Ammonium nitrate (NH(4)NO(3)) is a common water pollutant associated with many industrial and municipal activities. One solution to reduce exposure of sensitive aquatic systems to nitrogenous compounds is to atomize (atmospherically disperse in fine particles) contaminated water over the Arctic tundra, which will reduce nitrogen loading to surface water. The toxicity of ammonium nitrate to Arctic soils, however, is poorly understood. In the present study, we characterized the biogeochemical toxicity and phytotoxicity of ammonium nitrate solutions in four different Arctic soils and in a temperate soil. Soil was exposed to a range of ammonium nitrate concentrations over a 90-d period. Dose responses of carbon mineralization, nitrification, and phytotoxicity endpoints were estimated. In addition to direct toxicity, the effect of ammonium nitrate on ecosystem resilience was investigated by dosing nitrogen-impacted soils with boric acid. Ammonium nitrate had no effect on carbon mineralization activity and only affected nitrification in one soil, a polar desert soil from Cornwallis Island, Northwest Territories, Canada. In contrast, ammonium nitrate applications (43 mmol N/L soil water) significantly impaired seedling emergence, root length, and shoot length of northern wheatgrass (Elymus lanceolatus). Concentrations of ammonium nitrate in soil water that inhibited plant parameters by 20% varied between 43 and 280 mmol N/L soil water, which corresponds to 2,100 to 15,801 mg/L of ammonium nitrate in the application water. Arctic soils were more resistant to ammonium nitrate toxicity compared with the temperate soil under these study conditions. It is not clear, however, if this represents a general trend for all polar soils, and because nitrogen is an essential macronutrient, nitrogenous toxicity likely should be considered as a special case for soil toxicity.

Industrial and human activities in the Arctic regions may pose a risk to terrestrial Arctic ecosystem functions. One of the most common terrestrial toxicological end points, primary productivity, typically is assessed using a plant phytotoxicity test. Because of cryoturbation, a soil mixing process common in polar regions, we hypothesized that phytotoxicity test results in Arctic soils would be highly variable compared to other terrestrial ecosystems. The variability associated with phytotoxicity tests was evaluated using Environment Canada's standardized plant toxicity test in three cryoturbated soils from Canada's Arctic exposed to a reference toxicant, boric acid. Northern wheatgrass (Elymus lanceolatus) not only was more sensitive to toxicants in Arctic soils, its response to toxicants was more variable compared to that in temperate soils. The phytotoxicity of boric acid in cryosols was much greater than commonly reported in other soils, with a boric acid concentration of less than 150 microg/g soil needed to inhibit root and shoot growth by 20%. Large variability also was found in the phytotoxicity test results, with coefficients of variation for 10 samples ranging from 160 to 79%. The increased toxicity of boric acid in cryosols and variability in test response was not explained by soil properties. Based on our admittedly limited data set of three different Arctic soils, we recommend that more than 30 samples be taken from each control and potentially impacted area to accurately assess contaminant effects at sites in northern Canada. Such intensive sampling will insure that false-negative results for toxicant impacts in Arctic soils are minimized.

Industrial and human activities in the Arctic regions may pose a risk to terrestrial Arctic ecosystem functions. One of the most common terrestrial toxicological end points, primary productivity, typically is assessed using a plant phytotoxicity test. Because of cryoturbation, a soil mixing process common in polar regions, we hypothesized that phytotoxicity test results in Arctic soils would be highly variable compared to other terrestrial ecosystems. The variability associated with phytotoxicity tests was evaluated using Environment Canada's standardized plant toxicity test in three cryoturbated soils from Canada's Arctic exposed to a reference toxicant, boric acid. Northern wheatgrass (Elymus lanceolatus) not only was more sensitive to toxicants in Arctic soils, its response to toxicants was more variable compared to that in temperate soils. The phytotoxicity of boric acid in cryosols was much greater than commonly reported in other soils, with a boric acid concentration of less than 150 microg/g soil needed to inhibit root and shoot growth by 20%. Large variability also was found in the phytotoxicity test results, with coefficients of variation for 10 samples ranging from 160 to 79%. The increased toxicity of boric acid in cryosols and variability in test response was not explained by soil properties. Based on our admittedly limited data set of three different Arctic soils, we recommend that more than 30 samples be taken from each control and potentially impacted area to accurately assess contaminant effects at sites in northern Canada. Such intensive sampling will insure that false-negative results for toxicant impacts in Arctic soils are minimized.

Ammonium nitrate (NH(4)NO(3)) is a common water pollutant associated with many industrial and municipal activities. One solution to reduce exposure of sensitive aquatic systems to nitrogenous compounds is to atomize (atmospherically disperse in fine particles) contaminated water over the Arctic tundra, which will reduce nitrogen loading to surface water. The toxicity of ammonium nitrate to Arctic soils, however, is poorly understood. In the present study, we characterized the biogeochemical toxicity and phytotoxicity of ammonium nitrate solutions in four different Arctic soils and in a temperate soil. Soil was exposed to a range of ammonium nitrate concentrations over a 90-d period. Dose responses of carbon mineralization, nitrification, and phytotoxicity endpoints were estimated. In addition to direct toxicity, the effect of ammonium nitrate on ecosystem resilience was investigated by dosing nitrogen-impacted soils with boric acid. Ammonium nitrate had no effect on carbon mineralization activity and only affected nitrification in one soil, a polar desert soil from Cornwallis Island, Northwest Territories, Canada. In contrast, ammonium nitrate applications (43 mmol N/L soil water) significantly impaired seedling emergence, root length, and shoot length of northern wheatgrass (Elymus lanceolatus). Concentrations of ammonium nitrate in soil water that inhibited plant parameters by 20% varied between 43 and 280 mmol N/L soil water, which corresponds to 2,100 to 15,801 mg/L of ammonium nitrate in the application water. Arctic soils were more resistant to ammonium nitrate toxicity compared with the temperate soil under these study conditions. It is not clear, however, if this represents a general trend for all polar soils, and because nitrogen is an essential macronutrient, nitrogenous toxicity likely should be considered as a special case for soil toxicity.