SFS Annual Meeting

Dana Warren (Co-Presenter/Co-Author)
Oregon State University, dana.warren@oregonstate.edu;

Allison Swartz (Primary Presenter/Author)
Oregon State University, allison.swartz@oregonstate.edu;

Abstract: Primary production is a key driver of aquatic nutrient cycling and provides a vital energy source for stream food webs. Dense canopy cover often limits primary production; however, in streams with canopy gaps, the limitation can shift from light to nutrients. Although much research has assessed effects of light and macronutrients (N, P) on primary production in headwater streams, few studies have explored co-limitation considering light as a spatially heterogeneous resource or potential micronutrient limitations. To explore the role of canopy gaps in creating macro and micronutrient limitation hotspots, we deployed nutrient diffusing substrates (NDS) along 12 forested headwaters, 9 in the Cascade Range, OR and 3 in the White Mountains, NH. Within each stream, we deployed 6-9 NDS arrays with replicate control and +NP cups. Arrays were placed in shaded and gap areas, and chlorophyll-a was measured after 3-4 weeks. We also included Mo treatments as this micronutrient is required for N-fixation and may increase chlorophyll-a by alleviating N demand. Results suggest an association between background nutrient concentration and difference in chlorophyll-a in gaps versus shade for both control and +NP substrates, although Mo additions caused no observed increases.

Elizabeth Renner (Primary Presenter/Author)
South Dakota Department of Game and Fish, elizabeth.renner@state.sd.us;

Keith Gido (Co-Presenter/Co-Author)
Kansas State University, kgido@ksu.edu;

Ben Neely (Co-Presenter/Co-Author)
Kansas Department of Wildlife and Parks, ben.neely@ks.gov;

Jeff Koch (Co-Presenter/Co-Author)
Kansas Department of Wildlife and Parks, jeff.koch@ks.gov;

Connor Chance-Ossowski (Co-Presenter/Co-Author)
Kansas Department of Wildlife, Parks and Tourism, connor.ossowski@ks.gov;

Abstract: Gizzard shad (Dorosoma cepedianum) are important prey for sportfish in small impoundments. However, overabundant shad create problems by depleting zooplankton and translocating nutrients from benthic detritus into the water column, compounding eutrophication. Understanding how gizzard shad regulate pelagic food webs in small impoundments may aid managers in anticipating and mitigating water quality issues stemming from extrinsic nutrient input. We measured a suite of limnological parameters in 12 small Kansas impoundments as part of a four-year gizzard shad eradication study. Shad densities in 12 impoundments were estimated from standardized fall gill-net sampling from 2010 - 2020. Compartments of the pelagic food web in these impoundments were also sampled in June, August, and October from 2017 through 2020. We fit generalized linear regression models to assess the fixed effects of lake treatment group and time (before/after shad eradication or introduction) on zooplankton and algal densities. Changes in community structure following shad removal or introduction were evaluated via non-metric multidimensional scaling and PERMANOVA. We anticipated decreases in cladoceran and copepod densities following gizzard shad introductions and increased densities of blue-green algae following shad introduction.

Fernando Vasquez (Primary Presenter/Author)
PONTIFICIA UNIVERSIDAD CATOLICA DEL ECUADOR , wfvg94@gmail.com;

Abstract: Freshwater ecosystems are organized in trophic guild that channelize energy and matter troughout by producers and consumers. These trophic guilds rely on predator-prey interactions that have produced differences in feeding strategies among species and habitat segregation, known as the ecological niche. Fishes are predators and preys that occupied the bottom to the top of the trophic chain in aquatic systems. To recognize the ecological niche we studied stomach contents and gonads of native fishes from Atacames and Súa streams. The stomach content data was analyzed with bidimensional plots of occurrence and abundance frequencies. For sexual differentiation, we used the direct observation of gonads. We provide new records of the secondary sexual characteristics and trophic guilds of each species. In top of the trophic chain, we found A. blombergi (carnivorous), E. ecuadorensis and P. fria (two omnivorous), in the middle, R. altipinna (herbivorous) and in the bottom, P. gillii (detritivorous). Most species presented a low sexual dimorphism and high sexual dichromatism.

Iain Phillips (Co-Presenter/Co-Author)
Water Security Agency of Saskatchewan, iain.phillips@wsask.ca;

Stephen Srayko (Co-Presenter/Co-Author)
University of Saskatchewan, shs176@mail.usask.ca;

Aaron Bell (Co-Presenter/Co-Author)
University of Saskatchewan, aaron.bell@usask.ca;

Christy Morrissey (Co-Presenter/Co-Author)
University of Saskatchewan, christy.morrissey@usask.ca;

Veronicah Muiruri (Co-Presenter/Co-Author)
National Museums of Kenya, veronica.muiruri@yahoo.com;

Meg Bjordahl (Co-Presenter/Co-Author)
University of Saskatchewan, meg.bjordahl@usask.ca;

Paul Jones (Co-Presenter/Co-Author)
South Florida Water Management District, pajones@sfwmd.gov;

John Giesy (Co-Presenter/Co-Author)
University of Saskatchewan, john.giesy@usask.ca;

Tim Jardine (Primary Presenter/Author)
University of Saskatchewan, tim.jardine@usask.ca;

Abstract: Stable isotopes are useful tracers of organic matter and habitat use. Spatial differences in isotope ratios are transferred to mobile organisms who, upon capture, can be assigned back to their habitat of origin. Here we show lateral and longitudinal patterns in sulfur isotope ratios in the Saskatchewan River basin, a large prairie river surrounded by geographically isolated wetlands. We found that wetlands had insects with highly negative d34S (-20 to -10 permil) relative to those in the river (-5 to 5 permil). This enabled the tracing of migratory water boatmen (Corixidae) as they moved en masse from wetlands into the river in the fall where they are eaten by fish. Within the river, there were unique sulfur isotope ratios in baseline organisms (crayfish and mussels) in the two main branches, the North Saskatchewan River (2 to 6 permil) and South Saskatchewan River (-7 to -4 permil), allowing the identification of recent habitat use by endangered lake sturgeon caught near the confluence. Together, this isotopic template highlights key hidden connections among habitats and will enable the pursuit of questions of conservation significance.

Caroline Owens (Primary Presenter/Author)
UCSB, owens@ucsb.edu;

Abstract: Alpine lakes are sensitive and unique ecosystems, highly vulnerable to the impacts of interacting human-driven stressors like climate change and species introductions. In lakes across the Sierra Nevada, introduced predatory trout have been shown to greatly reduce emerging insect abundance. However, the role of changing climate and precipitation regimes – and the interactions between climate and trout presence – are not well understood. Since summer 2019, we have been surveying emerging insects from fish and fishless lakes across a climate gradient in order to elucidate the effects of these interacting drivers and their cascading impacts on alpine lake ecosystems. A warming climate seems to dampen the effects of trout presence, although more data is needed to confirm this result and further trace its effects on novel algal blooms and water quality.

Holly Wellard Kelly (Primary Presenter/Author)
University of Minnesota-Duluth NRRI, hwellard@d.umn.edu;

Katya Kovalenko (Co-Presenter/Co-Author)
Natural Resources Research Institute, Univ. Minnesota Duluth, philarctus@gmail.com;

Tyler Ahrenstorff (Co-Presenter/Co-Author)
Minnesota Department of Natural Resources, tyler.ahrenstorff@state.mn.us;

Bethany Bethke (Co-Presenter/Co-Author)
Minnesota Department of Natural Resources, bethany.bethke@state.mn.us;

Valerie Brady (Co-Presenter/Co-Author)
Natural Resources Research Institute, University Minnesota Duluth, vbrady@d.umn.edu;

Josh Dumke (Co-Presenter/Co-Author)
Natural Resources Research Institute, University of Minnesota, jddumke@d.umn.edu;

Gretchen Hansen (Co-Presenter/Co-Author)
University of Minnesota, ghansen@umn.edu;

Heidi Rantala (Co-Presenter/Co-Author)
Minnesota Department of Natural Resources, heidi.rantala@state.mn.us;

Abstract: Small nearshore fishes are an important part of lacustrine and functional diversity and link pelagic and benthic habitats by serving as prey to larger nearshore and offshore fish. However, the trophic complexity of these small nearshore fish communities is often unrecognized and detailed studies of their food webs are often lacking or focus on larger predator or game fish. Here, we examined niche space patterns of small nearshore fish species using Bayesian analyses of carbon and nitrogen stable isotope data in nine Minnesota lakes. We found considerable intraspecific variability in fish niche areas among lakes and high variability in niche overlap across species. At the assemblage level, niche overlap decreased as whole-lake species richness increased, possibly indicating a greater degree of resource specialization in more speciose lakes. Overall fish niche space was weakly related to niche space of their invertebrate prey. Although nearshore benthic resources contributed to fish diets in all lakes, all fish species also had non-negligible and variable contributions from pelagic zooplankton. This inter- and intraspecific variability in trophic niche space likely contributes to the multi-level trophic complexity, functional diversity, and potentially food web resilience to ecosystem changes.

Dominik Martin-Creuzburg (Co-Presenter/Co-Author)
Limnological Institute, University of Konstanz, dominik.martin-creuzburg@uni-konstamz.de;

Christopher Robinson (Co-Presenter/Co-Author)
Swiss Federal Institute of Aquatic Science and Technology, EAWAG ; Aquatic Ecology dpt., Christopher.robinson@eawag.ch;

Carmen Kowarik (Primary Presenter/Author)
Swiss Federal Institute of Aquatic Science and Technology, EAWAG, carmen.kowarik@eawag.ch;

Abstract: PUFAs are essential resources unequally distributed throughout the landscape. Certain PUFAs, like eicosapentaenoic acid (EPA) are e.g. common in aquatic but scarce in terrestrial systems. In environments with low supply, meeting nutritional needs requires either adaptations in metabolism to PUFA-poor resources or selective foraging for PUFA-rich resources. Subsidies from adjacent systems, such as amphibiotic organisms that use different environments during their life cycle, represent such resources that can be exploited by predators. In this study, we quantified PUFA transfer from aquatic to terrestrial ecosystems starting with periphyton as the initial PUFA source, through emergent insects, to riparian spiders. We used a combination of carbon stable isotope and fatty acid analysis to follow the food web linkage across the ecosystem boundary. Results showed that riparian spiders consumed considerable amounts of aquatic-derived resources. EPA represented on average 15 % of the total fatty acids in riparian spiders. Season as well as spider lifestyle had a strong influence on PUFA profiles. We show that especially PUFA profiles of riparian web-building spiders in spring were tightly linked to those of emergent aquatic insects.

Christopher Groff (Primary Presenter/Author)
Texas A&M Corpus Christi, cgroff@islander.tamucc.edu;

Christopher Patrick (Co-Presenter/Co-Author)
Virginia Institute of Marine Science (VIMS), cpatrick@vims.edu;

Sean Kinard (Co-Presenter/Co-Author)
Virginia Institute of Marine Science, s2kinard@gmail.com;

Matt Whiles (Co-Presenter/Co-Author)
University of Florida, mwhiles@ufl.edu;

Hannah Vander Zanden (Co-Presenter/Co-Author)
UF, hvz@ufl.edu;

Amber Ulseth (Co-Presenter/Co-Author)
Sam Houston State University, amber.ulseth@epfl.ch;

Bradley Strickland (Co-Presenter/Co-Author)
Virginia Institute of Marine Science, bastrickland273@gmail.com;

Fernando Carvallo (Co-Presenter/Co-Author)
Texas A&M University–Corpus Christi, fcarvallo@islander.tamucc.edu ;

Victoria Jenkins (Co-Presenter/Co-Author)
Texas A&M Corpus Christi, vjenkins@islander.tamucc.edu;

Alexander Solis (Co-Presenter/Co-Author)
VIMS, alexander.tr.solis@gmail.com;

Desiree Corbiere (Co-Presenter/Co-Author)
Texas A&M University-Corpus Christi, Desiree.Corbiere@tamucc.edu;

Christopher Frazier (Co-Presenter/Co-Author)
Texas A&M Corpus Christi, christopher.frazier@tamucc.edu;

Connor Brown (Co-Presenter/Co-Author)
Sam Houston State University, clb150@SHSU.EDU;

James Hogan (Co-Presenter/Co-Author)
Texas A&M University – Corpus Christi, james.hogan@tamucc.edu;

Abstract: Global climate models forecast significant changes in precipitation patterns in coming decades, to which lotic systems are particularly sensitive. Yet, the impact of such changes on community composition and trophic structure within these systems remains unclear. Lotic community structure has traditionally been regarded as governed by hydrology (environmental constraints) and resources (bottom-up control); however recent evidence indicates that predators can shape these communities through top-down control. Given that the strengths of top-down processes can be affected by environmental variability, a key mechanism driving future shifts in community structure may lie in the link between climate (precipitation rate, hydrology) and top-down control. We are utilizing a naturally steep rainfall gradient along the Texas coastal plain in a space-for-time study of nine stream communities to address this hypothesis. Data indicate that predatory fishes increase in abundance and diversity with increasing precipitation rate. Coupled with analysis of stable isotope data, stomach contents, species’ functional traits, and in situ experiments, we aim to characterize each stream’s food web, testing the potential for environmentally-mediated top-down control. Ultimately, results will improve our understanding of lotic community assembly and ability to predict communities’ responses to climate change.

Sean Kinard (Primary Presenter/Author)
Virginia Institute of Marine Science, s2kinard@gmail.com;

Hannah Vander Zanden (Co-Presenter/Co-Author)
UF, hvz@ufl.edu;

Matt Whiles (Co-Presenter/Co-Author)
University of Florida, mwhiles@ufl.edu;

Amber Ulseth (Co-Presenter/Co-Author)
Sam Houston State University, amber.ulseth@epfl.ch;

Brandi K. Reese (Co-Presenter/Co-Author)
Texas A&M Corpus Christi, brandi.reese@tamucc.edu;

Christopher Groff (Co-Presenter/Co-Author)
Texas A&M Corpus Christi, cgroff@islander.tamucc.edu;

Bradley Strickland (Co-Presenter/Co-Author)
Virginia Institute of Marine Science, bstrickland@vims.edu;

Fernando Carvallo (Co-Presenter/Co-Author)
Texas A&M University–Corpus Christi, fcarvallo@islander.tamucc.edu ;

Victoria Jenkins (Co-Presenter/Co-Author)
Texas A&M Corpus Christi, vjenkins@islander.tamucc.edu;

Alexander Solis (Co-Presenter/Co-Author)
VIMS, alexander.tr.solis@gmail.com;

Desiree Corbiere (Co-Presenter/Co-Author)
Texas A&M University-Corpus Christi, Desiree.Corbiere@tamucc.edu;

Christopher Frazier (Co-Presenter/Co-Author)
Texas A&M Corpus Christi, christopher.frazier@tamucc.edu;

Connor Brown (Co-Presenter/Co-Author)
Sam Houston State University, clb150@SHSU.EDU;

James Hogan (Co-Presenter/Co-Author)
Texas A&M University – Corpus Christi, james.hogan@tamucc.edu;

Christopher Patrick (Co-Presenter/Co-Author)
Virginia Institute of Marine Science (VIMS), cpatrick@vims.edu;

Abstract: In the American Southwest, conditions are expected to become more arid throughout the next century. Subsequent changes in streamside vegetation could alter nutrient, carbon, and light inputs to streams and fundamentally alter stream primary production and energy flow. To enhance our understanding of how freshwater communities will adjust to these shifts in water-cycle dynamics, we employed a space-for-time substitution along a precipitation gradient from semi-arid to sub-humid on the Texas Coastal Plain. In March 2019, we sampled filamentous algae, leaf litter, macroinvertebrates, and fishes from three wadeable streams spanning the precipitation gradient. The samples were analyzed for stable isotopes of 13C, 15N, 2H, and 18O. We used Bayesian mixing models to estimate in-stream versus terrestrial basal carbon sourcing, and we compared food-chain length and niche widths of abundant taxa. Mean ??13C values differed significantly among the stream communities, and food webs increasingly utilized carbon from terrestrial sources with greater precipitation. Food-chain length and niche width estimates were higher in the mesic and sub-humid sites compared to the semi-arid site. These results indicate that small changes in precipitation in this region may result in cascading bottom-up effects on stream communities.

Wyatt Cross (Primary Presenter/Author)
Montana State University, wyatt.cross@montana.edu ;

Kurt Anderson (Co-Presenter/Co-Author)
University of California, Riverside, kurt.anderson@ucr.edu;

Arthur Benke (Co-Presenter/Co-Author)
University of Alabama, abenke@ua.edu;

Thomas Brey (Co-Presenter/Co-Author)
Alfred Wegener Institute, thomas.brey@awi.de;

Erin R. Hotchkiss (Co-Presenter/Co-Author)
Virginia Tech, ehotchkiss@vt.edu;

Alexander D. Huryn (Co-Presenter/Co-Author)
The University of Alabama, huryn@ua.edu;

Jeremy B. Jones (Co-Presenter/Co-Author)
University of Alaska Fairbanks, jbjonesjr@alaska.edu;

Lillian McGill (Co-Presenter/Co-Author)
University of Washington , lmcgill@uw.edu;

Christopher Patrick (Co-Presenter/Co-Author)
Virginia Institute of Marine Science (VIMS), cpatrick@vims.edu;

Parsa Saffarinia (Co-Presenter/Co-Author)
University of California, Riverside, psaff001@ucr.edu;

Eric Scholl (Co-Presenter/Co-Author)
U.S. Geological Survey, escholl@usgs.gov;

Matthew Troia (Co-Presenter/Co-Author)
University of Texas San Antonio, troiamj@gmail.com;

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

Matt Whiles (Co-Presenter/Co-Author)
University of Florida, mwhiles@ufl.edu;

Abstract: Considerable effort has been dedicated to understanding whether and how individual metabolism scales to influence energy use and production of populations within communities. The energy-equivalence rule posits that population-level energy use is independent of body size – and equivalent among populations – because of opposing body size-metabolism and body size-abundance relationships. Support for this hypothesis is mixed, and many previous studies suffer from comparing populations across disparate communities or estimating metabolic rate using general statistical models. We compiled thousands of direct estimates of annual population-level invertebrate production, a proxy for energy use, across stream communities that span a range of environmental conditions. As expected, we found that abundance (number/m2) was negatively correlated with body size, but slopes were shallower than predicted (-0.44-0.69 vs. -0.75). We also found that individual production scaled positively with body size, but the slope was steeper than predicted (0.84 vs. 0.75). Finally, relationships between body size and population-level production within communities were variable and trended positive, but slopes generally did not differ from zero. Our preliminary results suggest that the energy equivalence rule cannot be rejected for stream invertebrate communities, although alternative hypotheses merit further examination.

Jacob Diamond (Primary Presenter/Author)
INRAE, diamondjacob@gmail.com;

Florentina Moatar (Co-Presenter/Co-Author)
INRAE, florentina.moatar@inrae.fr;

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

Alain Poirel (Co-Presenter/Co-Author)
EDF, alain.poirel@wanadoo.fr;

Cécile Martinet (Co-Presenter/Co-Author)
EDF, cecile.martinet@edf.fr;

Anthony Maire (Co-Presenter/Co-Author)
EDF, anthony.maire@edf.fr;

Gilles Pinay (Co-Presenter/Co-Author)
CNRS, gilles.pinay@ens-lyon.fr;

Abstract: Aquatic ecosystem recovery from anthropogenic degradation are often by internal feedbacks that stabilize undesirable states. The challenges of managing and predicting alternative states in lakes are well known, but state shifts in rivers and their attendant effects on ecosystem function remain understudied. Using three decades of measurements of key state variables such as turbidity, nutrient concentrations, Corbicula fluminea densities, chlorophyll a, and hourly dissolved oxygen, we investigated a sudden shift from phytoplankton to macrophyte dominance in the Loire River, France, and its associated effects on metabolic regime. We show that despite large, synchronous shifts across all state variables, changes in gross primary production (-25%) and ecosystem respiration (-14%) were modest, and lagged the ecosystem state changes by a decade. The shift to a macrophyte-dominated state reduced the sensitivity of primary production to abiotic drivers, altered element cycling efficiency, flipped the net carbon balance from positive to negative, and, crucially, weakened the temporal coupling between production and respiration. This weakened coupling, detected using Granger causality, increased the autocorrelation of net ecosystem production, yielding a robust early warning indicator of both state- and metabolic-shifts that may provide valuable guidance for river restoration.

Francis Burdon (Primary Presenter/Author)
Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, Uppsala, Sweden, francis.burdon@slu.se;

Jasmina Sargac (Co-Presenter/Co-Author)
Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, Uppsala, Sweden, jasmina.sargac@slu.se;

Ellinor Ramberg (Co-Presenter/Co-Author)
Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, Uppsala, Sweden, ellinor.karin.ramberg@slu.se;

Cristina Popescu (Co-Presenter/Co-Author)
Department of Systems Ecology and Sustainability, University of Bucharest, Romania , cristina.popescu@g.unibuc.ro;

Darmina Nita (Co-Presenter/Co-Author)
Department of Systems Ecology and Sustainability, University of Bucharest, Romania , nitadarmina@gmail.com;

Corina Bradu (Co-Presenter/Co-Author)
Department of Systems Ecology and Sustainability, University of Bucharest, Romania , corina.bradu@g.unibuc.ro;

Marie Anne Eurie Forio (Co-Presenter/Co-Author)
Aquatic Ecology Research Unit, Department of Animal Sciences and Aquatic Ecology, Ghent University, Belgium , Marie.Forio@UGent.be;

Felix Witing (Co-Presenter/Co-Author)
Department of Computational Landscape Ecology, Helmholtz Centre for Environmental Research - UFZ, Leipzig, Germany, felix.witing@ufz.de;

Benjamin Kupilas (Co-Presenter/Co-Author)
Norwegian Institute for Water Research (NIVA), Oslo, Norway , benjamin.kupilas@niva.no;

Danny Lau (Co-Presenter/Co-Author)
Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, Uppsala, Sweden , danny.lau@slu.se;

Geta Risnoveanu (Co-Presenter/Co-Author)
Department of Systems Ecology and Sustainability, University of Bucharest, Romania , geta.risnoveanu@g.unibuc.ro;

Peter Goethals (Co-Presenter/Co-Author)
Aquatic Ecology Research Unit, Department of Animal Sciences and Aquatic Ecology, Ghent University, Belgium , Peter.Goethals@UGent.be;

Nikolai Friberg (Co-Presenter/Co-Author)
Norwegian Institute for Water ResearchNorwegian Institute for Water Research (NIVA), Oslo, Norway , Nikolai.Friberg@niva.no;

Richard Johnson (Co-Presenter/Co-Author)
Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, Uppsala, Sweden, richard.johnson@slu.se;

Brendan McKie (Co-Presenter/Co-Author)
Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, brendan.mckie@slu.se;

Abstract: Stream and riparian habitats are strongly connected via the emergence of aquatic insects, which form an important prey subsidy for a wide range of terrestrial consumers. Human perturbations that impact these habitats can disrupt aquatic-terrestrial food-web linkages, but gaps in our knowledge remain about the relative strength of different drivers contributing to altered connectivity. We investigated how stream productivity gradients, aquatic invertebrate dispersal traits, and recipient terrestrial predators influence cross-ecosystem connectivity in temperate streams across four European catchments with varying levels of human disturbance. We used fatty acid biomarkers to measure putative aquatic linkages to riparian spiders. Trophic connectivity, as measured by the proportion of eicosapentaenoic acid (EPA), was positively associated with abundances of ‘aerial active’ dispersing aquatic insects, although this influence was shared with changes in environmental context and spider beta diversity. Structural equation modelling helped further demonstrate the linkage between aquatic insect communities and trophic connectivity with riparian spiders after accounting for biological and environmental contingencies. Our study demonstrates that using trait-based ecology in conjunction with novel biomarkers provides a more comprehensive means to describe cross-ecosystem connectivity and assess the impacts of environmental change on food webs.

Phoenix Rogers (Primary Presenter/Author)
The University of Alabama, parogers@crimson.ua.edu;

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

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

Abstract: We currently lack experimental tests or theoretical predictions of how invertebrate community structure in freshwater ecosystems will change due to increasing temperatures. Empirical data suggest that warming may have a greater positive effect on smaller taxa, potentially altering the distribution of biomass in stream food webs. We are testing the effects of temperature in two forest streams (one reference, one experimentally warmed) in North Carolina, USA, by quantifying monthly invertebrate composition over three years. Preliminary analysis using one size fraction (>1 mm ) of stream invertebrate community data from three summer months (June–August) during the pre-treatment year and first year of warming (ambient plus 1.8°C) in the experimental stream show a clear separation in community structure, with both large (e.g. Diplectrona) and small taxa (e.g. Chironomidae, Ceratopogonidae) driving differences observed after warming. If additional data from the 0.25–1 mm size fraction and second year of greater warming (~2.5°C) support this pattern, our experimental results will suggest significant changes in community composition due to warming. Such shifts in the relative distribution of biomass could reduce the stability of forest stream communities and alter their important role in controlling carbon flow.

Jason Bohenek (Primary Presenter/Author)
The Ohio State University, bohenek.3@osu.edu;

S. Mažeika P. Sullivan (Co-Presenter/Co-Author)
The Ohio State University, sullivan.191@osu.edu;

Rebecca Czaja (Co-Presenter/Co-Author)
The Ohio State University, czaja.3@osu.edu;

Travonya Kenly (Co-Presenter/Co-Author)
The Ohio State University , kenly.1@osu.edu;

Kay C. Stefanik (Co-Presenter/Co-Author)
The Ohio State University, stefanik.13@osu.edu;

Lauren M. Pintor (Co-Presenter/Co-Author)
The Ohio State University, pintor.6@osu.edu;

Abstract: Food webs, which describe biotic interactions and integrate energy pathways within ecosystems, represent one of the principal categories of ecological networks. However, the impacts of nutrient enrichment – a global stressor in aquatic ecosystems – on key characteristics of ecological trophic networks remain largely unresolved. We assessed associations between nutrient enrichment (total nitrogen [N], total phosphorus [P]), diversity indices, land use (% agriculture), and aquatic invertebrate network characteristics at fourteen stream reaches in the Upper Big Walnut Creek watershed, Ohio (USA) across three seasons. Results revealed that both total abundance and Shannon’s diversity were not significantly associated with total N, total P, or agriculture land use. However, assemblage evenness was positively associated with total P, while species richness was positively associated with agricultural land use. When considering trophic network properties, agricultural land use was positively associated with link density, but not connectance or compartmentalization. Total N and total P had a negative relationship with compartmentalization, but nutrients had no relationship with link density or connectance. These finding suggest that variability in nutrients and surrounding land use patterns can have impacts on ecological invertebrate networks. Understanding how ecological networks respond to variability in nutrient concentrations, and associated land use changes, is critical for future the management and conservation of ecosystems in a eutrophic world.

Peter Kiffney (Co-Presenter/Co-Author)
Northwest Fisheries Science Center, peter.kiffney@noaa.gov;

Vail Dark (Primary Presenter/Author,Co-Presenter/Co-Author)
NOAA, vail.dark@noaa.gov;

Peter Aronson (Co-Presenter/Co-Author)
NOAA, peter.aronson@noaa.gov;

Abstract: Stream ecosystems are important for the rearing of juvenile salmon, and there is potential for cascading effects as food webs undergo changes, as determined by the interplay between dynamic processes of bottom-up and top-down control. On the Cedar River in Washington, construction of the Landsburg Dam in 1903 caused a local extinction of anadromous Pacific salmon (Oncorhynchus spp.) above the dam until 2003, when managers added a fish passage, allowing for the volitional recolonization of 33 km of high-quality habitat. We analyzed invertebrate drift and benthic periphyton data spanning before, during, and after Pacific salmon recolonization (2000-2016). From this years-long study, we estimate biomass at different trophic levels to examine the relative importance of top-down and bottom-up trophic effects on the stream ecosystem. Anadromous Pacific salmon are an important source of energy and nutrients for oligotrophic rivers of the Pacific Northwest; we expect to see a bottom-up effect from carcass nutrient subsidies (fertilization effect), leading to an overall increase in periphyton and invertebrate biomass. We may also see bottom-down effects from increased invertebrate grazing and competitive interactions between juvenile salmon and resident trout species.

Zacchaeus Compson (Primary Presenter/Author)
University of North Texas, zacchaeus.compson@unt.edu;

Megan C. Malish (Co-Presenter/Co-Author)
University of Oklahoma, megan.malish@ou.edu;

Stephen C. Cook (Co-Presenter/Co-Author)
University of Oklahoma, stephencook@ou.edu;

Thomas Neeson (Co-Presenter/Co-Author)
University of Oklahoma, neeson@ou.edu;

Daniel Allen (Co-Presenter/Co-Author)
The Pennsylvania State University, dca5269@psu.edu;

Abstract: Food webs are powerful tools for biodiversity assessment, yet most food web studies span limited spatial and temporal scales. While modeling has produced a rich literature of food web theory, these ideas are seldom tested empirically. Here, we capitalize on a large, multi-trophic dataset from the U.S. National Ecological Observatory Network (NEON) to generate trait-based, heuristic food webs using a previously published pipeline. We constructed heuristic food webs for NEON streams, across several seasons and years, and extracted their network properties to explore how they vary through space and time and what environmental drivers influence this variation. We then tested several hypotheses predicted from food web theory, yet seldom tested empirically, especially across large spatial and temporal scales: 1) food webs with higher maximum trophic position are more stable temporally, 2) omnivory stabilizes food webs, 3) as food web complexity increases, food web stability increases, and 4) trophic coherence increases food web stability. Testing these hypotheses will yield important insights into how real food webs function over space and time and help to reconcile different ecological predictions that have arisen from food web modeling.

Emily Arsenault (Primary Presenter/Author)
University of Kansas, erarsenault@ku.edu;

James H. Thorp (Co-Presenter/Co-Author)
University of Kansas/Kansas Biological Survey, thorp@ku.edu;

Michael Polito (Co-Presenter/Co-Author)
Louisiana State University, mpolito@lsu.edu;

Abstract: Characterizing the trophic bases of production supporting metazoan consumers in freshwater food webs has been a research priority for lotic ecologists for decades. In particular, the relative proportions of autochthonous versus allochthonous resources supporting consumer production may vary either predictably by stream position based on an upstream-downstream gradient (River Continuum Concept), or by hydrogeomorphic patches formed by punctuated, semi-predictable differences in physical channel complexity (Riverine Ecosystem Synthesis). We sampled individuals from the dominant fish species of major feeding groups at 56 headwater stream sites representing different functional process zones distributed across three ecoregions of the United States and Mongolia. We used carbon amino acid isotope analysis to estimate basal resources supporting fish production using an isotopic fingerprinting approach combined with Bayesian mixing models. Results suggest that carbon of terrestrial origin provided negligible support for fish food webs, while sources of autochthonous origin provided dominant support across all stream sites. In this study, we observed strong evidence for autochthonous support of fish food webs as has been observed for streams in other recent studies, but we did not find support for that aspect in predictions of the RCC or RES.

Emma Rosi (Co-Presenter/Co-Author)
Cary Institute of Ecosystem Studies, rosie@caryinstitute.org;

Tammy Wooster (Co-Presenter/Co-Author)
CARY INSTITUTE OF ECOSYSTEM STUDIES, woostert@caryinstitute.org;

Olivia Vought (Co-Presenter/Co-Author)
University of Vermont , olivia.vought@uvm.edu;

Heather Malcom (Co-Presenter/Co-Author)
Cary Institute of Ecosystem Studies, malcomh@caryinstitute.org;

Emily Bernhardt (Co-Presenter/Co-Author)
Duke University, emily.bernhardt@duke.edu;

Audrey Thellman (Primary Presenter/Author)
Univeristy of North Carolina at Chapel Hill, athellma@unc.edu;

Abstract: Recent observations document a greening of the headwater streams at Hubbard Brook Experimental Forest. It is presently unclear whether this greening is caused by the rising temperatures, altered terrestrial phenology, or shifting hydrologic regimes induced by climate change. These streams are also rebounding from a legacy of acid rain, associated with rising stream water pH, declining concentrations of toxic Al3+, and increasingly low conductivity. Three years of weekly algal data collection and comparison of historic and modern bryophyte cover are revealing important new insights about the interactions between these two groups of autotrophs. Instream, we measured 6.7 times more algal biomass accrual on artificial moss substrates than on ceramic tiles, and 50% more algal accrual on moss substrates under unlimited light and reduced flow. Further, microscopy reveals abundant filamentous algae in moss beds throughout the stream channels. We hypothesize that increases in the extent or surface area of stream bryophytes is allowing higher algal biomass to accrue because bryophytes provide physical protection from bed scour or abrasion, and bryophytes trap particulates and enhance nutrient availability for algae.

Renn Schipper (Primary Presenter/Author)
Michigan Technological University, rcschipp@mtu.edu;

Abstract: Autotrophic respiration (AR) and heterotrophic respiration (HR) together compose ecosystem respiration (ER), and these processes are likely to differ in environmental controls because they are performed by different groups of organisms. AR should be closely tied to factors that influence primary production, such as light availability, while HR should be influenced by factors such as organic carbon availability. In northern forested streams, dissolved organic carbon (DOC) is the largest pool of organic carbon, and DOC can limit light availability. We hypothesized that HR would increase with DOC concentrations and that AR would decrease with increasing canopy cover and DOC. We measured gross primary production, ER, and environmental characteristics at 8 sites in 4 streams in the Upper Peninsula of Michigan, and used quantile regression to estimate AR and HR. Across the streams, AR showed no correlation with canopy cover (r = 0.47, p > 0.05) or DOC concentrations (r = -0.12, p > 0.05), and HR showed no correlation with DOC (r = 0.44, p > 0.05). Light and DOC may influence temporal patterns of AR and HR in these streams, as may other factors like flow and nutrient supply.

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

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

Meredith Brehob (Primary Presenter/Author)
ORISE at EPA, meredithbrehob@gmail.com;

Abstract: Dense growth of aquatic plants can be a nuisance for recreation and water delivery by irrigation canals. Although excessive macrophyte growth is known to influence ecosystem metabolism, including production and respiration, canals that are drained during the winter provide an opportunity to investigate how the relationship between ecosystem metabolism and macrophyte density changes throughout the growing season when the canals are flowing. We investigated how the relationship between macrophyte density and ecosystem metabolism (gross primary production (GPP) and ecosystem respiration (ER)) varied across three irrigation canals during the late summer of 2020, as well as among ecosystem compartments within canals (sediment, water column, macrophytes). Among canals, macrophyte community respiration (CR) (mg/g/hr) was not correlated with macrophyte biomass density (g/m2) nor was sediment CR correlated with sediment organic matter (%). However, we observed a negative relationship between macrophyte biomass density and macrophyte GPP (mg/m2/hr), suggesting that heterotrophic and autotrophic respiration outpaces photosynthesis in these nutrient- and carbon-rich canal ecosystems. Future study will explore how the balance of GPP and ER changes during macrophyte community succession and will evaluate canal ecosystem resilience in response to ultraviolet-C light treatment used to manage macrophytes.

Colden Baxter (Co-Presenter/Co-Author)
Idaho State University, baxtcold@isu.edu;

Sawyer Finley (Co-Presenter/Co-Author)
Idaho State University, sawyerfinley@isu.edu;

Laurel Faurot (Primary Presenter/Author)
Idaho State University, laurelfaurot@isu.edu;

Abstract: Free-flowing, unfragmented river networks are increasingly rare and their study is vital to understanding natural river ecosystems. We are studying network complexity and its consequences for aquatic meta-food webs and biodiversity across four tributary confluence complexes (multiple tributaries entering a mainstem in close proximity) in a wilderness river. We hypothesized that these complexes create mosaics of habitats, biodiversity, and complexity in meta-food webs, each of which may contribute to community and food web stability. We performed aquatic vertebrate surveys and habitat measurements, and collected fish and amphibian stomach contents and samples for stable isotope analyses across 10 tributaries and 12 mainstem sites. We are analyzing these at nested spatial scales using an iterative, aggregation simulation to investigate the effect of increasing habitat complexity on biodiversity and food web metrics linked to its maintenance. Preliminary results from one confluence complex showed that, when compared to a null model that included no increased habitat complexity, sequentially increasing the suite of habitats included via the simulation not only led to increases in habitat heterogeneity and vertebrate diversity, but also increased the complexity and trophic niche space of the resultant meta-food webs.

Kelly McIntyre (Primary Presenter/Author)
Virginia Tech, mcintyrek@vt.edu;

Kelly Maloney (Co-Presenter/Co-Author)
U.S. Geological Survey, kmaloney@usgs.gov;

Sally Entrekin (Co-Presenter/Co-Author)
Virginia Tech, sallye@vt.edu;

Craig Snyder (Co-Presenter/Co-Author)
U.S. Geological Survey's (USGS) , cdsnyder02@gmail.com ;

Abstract: Acidification inhibits macroinvertebrate ion exchange causing decreased taxon fitness and survival. While it is understood that macroinvertebrate diversity declines with acidification, less is known about functional (e.g., secondary production) responses to acidification. Trait-based metrics (e.g., feeding group) approximate ecosystem function without direct measures. For example, changes in trait representation within macroinvertebrate communities predicts altered secondary production. While traits better correlate with function than taxonomically-based metrics, their predictive ability needs to be tested. We hypothesized that decreased trait richness will correspond to decreased production because of diminished resource use in acidified streams. From July 2019 - June 2020, five Hess samples were collected monthly from one acidified and one circumneutral stream in Shenandoah National Park. Trait richness and density were compared with measures of secondary production. Preliminary analyses suggest decreased richness and density of large bodied and semivoltine taxa could correspond to lower annual production in the more acidified stream. We will also present a comparison of trait structure and function to determine if changes in trait composition predict changes in macroinvertebrate secondary production.

Kate Evans (Primary Presenter/Author)
Flathead Lake Biological Station, katherine1.evans@umontana.edu;

John Ranieri (Co-Presenter/Co-Author)
Flathead Lake Biological Station, ranieri.john@gmail.com;

Tyler Tappenbeck (Co-Presenter/Co-Author)
Flathead Lake Biological Station, tyler.tappenbeck@flbs.umt.edu;

Emma Wear (Co-Presenter/Co-Author)
Flathead Lake Biological Station, emma.wear@flbs.umt.edu;

Matthew Church (Co-Presenter/Co-Author)
Flathead Lake Biological Station, matt.church@flbs.umt.edu;

Abstract: Phytoplankton often dominate primary production in large, deep lakes. In temperate lakes, phytoplankton community composition and physiology can vary widely over seasonal time scales. We used 2 years of near-monthly 16S rRNA gene sequences and phytoplankton photophysiology experiments, along with biogeochemical and physical data, to examine temporal dynamics in primary producers in oligotrophic Flathead Lake. Phytoplankton in the near-surface waters maintained elevated rates of carbon fixation per unit chlorophyll in the summer, when the lake was stratified and incident light flux was greatest, while phytoplankton growing in the low-light, deep chlorophyll maximum layer demonstrated less seasonal-scale variability. 16S rRNA gene sequence analyses revealed closely related members of the genus Cyanobium dominated cyanobacteria taxa, and eukaryotic phytoplankton (based on plastid rRNA genes) demonstrated clear seasonality. Relative abundances of Cryptophyceae were elevated during the well-mixed winter months, with Chrysophyceae becoming increasingly abundant during the summer. The phytoplankton composition, when compared across depths, indicates that summer lake stratification promotes vertically segregated phytoplankton communities. Together, our time series yield unique information on the seasonal phenology of the primary producer community in a large, oligotrophic lake.