MUGNI Hernan Diego
congresos y reuniones científicas
Phosphate and nitrogen compounds in streams of Pampean Plain areas under intensive cultivation (Buenos Aires, Argentine).
Sevilla, 9-12 September. EspaƱa.
Simposio; 4th Symposium on Phosphate in Sediments.; 2003
The objective of the present work was to study the N and P concentrations in streams in areas that undergo intense agricultural activity, mainly related to the cultivation of soya beans, in the Argentine Pampa plain. Four representative streams were chosen. Two of them developed well-defined flood plains covered by riparian vegetation. One also runs through a small natural wetland and the other has a small dam for recreational purposes upstream of the sampling site. Ionic composition, nutrients, O2, conductivity, pH, suspended matter and org-C in stream water were determined roughly every two weeks during soya bean growth. Concentrations of dissolved phosphate (i-Pdiss) were relatively high in spite of comparatively low fertilizer loads. Breeding cattle occupies a small proportion of the area but might represent a source of i-Pdiss. Experiments were performed to mimic nutrient release from the soil after rain events. A fast increase of pH, Ca2+, HCO3 - , and i-Pdiss concentrations was observed when deionized water was added to soil material, suggesting the contribution from the Ca2+-bound soil P fraction. Ca2+-bound P represented 14-21% of the soil extractable P. Org-P represented the main P pool and thus mineralization of soil organic matter seem likely the main P source of the streams. Because soya bean does not receive N-fertilizer, nitrate concentrations in the streams were lower than typically reported figures for intensively cultivated basins. Furthermore, in contrast to heavily fertilized basins, nitrate levels decreased in coincidence with flood peaks. Nitrate was lower in the two streams with a flood plain and an upstream wetland or dam, indicating the beneficial effect of these environments for N removal. It is suggested that denitrification represents a major N pathway in the floodplain environment.