Human-induced global stressors, such as climate change, land use intensification, and the spread of invasive species, are amongst the greatest challenges of the 21st century, with significant consequences for aquatic resources, ecosystem and human health, and the economy. Empirical studies across broad scales of space and time and that include tens to thousands of freshwater ecosystems are critical to further understand the potentially diverse responses of aquatic ecosystems to global changes. This session invites presentations that consider such issues in all types of freshwater ecosystems and for all types of response variables (biology, chemistry, physics). We also invite a broad representation of different analytical approaches for studying freshwater ecosystems at broad scales including, but not restricted to machine learning, artificial intelligence, statistical, process-based, and descriptive approaches. We invite presenters to consider emerging challenges and opportunities for addressing such challenges to conduct research at these broad scales of space and time, to understand freshwaters within diverse ecological contexts, and to look forward to future research directions.
Lead Organizer: Patricia Soranno, Michigan State University (soranno@msu.edu)
Co-organizers:
Kendra Spence Cheruvelil, Michigan State University (ksc@msu.edu)
Katherine E. Webster, Michigan State University (katherine.e.webster@gmail.com)
Presentations
05:00 PM
The salinisation of North American lakes (6853)
Primary Presenter: Yannick Huot, Université de Sherbrooke (yannick.huot@usherbrooke.ca)
The chloride ion is toxic to aquatic organisms. Around 15 million tons are spread as salts to de-ice roads in the US and Canada each year and more are used as dust suppressant and fertilizers. We used two large datasets of measured chloride concentrations from the US EPA National Lake Assessment (NLA; from 2012 and 2017; 1048 unique lakes) and the NSERC Canadian LakePulse Network (621 lakes) to derive statistical models to examine which lakes exceed natural concentration due to human activities. To account for the regional differences in natural concentrations, the analysis was conducted per ecoregions. Depending on the ecoregions, the length of roads within the watershed, other urban development indexes or agricultural indexes were most often associated with excess chloride in lakes. Based on these models we estimated the concentrations of chloride in lakes both in their natural (hypothetical unimpacted state) and human-impacted state. We applied these models to two large datasets of lakes that provide information about land use in the watershed as well as geomorphological information about the lakes: the LAGOS-US dataset and the LakePulse geomatics analysis of Canadian lakes dataset (61 804 US lakes and 258 255 Canadian lakes between 0.1 and 100 km2). These results show that lakes in the Northeastern US states and the southern part of the Eastern Canadian provinces are the most impacted. In total, we conservatively estimate that chloride concentrations in approximately 2.2x104 lakes in Canada and the US exceed natural concentrations.
05:15 PM
LAND USE SHAPES MULTI-TROPHIC DIVERSITY OF CANADIAN LAKES (4912)
Primary Presenter: Beatrix Beisner, University of Quebec at Montreal (beisner.beatrix@uqam.ca)
Aquatic communities consist of trophic guilds embedded in food webs with multiple interacting trophic levels, for which multi-trophic indices of diversity should provide deeper insight than do those estimated for individual trophic levels. We sampled bacterioplankton, phytoplankton, and zooplankton in 560 lakes across Canada as part of the NSERC Lake Pulse Network to evaluate predictors of diversity both between phylogenetic kingdoms and across orders. Individual kingdoms showed varied responses to lake physico-chemistry and climate, while scaling up diversity indices to incorporate multi-trophic variation revealed a significant role for climate variables in structuring community diversity. Watershed land use did not have significant direct effects on multi-taxa species diversity, but it did have important indirect effects via changes to local water chemistry. Our findings highlight how multi-trophic approaches may be beneficial for identifying general drivers of diversity across Canadian lakes, especially within a context of climate change.
05:30 PM
Does the theory of alternative stable states in shallow lakes stand the test of time? (7096)
Primary Presenter: Thomas Davidson, Aarhus University (thd@ecos.au.dk)
Since its inception the theory of alternative equilibria in shallow lakes has evolved and been applied to an ever wider of ecological and socioecological systems. The theory posits the existence of two alternative stable states each displaying resistance to changing environmental conditions with shifts between states being unpredictable. Here, use data covering a range of timescales to assess the generality of the theory in space and time. We show that a simple, deterministic link between shallow lake phytoplankton biomass (chlorophyll-a) and nutrient concentration becomes evident once a long-term (>3 years) perspective is taken. Specifically, we find a linear relationship between multi-year means of nutrient concentration and chlorophyll-a, for two independent shallow lake datasets in Denmark and North America (902 lakes in total). In addition, palaeolimnological data generated for three shallow lakes show that loss of submerged plants was preceded by decades of progressive, predictable biological change, with no clear evidence for sudden changes as indicative of alternative stable states shifts. This demonstrates that with a longer-term perspective, the notion of alternative equilibria is unnecessary for explaining the response of chlorophyll-a to nutrient enrichment. This in turn, questions the utility of the theory for explaining shallow lake response to and recovery from eutrophication.
05:45 PM
LARGE-SCALE VARIATION IN PHYTOPLANKTON COMMUNITY COMPOSITION OF >1,000 LAKES ACROSS THE USA (6605)
Primary Presenter: Jef Huisman, University of Amsterdam (j.huisman@uva.nl)
How does the species composition of lake phytoplankton respond to environmental variation across large spatial scales? We performed a comprehensive analysis of the phytoplankton community composition of >1,000 lakes across the conterminous USA, using data collected during the National Lakes Assessment of the US Environmental Protection Agency (EPA). Our analysis reveals that geographical variation in phytoplankton community composition is best explained by total phosphorus (TP), water temperature and pH. High TP concentrations were associated with high relative abundances of cyanobacteria and euglenophytes. High temperatures stimulated cyanobacteria, dinoflagellates, desmids and euglenophytes, whereas cryptophytes, golden algae and diatoms were relatively more abundant in colder lakes. Low pH correlated with high dissolved CO2 concentrations, which may explain why it benefitted phytoplankton with inefficient carbon concentrating mechanisms (CCMs) such as golden algae and euglenophytes. Conversely, cyanobacteria increased strongly with lake pH, probably because their CCMs can effectively take up bicarbonate. Biodiversity increased with lake temperature, but decreased at high TP concentrations and high pH. In total, our results illustrate the many insights that can be obtained from the investigation of large-scale patterns, and provide an important baseline to assess how anthropogenic pressures such as eutrophication, global warming and rising atmospheric CO2 may affect the biodiversity and taxonomic composition of lake phytoplankton.
06:00 PM
Hybrid modeling approaches for predicting water temperature in 50k stream segments across the continental United States (6643)
Primary Presenter: Samantha Oliver, U.S. Geological Survey (oliver.samanthak@gmail.com)
Water temperature drives many in-stream processes and is an indicator of both local and broad-scale changes in climate, land use, and channel modifications. Though temperature is generally inexpensive and easy to monitor, few locations have records long enough to elucidate how stream temperature might change in the future. For example, across the U.S., only 4% of ~50k stream reaches have a year or more of daily temperature records. This data sparsity limits our ability to discern what those sites might look like in the future, e.g., which of these sites are tightly coupled to atmospheric processes and will therefore change with air temperature. Two recent advances in machine learning approaches allow us to leverage sparse, broad-scale observations to make accurate predictions of stream temperature. First, we used a recurrent graph network to inform the model of stream connections and share information across the stream network. Second, we pre-trained the machine learning model on a process-based stream temperature model to produce physically consistent predictions prior to exposing the model to observations. These methods were applied to a subset of the Delaware River Basin, US, where we accurately hindcasted (RMSE = 1.40 deg C) and forecasted (RMSE = 2.03 deg C for 1-day ahead) water temperature. This presentation highlights extension of these methods to 50k stream segments across the continental US and an assessment of how well these models reproduce long-term water temperature dynamics.
06:15 PM
Historical Variations of Dissolved Organic Carbon Concentrations in Rivers: Can Land Use and Geomorphology Explain Regional Variability? (4663)
Primary Presenter: Jade Dormoy-Boulanger, Université du Québec à Trois-Rivières (jade.dormoy@hotmail.com)
In the last decades, recovery from acidification and climate change have caused a widespread dissolved organic carbon (DOC) increase in boreal rivers with impacts on water usages such as compromising drinking water supply. However, there are geographic differences in this increase, but the patterns and drivers remain unclear. To address these differences, we examined the effects of land uses and hydrogeomorphology on shaping DOC historical trends (1985-2019) in the St. Lawrence watershed in 91 stations in 54 different rivers. We measured a widespread increase, particularly in forested regions, but agricultural areas were more stable, or even decreased in DOC. Urban developments were found to have no impacts on historical variations. When adding hydrogeomorphological factors, elevation along with wetlands areas were found to promote DOC increases, emphasizing the importance of hydrogeomorphology and land uses when optimizing water treatment plant facilities.
SS083B How Data-Intensive Research Has Increased Understanding of Freshwater Ecosystems Across Broad Geographies and Through Time
Description
Time: 5:00 PM
Date: 8/6/2023
Room: Sala Portixol 1