Environmental Engineering Reference
In-Depth Information
Draft aggregations of level III ecoregions
for the national nutrient strategy
III
V
VIII
II
VIII
V
VIII
IV
XIV
VIII
VII
II
VII
II
VIII
VII
VIII
III
VI
XI
VII
XIV
III
VI
XI
II
IX
V
XIV
III
IV
IX
XI
IX
III
II
IV
XIV
XIV
II
X
XI
IV
V
IX
IX
IX
III
I. Willamette and Central Valleys
II. We stern forested mountains
III. Xeric west
IV. Great Plains grass and shrublands
V. South central cultivated Great Plains
VI. Corn belt and northern Great Plains
VII. Mostly glaciated dairy region
VIII. Nutrient poor largely glaciated upper Midwest and Northeast
IX. Southeastern temperate forested plains and hills
X. Te xas-Louisiana coastal and Mississippi alluvial plains
XI. Central and eastern forested uplands
XII. Southern coastal plain
XIII. Southern Florida coastal plain
XIV. Eastern coastal plain
IV
X
X
XII
XIII
FIGURE 14.26 United States ecoregions for contiguous states. (From USEPA, Nutrient criteria technical
guidance manual, lakes and reservoirs, 1st ed., U.S. Environmental Protection Agency, Washington, DC,
2000a; updated maps available from http://www.epa.gov/wed/pages/models.htm.)
14.6 PHOSPHORUS
Phosphorus occurs in lakes and reservoirs in organic and inorganic forms. Phosphorus is an essen-
tial component of all organisms. The most limiting nutrient is usually considered to be the one that
controls growth, and phosphorus is commonly considered to be the most limiting nutrient for most
freshwater systems. However, as illustrated in Table 14.5, that is not always the case.
As indicated by Wetzel (2001), no other element in freshwater systems has been studied as exten-
sively as phosphorus. The importance of phosphorus in controlling plant growth is well known, and
it is a common component of fertilizers. Understanding the sources and role of phosphorus is criti-
cal to the management of lakes and to determining their health.
Much of the effort associated with phosphorus is directed toward quantifying and managing
loads. Chapra (1997) described the phosphorus-loading concept and its history of use in lake man-
agement. Vollenweider (1968) irst introduced the relationships between loadings of phosphorus and
the trophic status of lakes, linking the management of loadings to lakes and lake water quality. As
described by Chapra (1997), developing phosphorus budget models was the basis for much of the
effort to reduce eutrophication in the Great Lakes and elsewhere. Currently, a common target of
lake restoration is the reduction of external or internal loadings of phosphorus.
Phosphorus is a component of igneous rock most commonly as the mineral apatite (Ca 5 (PO 4 ) 3 )
usually combined with either OH (hydroxyapatite) or luoride (luoroapatite). It is mined in many
areas to produce fertilizers, with some of the largest operations in the world in Florida.
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