Effects of elevated nitrate concentration on mortality, growth, and egestion rates of Gammarus pseudolimnaeus amphipods

Nitrate at environmental concentrations can cause toxicity in a variety of aquatic animal species. Most of the studies of nitrate toxicity in aquatic invertebrates have centered on taxa that primarily inhabit surface waters. Much less is known about the acute and chronic toxicity of nitrate for invertebrates inhabiting shallow sediments, where nitrate concentrations in the pore water can greatly exceed those in the surface water, particularly in regions with high nitrate inputs. Our target species was Gammarus pseudolimnaeus, a sediment-dwelling amphipod that is widely distributed in streams. The objectives were: 1) to determine if Gammarus experiences acute nitrate toxicity at environmentally realistic nitrate concentrations. 2) to assess the effects of elevated nitrate concentration on somatic growth, molting, and egestion rates of Gammarus. Organisms were exposed in the laboratory to seven nitrate concentration treatments (target concentrations were 0.2, 4, 8, 16, 32, 64, and 128 mg NO3-N/L) for three weeks. There were no effects of nitrate concentration on amphipod mortality, molting frequency or egestion rate. Elevated nitrate concentration had weak negative effects on Gammarus growth rate. Our results suggest that elevated nitrate concentrations up to 128 mg NO3-N/L have no lethal effect and weak nonlethal effects on Gammarus pseudolimnaeus.