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Effects of a Small-Scale Trout Farming Operation on Water Quality and Entomofauna of a Desert Stream in Southern California

R. Trudith Pachon, William E. Walton

Abstract


The impact of a small-scale trout farming operation on the Whitewater River, a small desert stream in southern California, was assessed at locations up to 8 km downstream of the effluent discharge. Ammonium nitrogen increased significantly downstream of the trout farm relative to an upstream reference site. The mean orthophosphate concentration in the trout farm effluent stream was 1.7-times higher than at the reference site but PO4-P levels were not elevated significantly in the Whitewater River across the entire study period (February to October). Algal abundance, both on cobble surfaces and suspended in the water column, downstream of the trout farm was significantly higher than upstream. The mass of suspended particulate matter at the confluence of the effluent stream and the Whitewater River was two-times higher than at the reference site, but declined downstream. The most abundant benthic insects in lower Whitewater Canyon were moderately pollution-tolerant generalist feeders and rapid colonizers: Simuliidae, Chironomidae, Baetidae and Hydropsychidae, in order of decreasing abundance. The mean density of all aquatic insects at sites enriched by trout farm effluent was 39-47% higher than at the reference site, with chironomid midge density increasing at all sites between the effluent discharge and 8 km downstream.

Keywords


aquaculture, desert stream, enrichment, pollution

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