Distribution of E. coli Levels and Recreation Use as Factor of Stream Order in the Central Great Plains, Central Oklahoma-Texas Plains, and South Central Plains Ecoregions

Abstract

This study examines the relationship of E. coli concentrations and recreational use to both stream order and watershed size. To determine possible ecoregion effects, the E. coli data used in this study were obtained from monitoring stations located on freshwater streams located in three ecoregions in Texas and Oklahoma – the Central Great Plains, Central Oklahoma/Texas Plains and South Central Plains (Ecoregions 27, 29, and 35, respectively). Median E. coli concentrations from the monitoring stations were analyzed for correlation with respect to the stream order of each monitoring site as well as the watershed size of each monitoring station. Geospatial analysis was used to determine stream order and watershed size and to identify un-impacted/least impacted streams in each ecoregion. Stream order was classified based on the traditional stream order classification method by Horton (1945) and Strahler (1957) and stream link magnitude analysis method by Shreve (1966). The analysis of two stream order systems and watershed size for each monitoring site with respect to median E. coli showed no significant relationship between E. coli and stream orders/watershed size of unimpacted watersheds. The watersheds with wastewater outfalls and urban areas exceeding 10% of land use showed a statistically significant, yet a weak negative relationship between E.coli and stream order/watershed size i.e. E. coli decreased with increase in stream order/watershed size.