Environment and development of benthos in earthen trout ponds in Central Scotland

Abstract

Soil and water chemistry and benthic macroinvertebrates were monitored for 21 months in a series of earthen ponds used for semi-intensive culture of brown trout, Salmo trutta. Paniculate organic matter and inorganic nutrients increased as water flowed from pond to pond, but final effluent quality was acceptable. Soil organic matter and sedimentation rate reflected the organic loading, dependent on artificial feed inputs. Benthic (especially oligochaete) abundance, biomass and production responded significantly to soil organic enrichment rather than dissolved nutrients. Benthos in on-growing ponds was dominated by Oligochaeta, comprising 86, 79 and 75% of mean total abundance, biomass and production, respectively; next came Chironomidae, with 12, 10 and 14%, respectively. Corresponding total annual dry weight production was 204–214 g m −2 year −1 and total mean biomass 48–59 mg m −2. A moderate intensity of management of earthen ponds for trout culture encourages the development of a rich benthic community, providing food for fish, assisting decomposition of organic wastes and lessening downstream environmental impact.