Impact of previous aquaculture (yellowtail), as persistent phosphorus, remains for decades in deeper sediments

Abstract

Feeds based on small (trash) fish contain much persistent phosphorus (P), such as Ca bound (Ca-P) and refractory P (Ref-P), which accumulates in high concentrations in the bottom sediments immediately below fish farms using this type of feed. This study designated three sampling locations based on their history concerning yellowtail fish farming (current, formerly or never) to investigate the sediment vertical distribution of phosphorus fractions and to test for detection of P impact on the bottom sediment. The aquaculture-free site was relatively low in Ca-P and Ref-P compared with continuous and previous aquaculture sites. The latter had high Ca-P and Ref-P content only in the depth range 17–29 cm, coinciding with the period during which aquaculture was conducted (1960–1998). The techniques used are expected to be useful to indicate bottom condition improvements and as a tracer of the effects of previous aquaculture farming.