SFS Annual Meeting

6/06/2024  |   13:30 - 13:45   |  Independence Ballroom A

ACKNOWLEDGING THE PIONEERING ROLE OF KEN CUMMINS IN THE STUDY OF LEAF BREAKDOWN IN STREAMS The recognition of the intimate connection between streams and their watersheds has markedly shaped the conceptual foundations of stream ecology. Key to this perspective is the pivotal role of allochthonous inputs, most notably as coarse particulate organic matter (CPOM) such as leaf litter from riparian vegetation. Moreover, the breakdown, or processing, of leaf litter by stream microbes and macroinvertebrates has become a central theme of investigations in stream ecology, and is now commonly used as a metric of ecosystem functioning in both fundamental and applied studies. This year marks the 50th anniversary of “Leaf Processing in a Woodland Stream” by R. C. Petersen and his doctoral advisor, K. W. Cummins, one of the very first studies and the most influential paper on leaf breakdown in streams. Building on pioneering work by Cummins, the study firmly established leaf litter as a major resource fueling stream communities, and highlighted the roles of temperature and leaf quality in governing breakdown rates. What is more, unlike most of the hundreds of subsequent studies, Petersen and Cummins depicted the breakdown process as an integral part of stream organic matter dynamics, developed a conceptual scheme of the process, provided first estimates of the contributions of microbes and macroinvertebrates, and set out to quantify the fate of leaf litter in addition to determining breakdown rates. The remarkable breadth and conceptual depth of the study continues to provide a canvas for exploring various avenues towards understanding leaf breakdown in streams, and remains a standard for future investigations.

Mark O. Gessner (Primary Presenter/Author), Leibniz Institute of Freshwater Ecology & Inland Fisheries (IGB), mark.gessner@igb-berlin.de;

Luz Boyero (Co-Presenter/Co-Author), University of the Basque Country (UPV/EHU), luz.boyero@ehu.eus;

Jennifer L. Tank (Co-Presenter/Co-Author), University of Notre Dame, jtank@nd.edu;

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6/06/2024  |   13:45 - 14:00   |  Independence Ballroom A

Patterns and controls on fungal decay of cellulose in rivers and riparian zones: more insights into the Global Cellulose Decomposition Experiment (CELLDEX) The decomposition of plant matter is a key process that dominates the flow of carbon and the cycling of nutrients in terrestrial and aquatic ecosystems. The rates of these processes are strongly influenced by microbial decomposers and their response to prevailing environmental conditions, such as temperature and nutrient availability. We analyzed the accrual of fungal biomass in standardized cotton-strip bioassays collected during the global-scale cellulose decomposition experiment (CELLDEX). As a proxy for fungal biomass, we quantified chitin (as glucosamine) in cotton-strips from 100 paired stream and riparian sites in 11 biomes worldwide. We then related glucosamine accrual rates to previously determined cotton-strip decay rates (k) and nutrient (nitrogen & phosphorus) immobilization rates. Globally, biome explained a significant portion (p<0.001) of the variation in glucosamine accrual rates in both rivers (33%) and riparian zones (18%), with decreasing accrual observed with increasing absolute latitude. Using quantile regressions (tau = 0.95), we observed positive relationships (p<0.01) between glucosamine accrual, cotton strip decay (k), and nutrient immobilization rates (except for k and N in riparian zones, p>0.05). Arrhenius plots show that glucosamine accrual rates exhibited temperature dependence in streams (p<0.01, slope -0.30) and riparian zones (p<0.01, slope -0.24), in contrast to previous work showing temperature dependence of nutrient immobilization in riparian zones but not in streams. Overall, our results support the hypothesis that temperature limits fungal biomass accrual, their immobilization of dissolved nutrients, and their decay activities, highlighting the quantitative effects of climate on fungal contributions to global carbon and nutrient cycling processes.

Kevin A. Kuehn (Primary Presenter/Author), University of Southern Mississippi, kevin.kuehn@usm.edu;

Lavanya Kanuri (Co-Presenter/Co-Author), University of Southern Mississippi, Lavanya.Chigurupati@usm.edu;

Charles T. Bond (Co-Presenter/Co-Author), University of Southern Mississippi, Charles.Bond@usm.edu;

Halvor Halvorson (Co-Presenter/Co-Author), University of Central Arkansas, hhalvorson@uca.edu;

David Costello (Co-Presenter/Co-Author), Kent State University, dcostel3@kent.edu;

Scott Tiegs (Co-Presenter/Co-Author), Oakland University, tiegs@oakland.edu;

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6/06/2024  |   14:00 - 14:15   |  Independence Ballroom A

Role of nutrients in mediating the effects of algae on the decomposition of labile and recalcitrant detrital organic matter in streams Interactions between primary producers and heterotrophic microorganisms influence the complex energy pathways in freshwater streams. Algal produced labile carbon exudates may either increase or decrease rates of recalcitrant terrestrial organic matter decomposition in streams, but the factors that determine if this priming effect is positive or negative are not fully understood. The goal of this study was to investigate whether the influence of algae on terrestrial organic matter decomposition varied between streams with different nutrient concentrations. We submerged rain gutters containing untreated cotton and wood veneer in 11 streams with varying N and P concentrations. Two gutters were deployed in each stream, where one was covered with a black shade and the other covered with clear plexiglass. Cotton and veneer decomposition was measured after incubation using cotton tensile strength and veneer strength. We also measured fungal and bacterial biomass, fungal sporulation rates, and the activities of three extracellular enzymes involved in the degradation of cellulose and lignin. Log response ratios between light and dark treatments for fungal and bacterial biomass indicated greater microbial biomass in the dark relative to the light with increasing nutrient concentrations. It is possible that under ambient light and higher N and P concentrations, labile exudates from algae allowed fungi to allocate more energy toward spore production and less to producing hyphae and extracellular enzymes required for degrading recalcitrant organic matter. These results suggest that increased nutrients and light might slow the decomposition of terrestrial organic matter in streams, which has ramifications for overall stream biogeochemistry.

Hanna Martin (Primary Presenter/Author), Commonwealth University of Pennsylvania , hem94662@huskies.bloomu.edu;

Steven Rier (Co-Presenter/Co-Author), Commonwealth University of Pennsylvania, srier@commonwealthu.edu;

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6/06/2024  |   14:15 - 14:30   |  Independence Ballroom A

TEMPORAL AND SPATIAL DYNAMICS OF DISSOLVED ORGANIC MATTER TRANSFORMATIONS IN GLACIER-FED STREAMS IN SVALBARD Glaciers and ice sheets distributed across polar and alpine regions cover approximately 10% of the Earth’s land and represent a unique biome supporting major biogeochemical processes from glacier to downstream ecosystems. Rapid shrinkage and mass loss due to climate change is expected to exert an impact on hydrological patterns, nutrients, and organic matter in glacier-fed streams. Dissolved organic matter (DOM) in glacial streams exhibit a wide range of diverse chemical compounds and is susceptible to climate-induced changes affecting its quality and composition. Here, we explore DOM dynamics in glacial streams by studying temporal and spatial changes in biotic and abiotic putative DOM transformations. We investigated temporal variations within a single High Arctic catchment in Svalbard, where we examined both supraglacial (surface) and subglacial (below-glacier) meltwater from July to September. In addition, we looked at spatial differences in DOM transformations across 19 diverse glacial sites of varying sizes within central Svalbard. Our findings will provide insights on the putative gain or loss of organic molecules and will contribute to the field by bridging the gap between temporal and spatial glacier studies.

Dillman Delgado (Primary Presenter/Author), Pacific Northwest National Laboratory , dillman.delgadoparedes@pnnl.gov;

Vanessa Garayburu-Caruso (Co-Presenter/Co-Author), Pacific Northwest National Laboratory , vanessa.garayburu-caruso@pnnl.gov;

Gabrielle Kleber (Co-Presenter/Co-Author), University of Tromsø, Norway, gakle2914@uit.no;

Jacob Yde (Co-Presenter/Co-Author), Western Norway University of Applied Sciences, Jacob.Yde@hvl.no;

James Stegen (Co-Presenter/Co-Author), Pacific Northwest National Laboratory, james.stegen@pnnl.gov;

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6/06/2024  |   14:30 - 14:45   |  Independence Ballroom A

Autochthonous carbon fuels stream metabolism in Antarctic polar desert streams The ephemeral streams in the McMurdo Dry Valleys (MDV) of Antarctica only flow 4-9 weeks each year, but are biogeochemical hot spots in this barren landscape, acting as crucial links between glaciers, soils, and lakes. Despite limited allochthonous inputs to the streams, many have abundant algal mats which grow rapidly at the onset of streamflow each summer and fuel in-stream and downstream biogeochemical cycles with autochthonous carbon. In the austral summers of 2021-2022 and 2022-2023 we used high-frequency dissolved oxygen measurements to model the temporal and spatial patterns of stream metabolism (i.e., primary productivity [GPP] and ecosystem respiration [ER]) in MDV streams, as well as drift nets and aeolian collectors to measure reach scale organic matter inputs and outputs. Daily rates of GPP and ER (g C/m2/day) were within the range for temperate streams, and most streams were autotrophic over the flow season (GPP/ER >1), which is expected given the continual summer sunlight, no canopy shading, and no major water column light attenuation due to shallow water depth. We ran a linear mixed effects model to assess the spatial and temporal controls on GPP and ER. ER rates were significantly correlated with GPP rates across both space and time, suggesting autochthonous carbon fuels respiration of these non-perennial streams. An imbalance of organic matter outputs to inputs to the system, with exports being more than 200x greater than the allochthonous inputs annually, emphasizes the substantial internal carbon cycling occurring within MDV streams during their short flow season.

Anna Wright (Primary Presenter/Author), University of Colorado Boulder, anna.t.wright@colorado.edu;

Michael Gooseff (Co-Presenter/Co-Author), University of Colorado, michael.gooseff@colorado.edu;

Matthew Cohen (Co-Presenter/Co-Author), University of Florida, mjc@ufl.edu;

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6/06/2024  |   14:45 - 15:00   |  Independence Ballroom A

Effect of Riparian Forest Cover on Cellulose Decomposition in Agricultural Streams Agricultural practices often result in human impacts to aquatic ecosystems. The presence of riparian forests has been shown to mitigate some of these impacts, however, there is limited knowledge of how riparian forests can mitigate human impacts on microbial community function. This study investigates effects of riparian forest cover on in-stream cellulose decomposition. The study used the cotton strip assay to compare two sets of streams in all four temperate seasons and assess the association between riparian forest cover and cellulose decomposition in summer in agricultural catchments. Preliminary results from summer and autumn show there is greater cellulose decomposition in streams with riparian forest cover than streams without riparian forest cover. Cellulose decomposition also increased linearly with riparian forest in the summer. Decomposition in the assessed streams were also compared to cellulose decomposition in least disturbed, reference streams within the same region. Significant differences were only observed between the reference streams and the two groups in autumn when forested sites exhibited greater decomposition. These preliminary results suggest that riparian forest cover influences the microbial community, but these differences are not explained by typical environmental parameters (e.g., temperature, nutrients). In future studies, considering agricultural contaminants (e.g., pesticides), looking at ground water and tile drain influences on stream temperature and nutrients, and investigating the differences in microbial community composition between groups may help close this knowledge gap.

Kristen Hewitt (Primary Presenter/Author), University of Waterloo, knsymons@uwaterloo.ca;

Adam Yates (Co-Presenter/Co-Author), University of Waterloo, adam.yates@uwaterloo.ca;

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