Dissertation Research: Ecosystem scale abiotic and biotic drivers of food web structure in deep phreatic aquifers

Texas State University - San Marcos, San Marcos TX

Investigators

Abstract

Karst aquifers are sources of groundwater for human use, are an integral component of the water cycle, and may contain diverse microbial, invertebrate, and vertebrate communities. Many karst aquifers are threatened by groundwater extraction and contamination, but relatively little is known about their community structure, ecosystem function, or biogeochemical cycling. This research, on the Edwards Aquifer of south-central Texas, will address links between hydrogeology and geochemistry, the distribution of organic matter, and the trophic structure of groundwater communities. Specific issues that will be addressed will include the ways that hydrology and geochemistry affect the spatial and temporal distribution of chemolithoautotrophic and photosynthetic organic matter and utilization by groundwater species, whether biodiversity in groundwater habitats is supported by resource partitioning, and whether the prevailing paradigm of truncated trophic structure in subsurface habitats is supported by isotopic data. These issues will be addressed by sampling across geochemical gradients in the freshwater and saline portions of the aquifer. Methods will include inorganic and organic geochemical characterization of groundwater, geospatial analysis of geochemical data, stable isotope analyses, and morphometric analyses of invertebrates. Preliminary results show that organic matter produced both by plants, using sunlight, and by microbes that derive energy from redox reactions involving inorganic substrates (chemolithoautotrophs) is utilized by invertebrates, and both types of organic matter are distributed unevenly within the aquifer, being controlled by the movement of water (photosynthetic matter being prevalent near recharge features) and geochemistry (chemolithoautotrophic production occurring where fresh and saline groundwaters mix). This project will have substantial societal importance because it directly relates to water quality and the maintenance of biodiversity in ecosystems that are intensively managed for human use. The project also will provide field and laboratory opportunities for students, including Hispanics and women employed or enrolled as graduate students in the PIs laboratory.