Abstract
The anoxic factor (AF, days per year or per season) can be used to quantify anoxia in stratified lakes. AF is calculated from oxygen profiles measured in the stratified season and lake surface area (A0) as urn:x-wiley:00243590:media:lno19954061100:lno19954061100-math-0001 AF represents the number of days that a sediment area, equal to the whole‐lake surface area, is overlain by anoxic water. Average AF for 56 central Ontario lakes, 19 additional eastern North American lakes, including the Laurentian Great Lakes and several acidified lakes, ranged from 0 to 83 d per summer. Of this variation, 65% (54%) is accounted for by average phosphorus (nitrogen) concentration and an indicator of lake shape, z̄/A00.5 (where z̄ is mean depth). Only 17% on average was explained by annual dissolved organic C (DOC) concentration. Annual variation within lakes was large and partly ascribed to variable annual loading of DOC. AF was not correlated with areal hypolimnetic oxygen depletion, because of the opposing dependency on lake shape, but was correlated with Reckhow’s probability of anoxia in eutrophic lakes. AF was also correlated with the redox potential of anoxic water at the end of summer stratification, especially after inclusion of an estimate of iron concentration in the sediment.
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