SFS Annual Meeting

6/06/2024  |   15:30 - 15:45   |  Freedom Ballroom E

MACROINVERTEBRATE COMMUNITY RESPONSES ALONG CLIMATE AND DISTURBANCE GRADIENTS: TESTING PREDICTIONS OF THE STREAM BIOME GRADIENT CONCEPT Rivers are complex, spatially structured, and often span pronounced environmental gradients that affect the composition and diversity of communities. The Stream Biome Gradient Concept (SBGC) posits that the composition of the surrounding terrestrial landscape, which is largely determined by regional climatic conditions, has a large impact on community composition and ecosystem functioning. It is widely acknowledged that benthic macroinvertebrate (BMI) communities respond to land cover patterns and perturbation gradients across riverscapes, but there is still a need to examine the SGBC and how large-scale environmental gradients influence BMI communities. The purpose of this study was to empirically assess predictions of the SGBC as it applies to BMI communities along climate and hydrological disturbance gradients in four drainage basins using trait-based and taxonomic approaches. We collected BMIs, water chemistry, and land-use data for 57 sites across four basins in Texas, (USA) that represent a range of terrestrial biomes (i.e., desert, grassland, savannah, and forest). We found that BMI community diversity and composition differed in lotic systems found among different biomes (i.e., forest and savannah biomes had the highest diversity), but BMI community composition was strongly influenced by local-scale water chemistry and water quality (~12% of the variation in BMI explained). Additionally, hydrological classification (perennial versus intermittent flows) and watershed size explained additional variation in BMI diversity within and among biomes. Overall, this study found that some of the predictions of the SBGC were supported but local-scale variation in water chemistry and quality still play an important role in BMI community composition.

Kierra Determan (Primary Presenter/Author), Texas State University, ldd90@txstate.edu;

Amy Yarnall (Co-Presenter/Co-Author), US Army Engineer Research and Development Center, amy.h.yarnall@usace.army.mil;

Mariana Perez Rocha (Co-Presenter/Co-Author), Texas State University, mperezrocha@txstate.edu;

Benjamin Schwartz (Co-Presenter/Co-Author), Department of Biology, Texas State University, San Marcos, Tx., bs37@txstate.edu;

Weston Nowlin (Co-Presenter/Co-Author), Texas State University, wnowlin@txstate.edu;

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6/06/2024  |   15:45 - 16:00   |  Freedom Ballroom E

Sticky situation: Insights from 12 years of monitoring emergent aquatic insects along the Colorado River in Grand Canyon The majority of aquatic insect monitoring programs focus on sampling larval insects from the benthic zone. While this traditional approach has lent itself to great insights and allows for data concatenation across study areas, it has limited applications for understanding the role of aquatic insect life cycles in their entirety. Sampling insects in their winged terrestrial life stage provides insights on adult phenology, voltinism, and life cycle synchronicity among regional taxa in additional to more typical measures of aquatic biodiversity such as species richness and relative abundance. Additionally, as a general methodology, sampling emergent aquatic insects does not require entering water and is therefore a method amenable to safety in large fast-current rivers as well as a resilient method for monitoring drying and intermittent water bodies. In this presentation, we review 12 years of monitoring data of aquatic insect emergence along the Colorado River in Grand Canyon using two different methods: sticky traps and light traps. We discuss the pros and cons of the two methods and compare the information gained from each method. Our results provide fodder for managers and researchers considering the addition of emergent insect sampling to their monitoring programs and provide novel insights on emergent aquatic insect phenology and life cycles in Grand Canyon.

Anya Metcalfe (Primary Presenter/Author), USGS Southwest Biological Science Center, Grand Canyon Monitoring and Research Center, ametcalfe@usgs.gov;

Ted Kennedy (Co-Presenter/Co-Author), USGS Southwest Biological Science Center, Grand Canyon Monitoring and Research Center, tkennedy@usgs.gov;

Jeffrey Muehlbauer (Co-Presenter/Co-Author), University of Alaska Fairbanks, USGS Alaska Cooperative Fish and Wildlife Research Unit, jdmuehlbauer@alaska.edu;

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6/06/2024  |   16:00 - 16:15   |  Freedom Ballroom E

Hippo dung provides food and shelter for invertebrates Animal subsidies can provide an important food source to recipient food webs. Little research has examined the potential complementary roles of subsidies such as providing habitat. Based on preliminary data from the Mara River in Kenya, we know that invertebrates consume hippo dung and we have observed high invertebrate abundance within hippo dung. We conducted an artificial stream experiment that tested if invertebrates use hippo dung as habitat and/or food. We set up 20 experimental streams that were inoculated with invertebrates and algae. We had three treatments – boiled (habitat), blended (food), or unprocessed (habitat and food) hippo dung – and we used a gradient design, following dung concentrations observed in the Mara River. We measured nutrient concentrations and algal abundance throughout the experiment and collected invertebrates after two weeks. Nitrogen levels increased up to 5x with addition of blended and unprocessed hippo dung immediately after the dung was added, but these levels returned to background concentrations (5 µg N/L) by the first week. Algal abundance was highest in streams with blended dung, while there was no difference in algal abundance after boiled dung was added. Invertebrate biomass increased with more hippo dung across all three treatments, but we saw the strongest increase with the habitat and food treatment, followed by the food only treatment. Our results indicate that hippo dung provides both food and habitat for invertebrates, which could increase the impact of this resource subsidy on secondary production and stability in rivers systems.

Therese Frauendorf (Primary Presenter/Author), Colgate University, tfrauendorf@colgate.edu;

Amanda Subalusky (Co-Presenter/Co-Author), University of Florida, asubalusky@ufl.edu;

Anna Reside (Co-Presenter/Co-Author), Yale University, anna.reside@yale.ed;

Christopher Dutton (Co-Presenter/Co-Author), University of Florida, cldutton@gmail.com;

Joe Coolidge (Co-Presenter/Co-Author), Colgate University, jcoolidge@colgate.edu;

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

David Post (Co-Presenter/Co-Author), Yale University, david.post@yale.edu;

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6/06/2024  |   16:15 - 16:30   |  Freedom Ballroom E

Nitrogen removal in Lower Mississippi River floodplain lakes is complicated by complex N cycling dynamics. Denitrification in Lower Mississippi River (LMR) backwater areas potentially reduces nitrogen (N) loading to the Gulf of Mexico. We hypothesized that NO3-N introduced to backwater lakes through connection with the river is denitrified during summer disconnection. We tracked summer dissolved NO3-N, NH4-N and N2-N gas in the hypolimnion of a large oxbow lake with seasonal hydrologic connection to the LMR. Denitrification rates were estimated by measuring changes in hypolimnetic excess N2-N concentrations over time and from incubated sediment cores. In both years, hypolimnetic N2-N increased while NO3-N declined to almost 0. We also found N2-N in excess of equilibrium during a mid-summer survey of seven lakes distributed across 560 km of the LMR floodplain, indicating that denitrification is active in backwater areas throughout the lower basin. However, other results point to the importance of considering alternative N cycling processes. For example, excess N2-N in our focal lake declined in late summer suggesting that diffusive loss or N fixation may influence the ultimate fate of excess N2-N. Complimentary sediment core N2-N flux measurements indicated that sediments shifted to net N fixation during periods of NO3-N limitation and decreasing N2-N concentrations. Additionally, hypolimnion NH4-N increased throughout summer in both years demonstrating that processes including dissimilatory nitrate reduction to ammonium (DNRA) and organic matter decomposition need to be considered. While denitrification is an active N removal process in LMR lakes, accounting for the complex dynamics of alternative N-transformations is needed to quantify the magnitude of N removal potential for these understudied habitats.

Jason Taylor (Primary Presenter/Author), USDA-ARS, Jason.Taylor@usda.gov;

Clifford Ochs (Co-Presenter/Co-Author), University of Mississippi, byochs@go.olemiss.edu;

Jaylen Powell (Co-Presenter/Co-Author), Baylor University, Jaylen_Powell1@baylor.edu;

Douglas Shields Jr. (Co-Presenter/Co-Author), Shields Engineering, LLC, doug2shields@gmail.com;

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6/06/2024  |   16:30 - 16:45   |  Freedom Ballroom E

NUTRIENT AND WATER QUALITY RESPONSES TO LAND USE/LAND COVER PATTERNS ACROSS A CLIMATE DRIVEN STREAM BIOME GRADIENT Understanding how land-use/land-cover (LULC) patterns within and across watersheds affects ecosystem functioning and nutrient processing respond to both natural and anthropogenic watershed characteristics is key for water quality management. The Stream Biome Gradient Concept (SBGC) theorizes that ecosystem functioning and nutrient processing changes predictably along broad-scale climate and physiographic gradients which in turn drive hydrology, geomorphology, and terrestrial vegetation types in watersheds (e.g., forest, grassland, desert). It also predicts that the intensity of nutrient chemistry and water quality responses to LULC modifications will vary among watershed vegetation types. In this study, we examined the influence of LULC patterns and physiographic characteristics on water quality and chemistry at 58 sites across four watersheds that lie along a terrestrial biome and aridity gradient in Texas, USA. The watersheds encompassed a range of biomes, including desert, grassland, savannah, and forest. We hypothesized that nutrient chemistry and quality would vary systematically among biome types, but the type and magnitude of water chemistry responses to LULC modification would differ among biome types. Our results indicate that the baseline water chemistry characteristics differed among biome types, but that the intensity and types of water quality responses to LULC modifications varied with biome type (e.g., suspended solids versus inorganic nitrogen concentrations). Findings from this study have important implications for land use planning and water resource management in Texas and similar regions across the globe, especially under changing climates.

Hannah Mattes (Primary Presenter/Author), Texas State University, ham68@txstate.edu;

Kierra Determan (Co-Presenter/Co-Author), Texas State University, ldd90@txstate.edu;

Matthew Stehle (Co-Presenter/Co-Author), Texas State University, mrs239@txstate.edu;

Weston Nowlin (Co-Presenter/Co-Author), Texas State University, wnowlin@txstate.edu;

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6/06/2024  |   16:45 - 17:00   |  Freedom Ballroom E

Variability across scales in a threatened ecosystem provides insights into the importance of maintaining environmental heterogeneity. Variability within and among communities is an important aspect of stability in ecology. However, the scale at which we measure variability can greatly affect how stable a system is thought to be. Despite observations of local variability, regional variability is possibly dampened by the effects of abiotic (spatial) and biotic (species) asynchronies at a local scale. Thus, we investigated local and regional variability across a physically dynamic riverscape, by sampling local and regional spatial and species variability in terrestrial and aquatic habitats. We expected (i) local biomass variability (measured as coefficient of variation, CV) of aquatic communities to be higher than meta-community variability; (ii) regional variability to be driven by physical asynchronies in channel characteristics; and that (iii) metacommunity variability would be higher than community variability in counts of terrestrial invertebrates due to higher spatial synchrony in environmental variables, such as air temperature. We found high variability at the local scale in both biomass and species composition of aquatic invertebrates, and both aggregate (spatial) and compositional (species) variability was lower at the whole-river scale. Counts of terrestrial invertebrates from pitfalls had slightly higher community variability than at the metacommunity scale, but much higher spatial synchrony than the aquatic communities. While challenges remain, these results demonstrate the likely importance of maintaining local-scale heterogeneity in these locally and globally threatened river ecosystems.

Holly Harris (Primary Presenter/Author), University of Canterbury, holly.harris@pg.canterbury.ac.nz;

Jonathan Tonkin (Co-Presenter/Co-Author), University of Canterbury, jonathan.tonkin@canterbury.ac.nz;

Tara Murray (Co-Presenter/Co-Author), Department of Conservation, tmurray@doc.govt.nz;

Angus McIntosh (Co-Presenter/Co-Author), University of Canterbury, angus.mcintosh@canterbury.ac.nz;

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