Nitrates. Nitrates are nutrients and do not bioaccumulate. However, at higher concentrations they have been shown to cause effects to amphibians that are similar to those caused by toxic contaminants. Because less research and monitoring data are generally available for amphibian populations as a group, the mechanisms for the observed biological effects of nitrates are not as clearly defined as those for other organisms. A short summary of what is known is provided below. A review by Xxxxx et al. (1999) evaluated the risk of direct and indirect effects of nitrate on amphibian populations. This review used a simple comparison of known environmental nitrate concentrations in North American waters to nitrate concentrations known to cause toxicity in a laboratory setting to amphibian larvae and other species that play an important role in amphibian ecology. Lethal and sublethal effects in amphibians are detected in laboratory tests at nitrate concentrations between 2.5 and 385 mg/L (Table 4.8). Amphibian food sources such as insects and predators such as fish are also affected by elevated levels of ammonia and nitrate in surface waters (Xxxxx et al., 1999). This may have important implications for the survival of amphibian populations and the health of food webs in general. Species Stage Endpoint Concentration of Nitrate (mg/l) Bgfo americangs Tadpole 96h-LC50 13.6 & 39.3 Psegdacris triseriata Tadpole 96h-LC50 17 Rana pipiens Tadpole 96h-LC50 22.6 Rana clamitans Tadpole 96h-LC50 32.4 P. triseriata Tadpole Developmental 2.5-10 R. pipiens Tadpole Developmental 2.5-10 R. clamitans Tadpole Developmental 2.5-10 Bgfo bgfo Tadpole 96h-LC50 385 Bgfo bgfo Tadpole Developmental 9 Bgfo bgfo Tadpole Death 22.6 Litoria caerglea Tadpole Developmental 9 Litoria caerglea Tadpole Death 22.6 Rana temoraria* Adult EC50-paper 3.6 g/m2 Rana temoraria Adult EC50-soil 6.9 g/m2 Table 4.8 Toxicity of Nitrate to Amphibians (Xxxxx et al., 1999) S e c t i o n 4 * Frogs were placed on moist paper or soil spread with ammonium nitrate granules LC50=lethal concentration required to kill 50 percent of the test population within 96 hours EC50=lethal concentration for 50% of the population Environmental concentrations of nitrate in surface waters in agricultural watersheds in southwestern Ontario and US states in the Lake Erie watershed ranged from 1 to 40 mg/L. Of 8000 water samples from rivers in the watersheds of Lake Erie and St. Clair in the Canadian Great Lakes and in US states in the Lake Erie wat...
Nitrates. In the case of nitrates, seasonal fluctuation of the measured values is characteristic, which is less apparent in the seepage channel. Seasonal fluctuation is related to the growing season and the consumption of nutrients in the water. In the growing period, the nitrates content usually decreases to a half of the winter amount. Except the seepage channel, the course of values was similar on individual sites and the concentrations varied from 3.5 to 15.2
