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DO depletion-excerpts from leading literature

S.M. Mandaville Post-Grad Dips., Soil & Water Conservation Society of Metro Halifax (SWCSMH)

Dated: March 27, 2019           Soil & Water Conservation Society of Metro Halifax (SWCSMH) Master Homepage


Contents:


Formal definition of trophic status


For establishing trophic status reliably, access our web page on the Formal definition of trophic status
.

Several variables have to be taken into account in addition to DO depletion. Access the aforesaid web page for extensive scientific rationale.


Oxygen deficits

Excerpts from Mackie, G.L. 2004. Applied Aquatic Ecosystem Concepts. Second Ed. Kendall/Hunt Publishing Company. 784 pp. ISBN 0-7575-0883-9.

The oxygen deficit in a lake is the amount of oxygen required to reach the saturation level. All calculations must account for the atmospheric pressure at the surface of the lake by using correction factors.

The most meaningful oxygen deficit measurement is the relative hypolimnial oxygen deficit because it accounts for oxygen deficits in layers below the hypolimnetic surface.

Essentially, one measures the dissolved oxygen contents of several vertical columns of water at the beginning and at the end of the stratification period. Each column has a cross-sectional area of 1 cm². The height (depth) of a column is usually 1 to 2 m. The difference in oxygen content for each layer (column) between the beginning and the end of the stratified period is summed to give a relative areal hypolimnial oxygen deficit, or RAHOD.

Oligotrophic lakes have RAHOD values of <0.017 mg O2 lost cm-² day-¹, and eutrophic lakes have >0.033 mg
O2 lost cm-²day-¹.

The other two kinds of oxygen deficit are, actual and absolute, depending upon the saturation temperature used in the calculation. The main criticism of actual oxygen deficits is it assumes that the water was saturated at the observed temperature during spring turnover. The absolute oxygen deficit suffers the same criticism as the actual oxygen deficit in that it assumes saturation at 4 ºC, which is not necessarily true.


Calculation of stratum areas/volumes:

Alternately to a planimetre, one can rely on computer technology and use a digitizer for lot higher accuracy. With proper software, one can make areal estimates for any shape accurately and quickly. In this method, a mouse with a pointer is used to trace the outline of the image. The mouse button is pressed several times as the outline is traced. The more often the button is pressed, the more accurate the estimate of the area enclosed, or the length of line being traced. The computer program integrates the data and converts it into area (e.g. lake area) or length of line traced (e.g. shoreline length). Some digitizers can calculate the volumes of each stratum as well.


Solubility of oxygen from an atmosphere containing 20.9 percent oxygen by volume:

Note:

Lakes at high elevations (where there is less oxygen per unit volume of air)  contain less dissolved gas per unit volume than do lakes with the same temperature at sea level.


Temp.

Oxygen from normal atmosphere

Correction factors for oxygen
saturation at various altitudes


o
C


mg per L

Altitude
Pressure

m
mm
Factor
0
14.62
0
760
1.00
1
14.23
100
750
1.01
2
13.84
200
741
1.03
3
13.48
300
732
1.04
4
13.13
400
723
1.05
5
12.80
500
714
1.06





6
12.48
600
705
1.08
7
12.17
700
696
1.09
8
11.87
800
687
1.11
9
11.59
900
679
1.12
10
11.33
1000
671
1.13





11
11.08
1100
663
1.15
12
10.83
1200
655
1.16
13
10.60
1300
647
1.17
14
10.37
1400
639
1.19
15
10.15
1500
631
1.20





16
9.95
1600
623
1.22
17
9.74
1700
615
1.24
18
9.54
1800
608
1.25
19
9.35
1900
601
1.26
20
9.17
2000
594
1.28





21
8.99
2100
587
1.30
22
8.83
2200
580
1.31
23
8.68
2300
573
1.33
24
8.53
2400
566
1.34
25
8.38
2500
560
1.36





26
8.22



27
8.07



28
7.92



29
7.77



30
7.63





The Corvallis LEI (Lake Evaluation Index)

References: The superb LEI proposed by Porcella et al (1979) is a rare composite trophic state index that includes Total Phosphorus (TP), Total Nitrogen (TN), Chlorophylla (Cha), Secchi Disk (SD), macrophyte coverage, and dissolved oxygen values in lakes.

Download the full document in PDF (https://1drv.ms/b/s!Au0xeIA-MCofg3ShH_HmNC5EW7Oe)

Excerpts from Porcella et al:

lake eutrophication ....Porcella et al

Below, the scan inserts are only for DO:

DO1..Porcella.JPG
DO2..Porcella.JPG





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