Use of macroinvertebrate and chemical indices to assess water quality of an irrigation wasteway

Abstract

The Amon Wasteway is an engineered drainage waterway for the Kennewick Irrigation District, which receives its water from the lowerYakima River near Prosser, Washington. Reference conditions that were established in a basin-wide macroinvertebrate and physicochemical study of the Yakima River were used to generate a macroinvertebrate community condition index and a non-pesticide agricultural intensity index. These indices were utilized to ascertain the ecological integrity of the wasteway. Despite the negative connotation often associated with such bodies of water, the wasteway compared well against both reference condition indices for the lower basin. The overall water quality of Amon Wasteway, as measured by macroinvertebrate and physicochemical analysis, was found to be better than its source, the Yakima River. The species composition of the wasteway most closely resembled the makeup of the Yakima River. This river is many times the size of the wasteway, but the nearest source in an arid climate to provide immigrants.