission increased in summer, under dry conditions. Net CO2 consumption is detected under water-saturated conditions only.
- The CO2 emissions decreased in incubations where the surface biofilm remained undisturbed, as opposed to those where it was removed.
- Most subsurface CO2 emission originates from just below the crust (ca. 1 cm depth) to 8 cm depth.
- Under dry conditions, primary productivity of phototrophs at the top biofilm crust is insufficient to account for the observed decrease in CO2
Overall, these results suggest that although the upper layer is not an impermeable barrier to gas flows, such as CO2, it transiently mitigates its seepage into the atmosphere.
How to cite: Butturini, A., Cabestrero, O., Ferriol, J., Blasco, A., García, Y., Berlanga, M., Picart, P., Gomez, R., Urmeneta, J., Romaní, A. M., and Sanza-Montero, E.: CO2 fluxes at a hypersaline shallow playa. The organomineral crust makes the difference. , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1409, https://doi.org/10.5194/egusphere-egu25-1409, 2025.
Over the past 10,000 years since the last reemergence of marine systems from glacial conditions, the Arabian Gulf has become a well-known semi-restricted basin with no equal. Despite its importance as a present-day analogue for past geological environments and events, such as the Messinian Salinity Crisis and the rise and fall of the Dammam Sea during the Middle Eocene, there has been limited research development from academia, and these studies tend to be localized. The resilience of living marine organisms, particularly biocalcifiers, in the face of future climate change and global warming within this naturally stressed environment is also a major concern.
This work elaborates on the progress in understanding the impact of stressed environments on living biocalcifiers amid uncertainties in future climatic perturbations and human-induced problems. Various approaches have been used in the region, including thermal tolerance experiments, global warming predictions, and studies of human waste impacts (heavy-trace elements, microplastics, etc.). Several advancements have been made, such as experimenting with the thermal tolerance of intertidal and shallow-water benthic biocalcifiers, observing a “kill zone” linked to prolonged summer heat and desalination plant plumes, and studying the occurrence of microplastic waste in the soft tissues of selected biocalcifiers. To develop a comprehensive understanding and provide accurate proxies for past and future conditions, and to understand how marine biocalcifiers and their habitats in the Arabian Gulf change spatio-temporally, more work and collaboration are needed. As an academic institution in the region, we welcome future collaboration.
How to cite: Prayudi, S. D., Tawabini, B., Ayranci, K., and Kaminski, M.: The Arabian Gulf: A Field Laboratory for Studying Marine Biocalcifier Resilience Under Natural and Anthropogenic Stress - Current Progress and Future Directions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1873, https://doi.org/10.5194/egusphere-egu25-1873, 2025.
Lakes that are supersaturated with nutrients often meet the definition of hypertrophy and draw scientific attention due to their distinctive biogeochemical dynamics. Salbker South, an urban lake located in Magdeburg, Germany, exemplifies such an environment. Since summer 2022, it has been the focus of a high-frequency monitoring that reported total phosphorus (TP) and chlorophyll a (chl a) levels as high as 1.4 mg L⁻1 and 417 µg L⁻1, respectively. TP and chl a contribute to substantial organic carbon (OC) accumulation and create a fragile ecosystem where biological communities are under threat from processes such as anoxia induced by OC-mineralisation during thermal stratification between May and September. Anoxic events involve both the hypolimnion, which becomes undersaturated in DO down to 0.0 mg L-1within a week from the onset of thermal stratification, and the epilimnion where diurnal changes in DO span from 0.0 to > 20 mg L-1. Additionally, the high sulphate (SO₄) levels in the lake (up to 1.46 mg L-1) that are derived from the Zechstein Formation and hamper water electrical conductivity to 4 – 5 mS cm-1 facilitate the production of hydrogen sulphide (H₂S). As a result, H₂S concentrations in the deeper waters have been recorded to exceed 8.2 mg L-1. These dynamics position Salbker South as a natural H₂S generator. To mitigate these issues and reduce yearly cyanobacterial blooms, targeted restoration programs aimed to lower nutrient concentrations and stabilize lake biogeochemical balances are urgently needed. Our monitoring program that includes nearby groundwater wells, the Elbe River, and Lake Salbker North, is set to continue, aiming to establish this site as a hub for scientific innovation and interdisciplinary collaboration.
How to cite: Dordoni, M., Coder, L., Rosenlöcher, Y., and Tittel, J.: Oxygen and sulphur trends in a highly hypertrophic lake: a case study from Salbker South, Germany, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2083, https://doi.org/10.5194/egusphere-egu25-2083, 2025.
Organic carbon (OC) in rivers is one of the most rapidly recycled carbon pools. However, there is no consensus on the mechanisms that determine which compounds are remineralized. We studied the radiocarbon age of dissolved OC (DOC) that is decomposed in laboratory experiments across a range of stream bulk DOC ages. Stream DOC was collected from small forested catchments under summer dry flow, average flow and storm flow conditions. The ∆14C of respiratory CO2 increased with the ∆14C of stream DOC (P = 0.006, N = 16). However, the slope of the regression was small (0.20 ± 0.06) and the dependence was weak (R2 = 0.43). In further experiments, we used leachates of catchment soil from 0-8 cm and 8-20 cm depth and a 1:1 mixture of the two depths as initial DOC. Again, the increase in ∆14C-CO2 as a function of ∆14C-DOC was significant (R2 = 0.74, P = 0.028, N = 6), but the slope was small (0.13 ± 0.04) and the age range of respired DOC was narrow (modern to 280 years BP) compared to initial leachate DOC (600 to 3400 years BP). Fourier-transform ion cyclotron resonance mass spectrometry showed that similar (small, unsaturated, oxygen-rich) CHO molecules were consumed regardless of DOM source. The narrow age ranges of respired DOC suggest that intrinsic chemical quality sets the limits for which compounds can be utilized under given geochemical conditions. However, strategies of microorganisms to optimize growth (optimal foraging) may modulate their specific substrate choice, as indicated by the dependence of the age of respired OC on the age composition of the original DOC.
How to cite: Tittel, J., Lüderitz, V., Radke, S., Rosenlöcher, Y., and Lechtenfeld, O. J.: Invariable selection of compounds from organic matter by stream microbes, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2753, https://doi.org/10.5194/egusphere-egu25-2753, 2025.
This study investigates the spatiotemporal dynamics of water quality, phytoplankton, and zooplankton communities in two hydrologically connected reservoirs, Lantan and Renyitan, where water is transferred from Renyitan to Lantan. Seasonal and spatial analyses were conducted on key water quality parameters, including ammonia nitrogen (NH₄-N), total phosphorus (TP), dissolved oxygen (DO), and chemical oxygen demand (COD), and their influence on plankton abundance and diversity was assessed. Zooplankton abundances averaged 1500 ± 200 individuals/mL during the wet season, significantly higher than the dry season’s 1200 ± 150 individuals/mL (p = 0.0096, d = 1.58). Phytoplankton abundances also increased significantly during the wet season (p = 0.013), driven by nutrient enrichment from surface runoff and hydrological mixing. Diversity indices, such as the Shannon-Wiener Index (H') and Margalef’s Richness Index (DMg), displayed notable seasonal variations (p < 0.001), suggesting greater diversity and community balance in the wet season. Depth-related variations were more pronounced for zooplankton, with higher species richness (50 ± 8 species) and diversity (H' = 2.5 ± 0.2) in shallow zones, compared to opportunistic dominance in deeper waters (Dominance Index D = 0.7 ± 0.1). Phytoplankton depth-related differences were minor, with shallow samples averaging 5200 cells/mL compared to 4900 cells/mL in deep waters (p = 0.537). Inter-reservoir comparisons revealed higher biodiversity and community balance in Renyitan, whereas Lantan exhibited localized nutrient imbalances, promoting dominance of specific taxa. Non-Metric Multidimensional Scaling (NMDS) analysis highlighted significant seasonal shifts in plankton communities, with broader dispersion in the wet season due to dynamic environmental conditions. Deep-water habitats exhibited greater ecological stability, clustering tightly around NMDS centroids. Canonical correlation analysis (CCA) identified TN, TP, and DO as critical environmental drivers (p < 0.01). These findings emphasize the influence of seasonal and depth-related dynamics on plankton communities within connected reservoirs. Insights derived from this study provide valuable foundations for nutrient management, bloom mitigation strategies, and sustainable reservoir ecosystem management. Future research incorporating molecular tools and long-term monitoring is recommended to enhance understanding of community resilience in the face of climate-driven changes.
How to cite: Kuo, Y.-M.: Spatiotemporal Dynamics of Water Quality and Plankton Communities in Hydrologically Connected Reservoirs, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3050, https://doi.org/10.5194/egusphere-egu25-3050, 2025.
This study focuses on exploring the dynamics of dissolved organic matter (DOM) using high-frequency, continuous monitoring coupled with advanced fluorescence spectroscopy and statistical modeling. By combining continuous fluorescence sondes with spot sampling, we show temporal and longitudinal dynamics of DOM over a 14-month period in two UK rivers. The integration of fluorescence excitation-emission matrix (EEM) spectroscopy and Parallel Factor Analysis (PARAFAC) enabled the identification of key fluorescent components, including humic and protein-like substances. Real-time monitoring of these two DOM components reveals significant diel and seasonal variations in both the quantities and characteristics of DOM. External carbon sources (treatment works, agricultural land use) showed increased protein-like DOM, particularly during summer, indicating the influence of labile organic matter. A new fluorescence ratio (humic DOM/protein-like DOM) proved to be a robust indicator for differentiating between microbial-derived labile DOM and more refractory humic substances, offering new insights into organic matter processing and nutrient cycling in the studied ecosystems.
Modeling approaches, based on ANCOVA and logistic regression, demonstrated that allochthonous sources, precipitation, and seasonal temperature variations were key drivers of DOM dynamics. Periods of low temperature and high precipitation were characterized by a notable increase in humic-like DOM concentrations, primarily due to enhanced runoff of terrestrial organic matter into the river system. In contrast, as temperature increased, tryptophan-like DOM concentrations rose, reflecting heightened microbial activity driven by warmer conditions. The elevated temperature not only stimulated microbial metabolism but also accelerated the decomposition of organic matter, leading to the production of more labile, protein-like substances. These contrasting seasonal trends highlight the dual influence of hydrological inputs and temperature-driven biological processes on DOM patterns.
How to cite: Liu, X., Loiselle, S., Galgani, L., Boldrini, A., Polvani, A., and Cirrone, R.: Fluorescence Monitoring and Modeling for Understanding Organic Matter Dynamics in European Rivers, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4232, https://doi.org/10.5194/egusphere-egu25-4232, 2025.
Inland aquatic ecosystems play a crucial role in the carbon cycle, acting as an interface for carbon exchange between the atmosphere, terrestrial ecosystems, and the oceans. Due to their importance, dissolved organic matter (DOM) dynamics in continental water bodies have been widely studied. However, most studies are limited to specific sections of river basins, such as headwaters or estuaries, leaving a significant gap in understanding continuous fluvial systems encompassing the entire watershed, particularly regarding the behavior of DOM at the basin scale. To address this gap, we investigated the DOM dynamics within a watershed of 14,000 km² with diverse geomorphological features, following its entire course from the Andes to its only outlet into the Pacific Ocean. This watershed is highly diverse, combining high mountain areas impacted by mining activities with intensively farmed agricultural zones, livestock production in the central region, residential areas, and various recreational activities. The study aims to analyze variations in DOM characteristics along a fluvial continuum and their relationship with land use in different basin sections. A total of 25 sampling points were selected across the basin, including locations within the three sub-basins and the most significant tributaries. At each station, water physicochemical properties were measured by using a portable multiparametric probe, and water samples were collected for measurements of dissolved organic carbon (DOC) concentration, DOM optical properties (fluorescence and absorbance spectroscopy), isotopic analyses, as well as metalloids. A portable sensor was also used to measure nitrate concentrations directly on site. The results allowed us to (i) identify the sources of DOM, (ii) characterize DOM dynamics along the continuous river, and (iii) establish the relationship between DOM sources and different land use types across the basin's sections. This study provides the first regional-scale investigation of DOM dynamics along a river continuum in Chile and offers valuable insights into DOM responses across such systems, raising questions about existing theories of the river continuum concept. Finally, this study represents the first step of a more comprehensive and multidisciplinary study that will also cover seasonality and interannual variability of DOM dynamics and aquatic microbial community diversity in this region.
How to cite: Derrien, M., Retelletti Brogi, S., Chasselin, L., Lizana, F., Hayet, Z., Flores, M., Yanten, I., Santinelli, C., and Lavergne, C.: Unraveling dissolved organic matter sources and their link to land use along the Rapel River Continuum, Chile, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7203, https://doi.org/10.5194/egusphere-egu25-7203, 2025.
Impacts of natural and anthropogenic factors on microbiological water quality indicators along an urban riverine tropical wetland
Flavia Byekwaso1,3,6, Guenter Langergraber2, Gabriele Weigelhofer1,3, Rose Kaggwa4, Frank Kansiime5, Thomas Hein1,3
1 University of Natural Resources and Life Sciences, Vienna (BOKU), Department of Ecosystem Management, Climate and Biodiversity, Institute of Hydrobiology and Aquatic Ecosystem Management, Gregor-Mendel-Strasse 33, 1180 Vienna, Austria
2 University of Natural Resources and Life Sciences, Vienna (BOKU), Department of Landscape, Water and Infrastructure, Institute of Sanitary Engineering and Water Pollution Control, Muthgasse 18, 1190 Vienna, Austria
3 WasserCluster Lunz, Dr. Kupelwieser-Promenade 5, 3293 Lunz am See, Austria
4National Water and Sewerage Corporation, P.O. BOX 7053, Kampala, Uganda
5 Makerere University, Department of Environmental Management, P.O. BOX 7062, Kampala, Uganda
6 Ministry of Water and Environment, Climate Change Department, P.O BOX 20026, Kampala, Uganda
ABSTRACT
Water quality monitoring is essential for understanding seasonal variations in microbiological indicators and their implications for public health. Waterborne bacteria and pathogens are a significant cause of human diseases, especially in developing countries. The study aimed to understand the factors that cause seasonal changes in the concentrations of microbiological water quality indicators along a riverine tropical wetland. In total, 144 water samples were collected for 12 months at six sites along Lubigi wetland in Kampala, Uganda, receiving varying stormwater and wastewater inputs from urban water infrastructure during the dry and wet seasons. Water samples were analysed using specific microbiological assay tests for Escherichia coli, faecal coliforms, heterotrophic plate counts, Enterococcus and Salmonella species. Generally, the highest concentrations of microbial contamination were detected during the dry season at all sites. There was a decreasing trend in microbial contamination for all the selected five microbiological indicators with increasing distances from the sources of stormwater and wastewater inflows in the upstream reaches towards the downstream areas of Lubigi wetland. Nitrogen compounds, Escherichia coli, faecal coliforms, Enterococcus and Salmonella species originated from stormwater, whereas wastewater discharges delivered primarily phosphorus compounds, organic matter and heterotroph plate counts. E. coli and heterotrophic plate counts were positively correlated with water temperature and salinity. E. coli, faecal coliforms and heterotroph plate counts were positively associated with Biological Oxygen Demand (BOD5). Escherichia coli, faecal coliforms and Enterococcus species were positively correlated with NH4-N. Escherichia coli, faecal coliforms, and heterotrophs dominated with high concentrations during the dry seasons, while Enterococcus and Salmonella species were more prevalent in the wet season. Escherichia coli, faecal coliforms and Salmonella showed insignificant logarithmic reductions during both seasons, showing when the carrying capacities of Nsooba main channel and Lubigi sewage treatment plant systems were exceeded. Enterococcus species showed no reduction in both seasons, which implied continuous high in-stream contamination. Heterotrophs showed significantly higher logarithmic reduction during the wet season than in the dry season. This suggested a concentration reduction during the wet season and loading/increase in the dry seasons. Our research findings may be used by the public health sector to understand relationships between the occurrence of surface water quality microbiological indicators and the prevalence of diseases through strategic seasonal monitoring and evaluation in Kampala and the region.
How to cite: Byekwaso, F., Langergraber, G., Weigelhofer, G., Kaggwa, R., Kansiime, F., and Hein, T.: Impacts of natural and anthropogenic factors on microbiological water quality indicators along an urban riverine tropical wetland , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9005, https://doi.org/10.5194/egusphere-egu25-9005, 2025.
The Arctic Ocean is experiencing rapid environmental changes, with current warming rates exceeding the global average. This accelerated warming has triggered profound shifts in sea ice extent, thickness, and seasonal dynamics. As a result, these alterations impacted the timing of phytoplankton blooming, expanded open-water habitats, and modified the timing of primary production with far-reaching implications for benthic-pelagic coupling processes and benthic ecosystems. This study investigates benthic microfaunal communities, particularly benthic foraminifera (Rhizaria) and ostracoda (Crustacea), as they serve as sensitive indicators for contemporary Arctic conditions. Their distribution, abundance, and standing stocks reflect key factors such as organic matter availability, seasonal ice cover, and water mass properties (e.g., salinity and temperature). The materials for this study were collected during the expedition PS92 (ARK-XXIX/1) "TRANSSIZ" (Transitions in the Arctic Seasonal Sea Ice Zone, 19 May – 28 June 2015) aboard the German research icebreaker Polarstern. This six-week mission focused on early spring ecological and biogeochemical processes across the European Arctic margins. The study area covers the eastern flank of the Yermak Plateau and the northern continental slope of the Barents Sea. Sampling water depths ranged from 470 m to 1829 m. The four cores (PS92/19, PS92/27, PS92/31, PS92/39) were collected with a multiple corer (MUC) with an internal diameter of 10 cm (surface area 78,5 cm2). The MUC frame was equipped with a live broadcasting video system that transfers pictures to the ship via glass fibre cable. A Sanyo HD400P camera (10x optical zoom) captured images of under-ice fauna, marine snow in the water column, and phytodetritus originating from the spring blooms. Surface sediment samples were collected and analysed in the 63 and 125 μm size fractions to identify and characterise microfaunal communities. The results will provide a better understanding of how Arctic benthic ecosystems are adapting to a rapidly transforming environment. Additionally, current spring results will provide data that attempts to fill an existing gap in Arctic benthic foraminifera and ostracoda sampling.
How to cite: Faizieva, K., Wollenburg, J., Berndt, C., and Heinz, P.: Deep-sea living benthic foraminifera and ostracoda from the European Arctic margin and the Yermak Plateau during the spring phytoplankton blooms in the Arctic Ocean: distribution, abundance, and standing stocks, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10942, https://doi.org/10.5194/egusphere-egu25-10942, 2025.
The radiocarbon (14C) dating of lake sediments is widely used to estimate the so-called reservoir age (RA), i.e. the 14C age difference between the atmospheric and lake ecosystem carbon reservoirs. However, lake sediments are a mixture of autochthonous and various allochthonous carbon sources having distinct 14C specific activities. The RA depends on the catchment bedrock, CO2 exchange rates between water and the atmosphere, which are affected by organic carbon production and decomposition rates, inflow/outflow of organic and inorganic mater, water residence time, water level fluctuations, climate change, and other environmental factors impacting the lake’s catchment area. Every disturbance affecting carbon exchange between the water ecosystem, the terrestrial environment, and the atmosphere impacts carbon isotope distribution in the lake ecosystem.
Lake Plateliai is the largest lake in the north-western part of Lithuania (Samogitia). It is located on the territory of Samogitia National Park. The absence of cultivated fields on the park’s territory conditioned the lake to remain one of the cleanest in Lithuania. The present study focusses on sediment records from Lake Plateliai over the last 130 years. This time period is related to dam-induced lake’s water level fluctuations, increase/decrease in primary productivity due to intensive agricultural development since the 1960s, and its decline in the 1990s.
The aim of this work was to estimate how environmental factors have influenced the carbon cycle within the lake and how these impacts are recorded in sediments, i.e., changes in sedimentation rate, carbon isotope distribution among organic sediment fractions.
During the last 130 years, the radiocarbon reservoir age of the of the alkali soluble and alkali insoluble fractions of lake sediments has been reduced by 872.4 ±80 years, and a decreasing trend of 14C concentration values is recorded/observed in the upper layers. The14C specific activity values in both sediment organic fractions coincided during the last ten years and 1885-1932. However, changes in the water level during the period 1963-1976 and unknown events in 1939-1940 led to the introduction of allochthonous origin matter into the lake ecosystem, resulting lower 14C concentrations in the alkali soluble fraction compared to the alkali insoluble fraction.
How to cite: Barisevičiūtė, R., Mažeika, J., Karosiene, J., Kasperovičienė, J., Ežerinskis, Ž., and Šapolaitė, J.: Changes in carbon isotope distribution in sediments of Lake Plateliai, Lithuania, over the last 130 years, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10385, https://doi.org/10.5194/egusphere-egu25-10385, 2025.
Mineral and organic fertilization is estimated to be responsible for 70% of N2O emissions worldwide, a greenhouse gas which is approximately 270 times more potent than CO2. N2O emissions occur during biogeochemical processes of the nitrogen cycle, which take place in the various compartments of the water cycle (soil, aquifer, hyporheic zone, streams, etc.). During the transport of nitrate in the aquifer, incomplete denitrification can produce N2O and lead to groundwater concentration of N2O higher than the atmospheric equilibrium concentration. As groundwater then discharges into streams, excess N2O can be released to the atmosphere7. N2O can also be produced through incomplete denitrification in the hyporheic zone.
The emission of N2O from a stream depends on the denitrification occurring in the contributing compartments but also of the rate of gas exchanges between the stream and the atmosphere. Recent studies have shown that small-scale streambed heterogeneities are hot spots for gas exchanges. Yet, they are not considered in empirical equations to calculate gas exchange rates. Empirical equations only consider global parameters of the stream (ex: slope, water velocity, depth) and overlook local hot spots for gas exchanges. This suggests that N2O emissions from headwaters could be underestimated. Since headwater streams drain about 70% of the land surface on Earth, underestimating their rule in N2O emissions may lead to a significant bias in the global estimation of N2O emissions from freshwater ecosystems.
Here we investigate the rule of headwaters in the global N2O emissions, in order to better characterize the N-cycle in headwaters and the associated greenhouse gas emissions. We measure N2O along various headwater streams in agricultural areas using gas chromatography coupled to electron capture detection (GC-ECD). We further perform in-situ monitoring of N2O on a few representative sites using a continuous flow membrane inlet mass spectrometer (CF-MIMS) which is brought to the field in a mobile laboratory. To trace the origin of N2O, measurements are coupled with other tracers (nitrate, nitrite, nitrogen isotopes, radon, dissolved silica, etc.). Results reveal a large oversaturation of N2O in agricultural headwater streams and allow to track the production and emissions of N2O along headwater streams. This research links the disruption of biogeochemical cycles to another largely crossed planetary boundary, global warming. It therefore addresses a crucial issue of ecological transition in rural areas, the use of fertilizers, from the global perspective of greenhouse gas emissions.
How to cite: Vautier, C., Gokhale, P., Béraud, D., Bagagnan, R. S., Yvard, B., Chatton, E., and Laverman, A.: Impact of headwater streams on N2O emissions from agricultural catchments, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13388, https://doi.org/10.5194/egusphere-egu25-13388, 2025.
Biomineralization in pearl oysters (Pinctada fucata) is well-studied due to their economic value and research accessibility. Their shells comprise an outer calcite prismatic layer and an inner aragonite nacreous layer, presenting the classic calcite-aragonite polymorphism problem in biomineralization research. While molecular and genetic aspects of shell formation are increasingly understood, direct observation of formation mechanisms remains limited.
This study applied microscopic pH imaging techniques, previously successful in foraminifera research, to observe pH dynamics during shell development. Post-settlement individuals (shell length ~0.5 mm) from Mie Prefecture Fisheries Research Institute were examined using HPTS (pyranine) fluorescence microscopy. Observations revealed specific pH distributions, with elevated levels (~8.1 compared to ambient seawater ~7.7) parallel to growth lines near shell thickening areas, while soft tissue regions showed lower pH (<6.0), likely corresponding to digestive areas. These findings indicate active pH regulation during shell formation in bivalves.
Further research should investigate pH pattern responses to varying environmental conditions, particularly regarding climate change parameters. Studies of specific mechanisms creating these pH gradients and comparisons across developmental stages would enhance our understanding of biomineralization processes, benefiting both fundamental research and pearl cultivation practices.
How to cite: Toyofuku, T., Nagai, Y., Suzuki, M., and Atsumi, T.: Development of pH Visualization Methods to Study Shell Formation in Juvenile Pearl Oyster Pinctada fucata, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14264, https://doi.org/10.5194/egusphere-egu25-14264, 2025.
Here we propose an AI-based approach using Machine Learning (ML) to assist species identification and reduce morphotype redundancy in the study of monothalamous foraminifera. In fact, this group of protists, is often overlooked in taxonomic studies due to their morphological simplicity and diversity. These single-celled organisms with "soft" tests are poorly studied, with only a few species identified, while many morphotypes remain undescribed. Taxonomic research on monothalamids is limited by challenges in identification, lack of fossilization, and the time-intensive nature of the work. This gap may lead to underestimating biodiversity and hinder detecting ecosystem degradation. Despite these challenges, monothalamids play key roles in marine ecosystems, making their diversity crucial for conservation and resource management. With this in mind, we analyzed images from the scientific literature, extracting key morphological traits, such as chamber shape, shell type, composition, and aperture type, through objective human annotation to build a dataset processed by ML algorithms. Clustering techniques, such as K-Means, revealed that basic shape, followed by shell type and composition, were the primary features distinguishing clusters. This approach enabled more objective morphotype classification, improving consistency and reducing human bias. These findings align with recent taxonomic revisions and demonstrate that applying unsupervised ML methods enhances species identification accuracy and streamlines the analysis of high-dimensional datasets.
How to cite: Negri, A., Sabbatini, A., Caridi, F., and Potena, D.: Machine Learning for identification and classification of Foraminifera: testing on monothalamids, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16261, https://doi.org/10.5194/egusphere-egu25-16261, 2025.
The presence of algal symbionts in Large Benthic Foraminifera (LBF) facilitates the success of the group as important carbonate producers in the ocean. However, the symbiosis makes the holobiont more susceptible to heat stress. Modulating the foraminiferal host-symbiont relationship is one approach that could serve as an adaptation mechanism to elevated temperatures. Recently, a menthol-DCMU (3-(3,4-dichlorophenyl)-1,1-dimethylurea) bleaching method made investigations of host-symbiont combinations in foraminifera possible. Here, we performed a manipulative temperature experiment at three temperatures (25°C, 28°C, and 31°C) on the dinoflagellate-bearing Sorites orbiculus for two weeks. Before the experiment, specimens were menthol-DCMU bleached and inoculated with strains of Symbiodiniaceae (ITS2 strains: F2 sensu stricto, CCMP2467, and KB8) previously isolated from cnidarian hosts. Three controls, including untreated specimens, menthol-DCMU bleached specimens continuously treated with DCMU, and menthol-DCMU bleached specimens recovering in artificial seawater, were used. To assess the physiological impact of the treatments on the specimens, the survivorship and growth of the hosts, and the efficiency of photosystem II (Fv:Fm) of the symbionts were measured. Survivorship was between 75-100% based on PAM fluorescence values and light microscopy. Inoculated specimens with strain KB8 exhibited similar growth to the controls at 31°C. Contrastingly, strain CCMP2467 had lower growth than the controls at each temperature. Growth did not differ between the controls. PAM fluorometry revealed that photosynthetic yields (Fv:Fm) between the 25°C and 31°C treatments were not different between strains, while in the 28°C treatment, strain CCMP2467 showed low photosynthetic activity, indicating stress in the photosystems. Contrary to our expectations, menthol-DCMU bleached individuals continuously treated with DCMU, exhibited similar growth rates as untreated holobionts. The results suggest that S. orbiculus can sustain growth between a temperature range of 25°C to at least 31°C independently of a functional symbiosis. Further investigations are needed to gain insights into the host-symbiont relationship, the potential of its modulation as an adaptation mechanism to elevated temperatures, and the role of symbionts in the growth and calcification of foraminifera.
How to cite: Schoerghofer, A., Timme, L. T., Manda, S., and Schmidt, C.: Manipulative temperature experiments with the foraminifer Sorites orbiculus using inoculated Symbiodiniaceae symbionts, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16513, https://doi.org/10.5194/egusphere-egu25-16513, 2025.
There is a close relationship between the face of benthic foraminifera and water masses. Benthic foraminifera are sensitive to changes in seawater temperature, nutrients, and dissolved oxygen, making them a good material for reconstructing paleoceanographic environments, and thus are frequently used as indicators of the sedimentary environments. An alternation of brownish gray to greenish gray (“red-green”) intervals was observed at IODP Expedition 368 Site U1502 in the northern South China Sea. In this study, we analyzed benthic foraminiferal assemblages in sediments from two sections of Hole U1502A to reconstruct changes in bottom water mass properties in the northern South China Sea during the Middle-Late Miocene.
Abundant benthic foraminifera were found in both sections, with higher abundance in the Late Miocene section (10R1W) than in the Middle Miocene section (29R5W-30R6W). Among them, a total of 78 genera and 225 species of benthic foraminifera were identified, and both sections were dominated by Epistominella exigua, Nuttallides umbonifera, Globocassidulina subglobosa, Gyroidinoides orbicularis ,and Oridorsalis umbonata，indicating a long-term deep-sea environment.
Additionally, significant variations in the abundance of Uvigerina peregrina and Bulimina alazanensis were found in the two sections. The abundance of U. peregrina was much higher than that of B. alazanensis in the Middle Miocene section, whereas in the Late Miocene section, the abundance of U. peregrina decreased dramatically while that of B. alazanensis increased significantly. Since B. alazanensis occupied the same niche in the South Pacific deep water as U. peregrina in the North Pacific, this may suggest that the northern South China Sea was influenced by alternating deep water masses originating from the North Pacific to the South Pacific during the Middle-Late Miocene.
This work is supported by the CAS Strategic Priority Project (XDB XDB26000000) and the National Natural Science Foundation of China (Grants 41776073).
How to cite: Zhang, K. and Li, B.: Reconstructing Middle-Late Miocene Bottom Water Mass Properties in the Northern South China Sea: Insights from Benthic Foraminifera, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3932, https://doi.org/10.5194/egusphere-egu25-3932, 2025.
Due to the ubiquitous anthropogenic and climatic changes altering the marine habitat and ecology of biotoxin producers, the aim of this study was to assess the risk of human consumption associated with the accumulation of lipophilic toxins in the commercially important bivalve mollusc (mussel Mytilus galloprovincialis Lamarck, 1819) in the Krka River estuary located in the central part of the Croatian Adriatic Sea coast. Shellfish samples were collected weekly at three sampling stations during 2024, with a focus on monitoring lipophilic biotoxins. This study confirmed the first occurrence of the azaspiracid biotoxin, namely azaspiracid-2 (AZA-2), in shellfish from the Croatian part of the eastern Adriatic Sea coast. However, the toxicity only occurred in the first five months of the investigated year, as no AZA-2 toxin could be detected in shellfish sampled after May. Shellfish soft tissue samples were subjected to liquid chromatography–mass spectrometry (LC–MS) analysis to determine the presence of okadaic acid, dinophysistoxins, pectenotoxins, azaspiracids, yessotoxins and spirolides. The presence of lipophilic toxins in the samples was confirmed by comparing the retention times in the chromatograms and the fragmentation spectra with those of certified reference materials from the National Research Council, Canada. In particular, levels of azaspiracid-2 in the range of 0.03 -146.90 µg/kg were determined. The highest AZA-2 concentrations were found in the January samples. Thereafter, the concentrations showed a decreasing trend until the end of May, when they were no longer detected for the rest of the year. The concentration of this toxin was below the maximum permitted level in all samples in accordance with the EU regulation. Azaspiracids (AZAs) are a group of polyether compounds with a spirocyclic structure that can cause symptoms such as nausea, vomiting, diarrhoea and stomach cramps in humans. This is the first report on the occurrence of AZA-2 in the Croatian part of the Adriatic Sea and proves that the occurrence of lipophilic biotoxins needs to be further investigated and monitored in order to protect public health, but also with regard to aquaculture activities and their socio-economic benefits.
How to cite: Roje-Busatto, R., Ujević, I., Bulić, A., Orhanović, S., Pezelj, I., and Bogdanović, T.: First detection of azaspiracid-2 in shellfish from the Croatian coast of the Adriatic Sea, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21176, https://doi.org/10.5194/egusphere-egu25-21176, 2025.
