Water and Nutrient Movement in Small, Forested Watersheds in the Boston Mountains of Arkansas

Abstract

Abstract Four small (< 13.5 ha), upland, hardwood watersheds were selected for a study of the changes in water dynamics and associated chemical changes as water moves through various components of the ecosystem. These watersheds were also used to determine what changes in water movement and chemistry are related to silvicultural treatments of conversion to pine, a shelterwood cut or a clearcut applied 6 yr earlier. A fourth watershed served as a control. It was estimated that 29% of the rainfall left the watersheds. The ratio of Na+ and Cl- indicated a marine source of these elements. Enrichment from terrestrial sources was indicated for Mg+2, Ca+2, K+, and SO42-.The major changes in water movement and in water chemistry occurred between the surface of the litter layer and the bottom of the A horizon where 55% of the water and most of the nutrients that entered the watersheds were absorbed by a root network that develops at the litter A horizon interface. The degree of absorption varied from 30% for Na+ to 86% for H+. In general, nutrients that passed the A horizon also passed the E horizon and were transported out of the watersheds. SO42- was the major nutrient deposited (21.5 kg ha-1) and accumulated (15.6 kg ha-1) in the watershed followed by NO3- (9.8 and 8.2 kg ha-1) and Ca+2 (9.6 and 5.6 kg ha-1). Cl- behaved differently than other nutrients because it was stored in the canopy and surface soil layers but lost from deeper zones in the watershed. Mg+2 also differed in that it was the only nutrient to have a net loss from the watersheds.Magnesium, K+, H+, and NO3- had differences related to silvicultural treatments. Magnesium was leached from the canopy in the control and shelterwood. K+ was enriched in the throughfall of the control and possibly shelterwood. Hydrogen was absorbed in the control canopy and leached from the clearcut canopy. FOR. SCI. 46(3):335–343.