SFS Annual Meeting

6/05/2024  |   13:30 - 13:45   |  Philadelphia Ballroom

SEASONAL CHANGES IN THE CONTRIBUTION OF STREAM VS. TERRESTRIAL SOURCES TO CO2 EMISSIONS IN AN INTERMITTENT MEDITERRANEAN STREAM Headwater streams are control points for carbon dioxide (CO2) emissions to the atmosphere, with CO2 primarily assumed to originate from terrestrial sources. However, in-stream metabolic activity can become a significant CO2 source in net heterotrophic streams, particularly during periods of high ecosystem respiration and low groundwater inputs characteristic of water-scarce regions. To explore this idea, we used high-temporal resolution CO2-oxygen (O2) patterns and stream metabolic rates to assess seasonal variations in CO2 sources in an intermittent Mediterranean stream characterized by marked seasonality of discharge and riparian-stream hydrological connectivity. These analyses were complemented by estimates of gross primary production (GPP) and ecosystem respiration (ER) derived from O2 time-series. During fall and winter, mean ER was the highest (2.3 g O2 m2 d-1), while stream O2 and CO2 concentrations displayed no correlation, and CO2-O2 patterns indicated CO2 oversaturation. These findings suggest lateral groundwater inputs are primary sources of CO2 during seasons with high hydrological connectivity. Conversely, a strong negative inverse relationship between CO2 and O2 concentrations emerged in spring and early summer, coinciding with GPP peaks (0.2 g O2 m2 d-1). This pattern suggests that stream metabolic activity governs CO2 dynamics during seasons with low hydrological connectivity. Our results support the idea of headwater streams as CO2 emitters, highlighting how hydrological conditions can dictate their function as chimneys for terrestrially-derived CO2 or as carbon biogeochemical reactors within landscapes.

Susana Bernal (Primary Presenter/Author), Center for Advanced Studies of Blanes (CEAB-CSIC), Spain, sbernal@ceab.csic.es;

Carolina Jativa (Co-Presenter/Co-Author), Integrated Freshwater Ecology Group, Center for Advanced Studies of Blanes (CEAB-CSIC), Blanes, Girona, Spain., carito.jativa@gmail.com;

Anna Lupon (Co-Presenter/Co-Author), Center for Advanced Studies of Blanes (CEAB-CSIC), Spain, alupon@ceab.csic.es;

Eugènia Martí (Co-Presenter/Co-Author), Center for Advanced Studies of Blanes (CEAB-CSIC), eugenia@ceab.csic.es;

Xavi Peñarroya (Co-Presenter/Co-Author), Integrated Freshwater Ecology Group, Center for Advanced Studies of Blanes (CEAB-CSIC), Blanes, Girona, Spain., xp.galceran@gmail.com;

Emma Lannergård (Co-Presenter/Co-Author), Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, Uppsala, Sweden, emma.lannergard@slu.se;

Montserrat Soler (Co-Presenter/Co-Author), Center of Advanced Studies of Blanes (CEAB-CSIC), Spain, msoler@ceab.csic.es;

José Ledesma (Co-Presenter/Co-Author), Department of Hydrogeology, Helmholtz Centre for Environmental Research (UFZ), Leipzig, Germany, jose.ledesma@ufz.de;

Gerard Rocher-Ros (Co-Presenter/Co-Author), Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden. Integrative Freshwater Ecology Group, Centre for Advanced Studies of Blanes (CEAB-CSIC), Blanes, Spain, g.rocher.ros@gmail.com;

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6/05/2024  |   13:45 - 14:00   |  Philadelphia Ballroom

Linking algal assemblages to reach-scale metabolism estimates in a productive river Rivers tend to be heterotrophic, but algal dynamics can drive river ecosystem processes. Filamentous algae often cause nuisance algal blooms, altering the autotrophic community's structure, yet effects of these blooms on stream ecosystem processes remain unknown. This study explored the structural and functional roles of filamentous and epilithic algae by linking algal biomass measurements with daily primary production fluxes across six sites along the Upper Clark Fork River in western Montana, USA. We allocated daily productivity estimates among different algal groups using the spatial and temporal variability in algal biomass assemblages, allowing for an assessment of in situ turnover rates of algal groups at the whole-ecosystem level. Throughout two growing seasons, we observed high fluxes of primary productivity (9.2 ± 3.4 g O2 m-2d-1), most of which could be attributed to the epilithic algae despite its low standing crop (11 ± 7 gm-2) and the variable presence of large filamentous algae blooms (56 ± 13 gm-2). Filamentous algae blooms influenced ecosystem structure in terms of total biomass and algal turnover times. However, they did not substantially contribute to gross primary productivity, ecosystem respiration, or net production. Epilithic algae grew and turned over rapidly, driving total biomass production and ecosystem metabolism.

Alice M. Carter (Primary Presenter/Author), Flathead Lake Biological Station, University of Montana, alicecarter05@gmail.com;

Robert O. Hall (Co-Presenter/Co-Author), Flathead Lake Biological Station, University of Montana, bob.hall@flbs.umt.edu;

Rafael Feijó de Lima (Co-Presenter/Co-Author), University of Montana, rfeijod@clemson.edu;

Michael DeGrandpre (Co-Presenter/Co-Author), University of Montana, michael.degrandpre@umontana.edu;

Qipei Shangguan (Co-Presenter/Co-Author), Woods Hole Oceanographic Institution, qipei.shangguan@whoi.edu;

H. Maurice Valett (Co-Presenter/Co-Author), University of Montana, Division of Biological Sciences, maury.valett@umontana.edu;

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6/05/2024  |   14:00 - 14:15   |  Philadelphia Ballroom

PATTERNS OF RIVER ECOSYSTEM FUNCTIONING INFERRED FROM PAIRED CO2:O2 MEASUREMENTS Biogeochemical reactions in river ecosystems are often reflected in dissolved oxygen (O2) and carbon dioxide (CO2) concentrations. Under aerobic metabolism, O2 and CO2 are produced or consumed equivalently, and therefore measurements of O2 and/or CO2 are central in assessing river metabolism and ecosystem functioning. However, multiple processes (physical, chemical, biological) have unequal effects on O2 and CO2 concentrations, and thus, complicates how paired CO2:O2 measurements can be used to infer river ecosystem processes. Here we use a simple mechanistic model that represents river metabolism, gas exchange, groundwater inputs and carbonate equilibrium to assess how each of these processes imprint CO2:O2 patterns. We test the model in two settings based on empirical observations: across the river continuum and among streams with contrasting metabolic regimes. Along the river continuum, changes in metabolic rates and gas exchange result in longer and wider trajectories across the CO2:O2 space, and the gradual decrease in groundwater inputs contribute to increase the CO2:O2 ratio. Rivers with high metabolic rates show high correlation between CO2 and O2, while rivers with non-stable flows show more dispersed and low correlation of CO2 and O2 concentrations. Our results clearly illustrate that a variety of biological, chemical and physical processes affect CO2 and O2 concentrations in unique ways that lead to specific patterns in CO2:O2 relationships. Still, CO2:O2 concentrations alone can hardly provide quantitative measurements of river ecosystem functioning within and across sites, especially when several of these processes operate simultaneously.

Gerard Rocher-Ros (Primary Presenter/Author), Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden. Integrative Freshwater Ecology Group, Centre for Advanced Studies of Blanes (CEAB-CSIC), Blanes, Spain, g.rocher.ros@gmail.com;

Nuria Catalan (Co-Presenter/Co-Author), Institute of Environmental Assessment and Water Research (IDAEA), CSIC, Barcelona, Spain., nuria.catalan@idaea.csic.es;

Carolina Jativa (Co-Presenter/Co-Author), Integrated Freshwater Ecology Group, Center for Advanced Studies of Blanes (CEAB-CSIC), Blanes, Girona, Spain., carito.jativa@gmail.com;

Emma Lannergård (Co-Presenter/Co-Author), Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, Uppsala, Sweden, emma.lannergard@slu.se;

Hjalmar Laudon (Co-Presenter/Co-Author), Swedish University of Agricultural Sciences, hjalmar.laudon@slu.se;

Anna Lupon (Co-Presenter/Co-Author), Center for Advanced Studies of Blanes (CEAB-CSIC), Spain, alupon@ceab.csic.es;

Lluís Gomez-Gener (Co-Presenter/Co-Author), CREAF, Barcelona Spain, l.gomez@creaf.uab.cat;

Eugènia Martí (Co-Presenter/Co-Author), Center for Advanced Studies of Blanes (CEAB-CSIC), eugenia@ceab.csic.es;

Xavi Peñarroya (Co-Presenter/Co-Author), Integrated Freshwater Ecology Group, Center for Advanced Studies of Blanes (CEAB-CSIC), Blanes, Girona, Spain., xp.galceran@gmail.com;

Ryan Sponseller (Co-Presenter/Co-Author), Department of Ecology and Environmental Science, Umeå University, 901 87 Umeå, Sweden, ryan.sponseller@umu.se;

Susana Bernal (Co-Presenter/Co-Author), Center for Advanced Studies of Blanes (CEAB-CSIC), Spain, sbernal@ceab.csic.es;

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6/05/2024  |   14:15 - 14:30   |  Philadelphia Ballroom

An Investigation of the Drivers of Harmful Algal Blooms (HABs) in Virginia The U.S. Geological Survey, in cooperation with Virginia Department of Environmental Quality, is conducting two studies to better understand the drivers of harmful algal blooms (HABs) in Lake Anna and the upper Shenandoah River Basin in Virginia. Excessive algae in streams and lakes may adversely impact the ecosystem, reduce the water quality, and, if toxigenic cyanobacteria are present, produce cyanotoxins that can pose health risks to humans and wildlife. Nutrient and sunlight are well documented drivers of HABs, however, the interaction among these and other potential factors influencing HAB growth is less understood. The focus of the presentation is to give an overview of the intensive and extensive monitoring programs that have been established, unique to each study area. The monitoring program evaluates the hydrology, geochemistry, climate, stream metabolism, community dynamics, and environmental DNA and RNA to identify the potential factors and interactions during HAB formation, persistence, and decline in these systems.

Carly Maas (Primary Presenter/Author), U.S. Geological Survey, cmaas@usgs.gov;

Brendan Foster (Co-Presenter/Co-Author), U.S. Geological Survey, bfoster@usgs.gov;

Douglas Chambers (Co-Presenter/Co-Author), U.S. Geological Survey, dbchambe@usgs.gov;

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6/05/2024  |   14:30 - 14:45   |  Philadelphia Ballroom

UPSTREAM EFFICIENCY AND DOWNSTREAM PRODUCTIVITY: LINKING MOUNTAIN STREAM PROCESSES WITH NEAR-SHORE PRODUCTIVITY IN THE LAKE TAHOE BASIN (CA-NV, USA). Upland processes (snowmelt, streamflow, and stream temperature) can influence nearshore productivity dynamics by modulating the timing and delivery of materials to lakes. The degree to which upland processes influence nearshore productivity as a function of their catchment characteristics relative to the influence of internal lake processes remains unclear. We continuously monitored dissolved oxygen, temperature, and specific conductance (SPC) in the nearshore of Lake Tahoe (USA) and at the stream outlets of two watersheds with differing flow regimes for three consecutive years. We also modeled nearshore metabolism using the o2_model_inhibition implemented in stan. Nearshore gross primary productivity (GPP) immediately around inflowing streams was up to 60% higher relative to areas 1 km or more away from surface water inflows. Across all locations, GPP was strongly related to the previous days’ GPP and negatively associated with variation in daily shortwave radiation, wind speed), and stream water SPC. Our findings indicate that nearshore metabolism is sensitive to daily variations in weather; these patterns were more pronounced for the west shore of Lake Tahoe which accumulates greater amounts of annual precipitation, typically as snow, relative to the drier east shore. Additionally, the impact of upland processes on nearshore metabolism varied with winter precipitation, indicating drier years may lead to increased GPP. Given the anticipated climate warming in western US mountain basins, changes to upland processes (i.e. warmer temperatures, prolonged droughts, and enhanced groundwater nutrient delivery), may also promote unwanted algal growth.

Kelly Loria (Primary Presenter/Author), University of Nevada Reno, kellyloria@gmail.com;

Heili Lowman (Co-Presenter/Co-Author), Global Water Center and Biology Department, University of Nevada, Reno, hlowman@unr.edu ;

Jasmine Krause (Co-Presenter/Co-Author), Oregon State University, krausjas@oregonstate.edu;

Leon Katona (Co-Presenter/Co-Author), Global Water Center and Biology Department, University of Nevada, Reno, lkatona@unr.edu ;

Ramon Naranjo (Co-Presenter/Co-Author), U.S Geological Survey in Carson City, NV, rnaranjo@usgs.gov;

Facundo Scordo (Co-Presenter/Co-Author), Instituto Argentino de Oceanografía -CONICET-UNS, scordo@agro.uba.ar ;

Adrian Harpold (Co-Presenter/Co-Author), University of Nevada Reno, aharpold@unr.edu;

Sudeep Chandra (Co-Presenter/Co-Author), Global Water Center and Biology Department, University of Nevada, Reno, sudeep@unr.edu;

Joanna Blaszczak (Co-Presenter/Co-Author), University of Nevada, Reno, jblaszczak@unr.edu;

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6/05/2024  |   14:45 - 15:00   |  Philadelphia Ballroom

METABOLISM VIA DIC IN RIVERS: A DIFFERENT STORY THAN OXYGEN River ecologists have rich datasets of gross primary productivity (GPP) and respiration (ER) inferred from daily variation in dissolved oxygen (DO). DO is useful as it represents splitting of water during photosynthesis, is the terminal electron acceptor in aerobic respiration and is straightforward to measure. Inference of metabolism from DO is common, even though the stoichiometric links to ecosystem anabolism and catabolism of organic carbon remain largely unknown. Inferring metabolism from dissolved inorganic carbon (DIC) provides direct estimates of carbon fluxes, but this approach has its own uncertainties. We have overcome 3 problems estimating metabolism via DIC to allow comparison to DO metabolism. 1-Use accurate dissolved CO2 sensors, 2-Solve for DIC at each time step by estimating speciation of the inorganic carbon. 3-Use two-station approaches because the river’s memory for past concentrations of DIC can exceed that for DO. GPP and ER estimated via DIC or DO greatly can differ, but we do not know why. Aside from photosynthetic and respiratory quotients, the inferential specters of potentially oversimplified models haunt each method: groundwater inputs differ for DIC and DO, direct uptake of bicarbonate, underwater bubbles, carbonate dissolution or precipitation, other biochemical processes that use oxygen, and anaerobic use of alternative electron acceptors in respiration. We suggest that future progress in understanding controls on metabolism in rivers will require both DO and DIC perspectives. Both metabolites give different perspectives on stream processes and neither provides a complete reflection of metabolism by itself.

Robert O. Hall (Primary Presenter/Author), Flathead Lake Biological Station, University of Montana, bob.hall@flbs.umt.edu;

Qipei Shangguan (Co-Presenter/Co-Author), Woods Hole Oceanographic Institution, qipei.shangguan@whoi.edu;

Robert Payn (Co-Presenter/Co-Author), Montana State University, Montana Institute on Ecosystems, rpayn@montana.edu;

Kelly Aho (Co-Presenter/Co-Author), Michigan State University, kellyaho@msu.edu;

Michael DeGrandpre (Co-Presenter/Co-Author), University of Montana, Department of Chemistry and Biochemistry, michael.degrandpre@mso.umt.edu;

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