Sedimentation and resuspension in earthen fish ponds

Resuspension of particles from pond sediment into the water column may be a n important nutrient transfer mechanism in aquaculture ponds. However, the magnitude of sediment resuspension cannot be determined directly because se diment traps collect particles settling from the water column as web as tho se resuspended from the pond bottom. We developed a dilution analysis metho d to differentiate the magnitude of the two particle source fluxes based up on the concentration of soil-derived elements (Si, Al, and Fe) and water-de rived elements (C, N) in material collected by sediment traps placed in ear then ponds. Estimated organic C sedimentation from feed residues and algae was compared with trapped organic C as an independent and approximate measu re of resuspension. Resuspension fluxes based independently on analyses of three soil-derived elements and on the estimation of expected C sedimentati on were similar and accounted for 60-90% of the total solids flux (121-2,67 6 g/m(2) per d) in most ponds sampled. The proportion of total flux that wa s derived from resuspension in ponds stocked with common carp Cyprinus carp io and tilapia Oreochromis spp. was modeled as a hyperbolic function of fis h size and density, with a threshold fish size of 200-300 g. Resuspension f lux was conservatively estimated to be equivalent to the daily suspension o f a few mm of the pond bottom. These results indicate that sediment resuspe nsion is a major process in carp and tilapia ponds, suggesting that the exc hange of nutrients between the sediment and overlying water is intensive.