Seasonal variation of tropical precipitation chemistry: La Selva, Costa Rica

The chemistry of wet precipitation was measured from February 1992 to February 1995 at La Selva Biological Station, Costa Rica. Sea salt aerosols were the primary contributors to Na+, Cl−, and Mg2+; however, K+, Ca2+, and SO42− were derived primarily from non-sea-salt sources. Seasonal patterns, with concentrations inversely proportional to rainfall, were found for marine salts and aerosols (Na+, Cl−, and Mg2+) and inorganic nitrogenous compounds (NO3− and NH4+). DON accounted for a significant fraction (30%) of total dissolved nitrogen deposition. Terrigenous dust from local agricultural or natural aeolian processes appeared to be the primary influence on concentrations of non-sea-salt cations. High concentrations of non-sea-salt sulfate (SO4*) were correlated with both non-sea-salt chloride (Cl*) and high H+ concentrations as well as a shift in wind direction from the northeast to the southwest, which may indicate a strong volcanic influence on precipitation chemistry during a few weeks of the year. Annual fluctuations in distribution and amount of rainfall contributed to differences in precipitation chemistry over the course of the study.