Effects Of Landuse And Weathering On Available Nutrients In Volcanic Ash Soils Of Costa Rica PDF Download

The effect of land-use on nutrient cycles of tropical streams on the Osa Peninsula, Costa Rica: a paired catchment approach to investigate current conditions and projected changes. Kelly N. Bringhurst Abstract This study is concerned with potential environmental degradation of soils, rivers and coastal regions of the Osa Peninsula, Costa Rica due to deforestation. A paired, small-catchment approach to the study of environmental pressures on nutrient transfer and aquatic enrichment was used with one catchment that had been cleared for pasture (CN9) and the second primarily undisturbed tropical wet forest (CS 1). Nutrients and related parameters in soils and transferred in normal hydrological discharge were investigated. Soils in the study area are oxisols with concentrations of organic matter, total and plant available P higher in the forested catchment. Indirect measures of suspended sediment by turbidity showed an increase in the deforested catchment stream. Water input via rainfall for the year June 2008-June 2009 was approximately 5000 mm. Stream discharge was approximately 3300 mm year" for each catchment as measured by continuous recorders and evapotranspiration was, on average, 1500 mm year". These data suggested a good resolution of the water balance from independent measurements. The effect of deforestation on stream discharge was a 59% increase in flow during the wet season and an increase in the Q5:Q95 ratio showing that the deforested stream was flashier. Loss of forest canopy and decreased organic matter in the soil resulted in a depletion of available N. The deforested catchment loss of dissolved inorganic nitrogen (DIN) increased 33% over the forested catchment. Soluble reactive phosphorus (SRP) showed a 47% increase in the deforested catchment compared with the forested catchment. The molar N:P ratios were lower than expected and both streams were well below the 0.06 mg L-1 level at which N- limitation has been reported. Effects of nutrient loading have been observed through increased algal growth on equipment surfaces in the deforested catchment stream and increased nutrient yields will likely lead to eutrophication of coastal waters. Key Words - eutrophication, phosphorus, nitrogen, suspended sediment, deforestation, tropical forest.