SFS Annual Meeting

6/03/2024  |   10:30 - 10:45   |  Independence Ballroom D

FROM HURRICANES TO DROUGHTS AND RISING TEMPERATURES: THE IMPACT OF CLIMATE CHANGE ON CARIBBEAN STREAMS Climate change impacts lotic ecosystems by altering rainfall patterns, elevating temperatures, and intensifying extreme events, significantly impacting ecosystem structure and function. Although research on the effects of climate change continues to increase, most of our understanding comes from temperate regions. This study is an assessment of this knowledge gap. We conducted a literature search spanning 2000 to 2022 on the primary impacts of climate change in the Caribbean region, focusing on its effects stream ecosystems. The region, renowned for its biodiversity and unique interconnectivity between ecosystems, is a biodiversity hotspot. We found that hydrology and hydrogeology, ecology, and disturbances are among the most studied topics in the Caribbean. Puerto Rico, Costa Rica, and Colombia were leaders in the number of studies concerning climate change, extreme weather events, and water temperature. Reduced precipitation and elevated temperatures in the Caribbean contribute to diminished water flow, disrupting water chemistry, and loss of habitats for aquatic communities. Hurricanes cause disruptions by altering water chemistry and inducing abrupt changes in stream flow and physical conditions. Major disturbances (e.g., hurricanes and droughts) challenge the resilience of aquatic ecosystems, posing significant threats to biodiversity, by disrupting habitats and ecological functions. Our understanding of Caribbean stream ecosystem responses to these climate change effects is limited; however, their potential impacts could profoundly reshape ecosystem dynamics and functionality.

Ana Meza-Salazar (Primary Presenter/Author), North Carolina State University, ammezasa@ncsu.edu;

Alonso Ramírez (Co-Presenter/Co-Author), North Carolina State University, alonso.ramirez@ncsu.edu;

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6/03/2024  |   10:45 - 11:00   |  Independence Ballroom D

The changing role of climate in driving dissolved organic carbon concentrations in historically acidified lakes Changes in climate and atmospheric deposition interact with localized watershed characteristics to influence dissolved organic carbon (DOC) concentrations in lakes. In regions historically impacted by acidic deposition, lakes show signs of recovery but remain vulnerable to impacts from climate change. Leveraging over 30 years of surface water chemistry, atmospheric deposition, and climate data, we examined shifts in the relative influence of drivers of lake DOC over time. Results show that watershed characteristics consistently drive DOC concentrations across all decades. Climate impacts become the most pronounced in the most recent decade, superseding the marginal significance of sulfate deposition observed only in the 1980s. Watershed characteristics were an important control on within-lake variability in DOC, with finer, shallower, and more poorly drained soils leading to greater lake DOC variability. Elevated spring DOC concentrations were related to rainier winters, suggesting that as winters continue to warm and the dominant precipitation phase shifts from snow to rain, lakes may receive a greater influx of C in the spring. The intricacies of soil and watershed characteristics and their interactions with climatic impacts underscores the importance of adopting a nuanced, site-specific approach for forecasting future trends and variability in lake DOC concentrations.

Allison Herreid (Primary Presenter/Author), USDA-ARS, Allison.Herreid@unh.edu ;

Hannah Fazekas (Co-Presenter/Co-Author), University of New Hampshire, hannah.fazekas@unh.edu;

Sarah Nelson (Co-Presenter/Co-Author), Appalachian Mountain Club, sarah.j.nelson@maine.edu;

Adam Wymore (Co-Presenter/Co-Author), University of New Hampshire, adam.wymore@unh.edu;

Desneiges Murray (Co-Presenter/Co-Author), University of New Hampshire, desneiges.murray@unh.edu;

Ruth Varner (Co-Presenter/Co-Author), University of New Hampshire, ruth.varner@unh.edu;

William McDowell (Co-Presenter/Co-Author), Department of Natural Resources and the Environment, University of New Hampshire, 03824, Durham, New Hampshire, bill.mcdowell@unh.edu;

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6/03/2024  |   11:00 - 11:15   |  Independence Ballroom D

CLIMATE- VERSUS RESOURCE-DRIVEN VARIATION IN A SOUTHERN APPALACHIAN STREAM INVERTEBRATE COMMUNITY Understanding how populations and communities respond to environmental variability is crucial for predicting consequences of global change and habitat management. In stream ecosystems, climate warming is altering hydrologic and thermal regimes and vegetation cover that affect resource availability, particularly for forest stream food webs. In these systems, it is imperative to understand the relative effects of discharge, temperature, and organic matter (OM) quantity on consumer assemblages. We used a long-term (13-yr) data set of mean annual invertebrate biomass in a southern Appalachian headwater stream to evaluate effects of interannual variation in discharge, temperature, and OM quantity on temporal turnover of community structure. We also assessed whether habitat (rock-face vs. cobble) mediated response to climate and OM variables. Rockface communities exhibited greater temporal turnover than cobble communities. Climate-driven variables typically had smaller effect sizes than OM quantity on turnover. We found that higher winter discharge increased temporal turnover in both cobble and rockface habitat. Temperature had positive effects on turnover, primarily via effects on community biomass in cobble habitat. However, only one taxon for each habitat was identified as a significant driver of community change. Overall, we found that climate-driven variation had subtle effects on temporal turnover despite periods of intense drought and rainfall during the study. Our results suggest that habitat likely mediates responses to climate variation, via physical conditions or life-history characteristics of taxa occupying those habitats, and that invertebrate communities in forest streams may be more responsive to changes in forest cover than variation in discharge and temperature.

Phillip Bumpers (Primary Presenter/Author), University of Georgia, bumpersp@gmail.com;

Seth Wenger (Co-Presenter/Co-Author), Odum School of Ecology, University of Georgia, swenger@uga.edu;

Amy Rosemond (Co-Presenter/Co-Author), University of Georgia, rosemond@uga.edu;

Jonathan P. Benstead (Co-Presenter/Co-Author), The University of Alabama, jbenstead@ua.edu;

Mary Freeman (Co-Presenter/Co-Author), US Geological Survey, mcfreeman@usgs.gov;

Sue Eggert (Co-Presenter/Co-Author), USDA Forest Service, Northern Research Station, seggert@fs.fed.us;

J. Bruce Wallace (Co-Presenter/Co-Author), Dept. Entomology and Odum School of Ecology, University of Georgia, bwallace@uga.edu;

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6/03/2024  |   11:15 - 11:30   |  Independence Ballroom D

Impact of aquatic heatwaves on river metabolism in the United States Climate change has increased anomalous temperature events, including discrete periods of extremely high temperatures called heatwaves. Aquatic heatwaves are 5+ consecutive days of daily mean temperature above a long-term seasonally-varying 90th percentile threshold. These pulsed heating events can disproportionately negatively impact aquatic ecosystems relative to a long-term, gradual increase in mean temperature. Recent results suggest that aquatic heatwave frequency has increased in rivers throughout the U.S. however, it remains unclear if heatwaves impact temperature-dependent processes like gross primary production (GPP) and ecosystem respiration (ER), which together comprise aquatic metabolism. We aimed to determine the impact of aquatic heatwaves on GPP and ER by comparing a published riverine metabolism dataset for the years 2007-2017 with water temperature data from 48 USGS sites throughout the U.S. We identified 2,129 riverine heatwaves across these sites over 20 years (1997-2017). Furthermore, heatwave severity was categorized based on multiples of the temperature difference between the climatological norm and the 90th percentile threshold. Preliminary results suggest moderate-to-strong heatwaves (1-2x above threshold) stimulate GPP by 9-29%, while less frequent but more severe heatwaves (3-4x above threshold) reduce GPP by 29-84%. All heatwave severity classifications enhanced ER relative to non-heatwave conditions by 9-39%. These results suggest that more frequent moderate-to-strong heatwaves have little impact on the ratio of GPP and ER, while less frequent but more severe heatwaves can make rivers significantly more heterotrophic (ER > GPP). If riverine heatwaves become increasingly severe, rivers could become greater emitters of greenhouse gases as respiration exceeds production.

Spencer Tassone (Primary Presenter/Author), Michigan Technological University, sjtassone1@gmail.com;

Michelle Kelly (Co-Presenter/Co-Author), Michigan Technological University, mckelly1@mtu.edu;

Amy Marcarelli (Co-Presenter/Co-Author), Michigan Technological University, ammarcar@mtu.edu;

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6/03/2024  |   11:30 - 11:45   |  Independence Ballroom D

Trophic efficiency from primary producers to secondary consumers decreases with temperature We tested how temperature and algal type interact to influence photosynthesis, nitrogen fixation and carbon and nitrogen transfer to higher trophic levels. We manipulated temperature using an artificial stream facility with three temperature regimes. We compared seven algal types including Mougeotia sp., Spirogyra sp., Nostoc sp., Anabaena sp., and three successional stages of Cladophora glomerata that vary in epiphyte load. Carbon fixation rate increased with temperature, increasing carbon availability at the base of the food web. We measured the rate at which grazing caddisflies (Gumaga sp.) assimilate carbon and nitrogen across temperature and algal treatment using algae labelled with stable isotopes of 13C and 15N. Assimilation by caddisflies was calculated using a 2-pool mixing model. Caddisflies assimilated carbon and nitrogen from all algal types but assimilated the most carbon from Cladophora glomerata with high epiphyte loads, dominated by the diatom Epithemia which has an N-fixing symbiont. Carbon assimilation by caddisflies did not increase with temperature indicating that increases in primary production are not transferred to secondary consumers. This study shows that although warming increases carbon fixation for freshwater algae, warming did not result in more carbon or nitrogen moving up the food chain.

Michael Zampini (Primary Presenter/Author), Northern Arizona University, mcz39@nau.edu;

Mary Power (Co-Presenter/Co-Author), University of California, Berkeley, mepower@berkeley.edu;

Steven Thomas (Co-Presenter/Co-Author), University of Alabama, sathomas16@ua.edu;

Jane Marks (Co-Presenter/Co-Author), Northern Arizona University, jane.marks@nau.edu;

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6/03/2024  |   11:45 - 12:00   |  Independence Ballroom D

Responses of Aquatic Fungi to Stream Warming: Identifying Ecologically Important Species This study investigates how stream warming affects aquatic fungi on decomposing leaves in freshwater streams. We analyzed differences in fungal species composition and growth rates across temperature treatments and successional stages using quantitative stable isotope probing (qSIP). Temperature manipulation was achieved through artificial stream mesocosms containing sycamore leaves. Harvests were performed on day 7 and day 49. For qSIP, leaf discs at each harvest were incubated in stable isotope labeled 18O-enriched water and unlabeled water for an additional week. 18O isotope assimilation into individual species’ DNA reveals each taxon's growth rate. Findings from this investigation aims to enhance our understanding of the interactions between aquatic fungi, nutrient cycling and a changing climate.

Amanda Rouillard (Primary Presenter/Author), Northern Arizona University, afr96@nau.edu;

Helen Ochs (Co-Presenter/Co-Author), Northern Arizon University, hco9@nau.edu;

Michael Zampini (Co-Presenter/Co-Author), Northern Arizona University, mcz39@nau.edu;

Michaela Hayer (Co-Presenter/Co-Author), Northern Arizona University, michaela.hayer@nau.edu;

Egbert Schwartz (Co-Presenter/Co-Author), Northern Arizona University, egbert.schwartz@nau.edu;

Jane Marks (Co-Presenter/Co-Author), Northern Arizona University, jane.marks@nau.edu;

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