Effects of land use in the drainage area on phosphorus binding and mobility in the sediments of four drinking-water reservoirs |
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Authors: | Ulrich Kai-Uwe |
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Affiliation: | (1) Ecological Laboratory Neunzehnhain, Technical University of Dresden, Neunzehnhainer Str. 14, D-09514 Wünschendorf, Germany |
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Abstract: | The study of four drinking-water reservoirsdemonstrates how the anthropogenic land use of acatchment may affect binding and mobility ofphosphorus in the sediment. Pdiss concentrationgradients at the sediment–water interface weremeasured to calculate potential diffusive releaserates. P binding forms were determined by sequentialextraction of fresh sediment and settling seston. Mainstudy sites were Saidenbach Reservoir (mesotrophic,densely populated drainage area with 73% agriculturalland use) and Neunzehnhain Reservoir (oligotrophic,unpopulated drainage area forested to 80%) in thesilicate-rich Erzgebirge mountains of eastern Germany.Tot-P concentrations and P binding forms of typicalerosive matter from each catchment were similar to thesediment of both pre-reservoirs and reservoirs' mouth.In Saidenbach Reservoir, diatoms responded to highnutrient loading by incorporating ortho-P. Whilesettling, the org-P was partly transformed toFe(OOH)P. Apart from hypolimnetic O2depletion, this P binding form dominated in thesurface sediment mainly in front of the dam. Withincreasing sediment depth, org-P and Fe(OOH)Pnot only redissolved into the pore water, but alsoadsorbed onto Al compounds. In Neunzehnhain Reservoir,acidification of the low buffered catchment favouredloading of humic compounds and Al3+ ions, whichprecipitated and redox-independently adsorbed ortho-Pdue to a pH increase in the lake. Neunzehnhainsediment was able to immobilize Fe(OOH)P fromSaidenbach sediment in a batch experiment. Comparativesequential P extraction of sediment from SosaReservoir (oligo-mesotrophic, sparsely populateddrainage area forested to 94%) and Kleine KinzigReservoir (nearly unpopulated drainage area forestedto 98%) also demonstrated effective P immobilizationby Al-/humic compounds.It is concluded that the absence of settlements in thecatchment, together with forestry as dominating landuse, favour not only oligotrophic conditions in thereservoir but also confine internal P loading from thesediment. But attention should be paid toacidification problems. |
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Keywords: | drainage area reservoir sedimentcomposition phosphorus phosphate extraction |
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