Spatial variability of throughfall chemistry in a tropical rainforest (Central Amazonia, Brazil)

Abstract

A statistical analysis is made on throughfall data for a location in a ‘terra firme’ rain forest in central Amazonia. The results show a large variability in water and chemical fluxes. For all the ions there is a variance in the mean value due to the positions of sample collectors. Despite the large variability, throughfall volume is correlated with rainfall. This is not the case for any of the chemicals studied. The use of a transect design with collectors at variable positions is shown to be sound. It is concluded that to obtain flux estimates to within 10% of the mean at 90% confidence level, about 300 collections are required for the wet period and 200 collections are required for the dry period. It is proposed that in future studies, a minimum of 20 roving gauges over as wide an area as practical be employed to achieve reliable estimates. Sampling programmes should run for a period of at least one year.