High ammonium production from sediments in hypereutrophic shrimp ponds

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 (NH₄⁺), particularly in the inner sludge zone (up to 182 mmol m–2d–1). Inferred denitrification efficiency was low (