EVIDENCE FOR CONTROL OF WATER-QUALITY IN CHANNEL CATFISH ICTALURUS-PUNCTATUS PONDS BY PHYTOPLANKTON BIOMASS AND SEDIMENT OXYGENATION

A data set describing annual variation of water quality in ten commerc ial channel catfish Ictalurus punctatus ponds was subjected to explora tory statistical analysis to infer ecological processes affecting pond water quality. Two factors explained 67% of the variation in concentr ations of water quality variables. The first factor (Factor 1) explain ed 49% of the variance and was associated with a large negative loadin g by total ammonia-nitrogen and large positive loadings by total nitro gen, total phosphorus, chemical oxygen demand, and chlorophyll a, Fact or 1 was interpreted with respect to factor loadings to represent the effect of phytoplankton biomass. The second factor (Factor 2) explaine d an additional 18% of the variance and was associated with a large ne gative loading by soluble reactive phosphorus and large positive loadi ngs by nitrite-nitrogen and, to a lesser extent, nitrate-nitrogen. Fac tor 2 was interpreted to be related to variation in pond sediment oxyg enation. Although factor analysis indicated the overwhelming effect of phytoplankton biomass on water quality, opportunities for management of phytoplankton communities in large commercial aquaculture ponds are limited, However, maintenance of an oxidized sediment-water interface may improve water quality by limiting the diffusion of reductant-solu ble phosphorus from sediment to water and increasing sediment nitrific ation rates.