Submitted to: American Society for Microbiology
Publication Type: Proceedings
Publication Acceptance Date: 12/15/2002
Publication Date: 6/15/2003
Citation: Spencer, L.K., Duran, N.L. 2003. Effects of effluent-dependent streams on microbial loads and groundwater quality. American Society for Microbiology. Abstract 03:GM-A-4075-ASM Interpretive Summary:
Technical Abstract: Due to limited annual rainfall, streams of the arid west differ from the wet, flowing streams of perennial ecosystems in that they are dry most of the year and many are effluent-dependent. Effluent discharge from wastewater treatment plants is a growing source of water that can provide a constant stream flow in ephemeral streams. Although these streams cannot be used for recreational purposes, they allow riparian ecosystems to develop and contribute to groundwater recharge. The latter is particularly important to help replenish declining groundwater levels as a result of over-pumping of groundwater for urban and agricultural use. However, since microbial and chemical contaminants can persist in the treated effluent, it is necessary to evaluate the effects of effluent-dependent streams on groundwater quality. For this reason, surface and groundwater samples were collected from the effluent-dependent Santa Cruz River located near the city of Tucson, Arizona. Samples were then subjected to chemical and microbial quality analyses. Preliminary results demonstrated that, at the point of discharge, coliform numbers varied considerably over a twenty-four hour period emphasizing the need for average daily load measurements. Contrary to what might be expected, microbial numbers (E. coli, total coliforms, and heterotrophic plate counts) were greater downstream from the discharge. Although the groundwater samples had much lower bacterial counts than the surface water, Cryptosporidium and Giardia oocysts were identified in one groundwater sample as well as in the effluent. These preliminary results indicate that the impact of effluent-dependent streams on the underlying groundwater needs further assessment and highlights the need for proper monitoring of microbial survival, fate, and transport.