OUTPUT OF PHOSPHORUS, DISSOLVED ORGANIC CARBON, AND FINE PARTICULATE CARBON

The output of phosphorus, dissolved organic carbon (DOC), and fine particulate organic carbon (FPOC) was measured in two watersheds of the Hubbard Brook Experimental Forest, New Hampshire. One watershed had a cover of birch, beech, and maple; the other had been denuded of trees and regrowth prevented. Concentrations of DOC and dissolved plus fine particulate P changed little with changes in flow. Concentrations of FPOC, how-cvcr, were strongly dependent on flow and most of the FPOC was exported during a few periods of high runoff. Deforestation caused higher runoff (by 26 %), but also greatly increased erosion. Thus, DOC and FPOC output was similar in the two watersheds while the loss of large particulate phosphorus, mostly as inorganic bedload, increased 12 times in the treated watershed, With a rainwater input of 100 g P ha-l, there was an annual net gain of 87 g P in the undisturbed watershed and a net loss of 104 g P in the disturbed watershed. In view of the large amounts of phosphorus cycling in the natural forest (e.g. some 1,900 g P ha-l in annual leaf fall alone) this ecosystem is strongly conserving phos-phorus. The manipulation of small forested water-sheds has greatly increased our knowledge of the interactions between nutrient and hydrologic cycles. For Hubbard Brook, New Hampshire, the output of dissolve