The prediction of internal phosphorus load in lakes with anoxic hypolimnia1

Lakes with anoxic hypolimnia (anoxic lakes) have significantly lower values for phosphorus retention than do lakes with aerobic hypolimnia (oxic lakes). This difference may reflect an increased internal phosphorus load from the anoxic hypolimnia. Two models are given to predict internal phosphorus load ( L int ) in such lakes. The first predicts internal load as the difference between the observed phosphorus retention in anoxic lakes and that predicted ( R pred ) by a formula that adequately describes phosphorus retention in oxic lakes. The second predicts internal load as the product of an average rate of phosphorus release from anoxic sediments, the surface area of the anoxic sediment, and the period of anoxia. Predictions of the first model compare favorably with 17 observed values of internal load; further data are required to test the second model. These models suggest that mean phosphorus concentration (TP) in anoxic lakes can be predicted in two ways. One can use whole‐lake phosphorus budget models which implicitly incorporate internal phosphorus load, because they include a measurement of phosphorus retention. Alternatively, a term to account for the internal load can be added to current models based on external load ( L ext ) and predicted retention (R pred ) where q s is areal water load: urn:x-wiley:00243590:media:lno19842910111:lno19842910111-math-0001