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N and P Fluxes and Transformations along an upland-riparian-stream transect in montane forest of the Andean Amazon Basin, San Alberto catchment, Peru.
Saunders, Thomas*,1, McClain, Michael1, 1 Department of Environmental Studies, Miami, FL
ABSTRACT- We investigated the dynamics of runoff and nutrient cycling in the riparian zones of a first order catchment in montane forest of the Peruvian Amazon. Losses of nitrogen from lowland Amazon forests to adjacent surface waters have been shown to be strongly regulated by processes operating in riparian environments. The study catchment is located at 2520 masl and covers an area of approximately 5 ha. Soils are Inceptisols of variable depth and hill slopes are steep (averaging 50 degrees). We measured fluxes and concentrations in streamflow, throughfall, overland flow, soil water and ground water. Samples were analyzed for NO3-, NH4+, total dissolved nitrogen, PO43-, and total dissolved phosphorus. Dissolved organic species were calculated by difference. Initial hydrologic data demonstrate significant stormflow fluctuations in total hydraulic head within a transect of piezometers, indicating seasonal and storm induced riparian fluxes. We also recorded return flow in one location. Initial nutrient data indicate significant variation in nutrient fluxes through a storm cycle and they are accompanied by decreases in NO3- concentrations from upland soil-water (4.5-35 M) to riparian ground water (0.3-1.7 M). During storm flow conditions, phosphate ions are relatively concentrated in throughfall and organic layer overland flow, with samples having concentrations of 1.1 M. Dissolved organic phosphorus, and thus total dissolved phosphorus, dominates the throughfall sample signature in storm conditions with a concentration of 3.2 M; and is subsequently diminished through the riparian zone yielding stream concentrations of 0.1 M PO43- and DOP. Our results indicate that patterns of N and P concentrations across the upland/riparian/stream transition of these montane forests are consistent with patterns found in other parts of the Amazon, demonstrating a significant riparian control over terrestrial to aquatic fluxes through the storm cycle.
KEY WORDS: riparian buffer, nutrient fluxes, Amazon river, ground water