Phosphorus and Eutrophicaation of Aquatic Term Paper

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To total P. In surface waters, which varied from about 5 to 75. The LOWESS (a locally weighted regression) best fits for chlorophyll a concentrations in the various lakes were different functions for total P. And total N. LOWESS regression slopes and intercepts shifted with changing N/P atomic ratios with slopes maximized and intercepts minimized at an N/P ratio of 22. Similar analyses for data from 1041 lakes, not selected for N/P ratios, found that the log of chlorophyll a vs. log of summer total P. concentrations in surface waters was a sigmoid relationship that tended to flatten out at very high P. concentrations, rather than -- the linear one often assumed in the literature. It is apparent, therefore, that if a lake is already highly enriched with P, then adding more will have little effect, while adding N. will bring about major additional eutrophication.

Thus, for lakes it seems quite clear that P. is the nutrient most likely to be potentially limiting. But can we make the same statement about streams and rivers, reservoirs, or estuaries and coastal waters? Certainly, for estuaries and coastal waters the situation with respect to P-limitation of primary production is different. One of the first papers to conclude that there is a shift from P. To N. limitation as we move from fresh water to coastal waters was Ryther and Dunstan (1971).

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Their view has become widely accepted (e.g., review by Nixon, 1981). However, Hecky and Kilham (1988) have challenged the basis for this conclusion. They felt that the generality and severity of N. limitation in" the oceans had not been rigorously established. Most scientists have put their efforts into determining why this apparent shift from P. limitation to N. limitation occurs.

Term Paper on Phosphorus and Eutrophicaation of Aquatic Assignment

Some of the more obvious reasons are the widely observed more efficient recycling of P. In estuaries, the high losses of fixed N. To the atmosphere due to denitrification in coastal waters (Nixon, 1981), and the role of sulfate in recycling P. In coastal sediments (Caraco et al., 1989). They found that a strong positive correlation existed between primary production and sulfate concentration in lakes and estuaries. The increases in primary production with increased sulfate concentrate had a higher slope in systems with anaerobic sediments, such as most estuaries. Under these conditions some of the sulfate is reduced to sulfides, which might bind the ferrous ions that are also produced in anaerobic sediments, preventing the ferrous ions from diffusing to the sediment/water column interface. In less reduced sediments a layer of oxidized sediments at the surface of the bottom sediments, coated with ferric hydroxide, is believed to form a barrier that traps diffusing phosphate before it can reach the overlying water column.

Regenerated phosphate is sufficient in Delaware Bay to supply almost all of the plankton P. demand except during the spring bloom (Lebo and Sharp, 1992). Estuaries, especially at their upstream ends, are transition zones. Sometimes they are P. limited in the spring, and N. limited in the summer and fall (Fisher et al., 1992; Lee et al., 1996). If lakes are primarily P. limited, the oceans ale primarily N. limited, and estuaries are transition zones, how about streams, rivers, and reservoirs? Although they are perhaps the least understood with respect to nutrient limitation, one might reasonably assume that they behave somewhat like lakes. However, unlike many lakes, unless they are highly enriched with nutrients they do not undergo anaerobic periods and thus are unlikely to release high concentrations of phosphate from bottom sediments. If they have long enough retention times, a given.volume of water moving downstream in a large river should behave much as though it were surface water in a lake or reservoir. Some differences include the "spiraling" of P. down the channel (Newbold et al., 1981; Elwood et al., 1983).

This is the result of uptake of P. By attached bacteria and algae (periphyton) and vascular plants and the binding of compounds in bottom sediments. When these P. compounds are released back into the water column, either from bottom sediments or attached biota, they move further down stream, before becoming attached again as the P. is cycled among the system components. Each such P. movement downstream in the water column is referred to as a "spiral." One of the earliest experimental studies of P. limitation in streams involved continuous addition for 8 d of diammoniump hosphate to a stream in Michigan. This resulted in an increase from <8 I~g total P/L to about 70 Ixg total P/L immediately downstream. Increased P. concentrations were observed for 4 km downstream and periphyton concentrations on artificial substrates increased threefold. Stream water was diverted from a stream in British Columbia to a series of wooden troughs (Stockner and Shortreed, 1978). One was enriched with phosphate, one with nitrate, and one with both. Background dissolved phosphate was 3 p~g P/L and the treatment raised this to 9 p.g P/L. Chlorophyll a in periphyton increased over fourfold in those enriched with P. In Tennessee two reaches of a wooded stream were continuously enriched with 60 and 450 txg phosphate P/L for 95 d (Elwood et al., 1981).

Background was about 4 ~g of P/L. The result was increased periphyton chlorophyll, higher rates of decomposition of leaf litter, and increased populations of snails and leaf-shredding macroinvertebrates. When phosphate was continuously added to a stream on the north slope of Alaska to increase the concentration in the stream by 10 ixg total P/L (Peterson et al., 1985), periphyton chlorophyll increased for 10 km downstream and the stream shifted from a heterotrophic to an autotrophic system. Effects ramified to increased bacterial activity and increases in the mean size of aquatic insects. These studies, although less numerous than was the case for lakes, strongly indicate that P. is also a key element controlling productivity of streams and rivers.

Are streams and rivers in the U.S.A. often highly polluted with P? The answer is yes. A trend analysis of 381 riverine sites in the USAfr om 1974 to 1981 (Smith et al., 1987) found that the average total P. concentration was 130 P/L, much higher than the levels attained in most of the fertilization experiments discussed above. Are these rivers improving with respect to P. concentrations? Fifty of these sites, mostly in the Great Lakes and upper Mississippi drainages, had declines in P. concentrations at 8.1% per year, mostly due to point source controls. Forty-three sites had increases at 7.4% per year, mostly due to increased diffuse sources of An interesting study by Soballe and Kimmel (1987) analyzed data from 345 streams from the National Stream Quality Accounting Network (NASOUAN) and 812 lakes and reservoirs from the National Eutrophication Survey (NES). A canonical discriminant analysis of algal cell abundance and nutrient status found that natural lakes and rivers formed end member populations, while reservoirs were intermediate and overlapping. Multiple regressions of algal cell abundance vs. total P. concentrations were significant, but different for all three categories of receiving water. Statistical models for each of the three types of water found that residence time, water depth, and water clarity were all important factors (r = 0.7. 0.6, and -0.4, respectively). Algal abundance per unit of increased from rivers to reservoirs to natural lakes. Thus, the effects of P. additions were most pronounced in lakes, primarily due to the long residence times typical of most lakes.People are attracted to lakes, rivers, and coastlines for diverse reasons. Clean water is a crucial resource for drinking, irrigation, industry, transportation, recreation, fishing, hunting, support of biodiversity, and sheer esthetic enjoyment. Throughout human history, water has been used to wash away and dilute pollutants. Pollutant inputs have increased in recent decades and have degraded water quality of many rivers, lakes, and coastal oceans. Degradation of these vital water resources can be measured as the loss of natural systems, their component species, and the amenities that they provide (U.S. EPA 1996, Postel and Carpenter 1997). Water shortages are increasingly common and likely to become more severe in the future (Postel et al. 1996, Postel 1997). Water shortage and poor water quality are linked, because contamination reduces the supply of water and increases the costs of treating water for use. Preventing pollution is among the most cost-effective means of increasing water supplies.

Eutrophication caused by excessive inputs of phosphorus (P) and nitrogen (N) is the most common impairment of surface waters in the United States (U.S. EPA 1990), with impairment measured as the area of surface water not suitable for designated uses such as drinking, irrigation, industry, recreation, or fishing. Eutrophication accounts for 50% of the impaired lake area and 60% of the impaired river reaches in the United States (U.S. EPA 1996), and is the most widespread pollution problem of U.S. estuaries (NRC 1993a). Other important causes of surface-water degradation are siltation caused by erosion from agriculture, logging and construction (which also contribute to eutrophication), acidification from atmospheric sources and mine drainage, contamination by toxins, introduction of exotic species, and hydrologic changes… [END OF PREVIEW] . . . READ MORE

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