Phytate as a novel phosphorus-specific paleo-indicator in aquatic sediments

A reliable geochemical paleo-indicator for phosphorus remains elusive, despite the importance of understanding historical changes in the nutrient status of aquatic ecosystems. We assessed the potential of phytate (salts of mvo-inositol hexakisphosphate) as a novel phosphorus-specific paleoindicator by measuring its concentrations in dated sediments from an embayment in Helsinki, Finland, with a known 200-year history of trophic changes. Phytate was extracted in a solution containing sodium hydroxide and EDTA and detected by solution P NMR spectroscopy with spectral deconvolution. Concentrations varied markedly with sediment depth and paralleled previously determined changes in diatom assemblages and geochemical indicators linked to trophic status. In contrast, total sediment phosphorus did not reflect phosphorus inputs to the embayment, presumably due to the mobilization of inorganic phosphate under anoxic conditions during B. L. Turner (El) Smithsonian Tropical Research Institute, Apartado 0843-03092, Balboa, Ancon, Republic of Panama e-mail: [email protected] K. Weckstrom Department of Quaternary Geology, Geological Survey of Denmark and Greenland, 0. Voldgade 10, 1350 Copenhagen, Denmark K. Weckstrom Institute for Limnology, Austrian Academy of Sciences, Mondseestrasse 9, 5310 Mondsee, Austria periods of high pollutant loading. Importantly, phytate appeared to be stable in these brackish sediments, in contrast to other organic and inorganic phosphates which declined abruptly with depth. We therefore conclude that phytate represents a potentially important indicator of historical changes in phosphorus inputs to water bodies, although additional studies are required to confirm its stability under conditions likely to be encountered in lakes and coastal ecosystems.