Fractionation and distribution of phosphorus as evidence of deposition by fish-farming in eutrophic Lake Kasumigaura, Japan

Abstract

To predict the impact of intensive net-pen fish farming on lake environments, sediment surveys were conducted in/around major carp-farming areas in Lake Kasumigaura, Japan. There was no significant difference in the ignition loss, total organic carbon, total nitrogen, and C/N ratio between fish-farming and non-fish-farming areas. In contrast, the content of fractional phosphorus, especially inorganic phosphorus, in fish-farming areas was different from that in non-fish-farming areas. The sediment in the former was clearly characterized by its high content of HCl reactive (Ca bound) phosphorus due to the accumulation of matter derived from feces. In conclusion, HCl reactive phosphorus was found to be suitable as a tracer for the impact of fish-farming activity on sediment quality. Mobile (Fe/Al bound) phosphorus was present in the sediment along with HCl reactive phosphorus, indicating the possibility that the sediment in fish-farming areas has a high-release potential.