Chloride cycling in two forested lake watersheds in the west-central adirondack mountains, New York, U.S.A.

Abstract

The chemistry of precipitation, throughfall, soil water, ground water, and surface water was evaluated in two forested lake-watersheds over a 4-yr period to assess factors controlling Cl− cycling. Results indicate that Cl− cycling in these watersheds is more complex than the generally held view of the rapid transport of atmospherically derived Cl− through the excosystem. The annual throughfall Cl− flux for individual species in the northern hardwood forest was 2 to 5 times that of precipitation (56 eq ha−1), whereas the Na+ throughfall flux, in general, was similar to the precipitation flux. Concentrations of soil-water Cl− sampled from ceramic tension lysimeters at 20 cm below land surface generally exceeded the Na+ concentrations and averaged 31 μeq L−1, the highest of any waters sampled in the watersheds, except throughfall under red spruce which averaged 34 μeq L−1. Chloride was concentrated prior to storms and mobilized rapidly during storms as suggested by increases in streamwater Cl− concentrations with increasing flow. Major sources of Cl− in both watersheds are the forest floor and hornblende weathering in the soils and till. In the Panther Lake watershed, which contains mainly thick deposits of till (>3 m), hornblende weathering results in a net Cl− flux 3 times greater than that in the Woods Lake watershed, which contains mainly thin deposits of till. The estimated accumulation rate of Cl− in the biomass of the two watersheds was comparable to the precipitation Cl− flux.