241,360 research outputs found

    The potential release of phosphorus in floodplains

    Get PDF
    In the Illinois River Watershed, there has been growing concern over elevated phosphorus concentrations in the water column. This study evaluated how much phosphorus is contributed from floodplain soils into surface waters, examining the relationship between the flux of phosphorus released and the amount of phosphorus stored in the soil. This was investigated by artificially inundating soil cores from four sites and determining the soluble reactive phosphorus concentrations of the overlying water and the levels of Water and Mehlich-3 extractable phosphorus in the soil. The flux of phosphorus to the overlying water ranged from 0.43 to 6.61 mg m-2 hr-1 within the short-term (16.5-hr incubation) and 0.06 to 1.26 mg m-2 hr-1 over the long term (282.5-hr incubation). Phosphorus flux to the overlying water was significantly correlated with the amount of phosphorus stored in the soil. This study showed that riparian soils with elevated phosphorus content have the potential to release phosphorus when flooded

    Structures, enthalpies of formation, and ionization energies for the parent and binary mixed carbon, silicon, nitrogen, and phosphorus cubane derivatives: A G4MP2 theoretical study

    Get PDF
    Gas phase standard state (298.15 K, 1 atm) structures, enthalpies of formation, and ionization energies (IEs) were calculated at the G4MP2 composite method level of theory for the parent and binary mixed carbon, silicon, nitrogen, and phosphorus cubane derivatives. Increasing nitrogen content increases the enthalpies of formation for the carbon-nitrogen, nitrogen-phosphorus, and silicon-nitrogen binary cubanes, with the opposite enthalpies of formation trend for increasing phosphorus content within the carbon-phosphorus, nitrogen-phosphorus, and silicon-phosphorus derivatives. Varying carbon/silicon content in the carbon-silicon cubanes results in no general trends for enthalpies of formation. Isomerization enthalpies within the homolog groups having more than one isomer vary widely with atomic composition and substitution patterns. Increasing nitrogen content of the carbon-nitrogen and nitrogen-phosphorus derivatives increases the IE, increasing silicon content in the carbon-silicon cubanes and phosphorus content of the carbon-phosphorus cubanes decreases the IE, while no IE clear trends are evident based on relative atomic content for the silicon-nitrogen and silicon-phosphorus compounds. The binary mixed carbon, silicon, nitrogen, and phosphorus cubane derivatives are predicted to display potentially tunable thermodynamic stability and redox behavior depending on the atom identities and relative positions

    Changes of water quality and sediment phosphorus of a small productive lake following decreased phosphorus loading

    Get PDF
    Esthwaite Water is the most productive or eutrophic lake in the English Lake District. Since 1945 its water quality has been determined from weekly or biweekly measurements of temperature, oxygen, plant nutrients and phytoplankton abundance. The lake receives phosphorus from its largely lowland-pasture catchment, sewage effluent from the villages of Hawkshead and Near Sawrey, and from a cage-culture fish farm. From 1986 phosphorus has been removed from the sewage effluent of Hawkshead which was considered to contribute between 47% and 67% of the total phosphorus loading to the lake. At the commencement of phosphorus removal regular measurements of phosphorus in the superficial 0-4 cm layer of lake sediment were made from cores collected at random sites. Since 1986 the mean annual concentration of alkali-extractable sediment phosphorus has decreased by 23%. This change is not significant at the 5% level but nearly so. There has been no marked change in water quality over this period. Summer dominance of blue-green algae which arose in the early 1980s after decline of the previous summer forms, Ceratium spp., has been maintained. Improvement in water quality is unlikely to be achieved at the present phosphorus loading