Detailed Analysis of Sulphate and Nitrate Atmospheric Deposition Estimates at the Turkey Lakes Watershed

Abstract

Daily concentrations of sulphates and nitrates in air and precipitation were measured atthe Turkey Lakes Watershed from September 1980 until December 1984. The measurement data were used to estimate wet, dry, and total deposition of sulphates and nitrates to the watershed. Over the 4 yr, the annual values of total (wet plus dry) deposition ranged from 34 to 38 (± 15%) mmol∙m −2 ∙yr −1 for SO 4 2− and from 38 to 47 (± 30%) mmol∙m −2 ∙yr −1 for NO 3 − . On a molar basis, the deposition of total NO 3 − exceeded the deposition of total SO 4 2− by 19%. However, when converted to equivalents, total SO 4 2− exceeded total NO 3 − by 68%. Dry deposition represented approximately 15 and 25% of the total deposition of SO 4 2− and NO 3 − , respectively, to the watershed. Wet and dry deposition of sulphate and nitrate was found to be highly episodic, with the top 20% of daily events delivering 60–70% of the total sulphur and nitrogen deposition to the watershed. Statistically significant seasonal cycles were found in the concentration and deposition values of most of the sulphur and nitrogen species measured at the watershed.