Intake and discharge nutrient loads at three intensive shrimp farms

Abstract

This study was conducted to help provide a framework for Australian regulation of shrimp farm siting and discharges. Monitoring of farm water usage, and intake and discharge water quality was conducted at three commercial intensive shrimp farms, chosen to represent different operating environments, latitudes, cultured species and management styles. Weekly samples were taken over 3 years, for 3–12 months at each farm, to investigate intake and discharge concentrations and loads of total suspended solids (TSS), total nitrogen (TN) and total phosphorus (TP). Mean water exchange was 1.4 ML ha−1 day−1 (about 10% day−1) at the first farm studied and 0.5 ML ha−1 day−1 (about 3.6% day−1) at the others. Farm mean discharge concentration varied as follows: TSS, from 36.9 to 119 mg L−1; TN, from 2.1 to 3.1 mg L−1 and TP, from 0.22 to 0.28 mg L−1. Farm mean intake concentrations were from 11% to 91% of equivalent mean discharge concentration (for TN at Farm B and TSS at Farm C respectively). Mean net discharge loads, related to area of production ponds at each farm, varied as follows: TSS, from 4.8 to 85.7 kg ha−1 day−1; TN, from 1 to 1.8 kg ha−1 day−1 and TP, from 0.11 to 0.22 kg ha−1 day−1. The highest net loads of TSS, TN and TP were all from the farm with the highest water exchange rate, located on a coastal river, and studied during a year of high rainfall with associated poor water quality. These results can be used to help predict likely discharge characteristics for new shrimp farms, and provide a benchmark against which to evaluate future improvements in shrimp farm environmental management.