Surface runoff and soil loss in tropical rainforest and pasture, Costa Rica, and indices explaining their variations

摘要

Field work was done at three plots on 32degrees to 46degrees slopes in the Upper Reventazon river basin, Costa Rica. The annual surface runoff was only 45 mm from the pasture and primary forest plots and about 30 mm from the secondary forest plot, out of an annual precipitation of 4750 mm, which suggests inflow areas with Horton overland flow. The annual inorganic soil loss was 2.9 tkm(-2) from primary forest, 0.3 tkm(-2) from pasture and 0.1 tkm(-2) from secondary forest. Of the annual soil loss, 51-87% were eroded during the same two storms for all the plots. Of the annual surface runoff, 20-23% occurred during the same two storms as for the soil loss, except for one event on the pasture.Surface runoff was best explained by linear regressions on the indices AI(30) and AI(15) in cm X cm h(-1), i.e. the product of storm rainfall amount and the 30-min. or 15-min. maximum intensity, both with daily and with event data. EI30 and EI15, i.e. the product of storm energy and the storm 30-min. or 15-min. maximum intensity, were also useful indices. The inorganic soil loss was best explained by AI(30) raised to a power, both with daily and with event data. In addition, AI(15) and EI30 raised to a power predicted soil loss well. The indices (AI(30))(2.1) and (EI30)(2) were accepted to predict daily soil loss in linear relationships.