The flux of nutrients into rivers is rising due largely to inputs from the expansion and intensification of agriculture along with inputs from treatment of human waste. This trend is set to continue due to changing climate and increasing population while we attempt to balance food security and environmental impact. While water quality legislation focuses on inorganic nutrients due to their bioavailability, the proportion of the total nitrogen (N) flux, which is organic in its molecular composition is important in many riverine systems. Despite this, the impact of organic N on ecosystem function is currently poorly understood. Here we address part of this knowledge gap using compound-specific stable isotope probing to investigate the extent to which dissolved organic matter substrates are bioavailable to stream biota and if they can be directly assimilated.

Stable isotope probing was used to identify and quantify the routes of biotic uptake of organic N and carbon (C) into stream biota. Here, we added ¹⁵N labelled (nitrate, ammonium, glucosamine, sheep urine) and doubly labelled (¹⁵N/¹³C) substrates (glutamic acid, urea, glycine) to in-stream mesocosms containing water and epilithon, and bryophyte communities from the River Conwy North Wales, UK. Samples of epilithon and bryophyte were removed from the incubations after 2, 6, 12, 24 and 48 h and rates of assimilation of the labelled substrate were determined using bulk ¹⁵N/¹³C, followed by compound-specific ¹⁵N/¹³C analysis of extracted amino acids. This method allowed us to demonstrate the assimilation of labelled organic substrates into newly biosynthesised proteinaceous amino acids and to determine if they were utilised as intact organic molecules.

The findings showed that the majority of the organic N substrates tested were directly bioavailable for utilisation as intact molecules by the stream biota, except for urea where transformation occurred before uptake. The data also showed that there were differences in the rates of assimilation both between the organic substrates added and between the epilithon and bryophyte communities. This work illustrates the analytical power of using doubly labelled ¹³C, ¹⁵N compounds in a stable isotope probing experiment, as the ability to trace the utilisation of both the N and C simultaneously had provided significant new insights in the biotic assimilation of organic-N substrates. Our findings confirm the importance of organic nutrients in ecosystem function and the need for changes to water quality legislation to reflect this.

How to cite: Lloyd, C., Johnes, P., Maberley, S., Yates, C., Mena Rivera, L., Reay, M., Brailsford, F., Glanville, H., Clarke, M., Evershed, R., and Jones, D.: Investigating biotic uptake of riverine organic nitrogen using a compound-specific stable-isotope probing approach., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9464, https://doi.org/10.5194/egusphere-egu23-9464, 2023.

Redfield first reported a carbon: nitrogen (C:N) ratio of approximately 6.6 in marine phytoplankton. However, recent studies show that phytoplankton C:N ratio has a large range (marine: 6.5-9.9; freshwater: 7.8-10.5) and is species-specific.These studies pose a great challenge to phytoplankton stoichiometric homeostasis, which traditionally refers to their ability to maintain relatively stable elemental composition with the variation in external nutrient availability. The underlying mechanisms of the interaction between phytoplankton stoichiometric homeostasis and nutrient availability need further clarification. Therefore, in the field seven reservoirs in Tianjin, North China, were investigated to understand their phytoplankton C:N ratios and the influencing factors, and in the laboratory, Chlamydomonas reinhardtii, as a model organism, was used to investigate its C and N metabolism and relevant physiological parameters under different C and N availability. Transcriptome sequencing, nano-scale secondary ion mass spectrometry, and C stable isotope analysis were used to understand cellular C-N metabolism at the molecular level, cellular C-N compartmentation, and C utilization strategy, respectively, in the culture experiment. The main aim of this study was to understand how C-N availability affects the C:N ratio of freshwater phytoplankton at the molecular level.

The results indicated that CO₂ limitation had no significant effect on the phytoplankton C:N ratio in either scene, whereas limitation of dissolved inorganic N induced the ratio to be a 35% higher in the field and a 138% higher in the laboratory, respectively. Under CO₂ limitation, algal CO₂-concentrating mechanisms were operated to ensure a C supply, and coupled C-N molecular regulation remained the cellular C:N ratio stable. Under nitrate limitation, differentially expressed gene-regulated intensities increase enormously, and their increasing proportion was comparable to that of the algal C:N ratio; cellular metabolism was reorganized to form a “subhealthy” C-N stoichiometric state with high C:N ratios. In addition, the N transport system had a specific role under CO₂ and nitrate limitations. This study implies that algal stoichiometric homeostasis depends on the involved limitation element and will help to deepen the understanding of C-N stoichiometric homeostasis in freshwater phytoplankton.

How to cite: Li, W., Yang, M., Wang, B., and Liu, C.-Q.: Regulation strategy for nutrient-dependent carbon and nitrogen stoichiometric homeostasis in freshwater phytoplankton, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3003, https://doi.org/10.5194/egusphere-egu23-3003, 2023.

Lateral nitrogen (N) transport from land to the ocean through rivers is an important component of global N cycling. In this study, we present the implementation of fluvial transport of nitrogen into ORCHIDEE-CNP (Organising Carbon and Hydrology in Dynamic Ecosystems-CNP), which explicitly simulates N biogeochemistry in terrestrial ecosystems coupled with carbon, water and energy transfers. This new model branch called ORCHIDEE-N_lateral, simulates the lateral transport of water, dissolved inorganic N (DIN), dissolved organic N (DON) and particulate organic N (PON) from land to the ocean through river networks, the decomposition of DON and PON, and the denitrification of DIN in transit. ORCHIDEE-N_lateral was parameterized and evaluated based on global observations of water discharge (Global Runoff and Dara Centre, GRDC) and N concentration in the global river network (Global Water Quality Archive, GRQA). The model reproduces well the observed riverine discharges of water and total nitrogen (TN), and N exports from the land to the ocean.  Globally, the TN flowing into rivers, denitrification of DIN and TN export to the ocean all increased from the year 1901 to 2015. The TN export to the ocean increased from 32 Tg N yr^-1 to 37 Tg N yr^-1 during 1901–2015, which is in good agreement with the corresponding global fluxes calculated from the well-established Global NEWS 2 model. In this study, we further re-assess the spatial and temporal distribution of global riverine N flows and stocks. Overall, our model approach represents a useful tool for simulating large-scale lateral N transfer and for predicting the future feedbacks between lateral N transfers and climate.

How to cite: Ma, M., Zhang, H., Regnier, P., Lauerwald, R., and Ciais, P.: Estimating the global lateral transfer of nitrogen through river network using a land surface model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8295, https://doi.org/10.5194/egusphere-egu23-8295, 2023.

Streams and rivers have been highlighted as significant but poorly constrained sources of nitrous oxide (N₂O), a greenhouse gas ≈300 times more potent than carbon dioxide. A large share of stream N₂O emissions arises from the use of nitrogen (N) fertilizers by agriculture and therefore most of the research on N₂O emissions from streams has focused on agricultural areas, especially on fertile calcareous soils having near-neutral pH.

However, recent research suggests that streams located in regions having low pH (<5.5) and high iron content in soils may promote disproportionally high N₂O emissions. We tested this hypothesis by investigating the drivers of N₂O emissions in agricultural and natural streams located in regions of Denmark where soils with low pH and high iron contents are prevalent.

We measured N₂O emissions monthly for a year in 10 streams located in agricultural and natural areas. Furthermore, we also measured N₂O emissions four times a year in 80 streams covering a broad gradient of land-use and soil properties.

The preliminary results indicate that, within agricultural and natural areas, streams with low pH have higher emissions of N₂O than those with higher pH. We will compare our results with the estimates calculated using the IPCC methodology and discuss the implications of our findings for national greenhouse gas inventories.

How to cite: Audet, J., Veraart, A. J., Wrage-Mönnig, N., and Carstensen, M. V.: Nitrous oxide emissions from streams in agricultural and natural areas, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3060, https://doi.org/10.5194/egusphere-egu23-3060, 2023.

Anthropogenic activities increase the contributions of inland waters to global greenhouse gas (GHG; CO₂, CH_4, and N₂O) budgets, yet the mechanisms driving these increases are still not well constrained. In this study, we quantified year-long GHG concentrations and fluxes, as well as water physico-chemical variables from 23 streams, three ditches, and two wastewater inflow sites across five catchments in Germany contrasted by land use. Using mixed-effects models, we determined the overall impact of land use and seasonality on the intra-annual variabilities of these parameters. We found that land use was more significant than seasonality in controlling the intra-annual variability of GHG concentrations and fluxes. Agricultural land use and wastewater inflows in settlement areas resulted in elevated riverine CO₂, CH_4, and N₂O emissions, as substrate inputs by these sources appeared to favor in situ GHG production processes. Dissolved GHG inputs directly from agricultural runoff and waste-water inputs also contributed substantially to the annual emissions from these sites. Drainage ditches were hotspots for CO₂ and CH₄ fluxes due to high dissolved organic matter concentrations, which appeared to favor in situ production via respiration and methanogensis. Overall, the annual emission from anthropogenic-influenced streams and rivers in CO₂-equivalents was up to 20 times higher (~71 kg CO₂ m^-2 yr^-1) than from natural streams (~3 kg CO₂ m^-2 yr^-1). Future studies aiming to estimate the contribution of riverine systems to GHG emissions should therefore focus on anthropogenically perturbed streams, as their GHG emission are much more variable in space and time.

How to cite: Mwanake, R., Gettel, G., Wangari, E., Glaser, C., Houska, T., Breuer, L., Butterbach-bahl, K., and Kiese, R.: Anthropogenic activities significantly increase annual greenhouse gas (GHG) fluxes from temperate streams, rivers, and drainage ditches in Germany, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3305, https://doi.org/10.5194/egusphere-egu23-3305, 2023.

The concentration of oxygen in aquatic environments influences redox reactions of chemicals, nutrient biogeochemistry, water quality, biological activities, and ecosystem health. While hypoxia and declining oxygen concentrations in marine environments have been widely reported, oxygen in global inland-water systems and its spatiotemporal changes with the changes in climate, hydrology and human activities remain unknown. To unravel the changing global inland-water oxygen cycle and driving mechanisms, here we quantify the global inland-water oxygen production, consumption, exchange with the atmosphere and transport along the aquatic continuum during 1900-2010 using the spatially-explicit, integrated assessment model IMAGE-DGNM including the mechanistic in-stream biogeochemistry module (DISC). The model keeps track of oxygen and nutrient supply from the land, and describes their coupled transformations and transport from upstream through various waterbodies to downstream. During 1900-2010, global inland-water oxygen production and consumption rapidly increased by over a factor of six and three, respectively, while river oxygen export to oceans stayed around 0.4 Pg yr^-1. Despite the increasing ratio of oxygen production to consumption, inland waters overall act as an increasing sink of oxygen in the atmosphere during 1900-2010. Globally, low-order streams contribute the most to the freshwater oxygen sink, followed by lakes and recently important reservoirs, while high-order rivers overall act as an oxygen source to the atmosphere.

How to cite: Wang, J., Bouwman, A. F., Vilmin, L., Beusen, A. H. W., Mogollón, J. M., van Hoek, W. J., Liu, X., Duan, W., and Middelburg, J.: Increasing oxygen consumption in global inland waters in the Anthropocene, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16452, https://doi.org/10.5194/egusphere-egu23-16452, 2023.

With human activity rapidly accelerating the global nitrogen cycle, aquatic environments are facing increasing eutrophication and ecosystem damage. Oligotrophic headwater streams are particularly susceptible to nutrient pollution, which is affecting biodiversity, ecosystem services and water quality. However, not much in known about biogeochemical nitrogen cycling in these remote environments. This research presents seasonal data for nitrate concentrations and stable isotope signatures from oligotrophic mountain stream-lake networks in the English Lake District, UK. While phosphate concentrations were frequently below detection limit, nitrate was present throughout the year with concentrations ranging from 0.01 to 0.49 mg N L^-1. Dual isotope analysis of δ¹⁵N-NO₃ and δ¹⁸O-NO₃ identified atmospheric deposition as an important nutrient source to the ecosystem and provided information on the fate of nitrate moving through hydrologically connected stream-lake networks. Some mountain lakes removed up to 69% of nitrate delivered by the inflow stream, while others were substantial sources compared to upstream concentrations. This contrasting lake response was consistent throughout the year, with in-lake nitrate subsidy being observed in systems where concentrations in the inflow stream dropped below 0.25 mg N L^-1. These findings suggest that dominant biogeochemical processes may be controlled by nutrient load, and ecosystem response could potentially change with increasing nutrient pollution.

How to cite: Grefe, I., Wynn, P., Mackay, E., Barker, P., Grant, H., Pereira, G., Maberly, S., and Surridge, B.: Nitrate retention and subsidy in oligotrophic mountain stream-lake networks, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5463, https://doi.org/10.5194/egusphere-egu23-5463, 2023.

Lake systems are facing long-term (>150 years) changes around the world acting on multi-decadal to centennial scales. Historic temperature warming at global scales, projected to continue by the end of the century, acting concomitant with eutrophication has modified ecosystem functioning in complex ways. Process-based lake models have emerged as powerful tools to assess the effects of climate and human activities on ecosystems, as well as the responses under future scenarios since they take into account the processes in the boundaries lake-catchment and lake-atmosphere. Most of these models are constrained by short-term monitoring limnological records, traditionally ranging from days to a few decades, potentially limiting the robustness of long-term reconstructions. The integration of lake modeling and paleolimnological records can overcome the short-term monitoring data temporal scale, thereby providing a long-term perspective on lake ecosystem dynamics related to climate variability and human pressures. The present study develops a methodological framework using paleolimnological records from well-dated lake sediment records to constrain, validate and model temporal changes in water quality over a period of 250 years (1850–2100). Lake Geneva (France, Switzerland) was selected as a case study in face of its similarity with other peri-alpine lakes and its representativeness as it is one of the most studied and well-known lentic ecosystems in the world. The 1D hydrodynamic-biogeochemical GLM-AED2 model was applied to simulate dissolved oxygen, nutrients, and chlorophyll-a concentrations along the water column. Pluri-decadal series of limnological data monthly collected by the French Observatoire des LAcs (OLA database) were used to calibrate and validate the model. In addition, model outputs were further validated with published paleolimnological records for the past 170 years. Preliminary results of the calibration procedure show that the GLM-AED2 model accurately predicts the magnitude and seasonal dynamics of the state variables with goodness-of-fit metrics under the literature range (e.g. RMSE = 0.96 mg L^–1 and RRMSE = 25% for dissolved oxygen; RMSE = 6.53 ug L^–1 and RRMSE = 37% for chlorophyll-a, both in the epilimnion). The integration of a one-dimensional lake model, paleolimnological records, and in situ measurements supports a better understanding of the historical dynamics and provides more robust long-term hindcast/forecast simulations to elucidate the impacts of climate change and critical implications for lake management and planning.

How to cite: Soares, L., Desgué-Itier, O., Domaizon, I., Barouillet, C., and Jenny, J.-P.: Integration of lake modeling and paleolimnological records to perform long-term simulations of water quality in Lake Geneva over 250 years (1850–2100 period), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15778, https://doi.org/10.5194/egusphere-egu23-15778, 2023.

The Radiocarbon Inventories of Switzerland (RICH) project aims to construct the first national-scale census of (radio)carbon across aquatic, terrestrial, and atmospheric reservoirs. Within the carbon cycle, inland waters play a crucial role with lakes integrating carbon from various sources within their catchments in addition to that fixed by local primary productivity. Here we will present radiocarbon measurements of water-column dissolved inorganic carbon (DIC), dissolved organic carbon (DOC), and particulate organic carbon (POC) from 15 lakes across Switzerland covering a range of sizes, elevations, and trophic states. In addition, a year of monthly water column measurements from Switzerland’s two largest lakes - Lake Constance and Lake Geneva - reveal seasonal trends resulting from changes in productivity and river inflow. Preliminary results show that the average radiocarbon signature of DIC in both Lake Constance and Lake Geneva is depleted in ¹⁴C relative to atmospheric CO₂, indicating a ca. 15-20% contribution from bedrock weathering (¹⁴C-dead carbon). The timeseries at Lake Constance builds on earlier measurements which have shown a decline in DI¹⁴C since the late 1960s due to decreasing concentrations of bomb radiocarbon in the atmosphere. DO¹⁴C values in Lake Constance are more enriched compared to DI¹⁴C, indicating the importance of terrestrial DOC sources. In contrast, DO¹⁴C values in Lake Geneva are similar to DI¹⁴C, consistent with lake primary productivity as the main source of DOC. Overall, variations in radiocarbon values between different lakes are much greater than seasonal variations observed in either Lake Constance or Lake Geneva. These results form the basis of a radiocarbon inventory of Swiss lakes and provide new insights into carbon cycling in these dynamic aquatic systems.

How to cite: White, M., Mittelbach, B., Rhyner, T., Haghipour, N., Blattmann, T., Wessels, M., Dubois, N., and Eglinton, T.: A Radiocarbon Inventory of Switzerland’s Lakes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5890, https://doi.org/10.5194/egusphere-egu23-5890, 2023.

There are over 76,000 stormwater ponds in Florida, USA, forming 2.7% of total urban land cover in the state. While stormwater ponds are constructed primarily for flood control, they are often expected to perform some level of pollutant removal as well. Urban runoff conveyed to stormwater ponds contains numerous pollutants, including sediments, nutrients, dissolved organic matter, pathogens, and heavy metals. Biogeochemical processes within stormwater ponds play a large role in how these pollutants are stored, transformed, and/or removed. This presentation discusses recent work on transformations of nitrogen, phosphorus, and carbon in small urban ponds, with emphasis on implications for how these ponds can be better managed for protection of downstream waterbodies. Example studies that will be highlighted include research on the molecular characterization and bioavailability of dissolved organic nitrogen in stormwater ponds, research on the utilization of dissolved organic nutrients in stormwater ponds by the harmful algal species Karenia brevis, and a study investigating carbon storage and greenhouse gas emissions from small urban ponds. ​

How to cite: Lusk, M.: Opening the biogeochemistry black box of small urban ponds, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16999, https://doi.org/10.5194/egusphere-egu23-16999, 2023.

Stream water chemistry at catchment outlets is commonly used to infer the flowpaths of water through the catchment and to quantify the relative contributions of various flowpaths and/or end-members during, e.g., storm events. For this purpose, the number and nature of these flowpaths or end-members are commonly defined a priori as part of the experimental design and previous knowledge, and their contributions are calculated based on the dynamics of the stream chemistry, with the inherent assumptions and uncertainties of this approach. Here, we present a methodology, which inverts this classical approach. We use the variability of the stream chemistry data to determine the minimum number of end-members needed and, more specifically, whether two end-members would be sufficient. In this methodology, we analysed the concentration-concentration relationships of several major ion combinations on the storm-event scale for multiple events, using a multi-year, high-frequency (< 60 minutes) timeseries of the major cations and anions from the outlet of two small (0.8 – 5 km²) french catchments with contrasting land-use (forest and mixed farming-cropping productions). The results indicate that a large number of storm-events (up to 92%) could be interpreted as the result of only two end-members, depending on the catchment and the ion combination used. These findings might help to revise some of the perceptual understandings of flowpath or end-member contributions in catchments during storm-events. In addition, they might stimulate the discussion about the definition of end-members or flowpaths in catchments, especially with regard to variable hydrological contributions.

How to cite: Brekenfeld, N., Fovet, O., Cotel, S., Faucheux, M., Floury, P., Fourtet, C., Guillon, S., Hamon, Y., Henine, H., Petitjean, P., Pierson-Wickman, A.-C., Pierret, M.-C., and Gaillardet, J.: Are there more than two end-members contributing to storm-events in small head-water catchments?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-786, https://doi.org/10.5194/egusphere-egu23-786, 2023.

River water quality is strongly affected by droughts and heatwaves worldwide. However, these effects have only been studied in a small number of river basins and regions, mainly in the US, Europe, or Australia. In this study, we analyse the large-scale responses in river water quality under droughts, heatwaves and compound events for 300,000+ water quality monitoring stations worldwide between 1980-2021. We include 16 water quality constituents in the analysis, grouped into general constituents (e.g. water temperature, salinity, dissolved oxygen), biological constituents (e.g. faecal coliform, biochemical oxygen demand) and emerging contaminants (e.g. pesticides and pharmaceuticals). Further, we assess the water quality responses to droughts and heatwaves in relation to climate, land use and level of wastewater treatment. We find a general deterioration in river water quality under droughts and heatwaves globally for most types of water quality constituents, with on average higher water temperatures (+27%), increases in salinity (+23%) and lower concentrations of dissolved oxygen (-17%). We also find that climate type, land use and level of wastewater treatment have a significant effect on the magnitude of water quality responses under droughts and heatwaves. The median increase in river temperature under compound drought-heatwaves strongly depends on climate, with for example higher increases in the Polar climate zone (+4.5°C) compared to the Tropical zone (+2.1°C). Increases in salinity under droughts are on average twice as large in irrigated regions compared to non-irrigated regions. Phosphorus and nitrogen concentrations in rivers can either increase or decrease during drought events, depending on the type of nutrient form (dissolved versus particulate) and land use (urban versus rural). Higher levels of wastewater treatment lead to a stronger reduction in faecal coliform (an indicator of pathogens) during droughts and heatwaves. Compared to previous local and regional-scale analyses, this study provides a more consistent and broader understanding of how droughts and heatwaves affect river water quality. In addition, the results from this study could be used to validate large-scale models of river water quality under droughts and heatwaves.

How to cite: Graham, D., Bierkens, M., and van Vliet, M.: Water quality responses under droughts and heatwaves in river basins worldwide, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4295, https://doi.org/10.5194/egusphere-egu23-4295, 2023.

Eutrophication of surface water bodies is an important factor that impairs the chemical quality of surface waters. In consequence, legislation and management efforts have been made over the past decades to reduce the agricultural nutrient input and meet the goals set by the EU Water Framework Directive and, more recently, by the UN Sustainability Goals.  

In this study, we evaluate trends in nitrate concentration and isotope composition at the entrance of the Elbe Estuary, Northern Germany.  We find a distinct seasonality of nitrate isotope composition and nitrate concentration, with high isotope values in summer, pointing towards assimilation and denitrification in the Elbe River and catchment.

Our data indicate that low discharge conditions intensify biological nitrate retention and nitrogen uptake during the growing season, leading to more intense nitrate isotope enrichments and low the water column concentrations. This suggests that recent reduction in Elbe River nutrient loads do not result from successful nutrient management but from a long-lasting drought in the catchment. In consideration of climate change predictions, we anticipate more frequent and extensive periods of low discharges, possibly even leading to a future nitrogen limitation in the lower Elbe River.  

This study was funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany‘s Excellence Strategy – EXC 2037 “CLICCS - Climate, Climatic Change, and Society” – Project Number: 390683824, contribution to the Center for Earth System Research and Sustainability (CEN) of Universität Hamburg.

How to cite: Schulz, G., Sanders, T., Ankele, M., van Beusekom, J., and Dähnke, K.: A possible nitrogen limitation ahead? Low discharges fuel nitrogen retention in the Elbe estuary, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14707, https://doi.org/10.5194/egusphere-egu23-14707, 2023.

Water tables in floodplain aquifers rise and fall over a variety of timescales in response to changes in recharge, discharge, floods, and water use. To investigate the effects of water table fluctuations on DOC delivery to groundwater, an experiment was conducted at two Mediterranean sites: a pristine forested stream and an urban coastal floodplain. Groundwater was pumped into and out of the bottom of the soil column at varying rates to simulate water table fluctuations over a period of 16 days. Flooding events were imitated by inundating the top of the column with water sourced from nearby surface water features. The effects of repeated wetting and drying events on carbon mobilization, DOM quality, and geochemical responses were measured. Preliminary analysis reveals strong downward movement of DOC from soil layers after wetting events. SUVA at 254 nm increased with DOC concentrations compounds within pore waters during wetting events. During initial water table fluctuations, redox potential near the soil-aquifer interface was relatively stable but declined after subsequent wettings. Forthcoming analyses will also examine changes in the humification, fluorescence, and freshness indices of DOM from excitation-emission matrices. This study shows the influence of multiple saturation events on carbon mobilization and shallow groundwater biogeochemistry in unique floodplains.

How to cite: Scaccia, M., Gabor, R., Wilbert, F., Roumelis, C., Bernal, S., Welch, S., Carrera Ramirez, J., Folch, A., Salgot, M., Insalaco, A., and H. Sawyer, A.: Carbon delivery to floodplain aquifers in response to water table fluctuations: Observations from soil column experiments, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16927, https://doi.org/10.5194/egusphere-egu23-16927, 2023.

Estuaries are an important component of the global carbon budget as sites of removal and transformation for carbon between land and coastal ocean. Drought conditions can lengthen river and estuarine water residence time, which can extend the retention and alter the cycling of organic carbon and nutrients. To better understand the functioning of an estuary under the current threat of climate change related droughts, we use the Elbe Estuary as an example, examining a period since 1997, when annual mean DIC in the mid to lower Elbe Estuary increased significantly, and with focus on the drought conditions since 2014. 

The recent (1997-2020) significant DIC increase by 6 to 15 µmol L^-1 yr^-1 we found is due to increase in upper estuary POC content of 8-14 µmol L^-1 yr^-1 in late spring and summer (May-August). The significant increase in POC was associated with dominating autotrophy (with negative AOU and pH > 9), and an overall improvement in water quality shown in significant (> 50%) decrease in BOD₇ since 1997. We found that microbial respiration of organic matter from upstream regions accounted for most of the DIC produced in the mid-estuary, therefore, the increased POC is efficiently remineralized to DIC by the mid-estuary region.

The Elbe River and estuary was subject to significantly lower river discharge between 2014 and 2020 (468 ± 234 m³ s^-1), nearly 40% of the long-term average (1960-2020, 690 ± 441 m³ s^-1). In addition, May was the only month with a significant negative trend in mean monthly river discharge from 1997, and down to 264 ± 19 m³ s^-1 by 2020, a discharge usually observed during summer and early autumn. During the recent drought period (2014-2020), the internal gain in the carbon load as DIC in the mid to lower estuary was significantly higher, by up to 3 times, compared to the non-drought period (1997-2013). This suggests that the drought in the Elbe watershed caused a significant reduction in the average river discharge in May, likely increasing the residence time in the estuary, subsequently permitting a longer period for remineralisation of POC and greatest production of DIC in the mid-lower Elbe Estuary.

How to cite: Rewrie, L., Voynova, Y., Beusekom, J., Körtzinger, A., Ollesch, G., and Baschek, B.: Recent inorganic carbon increase in a temperate estuary driven by water quality improvement and enhanced by droughts, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13399, https://doi.org/10.5194/egusphere-egu23-13399, 2023.

The role of rivers in global carbon cycles are important, especially in regard to the dissolved carbon dynamics and its variability for shorter period timescales. The contribution of non - perennial rivers on global carbon cycle has not been understood clearly, where the environmental controls on dissolved carbon in such rivers is not yet defined. Hence, the objective of the present study is to assess the seasonal and spatial variations of dissolved carbon export in a non-perennial river, Cauvery, India. The river water and the adjacent groundwater samples were collected along the river at 28 locations on quarterly basis from 2013 to 2021. The samples were analysed for pH, temperature, major ions, DIC, DOC, nutrients and ¹³C-DIC. The DIC concentrations were low at the locations near to the origin of the river, whereas it was vice-versa for DOC concentrations. The  source of DIC  was  due to both geogenic and biogenic, where the weathering of rocks majorly influences the DIC concentration. The silicate weathering is significant during the wet periods, whereas carbonate weathering was dominant during dry periods. The soil organic carbon along with microbial process, autrotrophic production influences the DOC concentration. The transport of dissolved carbon was high during monsoon periods and was very less during dry seasons due to lower discharge and damming.  It is estimated that the Cauvery river accounts about 5% of total DIC and 1% of total DOC transported to the Bay of Bengal from the rivers. Hence, the study implies that the seasonal variation of carbon exports in the rivers should be accounted in carbon budgets.

How to cite: Ramesh, R., Keerthan, L., and Lakshmanan, E.: Evaluation of the spatial and seasonal variations in the Dissolved Carbon Export of a non - perennial tropical river, Cauvery, Southern India, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13049, https://doi.org/10.5194/egusphere-egu23-13049, 2023.

With global warming, a rising amount of people will be affected by water scarcity and droughts. At the same time, precipitation intensities and thus flood risks are projected to increase. Since these extremes often occur in the same location, co-management strategies of floods and droughts may offer a promising solution. The project Smart-SWS, funded by the BMBF as part of the initiative WaX – Hydrological Extreme Events, links drought prevention and flood protection with a concept for infiltrating flood waves into riverine aquifers as decentralized, technically supported underground storage. The two main challenges of the project are ensuring water quality with respect to health and environmental risks and controlling clogging of the system. The temporal asymmetry between very rapid infiltration of a flood wave and long-term storage in the aquifer, coupled with relatively long periods of no infiltration, results in stringent requirements for infiltration system design and materials.

The goal of the infiltration process is to improve retention of undesirable materials while maintaining high infiltration rates. As part of this work, potential materials will be evaluated for their suitability for infiltration of flood waters into the aquifer. For this purpose, river water quality needs to be seasonally monitored. Parameterization and characterization of clogging can be performed in column experiments using different potential materials, at different hydrodynamic and hydrochemical conditions, and with defined infiltration and dry phases. Established concepts for the transport of (bio)colloids as well as the substitution of contaminants by fluorescent tracers with similar sorption properties can be used to demonstrate the efficiency of retention and the local formation of clogging in time and space.

To test potential materials for the infiltration ditches and their contaminant retention behavior during wetting and drying cycles, a transparent column setup with temperature, pressure, electrical conductivity, redox potential, pH, and turbidity probes, as well as visual monitoring was established. This allows to record spatially resolved breakthrough curves, depositions, and reactions. We expect an increase of contaminant retention with an increase of filtered fines from the infiltrated water. Both, inorganic and organic colloids, are tested for this purpose and supplemented by experimental data from field sites. The shear forces in the porous materials are matched to the expected shear forces in the infiltration ditch. The hydrochemical stress due to a reduction in ionic strength during infiltration is also simulated in the experiments.

With this work, the behavior of contaminants and particles in infiltration systems can be predicted and optimized in order to fulfil environmental and legal requirements for the water quality.

How to cite: Augustin, L. and Baumann, T.: Infiltrating flood waves into aquifers: Column experiments on the suitability of filter materials, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5723, https://doi.org/10.5194/egusphere-egu23-5723, 2023.

Cultural eutrophication due to the increasing demand of an expanding population has posed negative impacts on estuarine systems worldwide. In tropical regions, the variability in the inputs of nutrients and organic matter from rivers to coasts is further influenced by the changing monsoon seasons. This study examined the water quality and carbonate chemistry in a semi-enclosed estuary in the northwest Philippines that is used for farming milkfish and other aquaculture species. Data suggests that the mariculture area is a heterotrophic system enriched in dissolved inorganic carbon and pCO₂ but depleted of nitrate due to the decomposition of unconsumed and undigested fish feeds from mariculture activities. The different river systems surrounding the estuary act as nitrate sources that could relieve nitrogen limitation during the wet season. Results also show hypoxic conditions not only in mariculture waters but in river systems as well. Accounts of the overflow of hypoxic river waters to the mariculture area could potentially provide a different mechanism of fish kill occurrence and requires further scientific observations. pH data confirm fast rates of coastal acidification in mariculture waters due to organic matter decomposition to levels that are expected to be experienced by the end of this century in open ocean conditions considering the air-sea equilibrium of increasing atmospheric CO₂. These results highlight the need for more advanced biogeochemical and transdisciplinary investigations of these transition zones and their implications on climate, biodiversity, and sustainability.  

How to cite: Ferrera, C., Isah, R., Co, J., Tavita, R. A., and Perez, J. N.: Water quality and carbonate chemistry dynamics in an estuarine system impacted by mariculture, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16468, https://doi.org/10.5194/egusphere-egu23-16468, 2023.

Extreme weather events magnified by climate change will likely increase the frequency of severe flooding. In this work, we studied the effects of climate change on flooding and cholera infections associated with contaminated floodwater in the Alajo neighbourhood in Accra, Ghana, by considering projected rainfall from different climate scenarios of the GFDL-ESM4 climate model, SSP1-2.6, SSP3-7.0 and SSP5-8.5.

Rainfall of daily resolution projected by the climate scenarios was disaggregated into five-minute resolution time series using a multiplicative microcanonical cascade model, and resulting extreme events were simulated using a 1D SWMM model of the subcatchments coupled with a 2D parallel diffusive wave model (P-DWave) of Alajo. The concentration of V. cholerae in the floodwater was further simulated as coming from open drains in the neihbourhood.  

Following the flood simulation, the post-flood phase was further simulated, where the V. cholerae concentration was estimated using a constant pathogen die-off rate, and infiltration and evaporation of the post-flood ponds.

Using a quantitative microbial risk assessment (QMRA), the probabilities of infection for both adults wading and young children playing or swimming in the post-flood ponds was estimated with a Beta-Poisson dose response model for the El Tor V. Cholera biotype. The QMRA was integrated into the flood risk assessment framework, by replacing the consequence component with infection probability. The expected annual probability of infection (EAPI) for each climate scenario was then found by numerically integrate over the precedence probability.

It was found that the mean estimated EAPI is higher for young children than for adults in the study area, but only differs slightly between climate scenarios. This study highlighted the areas most vulnerable to flooding and associated cholera outbreaks, and further development of these techniques could help with decision making on preventative measures for affected areas.

How to cite: Jónsdóttir, A. E., Müller-Thomy, H., Leandro, J., and Huang, J.: Flood modelling using disaggregated rainfall time series and estimating the probability of cholera infection from post-flood ponds in Accra, Ghana, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16261, https://doi.org/10.5194/egusphere-egu23-16261, 2023.

High-quality inland water is crucial for human life, as well as for preserving the biodiversity of the involved ecosystems and habitats. The implementation of adequate monitoring systems for inland water quality is requested by the EU Water Framework Directive, as well as foreseen within the Sustainable Development Goals of the 2015 Agenda of the United Nations. Ocean-color remote sensing may represent a useful tool to complement ground-based measurements, since it ensures synoptic view as well as a good trade-off between spatial and temporal resolution. Among the water quality parameters that can be retrieved by satellite, Total Suspended Matter (TSM) is one of the most relevant, because its fluctuations can affect light penetration and phytoplankton productivity, thus threatening the ecological status of inland waters. Optical sensors such as OLI (Operational Land Imager) onboard Landsat 8 and 9 and (MSI Multispectral Instrument) on Sentinel 2A and 2B, have already demonstrated their capabilities in providing accurate TSM retrievals with spatial resolution up to 20 and a sub-weekly temporal resolution, especially when jointly used. In this work, the long-term spatiotemporal TSM variability by satellite data has been investigated for a subset of the Segre and Ebro river confluence, just downstream the Mequinenza dam (province of Saragozza, North-East Spain). This area has been studied within the framework of the IDEWA (Irrigation and Drainage monitoring by remote sensing for Ecosystems and Water resources management) project, funded by the EU PRIMA program, to assess the impacts of irrigation activities (including drainage) on water quality within the Algerri Balaguer irrigation district. The assessment of TSM climatology, its inter-annual variability and the identification of potential extreme TSM plumes have been performed also for comparison with river discharge (Q) data (free available by the Confederación Hidrográfica del Ebro), measured close to the Mequinenza dam for the 2015-2022 period and the achieved results will be discussed in this work.

How to cite: Lacava, T., Albano, F., Ciancia, E., Filizzola, C., Lahsaini, M., Mazzeo, G., and Pietrapertosa, C.: Analyzing Total Suspended Matter variability at the Ebro-Segre river confluence (North-East Spain) by satellite data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6719, https://doi.org/10.5194/egusphere-egu23-6719, 2023.