Sediment phosphorus cycling in a large shallow lake: spatio-temporal variation in phosphorus pools and release

Sediment and water column phosphorus fractions were recorded monthly for one year (April 2004–April 2005) in a shallow lake recovering from nutrient pollution (Loch Leven, Scotland). Equilibrium phosphate concentration (EPC0) and gross sediment phosphorus (P) release rates were estimated from laboratory experiments. Pore water and organic P pools were lowest during warm water periods whereas bottom water P was lowest during cold water periods. Reductant-soluble, organic, metal oxide-adsorbed, residual and sediment total phosphorus pools all varied significantly with overlying water depth. Short-term, high magnitude, redox initiated P release events occurred in late summer and winter as a result of anoxic sediment conditions. Lower magnitude long-term release conditions were maintained for most of the year, most likely as a result of organic P cycling and maintenance of high concentration gradients between the pore and bottom water P pools. Estimates of summer P uptake/release rates, across an intact sediment-water interface, suggested that maximum gross internal release was ~12 mg SRP m−2 lake surface area d−1 with EPC0 values ranging between 180 and 270 μg P L−1. This study highlights the biological mediation of internal loading in shallow eutrophic lakes, and in particular, the role of sediment algae in decreasing, and sediment bacteria in enhancing, sediment P release

Constructed wetlands: a review

The first aim of this invited literature review is critically to review and evaluate hydrological, physical and biochemical processes within natural and constructed wetlands. The second aim is to contribute the thoughts of the authors to the discussion with the help of a case study focusing on gully pot liquor treatment. The performances of constructed treatment wetlands with and without macrophytes, and aggregates of different adsorption capacities will be assessed, principle findings highlighted and conclusions, also relevant to the literature review, will be drawn. The relationships between aggregates, microbial and plant communities as well as the reduction of predominantly biochemical oxygen demand, suspended solids and heavy metals are investigated. After maturation of the biomass, which dominates the litter zone, organic and inorganic contaminants are usually reduced similarly for all wetland types. There appears to be no additional benefit in using macrophytes and expensive adsorption media in constructed wetlands

Effects of Cholesterol on Physical Properties of Human Erythrocyte Membranes: Impact on Susceptibility to Hydrolysis by Secretory Phospholipase A2

The ability of secretory phospholipase A2 (sPLA2) to hydrolyze cell membranes is highly dependent on the physical properties of the membrane. The effects of cholesterol on these properties have been characterized in artificial bilayers and found to alter sPLA2 activity significantly. It is hypothesized that the natural difference in cholesterol content between erythrocytes and leukocytes is in part responsible for their differing susceptibility to hydrolysis by sPLA2. To test this hypothesis, defined amounts of cholesterol were removed from erythrocyte membranes using methyl-β-cyclodextrin. Treatment of cells with methyl-β-cyclodextrin increased the hydrolysis rate and total substrate hydrolyzed by sPLA2. In general, this effect of cholesterol removal was more pronounced at higher temperatures. Comparison of the level of membrane order (assessed with the fluorescent probe laurdan) with hydrolysis rate revealed that sPLA2 activity was greatly enhanced upon significant reductions in lipid order. Additional treatment of the cells with calcium ionophore further enhanced the hydrolysis rate and altered the relationship with membrane order. These data demonstrated that interactions with sPLA2 observed in artificial bilayers apply to biological membranes. It is also proposed that the high level of cholesterol in erythrocyte membranes is a protective mechanism to guard against hydrolytic enzymes