The impact of harvesting and site preparation on nutrient dynamics, soil erosion and stream water quality in the Virginia Piedmont

Abstract

The impacts of clearcut harvesting and four intensities of mechanical site preparation were evaluated in the Virginia Piedmont using gauged watersheds. The four treatments were: 1) control, 2) chop and burn, 3) shear-disc, and 4) shear, rake-pile, disc. A combination of soil solution, streamwater and soil sampling and a series of soil incubations, both laboratory and <i>in situ</i> monitored changes in the treatment areas following site preparation. Available nitrogen reserves decreased substantially in the shear, pile, disc treatment area but increased in the chop and burn and shear-disc treatment areas following site preparation. Increased soil moisture and temperature following disturbance stimulated nutrient mobilization. Soil solution KCI extractable and <i>in situ</i> soil incubations all indicated that nitrogen mineralization was greater in the site prepared watersheds. Among the site prepared areas, treatment response followed a site preparation intensity dependent gradient. Fifteen, 26, 20 and 45% respectively of the available nitrogen reserves were mineralized within one year following site preparation in the control, chop and burn, shear-disc and shear, pile, disc watersheds. Streamwater nutrient export also increased following disturbance. Soil erosion increased in a 1:6:60 proportion in the chop and burn, shear-disc and shear, pile, disc treatment areas. Higher soil erosion led to increased sediment export in the site prepared areas.