The Austin reservoirs are in a constant state of flux. Natural and anthropogenic forces influencing the chemical, biological, and physical characteristics of Lake Austin and Lady Bird Lake include: altered flow regimes dictated by water availability, increased development, and introductions and control of species. Each reservoir is cherished for their aesthetic, recreational, commercial, and municipal benefits. In order to balance the needs of such different users while sustaining an ecologically desirable ecosystem, it is essential to understand the relationship between water chemistry and biological structure of the reservoirs.
One of the most important aspects of reservoir ecosystems influenced by the chemical and biological composition of the system is the flow of energy from primary producers to top consumers. Knowledge of the components of the food web (sources; e.g., aquatic vegetation, phytoplankton) supporting species of interest (consumers; e.g., largemouth bass) is necessary in order to make predictions of potential shifts in community structure that may result from environmental changes and for the implementation of adaptive management strategies ensuring sustainability of desired biological communities. This project aims to collect water and a myriad of potential sources and terminal consumers for measurement of 13C and 15N isotopic signatures.
Stable isotopes are a widely used tool for tracing the flow of nutrients and energy through aquatic ecosystems (Middelburg 2014). Data derived in this study should elucidate the linkages (i.e., source-consumer) and complexity (e.g., trophic levels, number of resources utilized) of the food web, as well as the importance of internal relative to external energy and nutrient inputs to the reservoirs of Austin. Mixing models will be developed to give frequency distributions (i.e., relative contributions) of lower trophic level components in a consumer’s diet (Phillips and Gregg 2003; Phillips et al. 2005). This study will serve to not only describe in quantified detail the current food web structure of the reservoirs, heretofore unknown, but will also serve as a baseline for comparison as the structure of the reservoir’s change under as yet unknown pressures or public desires (e.g., increased vegetation in Lake Austin; increased flows reducing vegetation in Lady Bird Lake).
