Environmental DNA (eDNA) analysis for rapid non-invasive species detection across the tree of life. Once the eDNA is released into the environment it can move through a landscape, aggregating as waterways converge. Thus, hydrological knowledge of a landscape benefits the interpretation of eDNA data. Simultaneously, eDNA may be utilized as a natural hydrologic tracer. To fully utilize eDNA as a tracer molecule, the ecology of eDNA i.e. its production, degradation, and transport have to be well understood. However, eDNA itself is a complex mixture comprising of different states, namely membrane-bound, dissolved, and adsorbed states with varying persistence times and transport potentials.
In this presentation, I will provide an overview of eDNA states, how they are formed and what we know about them. Then I will explore methods for sorting these eDNA states from a single sample. Lastly, I will show data from large study spanning eight lake watersheds comprising samples collected from 221 sites collected from the headwaters to lakes of 58 streams in eight Swiss watersheds. All the samples were state sorted and analyzed with board range metabarcoding assays for identifying metazoan diversity. The results show that while most biodiversity information is enveloped in the membrane-bound state, each eDNA state has a district diversity signature. Our results show that the metazoan diversity signals remain closely linked for samples within a given stream, they diverge significantly once the stream enters a lake, highlighting the use of natural eDNA input to track water movement.
How to cite: Kirtane, A., Doppman, Z., van der Loo, E., and Deiner, K.: From Fragments to Flow: Decoding eDNA States to Illuminate Hydrologic Processes, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21797, https://doi.org/10.5194/egusphere-egu25-21797, 2025.
The combined effects of rapid urbanization and climate change challenge ecohydrology and water quality in urban systems. Water related nature-based (aquaNBS) solutions such as stormwater ponds and streams are being widely implemented in cities to address ecological and hydrological challenges that threaten urban biodiversity and water security. However, there is still a lack of process-based evidence of ecohydrological interactions in urban aquaNBS, and their relationship to water quality and quantity at the ecosystem level. As part of a pan-European project aimed at understanding ecohydrological functioning and future resilience of aquaNBS, we applied a novel, integrative multi-tracer approach using stable water isotopes, hydrochemistry and environmental DNA to disentangle the effects of urbanization and hydroclimate on ecohydrological dynamics in urban aquaNBS. Insights from stable isotopes and microbial data show a strong influence of urban water sources (i.e. treated effluent, urban surface runoff) across stream NBS. This highlights potential limitations of aquaNBS contributions on water quality and biodiversity, as microbial signatures appear more biased towards potentially pathogenic bacteria in these streams, compared to non-effluent impacted systems. Urban ponds appear more sensitive to hydroclimate perturbations, causing increased microbial turnover and lower microbial diversity than expected. Within the European dataset, diatom richness revealed an overarching influence of urbanization and urban water sources, as well as the presence of unique species in more naturalized sites. This demonstrates the need to adequately consider nutrient variability as well as aquatic organisms in planned restoration projects, particularly those implemented in densely urbanized ecosystems. Our findings highlight the use of novel integrated tracer approaches to explore the interface between ecology and hydrology, and provide insights into the ecohydrologic functioning of aquaNBS and their potential limitations. We illustrate the benefit of coupling ecological and hydrological perspectives through multiple environmental tracers, and hope to support future aquaNBS design and applications that consider the interactions between water and the ecosystem more effectively.
How to cite: Warter, M. M., Tetzlaff, D., Vierikko, K., Goldhammer, T., Monaghan, M. T., and Soulsby, C.: Tracing ecohydrology and biodiversity in aquatic, urban nature-based solutions integrating water stable isotopes, water chemistry and eDNA , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2230, https://doi.org/10.5194/egusphere-egu25-2230, 2025.
The analysis of environmental DNA (eDNA) from sediments has become an important method to study past ecosystem dynamics, offering new perspectives for paleoecological research. Yet, the temporal and spatial variability in DNA sources and transport pathways to the sediment remain underexplored. We studied how the plant DNA signal varies between annual lamina (or varves) in the sediment from Nylandssjön, a small boreal lake in northern Sweden, between 1991 and 2020. During this time period the vegetation community composition in the catchment was stable without any known drastic changes between years. Hence, observed differences in the eDNA signal between varves (years) will be related to differences in DNA transport and preservation.
We find that the overall vegetation community structure is similar between varves (years), emphasizing the robustness of eDNA for whole-ecosystem analyses. However, both the number of taxa and genera varies considerably between varves, suggesting that there is significant between-year difference in the source area, transport, and/or preservation of DNA in the sediment. This implies that records of individual taxa – particularly more rare taxa – need to be interpreted with caution. Interestingly, some individual taxa have strong between-varve (year) fluctuations in absolute reads, suggesting differences in the transport and deposition of plant fragments could play an important role in forming the DNA signal. Our results highlight that we need a better understanding of the variability in transport pathways and deposition of DNA from the lake catchment to the sediments in order to reliably interpret eDNA signals in sediment records.
How to cite: Morlock, M. A., Blåhed, I.-M., Rydberg, J., Huang, D. Y.-T., Rodriguez Martinez, S., Klaminder, J., and Bigler, C.: Sources and transport pathways of plant DNA in lake sediments: Lessons from an annually resolved record, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8967, https://doi.org/10.5194/egusphere-egu25-8967, 2025.
Groundwater ecosystems host diverse and largely unexplored communities of planktonic prokaryotes that play critical roles in global biogeochemical cycling and maintaining drinking water quality. This study investigated the spatiotemporal dynamics of prokaryotic communities in a sandstone aquifer at depths of 70-338m. By integrating spatial surveys across 48 pumping boreholes in England with temporal analyses by seasonal repetition and groundwater ‘piston flow age’ analysis, we investigated how variations in age, depth, and drift thickness influence nutrient availability and microbial communities. The prokaryotic community structure was assessed by 16S rRNA gene amplicon sequencing, groundwater recharge age using CFC-12 (dichlorodifluoromethane), borehole characteristics and surface connectivity from using borehole logs, with further analysis of total dissolved nitrogen (TDN), dissolved organic carbon (DOC) and dissolved oxygen (DO) concentrations. Seasonal analyses revealed minimal shifts in dominant taxa between recharge and recession periods, with no detectable introduction or extinction of surface-derived taxa. However, there was 7% change in DOC, TDN and 35% reduction in DO between recharge and recession periods. This lack of community shift may be attributed to the high filtration capacity of the sandstone aquifer preventing surface taxa intrusion during recharge. A high Shannon diversity index (5.4) indicated a stable and highly diverse groundwater community. The microbial community structure and nutrient availability varied significantly along vertical gradients of groundwater age, screened interval depth, and drift thickness, with distinct assemblages in shallow unconfined versus deeper confined sites. Nutrient cycling patterns by these communities were inferred from nutrient profiles. Unconfined sites with thinner drift (1–10 m), shallower screen depths (23-36m) and younger water (1972–2023) exhibited abundance of ultrasmall heterotrophic families, including Omnitrophaceae, Nanoarchaeia, and classes Crenarchaea and Parcubacteria. In these primarily aerobic environments, DOC limitation (0.7 mg/L) could prevent denitrification resulting in higher legacy TDN accumulation (9.5 mg/L) from anthropogenic additions of nitrogen-based fertiliser. The dominant ultrasmall heterotrophic prokaryotes may perform cryptic (or hidden) carbon and nitrogen cycling where rapid turnover of redox species drive biogeochemical cycling or may act as parasites. Conversely, confined sites with thicker drift (10–142 m), deeper borehole perforation depths (40-124m) and older groundwater recharge ages (1953–1967) were dominated by autotrophic families such as Gallionellaceae, Rhodocyclaceae, Hydrogenophilaceae and Comamonadaceae. These autotrophs may facilitate iron and sulphur cycling in the anaerobic parts of the confined aquifer. The intermediate depth and age ranges exhibited a mix of both autotrophs and heterotrophs indicating a transition phase. These findings highlight the role of aquifer architecture and groundwater residence time in shaping the spatiotemporally heterogeneous prokaryotic communities. The spatially unique communities influence the local nutrient cycling and thus the water chemistry, which should be considered when designing sustainable groundwater management strategies.
Keywords: Groundwater, Planktonic prokaryotes, Spatio-temporal variation, Nutrient cycling, Groundwater age.
How to cite: Bhattacharyya, A., Goodall, T., Gooddy, D., Read, D. S., Sorensen, J., and Surridge, B.: Decadal evolution of groundwater planktonic prokaryotes in a sandstone aquifer, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9606, https://doi.org/10.5194/egusphere-egu25-9606, 2025.
Large floodplain rivers are among the most species-rich and complex systems, characterized by high spatiotemporal dynamics. The exchange between communities of different patches in space and in time depends on hydrological conditions that impact the distribution of species and their interactions. This complexity makes it particularly challenging to identify key features of communities, including species interactions, which are also influenced by dynamic dispersal patterns. We collected eDNA data for fish and amphibians across two floodplain systems along the Danube over three years, capturing a range of hydrological conditions from post-flood to extended dry periods. Using an approach based on Bayesian networks we analyze for species co-occurrence patterns accounting for spatial, temporal, and dynamic autocorrelation as well as environmental conditions. In the second step, we applied a graph-theoretic approach to depict and analyze the relationships between species and define discrete communities. Our results reveal that species differ in their migration intensity, as reflected in the varying significance of temporal and spatial autocorrelation within the system, i.e., having continuous impact in local communities or impact changes over time or hydrological conditions. Further, we identified different communities in the system, including one clearly delineated consisting of amphibians and a few stagnotopic fish species showing negative interaction with other fish communities, alongside more open fish communities, i.e., often showing positive interactions with other communities. Different species interactions such as predator-prey interactions within fish as well as between fish and amphibians, are well delineated in the network. Several invasive fish species are also strongly interacting, they show relatively high connectivity within the species network. Overall, our approach contributes to a more mechanistic understanding of species interactions in complex, dynamic systems.
This research acknowledged support from the Austrian Science Fund (FWF) project RIMECO (I 5006), the EU Projects H2020 MERLIN (grant agreement No 101036337), HEU Danube4all (grant agreement No 101093985) i-CONN’ H 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement number 859937. Furthermore, the Austrian Federal Ministry for Digital and Economic Affairs and the Christian Doppler Research Association supported the work via the Christian Doppler Laboratory for Meta Ecosystem Dynamics in Riverine Landscapes (CD Laboratory MERI).
How to cite: Funk, A., Erős, T., Landler, L., Meulenbroek, P., Pont, D., Recinos Brizuela, S., Bilous, O., Valentini, A., and Hein, T.: Analysis of species interaction networks in a fish and amphibian floodplain metacommunity using eDNA metabarcoding., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11269, https://doi.org/10.5194/egusphere-egu25-11269, 2025.
High-intensity rainfall events have become more frequent and occur erratically over the past decade. These intense storms can overwhelm agricultural soils and significantly modify the dynamics of drainage networks. Structural (legacy) connectivity, which self-organizes within the drainage system, interacts with functional (contemporary) connectivity—the various fluxes in and out of the system. Together, they affect the imprint of the landscape surficial mosaic and exert non-linear filters to key hydrogeomorphic and biochemical processes thereby impacting transport and transformation of water and other constituent fluxes in and out of a watershed.
In our study, we present a nested network of water–sediment–nutrient measurements strategically positioned within USDA-ARS LTAR (Long-Term Agricultural Research) drainage networks. This approach captures discrete snapshots of event hillslope evolution phases in space and with time to quantify the high spatial and temporal variability of property heterogeneity through the drainage network and the feebacks that heterogeneity modification has on fluxes in and out a hillslope. We propose a systems-based approach to identify key mechanisms and parameters driving system dynamics, aiming to develop monitoring schemes that account for both management practices and climate effects in agricultural watersheds. Researchers posit that both management practices and climate play a pivotal role in shaping the response of agricultural watersheds. Specifically, alterations in transport times and the fluxes of water, sediment, and nutrients are influenced by these factors. These findings contribute to a deeper understanding of landscape processes and serve as a foundation for developing improved management guidelines.
How to cite: Papanicolaou, T., Wacha, K., and Abban, B.: The role of connectivity (or lack of it) on biogeochemical signal propagation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4822, https://doi.org/10.5194/egusphere-egu25-4822, 2025.
River water quality is essential for ecosystem function and human well-being, yet anthropogenic impacts, such as pollutant input from agricultural activities or waste water, threaten water resources. An effective design of water quality monitoring networks is crucial to understanding and mitigating these impacts. However, optimizing monitoring is challenging because of the spatial and temporal variability of water quality, i.e. solute concentrations, driven by landscape and hydroclimatic heterogeneity.
This study uses a stochastic modeling approach applied to artificial river networks to explore how landscape and hydroclimatic heterogeneity at different spatial scales shape the space-time variance of water chemistry. Building on a previously developed headwater-scale stochastic water quality model, we simulated daily discharge and solute concentration time series for equal area subcatchments within these networks. We systematically varied the spatial configuration of subcatchment solute source concentration across the network, the source zone distribution within subcatchments, and imposed different hydroclimatic regimes. Simulated discharge and solute loads were routed through the network, incorporating in-stream processing, to generate water quantity and quality time series for each network node. A global sensitivity analysis using the Morris method was performed to assess the influence of key parameters on the space-time variance of solute concentration.
The results of the sensitivity analysis revealed that the macro-scale landscape configuration of source concentrations controls the spatial variability of solute concentrations in rivers and spatial stability, i.e. the persistence of spatial patterns through time. The relative influence of structured and random landscape heterogeneity on spatial variability was scale dependent, with distinct patterns observed across different stream orders. In contrast, subcatchment-scale processes, such as the source zone distribution, and the hydroclimatic forcing regulate temporal variability of water quality and synchrony between subcatchments. We conclude that optimal water quality monitoring network design should thus quantify spatial and temporal variability across scales, leveraging concepts like spatial stability and synchrony to maximize information gained and explicitly accounting for multiscale landscape heterogeneity.
How to cite: Schauer, L. S., Jawitz, J. W., Cohen, M. J., and Musolff, A.: Controls of space-time variance of water chemistry in river networks, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10419, https://doi.org/10.5194/egusphere-egu25-10419, 2025.
In Europe, water management at the river basin district scale requires to satisfy both human supply and ecological preservation to achieve the Water Framework Directive (WFD) objectives. Freshwater resources are essential for human needs and ecosystem balance, but factors like climate extremes, population growth, and pollutant pressures pose serious challenges. Environmental flow (e-flow) is defined as the water flow required to sustain aquatic ecosystems, but traditional methods to establish e-flow thresholds at large spatial scales lack comprehensive ecological relevance. This work discusses the effects of droughts on the ecological status of rivers, focusing on developing diagnostic tools to assess the impact of water scarcity. To address this, the study introduces the Eco-Hydrological Distance Index (EHDI), a metric that integrates hydrological balance, ecological indicators and anthropogenic pressures to evaluate how deviations from e-flow thresholds affect river ecosystems, especially during droughts. Using the Standardized Precipitation Index (SPI) to assess drought severity, the research analyses rainfall data from Tuscany (2001–2020) and compares SPI values with EHDI across different river basins in the Arno River system (Italy). The results reveal a strong correlation between SPI and EHDI, with droughts significantly impacting the ecological status of rivers. The study identifies critical SPI thresholds, below which river basins risk reaching "bad" ecological status, defined by a substantial loss of biological communities. These thresholds vary across basins due to factors like hydrological conditions, water abstraction, and anthropogenic pressures. This research highlights the need for integrating hydrological and ecological metrics to improve water management strategies at the river basin district scales. By providing tools to predict the ecological impact of droughts, it aims to support sustainable management of water resources and protect ecosystem services essential for biodiversity and human wellbeing.
Acknowledgment: This study was carried out within the RETURN Extended Partnership and received funding from the European Union Next-GenerationEU (National Recovery and Resilience Plan – NRRP, Mission 4, Component 2, Investment 1.3 – D.D. 1243 2/8/2022, PE0000005)
How to cite: Arrighi, C., Lompi, M., De Simone, M., and Castelli, F.: A New Diagnostic Approach to Assess the Ecological Impact of Droughts on Rivers , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10281, https://doi.org/10.5194/egusphere-egu25-10281, 2025.
Climate warming is causing more extreme weather conditions, with both larger and more intense precipitation events as well as extended periods of drought in many regions of the world. The consequence is an alteration of the hydrological regime of streams and rivers, with an increase in the probability of extreme hydrological conditions. Mediterranean-climate regions usually experience extreme hydrological events on a seasonal basis and thus, freshwater Mediterranean ecosystems can be used as natural laboratories for better understanding how climate warming will impact ecosystem structure and functioning elsewhere. Here, we revisited and contextualized historical and new datasets collected at Fuirosos, a well-studied Mediterranean intermittent stream naturally experiencing extreme hydrological events, to illustrate how the seasonal alternation of floods and droughts influence hydrology, microbial assemblages, water chemistry, and the potential for biogeochemical processing. Moreover, we revised some of the most influential conceptual and quantitative frameworks in river ecology to assess to what extent they incorporate the occurrence of extreme hydrological events. Based on this exercise, we identified knowledge gaps and challenges to guide future research on freshwater ecosystems under intensification of the hydrological cycle. Ultimately, we aimed to share the lessons learned from ecosystems naturally experiencing extreme hydrological events, which can help to better understand warming-induced impacts on hydrological transport and cycling of matter in fluvial ecosystems.
How to cite: Bernal, S., Ledesma, J. L. J., Peñarroya, X., Jativa, C., Catalán, N., Casamayor, E. O., Lupon, A., Marcé, R., Martí, E., Triadó-Margarit, X., and Rocher-Ros, G.: Expanding towards contraction: the alternation of floods and droughts as a fundamental component in river ecology, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3312, https://doi.org/10.5194/egusphere-egu25-3312, 2025.
The construction and operation of reservoirs disrupt the natural flow regime of rivers, reducing flow velocities and creating prolonged anaerobic conditions, particularly in steep-gradient, deeply incised river channels. These conditions facilitate microbial decomposition of organic matter—originating from terrestrial plants and soils—leading to greenhouse gas emissions, such as carbon dioxide (CO₂) and methane (CH₄). Cascade reservoir systems, composed of multiple reservoirs connected in an upstream-downstream configuration, introduce further complexities due to the interactions between upstream discharges and downstream reservoirs. These interactions influence water temperature, flow disturbance, and material transport, among other factors.
The study employed the CE-QUAL-W2 model to developed a coupled hydrodynamic and water quality model for analyzing carbon transmitting among the five cascade reservoirs along the Wujiang River in Southwest China (Figure 1). This two-dimensional model, uses x-z plane layered grids to simulate water flow, temperature, and carbon cycling dynamics under specific power station intake location scenarios. By simulating these scenarios, we assessed how changes in power station intake elevations influence the carbon balance of individual and cascade reservoir systems.
Figure 1 The Wujiang River basin and the spatial distribution of five cascade reservoirs
The results indicate that for individual reservoirs such as WJD Reservoir, raising the intake elevation of the power station enhances surface water disturbance, which enhanced CO₂ diffusion across the water-air interface near the dam (Figure 2). However, this adjustment significantly reduces carbon release to downstream areas, thereby increasing the reservoir’s overall carbon retention capacity.
Figure 2 Average CO2 diffusion fluxes across the water-air interface in the WJD Reservoir under different scenarios (scenario A-G represent progressively higher intake elevations at the WJD power station.
When the intake elevation of upstream DF Reservoir was raising, its carbon retention capacity improved. However, the warmer discharged water inhibits vertical carbon sedimentation in downstream reservoirs. This led to the accumulation of Total Inorganic Carbon (TIC) and Total Organic Carbon (TOC) in shallow water layers of downstream reservoirs (Figure 3).
Figure 3 Vertical distribution of TOC (left) and TIC (right) at the WJD reservoir dam under different intake elevations of upstream hydropower stations (Scenarios I–V represent progressively higher intake elevations).
Consequently, carbon transport to downstream reservoirs increased, reducing the total carbon sink capacity of the cascade reservoir system. The findings highlight a trade-off between local and system-wide carbon retention in cascade reservoirs. While elevating intake locations at individual reservoirs can improve carbon retention locally, the downstream impacts—such as reduced vertical carbon sedimentation and increased carbon transport—diminish the overall carbon storage efficiency of the cascade reservoirs system. Future reservoir management strategies should consider these complex interactions to balance energy production with environmental sustainability.
How to cite: Wu, X., Wang, Z., and Xiang, X.: The Impact of Water Intake Scheduling on Cascade Reservoirs on the Carbon Balance of Reservoir Systems , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-475, https://doi.org/10.5194/egusphere-egu25-475, 2025.
Headwater streams are critical control points for carbon dioxide (CO2) emissions to the atmosphere, traditionally assumed to originate primarily from terrestrial sources. However, in-stream metabolic activity can become a substantial CO2 source, particularly in water-scarce regions characterized by net heterotrophic streams and low groundwater inputs. To explore this idea, we analyzed patterns of CO2 and oxygen (O2) concentrations at high-temporal resolution alongside stream aerobic metabolic rates to identify CO2 sources under contrasting hydrological conditions in an intermittent, oligotrophic Mediterranean stream. During high-discharge periods, there was no correlation between O2 and CO2 concentrations, and O2-CO2 patterns indicated CO2 oversaturation. These results indicate that despite ecosystem respiration (ER) predominated over gross primary production (GPP) during high-discharge periods, lateral groundwater inputs were likely the dominant source of CO2 emissions within the stream. Under low-flow conditions, GPP was still low in this net heterotrophic stream. Yet. a negative relationship between O2 and CO2 concentrations emerged, suggesting a major role of in-stream metabolic activity in driving O2-CO2 dynamics. These findings reinforce the concept of headwater streams as key CO2 emitters, while emphasizing the influence of hydrological conditions on their dual role: acting as chimneys for terrestrially-derived CO2 during high-flow periods and as active carbon biogeochemical reactors during low-flow periods.
How to cite: Jativa, C., Bernal, S., Rocher-Ros, G., Peñarroya, X., Ledesma, J. L. J., and Lupon, A.: Inferring the role of fluvial metabolism in CO2 emissions from O2-CO2 paired measurements across contrasting hydrological conditions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16443, https://doi.org/10.5194/egusphere-egu25-16443, 2025.
The availability of Dissolved oxygen (DO) sensors and open-source modelling tools has greatly expanded the breadth of knowledge regarding the metabolism of aquatic systems. River metabolism is one of the most integrative indicator of ecological health, it can be applied across diverse water systems, through continuous measurement systems, and is highly sensitive to environmental stressors as it reflects shifts in anthropogenic disturbance or management actions. While former studies showed that the estimation of aquatic ecosystem metabolism can be used as a relevant tool for urban water management, long-term metabolism investigations remain currently scarce, especially in large rivers.
Relying on the MeSeine Observatory, a sensor network of 8 sites measuring continuously DO and water temperature in the Seine River from upstream to downstream of Paris region, we examined 25 years of spatial and temporal variability of the river metabolism and its underlying drivers. Daily metabolic rates, including gross primary production (GPP), ecosystem respiration (ER), which both contribute to the net ecosystem production (NEP), were estimated using the single-station open-channel method, integrating hourly DO, temperature, and river discharge data.
Preliminary results reveal distinct seasonal and inter-annual patterns in GPP, ER and NEP rates. ER and GPP peaked in late spring and in summer, driven by high light availability, warm temperatures and low discharge, while the lowest rates occurred in winter across all sites. Inter-annual variations were primarily influenced by hydroclimatic conditions and sewage inputs. Annual mean rates of GPP, ER and NEP across all sites ranged from ~0.29 to ~2.3, ~-5.65 to ~-0.53, and ~-4.16 to ~0.51 gO₂.m⁻³.d⁻¹, respectively. ER consistently exceeded GPP, indicating a predominantly heterotrophic status downstream of Paris. Notably, the upstream site of the observatory (the only one before Paris) exhibited several years with positive annual NEP values. Along the river, net heterotrophy increased downstream, likely due to urban organic matter inputs. While GPP and ER displayed similar temporal patterns, NEP followed a distinct trajectory, aligning more closely with water quality, organic matter and nutrient concentrations. Moreover, in recent years, NEP tends to increase, reflecting a decrease of the heterotrophy and nutrient concentrations in the river.
The analysis demonstrates that the Seine River's metabolism has exhibited distinct seasonal and upstream-to-downstream trends over the past 25 years, driven by urban impacts, seasonal dynamics, and hydroclimatic conditions. Future work will focus on refining these observations to uncover long-term trends and establish clear relationships between metabolic rates and key environmental stressors across shorter timescales, with special focus on the structural components, hydrological information and sewage effluents. To assess ecological status and develop effective management tools, it is essential to understand the interactions between river components and the cause-effect mechanisms underlying aquatic ecosystem alterations.
How to cite: Njapou Mawa, P., Mouchel, J.-M., Escoffier, N., and Mougin, J.: Long-term variability in the metabolism of an aquatic ecosystem: results from 25 years of continuous dissolved oxygen monitoring in a large urban river., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17491, https://doi.org/10.5194/egusphere-egu25-17491, 2025.
The river is one of the most important freshwater ecosystems serving as a hub for water, gas, and energy exchange among land, ocean, and atmosphere. River ecosystem metabolism vibrates with external stresses such as solar radiation, flow stability, and temperature. We discovered that the internal factor dissolved inorganic carbon (DIC) plays a hidden role in amplifying riverine metabolic sensitivity, which, however, is rarely concerned. In this study, machine learning is used to reproduce global riverine DIC datasets, and then the global rivers are divided into high-DIC and low-DIC rivers. Apparent oxygen utilization (AOU) is used as an indicator of ecosystem metabolism intensity. High-DIC rivers exhibit intensified ecosystem variability, which is more obvious in colder climate zones. Facilitated gross primary production (GPP) by DIC boosts ecosystem respiration, which increases the risk of hypoxia and biological stress in high-DIC rivers. A modified Michaelis-Menten equation-based model is developed and well simulates the historical variation of global mean annual AOU. The model was further applied to project DIC’s role in long-term river ecosystem variation under different future climate scenarios. The model results demonstrate that high-DIC rivers have a higher risk of oxygen depletion in all scenarios with different applications of fertilizer situations compared with low-DIC rivers.
How to cite: Qi, H. and Liu, Y.: Hidden Threats of Dissolved Inorganic Carbon to River Ecosystem Metabolism, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17639, https://doi.org/10.5194/egusphere-egu25-17639, 2025.
Alkalinity in river ecosystems plays a crucial role in regulating carbon cycle across basin, regional, and global scales. Streamflow alkalinity acts as a pH buffer and drives the relative abundance of the different chemical forms of dissolved inorganic carbon (DIC), such as CO2, bicarbonate and carbonate ions. Higher alkalinity supports greater carbon retention in non-gaseous forms, reducing atmospheric CO2 emissions, while lower alkalinity weakens the buffering capacity, increasing water acidity and facilitating carbon loss to the atmosphere. Rivers, as dynamic links between terrestrial and marine environments, transport significant amounts of organic and inorganic carbon, making alkalinity a key driver of CO2 exchange between rivers and the atmosphere.
Dissolved inorganic carbon (DIC) in stream networks can originate from allochthonous sources, such as catchment soil respiration and rock weathering, or from autochthonous processes driven by stream metabolism, i.e. the net ecosystem production (NEP), the balance between gross primary production and ecosystem respiration. As recent literature highlights, understanding the complex interplay among DIC, oxygen, and stream metabolism requires spatio-temporal characterization of alkalinity, which influences the different forms of DIC, its exchange with the atmosphere, and its biological availability.
This study contributes to this field by investigating the alkalinity dynamics in the Valfredda stream network, a 5 km2 catchment in the Italian Alps characterized by pristine alpine conditions. Fed mostly by snowmelt, the Valfredda stream features cold, clear, oxygen-saturated waters with low nutrient concentrations. Its snowmelt-driven hydrology produces marked seasonal variations in flow rates and water temperatures, providing an ideal natural laboratory to study diverse conditions throughout the year.
Alkalinity was sampled at 12 locations within the river network approximately once a month. Additionally, daily sampling was conducted at the catchment outlet. Using a stream transport model based on a mass balance approach, we characterized the alkalinity concentration in the lateral discharge across different stream reaches. The combination of the model and the two datasets allowed investigating how alkalinity varied seasonally and spatially, revealing potential drivers such as land use, hydrology, or biogeochemical processes. At a selected stream reach, we combined alkalinity measurements with continuous monitoring of metabolic indicators: dissolved oxygen, pH, water and air temperature, and light intensity, using deployable sensors. By integrating data from discrete sampling and continuous monitoring, we quantified the DIC balance at the scale of a single stream reach. Future work aims to extend this approach to the entire network.
These insights lay the groundwork for understanding the role of alkalinity in shaping river DIC balance and influencing CO2 emissions. The comprehensive dataset will support the identification of seasonal trends and spatial patterns, offering a complete view of alkalinity dynamics within complex river network system.
How to cite: Presotto, F., Grandi, G., Piazza, R., and Bertuzzo, E.: Unravelling alkalinity and dissolved inorganic carbon dynamics in an alpine stream network, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9625, https://doi.org/10.5194/egusphere-egu25-9625, 2025.
Rapid expansion of Moso bamboo (Phyllostachys edulis) has been noted in East Asian countries, and replacement of riparian vegetation by dense bamboo has been observed in many areas. Changes in riparian vegetation have significant effects on stream ecosystems, but the effects of bamboo remain uncertain. In this study, leaf litter breakdown and leaching of dissolved organic matter (DOM) and nutrients in stream were compared between Moso bamboo and other riparian tree species to assess the effects of bamboo expansion on stream organic matter and nutrient dynamics.
Leaf litter of Moso bamboo and two evergreen species in riparian area, Camphor laurel (Cinnamomum camphora) and Japanese cedar (Cryptomeria japonica), that provide leaves to the stream in the same season as bamboo were compared. Litter bags with 5 g of leaf litter were incubated on the streambed in four riffles in July and August. Litter bags were collected 1, 8, 15, 28 and 42 days after the start of incubation to measure breakdown rates and leaching of DOM and nutrients. Macroinvertebrates in the litter bags at day 8 were also examined.
Breakdown rates of Moso bamboo was significantly lower than those of Camphor laurel and Japanese cedar. Despite the low macroinvertebrate breakdown rates, the number and species richness of macroinvertebrate present were highest in the bamboo litter bags. These results suggest that bamboo leaves were not palatable compared to Camphor and cedar litter, but they functioned as habitat for macroinvertebrate. Leaching of DOM was highest from Moso bamboo leaves at day 0, and it rapidly declined as breakdown progressed. Japanese cedar, on the other hand, released smaller amount of DOM, but maintained the similar rates despite the progress of breakdown. Leaching of bioavailable DOM (BDOM) was lowest from bamboo, 0.64 (± 0.84) mg/g of litter, and highest from Camphor leaves, 5.48 (± 0.99) mg/g, at day 0, and by day 8, leaching of BDOM became similar among species, 3.30 (± 0.67) mg/g, 3.67 (± 0.16) mg/g, 2.37 (± 0.86) mg/g respectively for Moso bamboo, Camphor laurel, and Japanese cedar. Thus, bamboo leaves leached larger amount of DOM, but BDOM was low, and the effects on in-stream nutrient processes may be smaller than other two species.
How to cite: Kasahara, T., Gourlaouen, A., and Tanaka, A.: Effects of bamboo expansion on organic matter and nutrient dynamics in mountain streams, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3873, https://doi.org/10.5194/egusphere-egu25-3873, 2025.
Greening is the optimal way to mitigate climate change and water quality degradation caused by agricultural expansion and rapid urbanization. However, the ideal sites to plant trees or grass to achieve a win-win solution between the environment and the economy remain unknown. Here, we performed a 12-year comprehensive observation in the Jiulong River watershed (southeastern China) and a nationwide survey on groundwater in China (n = 90), combining them with statistical and AI models to explore the linkages between land use within hydrologically sensitive areas (HSAs) and nitrogen concentrations/fluxes from the perspective of hydrological connectivity. We found that HSAs occupy approximately 20% of the total land area and are hotspots for transferring nitrogen from the land surface to rivers and groundwater. Increasing the proportion of natural lands within HSAs improves river and groundwater quality and reduces the exports of riverine nitrogen to coastal zones. These new findings suggest that prioritizing ecological restoration in HSAs is conducive to achieving harmony between the environment (improving watershed water quality and reducing river nitrogen export flux) and the economy (reducing investment in area management).
How to cite: Wang, Y., Chen, N., and Luo, X.: Ecological restoration guided by hydrological connectivity reduces nitrogen fluxes from river to coast, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10937, https://doi.org/10.5194/egusphere-egu25-10937, 2025.
Watershed ecosystems rely on energy and nutrient exchanges between terrestrial and aquatic systems, which influence carbon and nutrient cycles, biodiversity, and overall ecosystem dynamics. The synchronization of terrestrial and riverine productivity, referred to as coupling strength (CS), provides a useful metric for assessing ecosystem integration and responses to environmental change. Despite its importance, the spatial variability of CS and its environmental drivers remain poorly understood, particularly across regions with diverse natural conditions and human impacts. This study quantifies CS across over one hundred river sites and their upstream watersheds in the continental United States. Using explainable machine learning, we identified key environmental factors, including water temperature, river width, leaf area index, and watershed area, that exhibit distinct nonlinear relationships with CS. Clustering analyses revealed spatially diverse coupling regimes, influenced by a combination of ecohydrological processes and anthropogenic activities. These findings advance the understanding of how environmental conditions mediate synchronization between terrestrial and aquatic productivity. The results provide a foundation for future research into the mechanisms of land-water interactions and their responses to environmental stressors. By integrating these insights into broader ecological and hydrological frameworks, this work can support the development of predictive tools for watershed management under changing environmental conditions.
How to cite: Chen, S., Blougouras, G., Calamita, E., Lee, S.-C., Huang, J., and Jiang, S.: Patterns and potential drivers of land-water productivity coupling across U.S. river systems, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6815, https://doi.org/10.5194/egusphere-egu25-6815, 2025.
The proliferation of Azolla filiculoides, a fast-growing invasive aquatic fern, threatens river ecosystems worldwide by altering water quality and outcompeting native species. This study presents a novel approach for the global detection of A. filiculoides using Sentinel-2 satellite imagery and Random Forest classification within the Google Earth Engine (GEE) platform.
We utilized the high-resolution spectral data from Sentinel-2 to capture the unique reflectance characteristics of A. filiculoides. A Random Forest classifier, trained with ground-truth data from multiple riverine environments, was applied to distinguish A. filiculoides from other aquatic vegetation and surface water features. The robustness of the model was tested across time to ensure broad applicability. The method was tested and validated on the Tagus River (Spain) with manually labeled speies observations over several years.
The primary objective is to develop a scalable and user-friendly GEE application that enables near real-time monitoring and detection of A. filiculoides in river systems globally. This app is designed to support environmental managers and policymakers by providing accessible tools for early detection and effective management of this invasive species as well as to provide large scale species distribution data to leverage biogeogeographic studies of A. filiculoides.
Preliminary results demonstrate high classification accuracy (R² = 0.94) and the potential for the GEE app to facilitate large-scale monitoring. By integrating machine learning with cloud computing, our approach offers a cost-effective and efficient solution for the global challenge of invasive aquatic plant detection.
How to cite: Plakias, A. and Draga, M.: Detection of Azolla fillaculoides in River Systems using Sentinel 2 Imagery and Random Forest Classification in the Google Earth Engine , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19517, https://doi.org/10.5194/egusphere-egu25-19517, 2025.
Eutrophication, usually considered an overproduction of biomass in water bodies due to an enrichment of nutrients such as phosphorus (P) and nitrogen (N), is a common thread to riverine ecosystems. In Europe, chlorophyll a (Chl-a) concentrations, an indicator for algae biomass, have been successfully reduced from the 1980s by limiting phosphorus input into rivers. However, elevated Chl-a levels in European rivers are still found until today. As recent algae blooms were rather linked with drought periods than with particularly high phosphorus concentrations, the question is raised whether other parameters than phosphorus concentrations might be more crucial for eutrophication management in the future.
To understand the conditions under which rivers are particularly prone to an efficient conversion of phosphorus into algae biomass, we analyzed a Germany-wide dataset of Chl-a and total phosphorus (TP) concentrations with 31661 measurement pairs at 330 stations between 2000 to 2019. To quantify this conversion efficiency, we used the measure of the degree of realized eutrophication, αrealized, which is the ratio between the realized (i.e. the Chl-a measurement) and the potential eutrophication (i.e. a theoretical upper Chl-a concentration at a given TP level if all TP is converted to biomass). In a preceding study, we found that station-wise medians of αrealized are mainly controlled by water residence time with high median αrealized being either related to large rivers with a long distance to source or small rivers with close upstream lakes. As management not only asks where but also when Chl-a concentrations are at critical levels, we here analyze the temporal variability of αrealized at different stations. To that end, we calculate the coefficients of variability of αrealized, TP, and Chl-a, and statistically relate these characteristics to other instream parameters and catchment attributes at each station.
We find both stations with low αrealized variability and a positive TP - Chl-a correlation and stations with high αrealized variability and no or even a negative TP and Chl-a correlation. The former case suggests stable controls of αrealized and good predictability of Chl-a based on TP concentrations at the respective stations. The latter case implies either variable water residence times or additional controls by parameters with strong seasonality, such as light availability, water temperature, or ecological community shifts.
In this contribution, we will present whether high temporal variability of αrealized is predictable from instream parameters or catchment attributes and discuss the underlying processes. We will further conclude on the implications of the results for river management, particularly in terms of algae control and in light of climate change.
How to cite: Hubig, A., Scharfenberger, U., and Musolff, A.: Temporal variability of the realized eutrophication in rivers across Germany, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20204, https://doi.org/10.5194/egusphere-egu25-20204, 2025.
Environmental DNA (eDNA) consists of genetic fragments suspended in the water column. Recently, it has been heralded as an effective tool for biodiversity monitoring (Blackman et al., 2024), resulting in a considerable diversity of studies and data collection. Most of the data from these studies are published in open access repositories (e.g., ENA, eDNAexplorer, Genbank) but have minimal or no re-analysis, therefore offering a currently up-to-date resource. Recently, eDNA observations have been explored as a tool for understanding hydrological processes (Good et al., 2018; Mächler et al., 2021; URycki et al., 2024). Here, we explore published eDNA datasets that contain hydrologic data or are relevant for hydrology.
We have compiled published eDNA datasets that might also inform hydrologic process knowledge or be otherwise relevant for hydrology. For the moment, this is a metanalysis of those datasets and their publications, but as this work continues, we are exploring genetic and hydrologic data mining to repurpose this data for something other than its original intended objectives. In this presentation, we give an overview of our proposed workflow for hydrological reanalysis of published genetic data and define a baseline for large-scale reanalysis and future projects that want to satisfy both objectives (i.e. understand biology and hydrologic processes).
References
Blackman, R., Couton, M., Keck, F., Kirschner, D., Carraro, L., Cereghetti, E., Perrelet, K., Bossart, R., Brantschen, J., Zhang, Y., & Altermatt, F. (2024). Environmental DNA: The next chapter. Molecular Ecology, e17355. https://doi.org/10.1111/mec.17355
Good, S. P., URycki, D. R., & Crump, B. C. (2018). Predicting Hydrologic Function With Aquatic Gene Fragments. Water Resources Research, 54(3), 2424–2435. https://doi.org/10.1002/2017wr021974
Mächler, E., Salyani, A., Walser, J.-C., Larsen, A., Schaefli, B., Altermatt, F., & Ceperley, N. (2021). Environmental DNA simultaneously informs hydrological and biodiversity characterization of an Alpine catchment. Hydrology and Earth System Sciences, 25(2), 735–753. https://doi.org/10.5194/hess-25-735-2021
URycki, D. R., Good, S. P., Crump, B. C., Ceperley, N. C., & Brooks, J. R. (2024). Microbial community storm dynamics signal sources of “old” stream water. PLOS ONE, 19(9), e0306896. https://doi.org/10.1371/journal.pone.0306896
How to cite: Blackman, R., Ammann, U., and Ceperley, N.: Reanalysis of published eDNA for Hydrologic Process Understanding , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9194, https://doi.org/10.5194/egusphere-egu25-9194, 2025.
Recent studies highlight the critical role of changes in connectivity, erosion processes and sediment sources in shaping biological communities in palaeo-environmental reconstructions (e.g., Giguet-Covex et al., 2023; Morlock et al., 2023). Such processes can lead to misinterpretations attributing shifts in biodiversity around lakes to environmental changes, when in fact they may be due to the introduction of previously unconnected sediment sources driven by human activities (e.g. land management) or extreme climate events.
To assess the impact of changes in connectivity and accelerated erosion on biological communities, we analysed sediment archives from the Dzoumogné reservoir (Mayotte Island, France). This reservoir drains a small catchment (1038 ha) that underwent significant land-use changes (e.g. deforestation, agricultural intensification) during a well-documented period (2011-2021). We reconstructed land-use changes, erosion rates and sediment sources, as well as biological communities using sediment DNA (sedDNA) based on seven genetic markers targeting plants (trnL, rbcL), fungi (ITS), metazoa (16S, 18S) and vertebrates (12S).
Our results show a 450% increase in operational taxonomic units (OTUs) and shifts in OTUs detected in 23 taxonomic groups following the first deforestation phase (2012-2013) and subsequent agricultural intensification resulting in landscape fragmentation. During this period, sedDNA identified an increase in forest-derived species (e.g. Streptophyta and terrestrial fungi) and agricultural species (e.g. banana, cassava, cattle). These changes coincide with accelerated sediment delivery and erosion rates (+310% between 2011 and 2015). Between 2015 and 2021, declining water levels (driven by climate and human activities) combined with high sediment and nutrient inputs continued to drive major shifts in aquatic communities. These included increases in OTUs belonging to the taxonomic groups Chlorophyta and Ciliophora - key indicators of eutrophication and water quality degradation. The high primary production associated with algae and microorganisms likely explains the observed increase in invertebrate and fish communities higher up the trophic chain within just two years of changes in sediment connectivity and sources.
This study highlights how rapid shifts in biodiversity in both terrestrial and aquatic systems are driven by increased erosion and connectivity of previously isolated land use areas (e.g. forests, croplands). Understanding these connectivity dynamics is crucial to avoid misinterpretation of biodiversity change in lake sediment records.
References:
Giguet-Covex, C., Jelavić, S., Foucher, A., Morlock, M. A., Wood, S. A., Augustijns, F., Domaizon, I., Gielly, L., & Capo, E. (2023). The Sources and Fates of Lake Sedimentary DNA (pp. 9–52).
Morlock, M. A., Rodriguez‐Martinez, S., Huang, D. Y., & Klaminder, J. (2023). Erosion regime controls sediment environmental‐based community reconstruction. Environmental DNA, 5(6), 1393–1404.
How to cite: Foucher, A., Evrard, O., Maresceaux, J., Debortoli, N., Ambroise, V., Cerdan, O., Landemaine, V., and Desprats, J.-F.: Erosion processes and connectivity shape biological communities recorded by environmental DNA in sedimentary archive: implication for paleo-environmental reconstruction, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11775, https://doi.org/10.5194/egusphere-egu25-11775, 2025.
Northern freshwater ecosystems face a wide range of environmental changes, including climate change, eutrophication, and browning. In Arctic regions, climate warming is occurring nearly four times faster than the global average, leading to higher water temperatures, shorter ice-cover periods, and extended growing seasons for aquatic biota. These changes are expected to have both direct and indirect impacts on these ecosystems, including the microbial communities that underpin their biodiversity and functioning. Building on prior research by the authors, we tested the hypothesis that microbial communities, particularly prokaryotes (bacteria and archaea), exhibit similarities across circumpolar freshwater systems. To investigate this, we surveyed 46 lakes and 30 streams between 2019 and 2022 in Arctic (>70º N) and sub-Arctic (55–70º N) regions spanning Alaska, Canada, Greenland, Norway (including Svalbard), and Sweden. For each waterbody, we collected environmental DNA (eDNA) for 16S rRNA gene metabarcoding and water samples to analyze physical and chemical parameters (temperature, pH, electrical conductivity, and dissolved O2), major ions, and nutrients (organic C, P, and N).
Bacteria predominantly represented the main prokaryotic group in this study, with archaeal contributions limited to a few lakes in Svalbard and the Canadian Northwest Territories. Our results revealed that latitude (i.e., Arctic vs. sub-Arctic locations) strongly determined community composition (p = 0.001; pseudo-F = 2.634), whereas the type of waterbody (i.e., lakes vs. streams) had a weaker influence on beta diversity (p = 0.012; pseudo-F = 1.813). Latitude, along with water temperature and dissolved O2, were the main explanatory variables shaping prokaryotic community composition in our study. The core microbiome differed significantly in abundance between Arctic and sub-Arctic locations (p = 0.005). Arctic freshwaters showed the highest alpha diversity (Shannon and Chao1 indices) and were dominated by the genera Rhodoferax, Arcicella, and Polaromonas, all of which positively correlated with increasing dissolved O2 concentrations. In contrast, sub-Arctic freshwaters were primarily dominated by Limnohabitans, a genus widely distributed in inland freshwater habitats. Regarding waterbody types, lakes were predominantly characterized by Flavobacterium, which positively correlated with increasing nutrient concentrations, and exhibited higher alpha diversity compared to streams. Streams, in turn, were largely dominated by Rhodococcus species, which showed significant positive correlations with water temperature. This study enhances our understanding of prokaryotic diversity across the circumpolar region and aims to further provide valuable insights into the assembly mechanisms of freshwater microbial communities.
How to cite: Valiente Parra, N., Eiler, A., Bertilsson, S., Chaguaceda, F., Christoffersen, K. S., Culp, J., Lavoie, I., Musetta-Lambert, J., Shaftel, R., and Hessen, D. O.: Patterns of prokaryotic diversity in freshwaters across the circumpolar region, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17219, https://doi.org/10.5194/egusphere-egu25-17219, 2025.
Global warming and anthropogenic activities have profoundly altered biodiversity and aquatic ecosystem stability, yet the underlying driving mechanisms remain inadequately understood. Here, we analyzed temporal patterns of biodiversity and community stability over the past century by constructing 29 temporal planktonic network models. These models were based on the sedimentary DNA (sedDNA) extracted from downcore sediments in Lake Chagan, a seasonally frozen lake in Northeastern China, using high-throughput sequencing techniques. Our findings identify the mid-1990s as a critical tipping point, marked by substantial shifts in nutrient levels and annual average temperatures. We demonstrate that the temporal network stability of plankton communities has been predominately compromised by climate warming, followed by nutrient enrichment. Our study highlights the intricate interplay between biotic and abiotic factors in determining the stability of aquatic ecosystems, which have significant implications for the management and conservation of freshwater ecosystems in the face of ongoing climate warming.
How to cite: Yu, S., Cao, X., and Qu, J.: Climate warming and nutrient enrichment destabilize plankton network stability over the past century, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-180, https://doi.org/10.5194/egusphere-egu25-180, 2025.
