The triple planetary crisis of climate change, biodiversity loss and pollution highlights the complexity of the effects of multiple stressors in aquatic ecosystems. Spatially and temporally co-occurring stressors show interacting effects such as additivity, antagonism or synergism. This makes the assessment, prediction and mitigation of the effects of multiple stressors a challenge. In freshwater and coastal systems, stressors arise at the local to catchment scale from land use patterns such as agriculture, urbanization or industrial activities. Their impacts spread further into the open ocean, such as nutrient pollution and the accumulation of plastics. There are several frameworks to mitigate these stressors in aquatic systems, e.g. the US Clean Water Act, the Chinese Water Ten Plan, the European Water Framework Directive or the European Marine Strategy Framework Directive. However, modifications in local combined stressor effects due to global climate change such as warming, hydrodynamics and extreme events or invasive species are likely, but causal links are rare. While awareness is growing that these stressors affect the resilience of our aquatic ecosystems to different stressor scenarios, they are rarely considered in management measures. Nevertheless, our mechanistic understanding of the interactions between stressors in the context of climate change and the corresponding management strategies remains limited.
This session welcomes contributions that address the interactions of multiple stressors in climate change scenarios. Case studies illustrating the impact of climate change on the vulnerability of ecosystems to other stressors, their interaction patterns or ecological thresholds are welcomed. Evidence can be derived from field studies, experimental investigations or data-driven studies. Modelling approaches that improve the prediction of multiple stressor effects under projected climate change scenarios will be considered, as well as diagnostic and assessment frameworks. Contributions that reconsider regulatory thresholds and management activities in the context of climate change and extreme events are particularly welcome. The aim of this session is to provide an overview of current knowledge, identify knowledge gaps and improve interdisciplinary communication to help protect healthy aquatic systems in a changing climate.
Lead Organizer: Mechthild Schmitt-Jansen, Helmholtz-Centre for Environmental Research UFZ (mechthild.schmitt@ufz.de)
Co-organizers:
Sabine Hilt, Leibniz Institute of Freshwater Ecology and Inland Fisheries (sabine.hilt@igb-berlin.de)
Peiyu Zang, Institute of Hydrobiology, Chinese Academy of Sciences,Chinese Academy of Sciences (zhangpeiyu@ihb.ac.cn)
Juan Du, Yangtze River Fisheries Research Institute, Chinese Academy of Fishery Sciences (dujuan@yfi.ac.cn)
Presentations
11:00 AM
MITIGATING FLOW REDUCTION WITH WASTEWATER REUSE: PROMISE OR PERIL FOR STREAM HEALTH? (10213)
Primary Presenter: Tanguy Nardon, INRAE (tanguy.nardon@inrae.fr)
In many parts of the world, climate change reduces summer baseflow and promotes flow-intermittency. The resulting reduction in dilution capacity of point sources is often considered a threat to aquatic ecosystems. Therefore, water managers often store treated wastewater in summer and release it in winter when flow is high. Today, this strategy is being questioned, as the stored wastewater could be used to sustain flow during summer. Few studies compare the hydrological, chemical and ecological effects of different wastewater discharge strategies, especially on temperate headwater streams. We chose 3 effluent-fed headwater streams in Brittany (France) and monitored discharge hourly, chemistry bi-weekly, biofilm communities monthly and aquatic invertebrate communities annually. In 2025, we implemented reduced wastewater discharges while increased or pulsed discharges are planned for 2026. In 2025, treated wastewater strongly contributed to the stream discharge (maximum between 39% and 87% from June to September). Effluents significantly altered the water quality, with an increase in mean temperature and nutrient concentrations (+2.2 °C, +21.5 mg/L for nitrate, +0.9 mg/L for phosphate). Diatoms dominated the communities and we observed a considerable increase of 517% in mean concentration from downstream to upstream. Aquatic invertebrate samples are still under analysis. We conclude that, even reduced, treated wastewater already substantially contributes to the natural discharge and highly influences the stream’s chemical and ecological conditions.
11:00 AM
WARMING, PRODUCTIVITY SHIFTS AND HABITAT RISK FOR OIL SARDINE IN THE SOUTHEASTERN ARABIAN SEA: AHP–PCA BASED VULNERABILITY ASSESSMENT (10220)
Primary Presenter: Shijin Ameri, Amrita Vishwa Vidyapeetham (shijinameri@am.amrita.edu)
Oil sardine (Sardinella longiceps) is a climate-sensitive pelagic species supporting major coastal fisheries in the southeastern Arabian Sea. This study assesses its climate vulnerability using a 20-year (2005–2024) dataset and an integrated AHP–PCA framework. Environmental variables including SST, chlorophyll-a, salinity, dissolved oxygen, mixed layer depth, pH, nutrients, and major climate indices (ENSO, IOD, PDO) were extracted and analysed using Python. PCA identified dominant environmental drivers, while AHP generated weighted exposure, sensitivity, and adaptive capacity indices. The present study shows a clear warming trend across the region, with higher SST coinciding with reduced habitat stability and shifts in sardine suitability zones. Declining chlorophyll and changes in nutrient availability indicate weakening productivity, directly influencing potential feeding conditions and spawning environments. Increased salinity variability was found to coincide with periods of lower predicted suitability, suggesting sensitivity during early life stages. Variability in mixed layer depth and upwelling intensity further highlights fluctuating nutrient supply and consequent changes in favourable habitats. Collectively, SST anomalies, productivity decline, and altered upwelling emerged as the strongest drivers influencing sardine vulnerability. The composite vulnerability index indicates moderate to high vulnerability in core fishing grounds, underscoring the need for climate-ready fisheries management aligned with SDG-14.
11:00 AM
Warming, food web simplification and surface runoff pollution additively reduce the functioning of shallow freshwater ecosystems (10274)
Primary Presenter: Peiyu Zhang, Institute of Hydrobiology, Chinese Academy of Sciences (zhangpeiyu@ihb.ac.cn)
Global declines in biodiversity are driving food web simplification, which threatens the functioning of freshwater ecosystems. These impacts are strongly affected by climatic and anthropogenic stressors, which further reduces biodiversity. However, how these stressors operate in concert to alter ecosystem functioning is still poorly understood. Here, we used 48 large-scale field mesocosms to test how the individual and combined effects of warming, surface runoff pollution (SRP), and food web simplification (FWS) affect the functioning of standing waters. We found that warming and pollution significantly altered primary producer community composition in simplified food webs by reducing the production of submerged macrophytes, with the associated reduction in shading increasing the growth of periphyton. Warming also suppressed the growth of submerged macrophytes, particularly M. spicatum. SRP (inorganic particles, organic matter and nutrients) stimulated filamentous algal (FLA) growth, as macrophytes provided suitable growth surfaces and the algae had stronger competition ability than macrophytes with pulse nutrient released into water. We further calculated the temporal stability of each primary producer group and found it decreased for macrophytes in the simplified food web treatments, while stability of FLA increased under SRP. Our findings demonstrate that when faced with an increasing range of global environmental stressors, which is often the case in natural ecosystems, shallow freshwaters lose functioning as the system shifts away from submerged macrophytes and towards benthic algal dominance. Our study provide a mechanistic basis for conservation strategies aimed at preserving shallow freshwater ecosystem functions.
11:00 AM
Salinization and warming effects on zooplankton community in Mediterranean shallow lakes: a mesocosm experiment (10549)
Primary Presenter: Meltem Kuyumcu, Middle East Technical University (korumeltem99@gmail.com)
Freshwater ecosystems in the Mediterranean climate zone are increasingly threatened by declining precipitation and rising evaporation, which reduce lake volumes, flushing out and in turn increase salinity. The effects of warming and salinity are often studied separately, while their combined influence is poorly understood. We elucidated how zooplankton communities respond to the combined effects of salinity and warming under future climate scenarios. A three-month mesocosm experiment was conducted in fall 2023 in Mediterranean Türkiye, applying two salinity levels (4 g/L and 40 g/L) crossed with two temperature treatments (ambient temperature and +4.5°C warming). Results showed a difference in community composition between salinity treatments. At 4 g/L, large-bodied cladocerans dominated the zooplankton community, whereas 40 g/L mesocosms were dominated by halotolerant small-bodied rotifers. Diversity and richness were consistently higher under low salinity treatment. PERMANOVA results indicated that warming had no significant effect on biomass. GAM analyses revealed salinity in combination with warming predominantly led to reduced zooplankton diversity with an additional small but significant non-linear effect of water clarity. The model explained 66% of the variation in Shannon diversity. Overall, our findings emphasize that increasing salinization, particularly with warming, may impoverish zooplankton community structure and induce major shifts in zooplankton community composition in Mediterranean lakes.
11:00 AM
Hydrological and ecosystem impacts of in-stream artisanal aggregate and tin mining in central Rwanda (11115)
Primary Presenter: Aelis Spiller, McGill University (aelis.spiller@mail.mcgill.ca)
The integrity of freshwaters is vital to maintaining healthy aquatic (and terrestrial) ecosystems. Though humans rely on freshwaters as a key natural resource and these systems support uniquely high levels of biodiversity, they are exceptionally threatened and highly exploited. The extraction of geologic commodities, including critical minerals and aggregate materials (sand, gravel, etc.), often occurs in river channels and/or the waste materials of these activities interact with water courses. Artisanal and small-scale mining is often overlooked in the evaluation of mining’s environmental impact and contribution to sustainable development. Understanding the hydrological and ecological responses to landscape disturbances caused by artisanal in-stream mining is important for the management of aggregate and mineral resources, freshwaters, and freshwater biodiversity. This work presents the case study of the Rusine River in Rwanda, in which both artisanal aggregate and tin mining occur. Primarily relying field data but supported by remote sensing, we present comprehensive data describing the abiotic and biotic components of the freshwater system along the course of the watershed. We explore the localized and system-scale impacts of these mining activities, evaluating the integrity of the watershed and its ecosystem functioning. We compare this system to similar rivers lacking some of the exploitative land uses in the Rusine. This work provides insight into responsible natural resource management in rural Rwanda with global lessons in preserving freshwater ecosystem services.
11:00 AM
PHYTOPLANKTON BIOMASS RESPONSES ARE AMPLIFIED WITH ELEVATED TEMPERATURE UNDER NITROGEN-LIMITING CONDITIONS (11188)
Primary Presenter: Eden Waters-Carpenter, Miami University (waterseg@miamioh.edu)
The availability and relative abundance of nitrogen (N) and phosphorus (P) in lake ecosystems can have a high degree of seasonal variability, which can influence the nutrient limitation dynamics of phytoplankton communities. Along with nutrient inputs, temperature plays a key role in promoting phytoplankton growth, further intensifying eutrophication in water bodies. In this study, we combined classic N and P nutrient limitation bioassays with an elevated temperature treatment to investigate seasonal limitation patterns and the extent to which warming alters nutrient effects on the phytoplankton community in a hypereutrophic reservoir. From May to October, we quantified biomass responses of the total phytoplankton assemblage and the three dominant divisions present: chlorophytes, cyanobacteria, and diatoms. The total phytoplankton community was P-limited from spring through August, then shifted to co-limitation for the remainder of the study. Chlorophytes and diatoms showed similar late-summer co-limitation patterns, whereas cyanobacteria instead shifted to strict N limitation. Temperature did not directly influence nutrient limitation status, but during periods of N limitation, elevated temperatures significantly increased the phytoplankton biomass response of the +N and +NP treatments. Therefore, our results suggest that elevated temperatures may magnify cyanobacteria blooms under N-limiting conditions. These findings indicate that reductions in both N and P are necessary for effective eutrophication management, especially as global temperatures continue to rise.
11:00 AM
SS067P Multiple Stressor Effects on Freshwater and Marine Ecosystems in a Changing Climate
Description
Time: 11:00 AM
Date: 15/5/2026
Room: 517C