The chemical composition of atmospheric deposition collected from six Louisiana sites from 1983 to 1992

Since 1983, precipitation samples have been collected weekly from six Louisiana sites. Analyses performed included pH, EC, Ca2+, Na+, Mg2+, K+, NH4+, Cl, NO3−, SO42−, PO43−, and precipitation amount. These data were used to determine quarterly and yearly regional trends in precipitation chemistry and deposition. Concentrations of K+ (< 0.2 mgℓ−1), Mg2+ (< 0.02 mgℓ−1) and PO43− (< 0.5 mgℓ−1) were below detection limits more than 90% of the time. Calcium, Na+, NH4+, SO42−, and Cl− had the highest deposition during the spring at most sites. The highest EC values were found in the summer, while the lowest were in the fall. Nitrate deposition was highest in the summer and lowest in the fall. Sulfate and NH4+ had the least deposition in the fall for most sites. The most acidic pH values were in the summer for all six sites. The lowest precipitation amounts were in the summer and fall, while the highest were in the winter. Yearly deposition amounts of nutrients were not sufficient to meet major crop requirements. Sulfur was deposited in quantities to meet one-half to one-third of its requirement in cotton, rice, soybeans, and wheat.