CONSUMER AGGREGATIONS AND BIOGEOCHEMICAL HOTSPOTS: Aggregations of consumers create local patches (hotspots) of nutrient regeneration and material flux that promote resource heterogeneity, increasing biodiversity. Understanding how different types of aggregations interact to influence resource distribution and fluxes is a key knowledge gap, particularly in how these dynamics change across spatial and temporal scales and environmental gradients. Stream fish and mussel assemblages are known to generate biogeochemical hotspots, but have very different characteristics based on species life history and behavior. Long-lived mussels are localized, stable, immobile, long-term hotspots that provide relatively constant nutrient subsidies. Shorter-lived fishes are mobile, widespread, short-term hotspots that provide nutrient subsidies more dependent on hydrologic conditions. How these two important hotspots overlap and interact to influence the functioning of stream networks is unknown. With funding from the National Science Foundation, we are examining how different and potentially interacting consumer aggregations influence resource distribution and fluxes across a gradient of biotic and abiotic conditions. Using fish and mussel consumer assemblages in streams as a model system, our project addresses two questions: (1) Where and when do fish and mussel hotspots overlap? and (2) How does overlap between consumer aggregations influence nutrient recycling and the distribution of resources throughout a stream network? These questions will be addressed with an integrative approach that incorporates species distribution mapping, correlative field studies and a mechanistic mesocosm experiment. To determine the spatial and temporal overlap of mussel and fish hotspots, a biomass distribution model will be generated for mussels and fishes under different hydrologic conditions in two rivers. To determine where and when each group’s function is strongest, path analysis will be used to characterize associations between nutrient dynamics and resource distribution when mussels and fish overlap (summer low flows) and when fish are more dispersed (fall higher flows). To explore mechanistic contributions of mussel and fish assemblages to nutrient and food web dynamics, experiments will be performed in large, replicated, flow-through experimental streams where the movement of nutrients from consumer aggregates (mussel and fish excreta) through the rest of the food web will be tracked with stable isotopes. Lastly, ecosystem dynamics will be scaled to whole rivers using fish and mussel distribution and hydrologic data generated in the field study. The end result will be a spatial and temporal model that overlays fish and mussel function and explores synergistic and antagonistic contributions between these groups
ECOLOGICAL COSTS & BENEFITS OF ENVIRONMENTAL FLOW RECOMMENDATIONS: Freshwater mussels are filter feeders and thus provide important ecosystem services in rivers, particularly water filtration and nutrient recycling. The ability of mussels to provide these services changes with different in-stream flows because water volume partially governs water temperature, and water temperature determines mussel filtration and nutrient recycling abilities. In addition, when mussel populations are adversely affected, it is likely that other aquatic species are at risk. Their high sensitivity to changes in flow regimes and water temperatures make freshwater mussels an early-warning test system for determining the ecological costs/benefits of environmental flow recommendations. We are combining information on (1) discharge and water temperature under various in-stream flows in different seasons with (2) information on how mussels perform the ecosystem services of water filtration and nutrient recycling under those conditions to (3) produce empirical, predictive models of the ecosystem services provided by mussels under various flow and atmospheric conditions.
USING AN ECOSYSTEM SERVICES FRAMEWORK TO EXAMINE THE SOCIAL, ECONOMIC AND ECOLOGICAL TRADEOFFS OF DIFFERENT WATER MANAGEMENT SCENARIOS: Freshwater is vital for both humans and fish and wildlife, but humans are using freshwater more rapidly than it can be replenished. The Kiamichi River watershed in southeastern Oklahoma is at the center of intense conflict over water ownership and use. The Tarrant County Water District (North Texas), Oklahoma City, and Chickasaw and Choctaw nations all want this water and are fighting each other in court. Missing from these disputes are the needs of the watershed’s rich animal and plant life, including three federally endangered freshwater mussels. We are using an ecosystem services framework to examine how different water management/environmental flow scenarios in the Kiamichi River watershed affect the delivery of ecosystem services, and thus contribute to the wellbeing of people living both in and outside the watershed. Our approach involves mapping the spatial delivery of a selection of watershed ecosystem services, and then exploring the tradeoffs between their biophysical, socio-cultural and economic values. Once these tasks are completed we can then examine the tradeoffs between different water management strategies and share our results with policy makers and managers.