High ammonium production from sediments in hypereutrophic shrimp ponds

Abstract

Intensive shrimp ponds are hypereutrophic ecosystems with high nutrient loading rates. The contribution of sediment nutrient fluxes to nutrient cycling in shrimp ponds was studied. Benthic processes were quantified using benthic chambers (clear and dark) on the sediment of intensive shrimp ponds at 3 farms. The ponds contained 2 distinct sediment zones: an outer zone of sand and rubble swept clean by the action of paddlewheels and other aerators (65 to 85% of the pond area), and an inner zone where settled particulate matter formed a sludge pile. The high nutrient loads, in the form of formulated feed, coupled with high sediment deposition resulted in an anoxic sediment in the pond center with a low respiratory quotient (oxygen:carbon dioxide ratio). The carbon dioxide effluxes were 2-to 4-fold higher than oxygen consumption. The highest nutrient flux rates from the sediment were those of ammonium (NH 4 + ), particularly in the inner sludge zone (up to 182 mmol m -2 d -1). Inferred denitrification efficiency was low (< 2%), particularly in the inner sludge zone. Denitrification rates, as measured by the acetylene block method, confirmed this. Denitrification may be limited by nitrate (NO 3 -) availability. It is unclear why NO 3 -concentrations were low, but nitrifiers either may have been inhibited by pond conditions or were unable to become established due to the routine water discharges to maintain adequate water quality. Fluxes of urea and PO 4 3 -were also low. This study shows that low rates of nitrogen loss from denitrification, relative to the high nitrogen inputs, results in high NH 4 + concentrations in the water column. The discharges of pond water mean that sediment processes in shrimp ponds ultimately affect the nitrogen loads discharged into the aquatic environment, exacerbating the potential for eutrophication caused by shrimp farming activities.

Effect of nutrient loading on biogeochemical processes in tropical tidal creeks

“…Denitrification provides a sink in the nitrogen budget and thereby plays an important role in controlling the degree of eutrophication in waters subjected to substantial anthropogenic input of nutrients (Seitzinger 1988;Rysgaard et al 1995). The low DE in BC is consistent with studies in other estuarine systems which have demonstrated that as nutrient loads increase, denitrification removes a smaller proportion of the load (Sloth et al 1995;Burford and Longmore 2001;Caffrey et al 2007). The effect of nutrient loading on DE has important implications for the nutrient status of the system and has flow-on effects that alter the structure of higher trophic levels such as fish and invertebrate communities (Kemp et al 2005).…”

Water quality, nutrient budget, and pollutant loads in Chinese mitten crab (Eriocheir sinensis) farms around East Taihu Lake

“…The percentage of loss due to denitrification and ammonia volatilization varies among reports, with estimations as high as 66% (Couch, 1998;Paez-Osuna et al, 1999), and as low as < 2% (Burford and Longmore, 2001). In the present study, the level of volatized ammonia was unclear.…”

Shrimp and fish pond soils: processes and management

“…Avnimelech (1995) estimated that the area covered by sediments in typical shrimp ponds in Thailand comprises nearly 50% of the pond bottom and suggested that shrimp growth, activity and health may be negatively affected in this region. Burford and Longmore (2001) found that the sludge zone represented 15-35% located at the center of a 10-ha shrimp. The pore water NH 4 concentration in this zone was 4220-8950 AM, as compared to 560 -1010 in peripherial zone.…”

“…Alongi et al (1999) estimated that the contribution to carbon oxidation was 41-60% through O 2 respiration, 7 -22% from Mn reduction, 5 -25% from iron reduction and 13-26% from sulfate reduction in shrimp pond sediments. Burford and Longmore (2001) reported that 50 -80% of the carbon degradation in shrimp pond soils was anaerobic, mostly coupled with sulfate reduction. Reduced inorganic species may affect biological activity.…”