DEGRADATION OF OLIGOTROPHIC STREAMS IN THE TEXAS HILL COUNTRY

Urban growth continues to encroach into sparsely populated rural areas outlying metropolitan areas. One challenge posed by this encroachment is that natural resources, including water supplies, are threatened or compromised by land-use changes. In particular, increased development, whether industrial, commercial, or residential, will change the composition of recharge to both surface-water and groundwater resources. These impacts can alter the trophic state of surface water, which can result in degraded recharge of groundwater. Nutrient concentrations, periphytons, and sestons are common indicators of the trophic state. Each indicator has been used to ascertain the trophic state of former rural areas located where the Texas Hill County is impacted by development from urban sprawl resulting from growth of the San Antonio metropolitan area. Sampling of nutrients, periphytons, and sestons from streams in the contributing zone of the karstic Edwards Aquifer provide the basis to determine the trophic state of the stream and to identify potential point and non-point sources of contaminants. Periphytons and sestons have been shown to provide increased resolution of the trophic state and to better identify sources of contaminants when compared with nutrient concentrations. Streams that were considered as oligotrophic in their natural state are now considered mesotrophic and even eutrophic due to this degradation when using periphytons and sestons as indicators of environmental degradation.