1Water Environmental Laboratory, Ibaraki Prefectural Kasumigaura Environmental Science Center, Tsuchiura, Ibaraki 300-0023, 2Department of Life and Environmental Sciences, Chiba Institute of Technology, Narashino, Chiba 275-0016, 3Environmental Biology Division, National Institute for Environmental Studies, Tsukuba, Ibaraki 305-8506, 4Lake Fisheries Division, Ibaraki Prefectural Freshwater Fisheries Experimental Station, Namegata, Ibaraki 311-3512, Japan
The distribution of phosphorus fractions in bottom sediment at a fish (carp) farming area and a non-farming area in three shallow eutrophic lakes, Nishiura, Kitaura and Sotonasakaura, and the characteristics of sediment at a carp farming area were examined. The total fractional phosphorus content in sediments at the carp farming area was relatively high. The inorganic phosphorus fraction, especially HCl-reactive phosphorus (HCl-RP) and citrate-dithionite-bicarbonate-reactive phosphorus (CDB-RP）, was high in the sediment of the carp farming area. According to principal component analysis for the content rate of six phosphorus fractions in sediment, the sediments of the carp farming area were interpreted as those of the non-farming area to which HCl-RP was added. It was suggested that the fish feed (fish meal) and/or excrement accumulated in sediment under the fish cage.