Organic Degradation Processes in Different Microenvironments(Seawater,Sinking Particles and Bottom Sediments)in Aquaculture Areas

摘要

Intensive fish cultivation often accelerates organic pollution due to surplus feed and fish excreta.In order to establish a sustainable aquaculture system,it is necessary to evaluate its microbial degrading and mineralizing capacity of organic loads from the fish cultivation.The aim of this study was to elucidate the microbial activity of organic degradation and mineralization in three different microenvironments in aquaculture areas,sinking particles,surrounding seawater and bottom sediments.From two different aquaculture areas,Tanabe Bay and Oshima area in Wakayama,Japan,seawater,sinking particle and bottom sediment samples were collected seasonally.Tanabe Bay is a semi-enclosed and eutrophic coastal region.The Oshima area is also coastal,however,the seawater exchange volume is greater than in Tanabe Bay.Extracellular enzyme and mineralization activity of each microenvironment were measured using fluorescent substrate analogs and[~(14)C]-substrates,respectively.Extracellular enzyme and mineralization activity in sinking particles were both significantly higher man those in bottom sediments throughout the year.The two activities in the surrounding seawater were far lower than those in the other two microenvironments.This result indicates that sinking particles are important microenvironments for the degradation and mineralization of organic substances in the water column.Higher peptidase activity was observed in the bottom sediment samples from Oshima area than that from Tanabe Bay.A higher rate of seawater exchange and lower level of organic pollution in Oshima area may support the higher natural purification ability.