Understanding key factors influencing habitat quality for the endangered fountain darter (Etheostoma fonticola) in the Comal River.

The research in this thesis was divided into 3 main studies that took place in Landa Lake: water column, sediment, and plant nutrient analyses, an herbivory and soil fertility experiment, and a spatial study of diel dissolved oxygen dynamics. Nutrient data were collected via water samples, nutrient diffusing substrata (NDS), sediment cores, and plant samples. The water samples and NDS results indicated a severe phosphorus limitation in the water column and some macrophyte species may be limited by phosphorus as well. Herbivory in Landa Lake, particularly by crayfish, appears to be much more severe than previously thought and increased soil fertility exacerbates the issue in Ludwigia repens. Diel dissolved oxygen varied across the lake, largely correlated with flow conditions. During drought, there may be several areas of the lake where DO is low enough to threaten fountain darter survival, but there is little cause for concern under current conditions.