The impact of sediment fecal coliform reservoirs on seasonal water quality in Oak Creek, Arizona

Physical and chemical parameters (including stream flow, temperature, pH, dissolved ion concentrations and biological oxygen demand) indicate that the water of Oak Creek, AZ is of high quality. However, fecal coliform enumerations of Oak Creek demonstrated an annual deterioration of water quality during the summer seasons of 1994, 1995 and 1996. The summer season is characterized by high recreational use and by summer storm activity. During the summer periods, violations (> 800 cfu/100 mi) of Arizona Department of Environmental Quality guidelines for its 'unique waters' designation were recorded during 17 out of 54 sampling days and seriously compromised (< 150 cfu/100 ml) water quality was recorded for 37 out of 54 sampling days. In addition, two sediment sites were identified with high fecal coliform counts, averaging 2200 times the fecal coliform counts of the water column. The results of this study show that sediment agitation by recreational activity and storm surges associated with the summer storm season are responsible for the impact to water quality and not recreational users directly, as suggested by previous studies. Sources of fecal pollution in the Oak Creek watershed may include grazing cattle, natural animal populations primarily elk and deer, septic tanks, failed municipal sewage systems and recreational users. (C) 1999 Elsevier Science Ltd. All rights reserved.