SOLUTE DYNAMICS IN SOIL-WATER AND GROUNDWATER IN A CENTRAL AMAZON CATCHMENT UNDERGOING DEFORESTATION

Hydrochemical changes caused by slash-and-bum agricultural practices i n a small upland catchment in the central Amazon were measured. Solute concentrations were analyzed in wet deposition, overland flow, shallo w throughflow, groundwater and bank seepage in a forested plot (about 5 ha) and an adjacent plot (about 2 ha) which had been deforested in J uly 1989 and planted to manioc, and in stream water in partially defor ested and forested catchments. Measurements were made from November 19 88 to June 1990. The effects of slash-and-bum agricultural practices o bserved in the experimental plot included increased overland flow, ero sion, and large losses of solutes from the rooted zone. Concentrations of NO3-, Na+, K+, SO42-, Cl- and Mn in throughflow of the experimenta l plot were higher than those of the control plot by more thana factor of 10. Extensive leaching occurred after cutting and burning, but sol ute transfers were diminished along pathway stages of throughflow to g roundwater, and particularly within the riparian zone of the catchment . High concentrations of N and P in overland flow indicate the importa nce of using forested riparian buffers to mitigate solute inputs to re ceiving waters in tropical catchments.