Instream community assessment of aquaculture effluents

Abstract

The regionally concentrated commercial catfish industry has attracted attention to its possible contributions to basin contaminant loading. This study was included in a screening process to establish baseline bioassessment information for commercial aquaculture of the southeast United States. One valuable aspect of the typical drainage system in this industry's landscape is the assimilative capacity and transformation of contaminants associated with ditches. Two extensive commercial fish farm drainage systems in northeast Arkansas and affected receiving streams were examined for their response to potential nutrient related contamination. The research utilized modified Rapid Bioassessment Protocols (RBPs), as applied nationwide, in characterization and identification of potential water resource impairments. Additional biological impairment testing of related pond discharges and affected receiving streams was also conducted to further characterize potential effluent impacts. There was no observed significant toxicity ( P<0.05) in Pimephales promelas exposed for 48-h to pond discharges, while neonate production in Ceriodaphnia dubia was significantly reduced. Upstream samples yielded significant ( P<0.05) C. dubia toxicity and reproduction impairments, while downstream samples only yielded reproduction impairments. While physicochemical analyses indicated minor differences between fish pond effluents and receiving stream water, benthic community responses measured as taxa richness were not significantly different ( P=0.395) between receiving systems—upstream, facility effluent and downstream. Taxa richness of benthic macroinvertebrates was unaffected by pond discharge at all sites. Ephemeroptera (mayflies), Plecoptera (stoneflies), and Trichoptera (caddisflies)—EPT taxa actually responded with increased abundance in receiving streams below the pond discharges. Taxa richness of fish was also unaffected in relation to upstream locations and downstream of the facility effluent release ( P=0.877) while fish abundance decreased. These findings suggest minimal detrimental instream effects result from the introduction of aquaculture effluents into receiving waters.