Phosphorus accumulation and eutrophication in feed-supply freshwater fishponds

Article type: Research Article

Authors: ZHANG, Ming-kui | FANG, Li-ping

Affiliations: Institute of Soil and Water Resources and Environmental Science, College of Natural Resource and Environmental Sciences, Zhejiang University, Hangzhou 310029, China

Note: [] Corresponding author. E-mail: mkzhang@zju.edu.cn

Abstract: The rapid growth and intensification of freshwater fishery can cause imbalances between phosphorus (P) input in feed and its output in produce. This aquaculture can result in enriching exogenous P in fishponds and, consequently, accelerates the process of eutrophication. To assess relations among input, accumulation, release of P and as a consequence degrading water quality in terms of chlorophyll-a (Chl-a) in freshwater fishponds, fourteen fishponds with feed supply, nine fishponds without feed supply, and five nonfish ponds in Shaoxing Plain, southeast China were selected for comparing P accumulation in their waters and surface sediments. Surface sediment samples were collected from each pond to evaluate their total P, water soluble P, Olsen P, algal available P, and P fractions. Water samples were also collected from the ponds to measure concentrations of dissolved P and Chl-a. Total P in the sediments ranged from 0.88 to 1.73 g/kg in the fishponds with feed supply, that in the non-fish ponds ranged from 0.47 to 0.86 g/kg. Organic P, accounted for 23% to 60% of total P in the sediments, was an important P fraction and increased linearly with increasing organic matter. Long-term application of feeds resulted in increased P availability in the bottom sediments and degradation of water quality in the freshwater fishponds. Compared with non-fish ponds, sediments from the feed-supplied fishponds contained considerably higher Olsen P, algal available P, and water soluble P. Higher proportions of the labile P (NH_4Cl-P) and potentially labile P (NaOH-IP) were also found in the sediments from the fishponds. High solubility of P in the sediments resulted in elevation of P and chlorophyl1-a concentration in the pond water. The dissolved P concentration in the pond water increased in the order of non-fish ponds (12 μg/L) < fishponds without feed supply (24 μg/L) < fishponds with feed supply (66 μg/L). Linear correlations between concentrations of total P, Olsen-P, algal available P, water-soluble P and P concentration in saturation extracts in the sediments and dissolved P in the pond water indicated that there was a buffering action of the sediment constituents on the dissolved P.

Keywords: eutrophication, freshwater fishery, phosphorus fraction, water quality

Journal: Journal of Environmental Sciences, vol. 18, no. 4, pp. 816-821, 2006