Lakes and Watercourses
Lakes and Watercourses
Lakes and Watercourses
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In lakes, seasonal mean values for TOC or COD Mn (May – October)<br />
over one year are used, based on monthly readings taken in the epilimnion<br />
or, if only one sample is taken, in surface water (0.5 m).<br />
Annual mean values are also assessed in watercourses, although here<br />
the assessment should be based on samples taken 12 times a year over<br />
one year.<br />
COD Mn is derived by dividing the permanganate value by 3.95. For<br />
practical reasons, the same scale is given here for TOC <strong>and</strong> for COD Mn .<br />
It should also be noted that the correlation between these variables may<br />
vary, both naturally <strong>and</strong> as a result of admixture of sewage or waste<br />
water, depending on the composition of the organic matter.<br />
Comments<br />
Classifications must be based on samples taken <strong>and</strong> analysed in accordance<br />
with the Swedish EPA Environmental Monitoring H<strong>and</strong>book.<br />
The scales should be used bearing in mind the wide natural variation<br />
between individual lakes <strong>and</strong> watercourses <strong>and</strong> from year to year. The<br />
number of sampling occasions or the time scale on which the various<br />
assessments are based represents minimum figures. If <strong>and</strong> when assessments<br />
are made on the basis of more limited data, this should be stated.<br />
References<br />
Alabaster, J.S. & Lloyd, R. (1982): Water quality criteria for freshwater fish. 2nd<br />
ed. – Butterworths, London.<br />
Doudoroff, P. & Shumway, L. (1970): Dissolved oxygen requirements of<br />
freshwater fishes. - FAO Fisheries Technical paper No. 86.<br />
US EPA (1986): Quality criteria for water. – EPA 440/5-86-001.<br />
Wiederholm, T. (1989): Bedömningsgrunder för sjöar och vattendrag. Bakgrundsrapport<br />
1. Näringsämnen, syre, ljus, försurning. (”Environmental Quality Criteria for<br />
<strong>Lakes</strong> <strong>and</strong> <strong>Watercourses</strong>. Background report 1 – Nutrients, oxygen, light,<br />
acidification”). Swedish EPA Report 3627.<br />
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