THE MARACA RAIN-FOREST PROJECT .2. SOIL HYDROLOGY, NUTRIENT AND EROSIONAL RESPONSE TO THE CLEARANCE OF TERRA FIRME FOREST, MARACA-ISLAND, RORAIMA, NORTHERN BRAZIL

This paper describes the background to the investigation and indicates and discusses the main results. Surface runoff is dominated by treatment with complete clearance yielding fivefold that on partially and uncleared sites. Subsurface fluxes reflect topography, which controls variable source areas, and the plinthitic layer at depth, which reduces vertical water movement. The erosional response is also determined by treatment with complete clearance yielding, on average, a sevenfold increase in sediment when compared with partially cleared and uncleared sites. Nutrient losses occur dominantly as eroded particulate organic material rather than as mineral sediments or in runoff waters and as much as 2.5 kg N, 0.45 kg P and 4 kg K can be washed off totally cleared sites in a single month. -from Authors