ABSTRACT
In this chapter, the authors measure the P concentration in different existing forms of phosphorus in fish pond sediment, i.e., in the fractions of loosely sorbed phosphorus, ligand exchangeable phosphorus, residual phosphorus and organically-bound phosphorus. The potential of the fractions to liberate phosphorus was evaluated experimentally. While the total phosphorus in the sediment of our experimental fish pond decreased slightly with depth over 10 cm, the decrease was less pronounced than that in less disturbed lakes. Aizaki reported that sediment phosphorus in shallow, eutrophic Lake Kasumigaura was distributed evenly down to 20 to 30 cm depth at most of the sample stations, due to anthropogenic activities such as fishing with nets. Normally, the sediments of aquatic systems are considered to be a phosphorus sink. The mixing movement of the water column brought about by pond aeration, and the biodisturbance caused by the benthivorous fishes stocked in fish pond can account for the rapid exchange of P between the pond sediment and water column.
