A survey of the aquatic insects, geology, and microbiology of Pena Spring, Big Bend National Park, Texas

Peña Spring is a perennial spring that forms an intermittent/ephemeral stream occurring within a transition zone between desert scrub and riparian habitats. It is an important resource for wildlife and vegetation. This research was conducted between 1998 and 1999 and included a qualitative survey of aquatic and semi-aquatic insects; quantitative analysis of coliform and heterotrophic microorganism contamination of the water, general water chemistry analysis; and mapping the geology of the area and interpreting the hydrology of the spring. The intention of this research was to provide preliminary and pertinent information necessary to establish a data base for reference and future monitoring of this spring, and to compare the data to that of other similar desert springs.;Results from the aquatic insect data revealed that there was an abundance of insect diversity along the stream and a direct correlation between aquatic indicator species and water quality. A new geographic distribution record was established for the dipteran Corethrella laneana Vargas. Colony counts for bacteria microorganisms tested were high; however, these results are also an indication of the natural processes of the stream ecology. The Peña Spring area is comprised of Quaternary alluvium and Tertiary tuffaceous sediments that are directly responsible for the hydrology of the spring.