CONICET | Buscador de Institutos y Recursos Humanos

Phosphorus (P) fractionation and sorption behavior were studied in the sedimentsof two calcium-sulfate (Ca-SO4: Ca2+170 mg L-1;SO42- 400 mg L-1) water reservoirs in the southerncentral Argentine Andes - El Carrizal Reservoir (ECR),which stratifies insummer and El Nihuil Reservoir (ENR),which is vertically mixed throughout theyear. Sediment size classes reflected the lithology of both basins and the reservoirsrelative location: ECR (downstream from a valley adjacent to a mountainenvironment) had higher clay proportions while the sand fraction was moreimportant in ENR (just next to a mountain environment). In both reservoirs, thechemical composition revealed low alteration and calcium enrichment. Total Pcontent was relatively high (1.1 ? 1.6 mg P kg-1 dry weight) asexpected from the contribution of marine formations. P fractionation wasdominated by Ca-P (ECR, 69% and ENR, 63%) followed by organic-P (23%) in summer-anoxicECR and by iron/aluminum (Fe/Al)-P (27%) in oxic ENR. Batch experiments showedthat sorption behavior in ECR had a typical Langmuir isotherm plot while in ENRthat model fitted only at low dissolved P values (<5 mg P L-1) andco-precipitation evidence was observed at higher P concentrations. It is proposedthat lower Fe/Al-P content in anoxic (ECR) vs.oxic (ENR) sediments results from the P released from iron-bound phosphorus dueto sulfate reduction-ferrous sulfide formation in an anoxic environment. Thiscondition should enable ECR sediments to adsorb P into fresh oxidized iron, andENR sediments to co-precipitate P with calcium due to Fe/Al-P saturation, asobserved in batch experiments. This paper constitutes the first description of phosphorouscontent and dynamics in reservoir sediments in arid central western Argentina,where water sulfate concentrations are naturally high due to basin lithology.

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