WATERSHED RESPONSES TO CLEAR-CUTTING - EFFECTS ON SOIL SOLUTIONS AND STREAM WATER DISCHARGE IN CENTRAL NEW-BRUNSWICK

Elemental concentrations (H, Ca, Mg, K, Na, NH4-N, NO3-N, P) and water flux data for precipitation and stream discharge as well as ion conce ntration data for soil solutions were collected and summarized for the Hayden Brook (HB) and Narrows Mountain Brook (NMB) watersheds of the Nashwaak Experimental Watershed Project (NEWP) in Central New Brunswic k. Elemental concentrations, fluxes and stream discharge from both wat ersheds were compared for pre- and post-harvest periods (1972-1978 and 1978-1984, respectively). For soil and streamwater solutions, element al concentrations were typically highest in late summer to fall, and c ontinued to be high throughout the dormant season. For the soil soluti on, concentrations of NO3-N, NH4-N, Ca and K peaked in midsummer. High est NO3-N concentrations were found in post-harvest soil solutions tak en from hardwood sites. Nitrate levels were low in soil solutions take n from conifer sites, with post-harvest levels slightly higher than pr e-harvest levels. Soil solution concentrations were found to vary with soil depth: pH values were lowest at the surface, and increased unifo rmly with depth; bases (Ca, Mg, K, Na) and NO3-N tended to be lowest a t intermediate soil depth. Seasonally divergent trends were observed f or post-harvest NO3-N in soil solutions and in streamwater: midsummer levels were high in the former, but low for the latter. Several aspect s likely contributed to this divergence: (1) enhanced rates of N miner alization and nitrification in upland soils during post-harvest midsum mers, (2) reduced post-harvest vegetational N uptake, (3) possibly acc elerated N absorption by microbes and vegetation in the wet areas of t he cut watershed. Altogether, post-harvest effects on stream discharge and streamwater chemistry were short-term: differences for elemental concentrations and stream discharge became insignificant after about 5 and 10-12 yr, respectively. Vegetation, especially tolerant hardwoods , recovered rapidly from stump and root sprouts.