Water and nutrient flows were measured in catchments on strongly weathered loamy sediments of the Zanderij formation in Suriname under undisturbed forest and forest silviculturally treated whereby 40 % of the biomass was killed. The topography of the two catchment areas studied (each of about 150 ha) is gently undulating. The main soil is a well drained loamy Ultic Haplorthox which covers most of the plateaus and upper slopes while sandy soils occur on lower slopes and in valley bottoms.Measured data on rainfall, discharge, evaporation, groundwater levels and hydraulic conductivity were used in computer simulation of water flows. It was found that large amounts of water were available to the forest and that transpiration reduction in the dry seasons was only small. The average effective rooting depth was calculated to be 450 cm. The contribution of transpiration, interception and soil evaporation to total water use (1640 mm/y) was calculated, annual rainfall being 2140 mm.Nutrient amounts and flows were determined in both the organic matter cycle and the hydrological cycle for the treated and untreated catchments. A computer simulation of organic matter flows showed that large amounts of nutrients were liberated during the 3 years after treatment. Only a very small proportion of these nutrients left the catchment area with the discharge water. The higher nutrient influx in rainwater than nutrient losses in drainage water indicates that there was a small accumulation of nutrients in both the untreated and treated catchments. Thus it is concluded that the forest treatment did not result in unacceptable losses of nutrients from the ecosystem.
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