Environmental Engineering Reference
In-Depth Information
TABLE 14.6
Summary of Recommended Criteria for Each of the Aggregate Nutrient Ecoregions
for Rivers and Streams and Lakes and Reservoirs
Rivers and Streams
Lakes and Reservoirs
TN
(mg L
-1
)
TN
(mg L
-1
)
Chl-a
(μg L
-1
)
a
Ecoregion
TP (μg L
-1
)
Chl-a (μg L
-1
)
a
TP (μg L
-1
)
I
47.00
0.31
1.80
II
10.00
0.12
1.08
8.75
0.10
1.90
III
21.88
0.38
1.78
17.00
0.40
3.40
IV
23.00
0.56
2.40
20.00
0.44
2 (S)
b
V
67.00
0.88
3.00
33.00
0.56
2.30 (S)
b
VI
76.25
2.18
2.70
37.50
0.78
8.59 (S)
b
VII
33.00
0.54
1.50
14.75
0.66
2.63
VIII
10.00
0.38
0.63
8.00
0.24
2.43
IX
36.56
0.69 (S)
b
0.93
20.00
0.36
4.93
X
128.00
0.76 (S)
b
2.10
XI
10.00
0.31 (S)
b
1.61
8.00
0.46
2.79 (S)
b
XII
40.00
0.9 (S)
b
0.4
10.00
0.52
2.60
XIII
17.50
1.27
12.35
XIV
31.25
0.71 (S)b
3.75
8.00
0.32
2.90 (T)
c
Source:
Data from USEPA Summary July 2002.
a
Chl-a = chlorophyll-a measured by the luorometric method, unless speciied.
b
S = spectrophotometric method.
c
T = trichromatic method.
Note:
TN, total nitrogen; TP, total phosphorus.
The chemistry of phosphorus is complex. However, for lake management, for assessing nutrient
health, and for nutrient criteria, only TP is often considered. Other than TP, the common forms
measured and used in lake management include organic phosphorus and (ortho) inorganic phospho-
rus, either as totals or analytically separated into dissolved and particulate fractions. The dissolved
inorganic phosphorus (DIP) is assumed to be the bioavailable form.
Organic phosphorus may include a variety of components, both living and nonliving, reactive
(labile) or inert, particulate or dissolved. Nonliving organic phosphorus will mineralize (either
slowly or quickly depending on the form) to inorganic forms. This may occur in the water column
or sediments (sediment diagenesis). Living plants will uptake phosphorus during growth, excrete
phosphorus, or produce nonliving phosphorus as they die.
An additional process impacting phosphorus and phosphorus management is the chemical deac-
tivation of available forms. For example, phosphorus inactivation using alum is a commonly used
method in lake restoration. The alum forms a precipitate or loc that scrounges phosphorus (and
other materials) as it settles through the water column, and it may also create a “blanket” over the
sediment that reduces sediment phosphorus release. It has long been known that there are similar
controls for the release of phosphorus from sediments resulting from sediment diagenesis. The
internal loads from sediments may be a major contributor to total lake phosphorus loads. Mortimer
(1941) postulated that some barrier exists in the aerobic portion of sediments due to the formation
of an iron hydroxide precipitate. Soluble forms accumulate in the anaerobic water column and
sediments. When those soluble forms are introduced to oxic conditions, they precipitate and form
locs that tie up phosphorus, which may remove it from the water column or inhibit its escape from
sediments (Di Toro 2001).
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