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Soil Hydrology, Nutrient and Erosional Response to the Clearance of Terra Firme Forest, Maracá Island, Roraima, Northern Brazil

S. M. Ross, J. B. Thornes and S. Nortcliff
The Geographical Journal
Vol. 156, No. 3 (Nov., 1990), pp. 267-282
Published by: geographicalj
DOI: 10.2307/635528
Stable URL: http://www.jstor.org/stable/635528
Page Count: 16
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Soil Hydrology, Nutrient and Erosional Response to the Clearance of Terra Firme Forest, Maracá Island, Roraima, Northern Brazil
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Abstract

An experiment was carried out on the Ilha de Maracá, Brazil to investigate the effects of partial and complete clearance of forest plots on subsurface soil moisture content, tension and water fluxes, overland flow, the production of water and sediment yield, and the losses of nutrients in eroded soil materials from the plots. 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 nitrogen, 0.45 kg phosphorous and 4 kg potassium can be washed off totally cleared sites in a single month.

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