Solute dynamics in soil water and groundwater in a central Amazon catchment undergoing deforestation

Hydrochemical changes caused by slash-and-bum agricultural practices in a small upland catchment in the central Amazon were measured. Solute concentrations were analyzed in wet deposition, overland flow, shallow throughflow, groundwater and bank seepage in a forested plot (about 5 ha) and an adjacent plot (about 2 ha) which had been deforested in July 1989 and planted to manioc, and in stream water in partially deforested and forested catchments. Measurements were made from November 1988 to June 1990. The effects of slash-and-bum agricultural practices observed in the experimental plot included increased overland flow, erosion, and large losses of solutes from the rooted zone. Concentrations of NO3-, Na+, K+, SO42-, Cl- and Mn in throughflow of the experimental plot were higher than those of the control plot by more thana factor of 10. Extensive leaching occurred after cutting and burning, but solute transfers were diminished along pathway stages of throughflow to groundwater, and particularly within the riparian zone of the catchment. High concentrations of N and P in overland flow indicate the importance of using forested riparian buffers to mitigate solute inputs to receiving waters in tropical catchments.

Keywords: Amazon, deforestation, hydrologic pathway, groundwater, nitrogen, rain, forest, slash-and-burn agriculture, solutes, tropical, rain-forest catchment, major ionic solutes, nutrient retention, , solution chemistry, boreal forest, nitrogen, basin, fire, ecosystem, , disturbance