An analysis of baitfish pond effluents, drainage ditch use, and effects of pond and ditch characteristics on solids

摘要

The Southern Regional Aquaculture Center, in preparation for impending Environmental Protection Agency regulations, funded this study to characterize baitfish pond effluents and document farm practices to be incorporated into Best Management Practices. Effluents from ten golden shiner (Notemigonous crysoleucas) ponds in Arkansas were analyzed for particle sizes associated with total suspended solids (TSS), volatile suspended solids (VSS), and 5-d biochemical oxygen demand (BOD5). The incidence of drainage ditch use, potential water reuse, and ditch effects on solids were also evaluated. Total suspended solids averaged 36.3 mg/L during the draining of the first 10% of pond volume and increased by 69.8% during the last 10%. Volatile suspended solids were more variable but averaged about 50% of TSS. The BOD5 averaged 9.0 mg/L and did not increase significantly in the last 10%. The VSS and BOD5 generally did not change with reductions in TSS through screening. Over 79% of suspended particles were less than 5 microm. Correlation between TSS and VSS and BOD5 varied between first and last 10% effluents. Observed particle settling rates in ditches suggests that fractionation affected effluent character. On average, VSS decreased 14.1% (P = 0.004) over the first 100 m of ditches, but TSS remained unchanged because of increases in fixed suspended solids. Net increases in TSS were associated with average effluent velocities exceeding 0.63 m/s. There was a high incidence of ditch use and high variability in ditch length distribution on farms. Farm block median ditch length was 106 to 1174 m. Potentially reusable water varied on farms from 0 to 56%. Results suggest that ditches would be effective solids settling systems if erosion in the ditch is prevented, especially at the point of discharge, and the ditches are engineered to minimize velocity. Water reuse designs should be encouraged in future pond construction.