Why water is the 'strangest' compound known to man? - page 2

As a result, organic particles that harbor microorganisms may not be completely removed before distribution. The growth of macrophytes and phytoplankton is stimulated principally by nutrients such as phosphorus and nitrogen. Nutrient-stimulated primary production is of most concern in lakes and estuaries, because primary production in flowing water is thought to be controlled by physical factors, such as light penetration, timing of flow, and type of substrate available, instead of by nutrients (McCabe et al., 1985). Freshwater system impacts: Generally, phosphorus (as orthophosphate) is the limiting nutrient in freshwater aquatic systems. That is, if all phosphorus is used, plant growth will cease, no matter how much nitrogen is available. The natural background levels of total phosphorus are generally less than 0.03 mg/l. The natural levels of orthophosphate usually range from 0.005 to 0.05 mg/l (Dunne and Leopold, 1978).

Many bodies of freshwater are currently experiencing influxes of phosphorus and nitrogen from outside sources. The increasing concentration of available phosphorus allows plants to assimilate more nitrogen before the phosphorus is depleted. Thus, if sufficient phosphorus is available, elevated concentrations of nitrates will lead to algal blooms. Although levels of 0.08 to 0.10 mg/l orthophosphate may trigger periodic blooms, long-term eutrophication will usually be prevented if total phosphorus levels and orthophosphate levels are Estuarine system impacts: In contrast to fresh water, nitrogen is generally the primary limiting nutrient in the seaward portions of estuarine systems (Paerl, 1993).

Here, nitrogen levels control the rate of primary production. If the system is supplied with high levels of nitrogen, algal blooms will occur. Systems may be phosphorus limited, however, or become so when nitrogen concentrations are high and N: P>16:1 (Jaworski, 1981). In such cases, excess phosphorus will trigger eutrophic conditions. The recommended level of total phosphorus in estuaries and coastal ecosystems to avoid algal blooms in 0.01 to .1 mg/l and 0.1 to 1 mg/l of nitrogen (a 10:1 ratio of N:P). The higher concentrations support less diversity (NOAA/EPA, 1988).