Aquatic ecosystems worldwide are facing unprecedented stress from anthropogenic activities and climate change. This session explores the question: How are aquatic ecosystems responding to these pressures, and have they experienced abrupt changes in their ecological states? Abrupt changes, defined as sudden and significant transitions between distinct ecological conditions, can manifest as smooth, threshold-like, or bistable changes, altering ecosystem structure and function. We invite contributions that use paleo records, contemporary research, or models to explore or assess these abrupt changes across diverse aquatic environments. The session will focus on deepening the understanding of climate influences, ontogenetic processes, and/or anthropogenic impacts on driving these abrupt changes. Additionally, we welcome research on ecosystem resilience, referring to the capacity of systems to withstand or adapt to stress, including the ability to maintain core functions despite undergoing abrupt changes. Given the current lack of knowledge on recovery following such changes, we are particularly interested in exploring whether ecosystems can rebound or stabilize after these significant transitions. We also invite contributions on remediation efforts and strategies aimed at managing or mitigating the impacts of abrupt changes to preserve ecosystem function.
Lead Organizer: Skylar Hooler, university at Albany (Shooler@albany.edu)
Co-organizers:
Aubrey Hillman, University at Albany (ahillman@albany.edu)
Presentations
09:00 AM
MEASURING RESILIENCE AND STABILITY WITH DISSOLVED OXYGEN AND PH DATA FROM WHOLE LAKE NUTRIENT ADDITIONS (9053)
Primary Presenter: Michael Pace, University of Virginia (mlp5fy@virginia.edu)
Dissolved oxygen (DO) concentrations and pH are commonly measured in situ with sensors and are sensitive to changes in primary production and phytoplankton biomass. We evaluated the potential use of DO and pH to distinguish alternate states of high and low phytoplankton using data from whole lake nutrient manipulations designed to promote blooms. These manipulations were conducted in five different years with differential responses including no blooms and substantial blooms related to environmental and ecological conditions. When phytoplankton increased in response to nutrient additions, dissolved oxygen saturation (DOsat) increased to above 120% and pH often exceeded 9. Daily average DOsat and pH data were fit with b-splines, and from these relationships, stability basins and unstable thresholds (= loss of resilience) for low and high biomass states were derived. In manipulations where only modest or temporary changes in DOsat and pH occurred, stability conditions and thresholds were not well resolved. Overall, the approach distinguishes important properties of stability and resilience while requiring much less data than more established methods.
09:15 AM
WINTER SEVERITY SHAPES UNDER-ICE DYNAMICS IN TWO LAKES OF CONTRASTING TROPHIC STATUS (9060)
Primary Presenter: Alia Benedict, University of Minnesota Duluth (bened109@umn.edu)
Winters are rapidly changing with significant effects on lake ecosystems. Extreme fluctuations in winter air temperatures, snow fall, and freeze-thaw patterns can change abiotic conditions under lake ice but we have yet to understand how fluctuations in winter severity shape winter biological activity. We monitored ice and snow cover, dissolved oxygen, chlorophyll, and zooplankton during a severe (2022-2023) and mild (2023-2024) winter in an eutrophic and oligotrophic lake. In both lakes, ice and snow cover were significantly thinner and oxygen was supersaturated directly under the ice during the mild winter. Chlorophyll a and zooplankton abundance were significantly higher during the mild winter, especially in the eutrophic lake. There was strong evidence of a negative effect of winter anoxia on zooplankton in the eutrophic lake during the severe winter. Lower trophic levels play a major role in lake nutrient processing, including during winter periods. Linking winter severity to food web structure is important to understand how lake ecosystems will change as winters continue to grow more unpredictable.
09:30 AM
TEMPURATURE MODULATES THE FITNESS EFFECTS OF A BROAD-SPECTRUM FUNGICIDE IN A ZOOPLANKTON HOST-FUNGAL PATHOGEN SYSTEM (9515)
Primary Presenter: Jeannette Cullum, University of Illinois Urbana-Champaign (jcullum2@illinois.edu)
The fungicide azoxystrobin is increasingly used for crop disease management and commonly enters lakes as runoff. Its impacts on disease dynamics in non-target aquatic organisms, however, are understudied, and changing global temperature patterns further complicate our understanding of such impacts. Daphnia dentifera, a planktonic crustacean found in midwestern lakes, is a host for the fungal pathogen, Metschnikowia bicuspidata. We explore how sublethal concentrations of azoxystrobin affect the fitness of this aquatic host and its fungal pathogen at different temperatures. In a series of experiments, D. dentifera were exposed to three azoxystrobin concentrations and Metschnikowia treatments at two temperatures. We found that the effects of these stressors on D. dentifera clonal growth rate, a proxy for host fitness, varied considerably by temperature. We assessed pathogen fitness by quantifying spore production within azoxystrobin-exposed and unexposed hosts, which we found did not vary across azoxystrobin treatments, nor did the viability of spores to infect future hosts. Because we used ecologically relevant concentrations of azoxystrobin and Metschnikowia spores in these assays, we interpret that azoxystrobin runoff can alter D. dentifera population dynamics, and temperature may modulate its effects on host fitness and resulting disease dynamics. As a keystone species in lake systems, understanding the interactions between anthropogenic stressors, disease, and their environment on Daphnia fitness can help us protect lake ecosystems and the important functions they serve.
09:45 AM
BACTERIOPLANKTON DYNAMICS DURING SEASONAL ANOXIA EVENTS IN THE POTOMAC RIVER (9266)
Primary Presenter: Alexis Berger, George Mason University (aberge2@gmu.edu)
Widespread anoxia has been observed in estuaries globally as a combined result of hydrodynamics and eutrophication. During these events, increases in nutrient input drive phytoplankton blooms and subsequent decomposition by heterotrophic bacteria, drawing down oxygen levels. Warm water and stratification also contribute to anoxia as oxygen concentrations are influenced by water exchange and vertical mixing processes. It is expected that anoxia events may increase in size and frequency due to climate change. The Chesapeake Bay is one of the most extensively studied hypoxic estuaries and ecosystems in the world, with drivers being a combination of eutrophication and density stratification. Similar drivers influence anoxic events in the Potomac River Estuary, a tributary of the Chesapeake Bay. However, there is a paucity of data on the dynamics of the microbial community during these events. Seasonal anoxic events have extended further upriver during summer months each year. Here, a long-term fixed monitoring station, Ragged Point (38°10'0.12" N, 76°34'58.8" W), was sampled during anoxia, hypoxia, and oxygenation in 2024. Water samples were collected and filtered from 5 depths to build a vertical profile of the microbial community using metagenomics. The goal of this study is to delve into the relationship between dissolved oxygen, including anoxic events, and their influence on the functional potential of bacterioplankton communities in the Potomac River.
10:00 AM
ABRUPT CHANGES TO LIMITING FACTORS OF CYANOBACTERIAL BLOOMS IN SUCCESSIVELY DOWNSTREAM LENTIC WATER BODIES (9197)
Primary Presenter: Raymond Lee, University of Wisconsin-Superior (ramalee420@gmail.com)
Cyanobacterial blooms in inland waters can degrade water quality and harm human health. Such blooms occur due largely to nutrients delivered allochthonously to a lake or reservoir, but also to additional factors, including fluvial seeding of cyanobacteria, autochthonous sediment release then entrainment of nutrients, and species preference for nutrients (e.g., diazotrophic vs. non-diazotrophic). To assess the impacts of these factors, we monitored the physicochemistry (including nitrogen and phosphorus concentrations) and the life cycles of cyanobacteria within diverse lentic water bodies along the flow direction (drinking water reservoir to throughflow then endorheic lakes along a freshwater to hypersaline gradient) in the Great Salt Lake basin, UT. Results showed that blooms occurred in different patterns despite being located in the same basin with the same regional climate. Blooms were limited by nitrogen at the freshwater reservoir (Phormidiaceae spp. succeeded by Microcystis spp.), phosphorus at the brackish throughflow lake (Aphanizomenon flos-aquae), and inflow at the hypersaline endorheic lake (Nodularia spp.). At the freshwater reservoir, there was a complete shift in the microbial community, from diazotrophic (historically) to non-diazotrophic species (currently), likely due to successful watershed management of phosphorus loading; at the hypersaline endorheic lake, the bay dried up, likely due to high regional water consumption. These results advance knowledge in the proliferation of cyanobacteria and, more broadly, the function of diverse aquatic systems.
10:15 AM
Characterizing a cyanobacteria-driven regime shift within Lake Mattamuskeet, NC using long-term monitoring datasets (9329)
Primary Presenter: Mary Kate Rinderle, University of North Carolina--Chapel Hill (rinderle@unc.edu)
Mattamuskeet National Wildlife Refuge houses the largest natural lake in North Carolina. Historically, this shallow lake was dominated by submerged aquatic vegetation (SAVs) and was an important feeding ground for migratory birds along the Atlantic Flyway. In the 1940s, HWY 94 was built through the middle of the lake, splitting the lake into two basins that have since shifted between alternative ecosystem states independently of one another. In recent years, the lake’s health has been further degraded by a lack of drainage, invasive common carp, and excessive nutrients from surrounding agricultural fields. These stressors forced a regime shift in the past decade. Today, the lake is absent from SAVs and is instead dominated year-round by small, filamentous cyanobacteria (Raphidiopsis and Komvophoron). High phytoplankton biomass (~100 μg Chl a L⁻¹) creates steep light attenuation that prevents re-establishment of SAVs. To identify the physical, chemical, and biological factors driving this shift and characterize the lake’s response to anthropogenic stress, we will analyze multiple long-term monitoring datasets from within the lake beginning in 2012. This data will be supplemented by our own monitoring program which began in January 2023 and utilizes twice-monthly samplings to measure parameters such as phytoplankton biomass, community composition, nutrient availability, and light attenuation. Together, this comprehensive analysis will provide insights into the ecological impacts of human activity on Lake Mattamuskeet to inform future restoration efforts.
SS42A - Abrupt Changes in Aquatic Ecosystems: Impacts of Anthropogenic Stressors
Description
Time: 9:00 AM
Date: 27/3/2025
Room: W205CD