Global climate change and other anthropogenic pressures have major impacts on the structure, biodiversity and functioning in aquatic ecosystems. Climate change pressures include transitional environmental change, increased variability and extreme events and long-term disturbance. It is still unclear how these pressures affect ecosystem responses, including their resilience and recovery. Large-scale mesocosm or enclosure experiments provide realistic settings by including higher system complexity in terms of species interactions at various trophic levels. Thus, mesocosm experiments are a powerful tool to obtain a mechanistic understanding of how various global change and other anthropogenic pressures affect ecosystem responses. Moreover, mesocosms offer the unique ability to test possible measures to mitigate or counteract anthropogenic pressures through environmental engineering and nature-based solutions. We welcome presentations on empirical studies where scientific questions about various aspects of aquatic ecosystem functioning have been tested using mesocosms or similar ecosystem level experimentations. We particularly invite scientists that study effects of increasing variability and extreme events on resilience and recovery of biodiversity and ecosystem structure and functioning or regime shifts that change ecosystem structure and functions in response to global climate and environmental change. We strongly encourage early career scientists who have participated in the AQUACOSM or AQUACOSM-plus (www.aquacosm.eu) Transnational Access (TA) programs to present their results from the mesocosm experiments. This session also aims to serve as a meeting point for all persons interested in ecosystems scale experimentation on a global scale (see mesocosm.org).
Lead Organizer: Stella Berger, Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IGB) (stella.berger@igb-berlin.de)
Co-organizers:
Jens Nejstgaard, Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IGB) (jens.nejstgaard@igb-berlin.de)
Tatiana M Tsagaraki, University of Bergen, Department of Biological Sciences (tatiana.tsagaraki@uib.no)
Meryem Beklioğlu, Middle East Technical University (meryem@metu.edu.tr)
Behzad Mostajir, Marine Biodiversity, Exploitation and Conservation (MARBEC), University of Montpellier-CNRS-Ifremer-IRD (behzad.mostajir@umontpellier.fr)
Presentations
10:30 AM
CELL SIZE EXPLAINS PHYTOPLANKTON COMMUNITY STRUCTURE FOLLOWING STORM-INDUCED CHANGES IN LIGHT AND NUTRIENTS (6406)
Primary Presenter: Alexis Guislain, Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB) (alexis.guislain@igb-berlin.de)
Phytoplankton cell size is a key trait subject to a ubiquitous trade-off between resistance to grazers and competitive ability. As a result, cell size holds the potential to explain and predict phytoplankton dynamics in response to storm-induced terrestrial runoffs in lakes under realistic environmental conditions. This study investigates whether cell size can explain phytoplankton community structure following transient changes in light and nutrient conditions in a clearwater lake. An in-lake enclosure experiment was conducted using a natural community, simulating different intensities of nutrient-replete coloured dissolved organic matter (cDOM) runoff. Over six weeks, phytoplankton species composition and biomass were monitored along gradients of light, phosphate and mesozooplankton biomass. Findings indicate that cell size explains phytoplankton community structure during transient reduction in light availability. Initially, the size distribution was unimodal with small-celled species dominating up to 60% of the community biomass. Phosphate addition and mesozooplankton biomass had no effect on phytoplankton size distribution. However, the relative biomass of large-celled species significantly increased as light availability decreased in enclosures with added cDOM. Our results suggest a distinct competitive advantage of larger cells over small-celled species under reduced light availability, significantly altering the phytoplankton size distribution following the mimicked storm event.
10:45 AM
Experimental effects of light and temperature on the growth and formation of blanket weed blooms at the mesocosm scale (6839)
Primary Presenter: Hannah Kemp, University of Nottingham (hannah.kemp@nottingham.ac.uk)
Shallow freshwater ecosystems are experiencing increasingly frequent blooms of macroalgal blanket weed, which can cause surface proliferations that can negatively impact aquatic ecosystem functions and aesthetics. Although elevated nutrient concentrations in freshwaters are a pre-requisite for excessive algal growth, much less is understood about other abiotic factors controlling bloom growth rate and extents. To address this knowledge gap, we carried out a series of 990L indoor mesocosm (Limnotron) experiments to investigate the effects of light intensity, photoperiod and water temperature on the growth and surface bloom formation of blanket weed. These experiments combined underwater and surface photography to quantify change in algal area over time. The results demonstrated the existence of a minimum threshold of photoperiod and light intensity for bloom formation and substantial algal growth. Surface blooms did not occur when the photoperiod was too short, suggesting day length is a limiting factor. We also found that temperatures between 16-22 degrees Celsius were the thermal optimum for algae to form surface blooms, whilst the highest growth rate of algae on the sediment occurred at 14 degrees Celsius. With the increasing impact of climate change on freshwater ecosystems, these data will help predict the occurrence of surface blooms and assess which waterbodies could be under threat of blanket weed blooms in the future.
11:00 AM
Brownification impacts on dissolved organic phosphorus bioavailability – a mesocosm study (7007)
Primary Presenter: Mayra Rulli, Lund University (mayra.rulli@nateko.lu.se)
Anthropogenic nutrient enrichment of stream and river waters can lead to the eutrophication of coastal ecosystems. While eutrophication in coastal waters is often a consequence of riverine loads of inorganic nitrogen (N) and phosphorus (P), these may also occur alongside increasing transports of coloured dissolved organic carbon (DOC) (i.e., brownification). Browning may, in turn, lead to increased inputs of potentially bioavailable fractions of organic N and P. Yet, while inorganic nutrient dynamics have been extensively researched, it is unclear how the pool of bioavailable dissolved organic P (BDOP) responds to the individual and interactive effects of reduced light, increased DOC and inorganic nutrients. To address this issue, we conducted a fully factorial mesocosm experiment manipulating inorganic nutrient supply, labile carbon (C) concentration and water colour, and we carried out bioassays to estimate BDOP. Whereas we found no link between C and BDOP, we found that inorganic nutrient enrichment corresponded to increases in BDOP. There was an interaction effect of BDOP concentration with colour, indicating that inorganic nutrients only triggered BDOP accumulation in clear waters, whereas in dark waters, BDOP remained relatively constant. We argue that, in clear and nutrient-rich waters, the increased turnover and degradation of phytoplankton biomass may contribute to increasing BDOP concentrations. Therefore, continued brownification and eutrophication of coastal waters, is likely to decrease DOP concentrations that are bioavailable for the plankton communities.
11:15 AM
Understanding the impact of run-off variability on dissolved organic matter for better management of lakes devoted to drinking water supply (4998)
Primary Presenter: Angela Pedregal, Catalan Institute for Water Research (apedregal@icra.cat)
Drinking water is an essential service provided by aquatic ecosystems that is increasingly threatened by human activities and climate change. Little is known about the impact of extreme weather events on freshwater due to their stochastic character. Yet, future scenarios project higher intensity and frequency of these events, intensifying uncertainty and challenges for water managers. Precipitation events boost the transport of dissolved organic matter (DOM) into lakes, impacting not only ecosystem processes but also the formation of non-desired carcinogenic disinfection by-products (DBPs) during drinking water disinfection. A spatially coordinated mesocosm experiment was designed in two Swedish lakes to study the impact of run-off variability on freshwater. To understand to what extent these effects differ with local climate and geography, standardized equipment and methods were applied at both sites. Three different pulse events (carbon and nutrient additions) were studied by varying their intensity and frequency to simulate extreme, intermediate, and continuous rainfall. Results confirmed that changes in concentration and composition of DOM were site-specific, were strongly dependent on run-off variability, and that the effect of pulses in input could be detected by monitoring proxies of DOM in the mesocosms. Also, DBP formation potential tests were performed, showing positive correlations with DOM proxies and sensitivity to pulse disturbances. These results can be used to support raw water management by developing, e.g., forecasting tools to control the formation of DBPs.
11:30 AM
WILL CLIMATE-INDUCED CHANGES IN LOW FLOW TIMING ALTER STREAM INSECT SUBSIDIES? EVIDENCE FROM A LARGE-SCALE EXPERIMENT (6601)
Primary Presenter: Charlotte Evangelista, UPPA/INRAE (charlotte.evangelista0@gmail.com)
Climate change-induced alteration of flow regimes is a major threat for organisms inhabiting mountain streams, particularly those experiencing earlier snowmelt. Yet, whole-ecosystem responses to prolonged low flow remain difficult to anticipate. This is mainly because stream food web components can respond differently to prolonged drought, and interactions among them can vary over the drought period. Here, we used large-scale flow-through mesocosms in California’s Sierra Nevada to assess how food webs will respond to end-of-century flow regimes (i.e. advancing snowmelt resulting in earlier flow recession to baseflow levels). We manipulated the flow regime (current versus early low flow treatments) crossed with brown trout presence or absence, across 24 channel sections. Extended low flow increased water temperature and reduced dissolved oxygen. The onset of early low flow immediately conferred a 3-fold increase in the abundance of emerging insects, but this effect was temporary. Flow alteration had a positive and long-lasting effect on cumulative abundance of emerging insects, suggesting that fine-scale changes occurring early in the season influenced the community trajectory. Surprisingly, insects emerged more when trout were present, indicating potential cascading effects on the ecosystem. Our results emphasise that the magnitude and timing of cross-ecosystem subsidies are likely to shift with climate change in mountain streams. Large-scale experiments may provide a realistic model to understand the full range of stream ecosystem responses to projected climate change.
11:45 AM
RECOVERING FROM RUN-OFF EVENTS: THE IMPORTANCE OF FREQUENCY AND AMPLITUDE FOR THE STOICHIOMETRIC RESPONSE OF A FRESHWATER PLANKTON COMMUNITY (5518)
Primary Presenter: Anika Happe, University of Oldenburg (anika.happe@uni-oldenburg.de)
Climate change is increasing the frequency and amplitude of extreme events such as heavy rainfall or storm-induced mixing which result in a temporally variable input and availability of nutrients and DOM for plankton communities in lakes. This leads to changes in the phytoplankton C:N:P elemental composition which impacts consumer growth and thus the energy transfer in the aquatic food-web. However, the current understanding of run-off impacts on producers and consumers is limited as studies on variability in run-off events including multiple trophic levels are rare. Here, we conducted a mesocosm experiment within the AQUACOSM-plus network at Lake Erken (SITES AquaNet) in Sweden to simulate a rainfall period with different amplitudes and frequencies of nutrient and cDOM pulses. The experimental treatments ranged from one extreme to multiple intermediate and low pulses of nitrate, phosphate and cDOM, with the same total addition, over a period of 20 days. This was followed by a 17-day recovery period without any input. Our results show that the extreme nutrient pulse enables fast recovery of phytoplankton biomass and C:N ratios but leads to phosphorus-driven decreases in C:P and N:P ratios compared to both higher frequency pulses. These effects translate into consumer level with differences between the functional groups of zooplankton (cladocerans and copepods). Overall, our study demonstrates that stoichiometric resilience and recovery not only depend on the amount of nutrient and DOM input but also the amplitude and frequency with which it is introduced into the ecosystem.
SS046B Mesocosm Based Experimental Studies to Address Challenges Emerging From Global Change on Stability of Aquatic Ecosystems
Description
Time: 10:30 AM
Date: 5/6/2023
Room: Auditorium Illes Balears