Chemical composition and spatial variation of bulk precipitation at a coastal plain watershed in South Carolina

Bulk precipitation was collected for analysis of ionic constituents at eight rainfall stations over a 4‐year period at a 500‐ha watershed in the Lower Coastal Plain of South Carolina. Mean annual deposition rates of ions in greatest supply, Cl⁻, SO4²⁻ ‐S, Ca²⁺, and Na⁺, were respectively 14.2, 7.51, 5.69, and 5.66 kg/ha. Annual deposition rate for total inorganic N (NH4⁺ −N plus NO3⁻ −N) was about 2.6 kg/ha and for orthophosphate‐P about 0.12 kg/ha. Spatial variation of annual depositions to the eight rainfall stations was smallest for SO4²⁻, NO3⁻, and Ca²⁺, with coefficients of variation (CV) less than 10%. Variation of annual inputs to the eight collectors was intermediate for Mg²⁺, Cl⁻, H⁺, and Na⁺ with CV ranging between 13.9 and 21.5%, whereas the CV for annual inputs of NH4⁺, PO4³⁻, and K⁺ exceeded 30%. Sample size estimates for this 500‐ha watershed indicated that 19 collectors should provide estimates of the annual bulk precipitation inputs within 10% of true means for 7 of 10 ions (SO4²⁻, NO3⁻, Ca²⁺, Mg²⁺, Cl⁻, H⁺, and Na⁺) and that more than 35 collectors would be necessary to provide similar confidence intervals for annual inputs of NH4⁺, PO4³⁻, and K⁺ (± 10% at P < 0.05). Although estimates of annual bulk precipitation inputs may be quite variable over local areas, control of sampling errors can be gained by increasing the number of collectors. This paper is not subject to U.S Copyright. Published in 1983 by the American Geophysical Union.

Duke Scholars

Author Daniel D. Richter Earth and Climate Sciences