Surface waters phosphorus control

A recent review of research on phosphorus input to surface waters from agriculture highlights the variability of particulate and dissolved phosphorus contributions to catchments. The input varies with rainfall, fertilizer application rates, the history of the application of the fertilizer, land use, soil type, and between surface and sub-surface water. The balance struck between export of nutrients from the catchment and recipient-water productivity is the primary factor which controls its quality. 

Romero O, Hebbeln D (2003) Biogenic silica and diatom thanatocoenosis in surface sediments below the Pern-Chile Curent Controlling mechanisms and relationship with productivity of surface waters. Max Micropaleontol 48(l-2) 71-90 Ruttenberg K (1992) Development of a sequential extraction method for different forms of phosphorus in marine sediments. Limnol Oceanogr 37(7) 1460-1482 Sabine CL, Mackenzie FT (1991) Oceanic sinks for anthropogenic CO2. Science 305(5682) 367-371... 

Calcium, magnesium, potassium, phosphates (phosphorus), silica, and carbon dioxide may be present in water, and their presence generally does not necessitate control. Calcium and magnesium are contributors to the hardness of water. The control of their levels in water may be required mainly as a preventive measure for scale formation especially on heated surfaces or for taste appeal of the water. 

Bowman G.T. and Delfino J.J. 1982. Determination of total Kjeldahl nitrogen and total phosphorus in surface waters and wastewaters. /. Water Pollut. Control Fed. 54 1324 1330. 

The most commonly used physical method for long-term eutrophication control in lakes is that of artificial destratification. This method is well tried and understood and uses either jetted water or compressed air bubbles to break down the lake stratification in the summer months. Algal growth is also affected by an increase in circulation. This is due to the artificial shading effect which results from the algae spending less time near the surface and consequently less time in the light. This technique also reduces the redox-dependent phosphorus release from sediments because the sediment surface remains aerobic. 

The polar lipid headgroup zone contains the phospholipid and steroid phosphorus-nitrogen, carbonyl, hydroxyl and hydration water moieties which combine to establish a substantial dipolar potential. This positive potential is of a magnitude of several hundred millivolts across the membrane headgroup zone. In the membrane hydrocarbon interior, the electrostatic field must be at least 450 to 750 mV (14) and controls ion current across the interior as we 1 1 as possibly influencing selective ion adsorption to the membrane surface. 

Many such studies of sedimentary phosphorus profiles, also incorporating pore water measurement of soluble reactive phosphate, have demonstrated that redox-controlled dissolution of iron (hydr)oxides under reducing conditions at depth releases orthophosphate to solution. This then diffuses upwards (and downwards) from the pore water maximum to be re-adsorbed or co-precipitated with oxidized Fe in near-surface oxic sections. The downwards decrease in solid phase organic phosphorus indicates increasing release of phosphorus from deposited organic matter with depth, some of which will become associated with hydrous iron and other metal oxides, added to the pool of mobile phosphorus in pore water or contribute to soluble unreactive phosphorus . The characteristic reactions involving inorganic phosphorus in the sediments of Toolik Lake, Alaska, are shown in... 

The in situ chemical controls on oceanic N2 fixation, in particular iron and phosphorus, are the topic of much current research effort and debate. Fueling these efforts has been the observation of extensive areas of excess N (relative to Redfield regeneration stoichiometry, often expressed as positive N anomalies) relative to P in subeuphotic zone waters in the North Atlantic that roughly correspond to regions which receive substantial aeolian dust deposition (Michaels et al, 1996 Gao et al, 2001 Gruber and Sarmiento, 1997). Wet and dry deposition of mineral aerosols fertilize the surface ocean with Fe (along with N and P) (Mahowald et al, 1999). 

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