Statistical investigations into indicator bacteria concentrations in Houston metropolitan watersheds

Bacterial pollution in the Houston metropolitan area (Texas) watersheds was studied using statistical methods to determine the Escherichia coli levels and causes of their spatial and temporal variability. Houston bayous generally exhibit elevated E. coli concentrations. The more urban watersheds had higher concentration ranges and geometric means and had more spatial variation with higher overall ranges at downstream monitoring stations. They also were less sensitive to temperature variations and more strongly influenced by rainfall events. The median flow in the more urban bayous is predominantly wastewater. Frequent rainfall in the region, combined with relatively long travel times in the bayous, results in elevated bacterial levels in the bayous. Multiple regression models using water quality parameters were more representative on the segment level and not at the watershed level and may not be useful for predictions that rely on conventional water quality measures, particularly in urban watersheds, such as those studied here. Cluster analysis for the segments resulted in two distinct clusters differentiated by their developed land-use, population density, domestic animal density, and grassy land-use.