Prediction of annual and seasonal phosphorus concentrations in stratified and polymictic lakes

Nü,rnberg, Gertrud

Limnol. Oceanogr., 43(7), 1998, 1544-1552 | DOI: 10.4319/lo.1998.43.7.1544

ABSTRACT: Phosphorus (P) concentrations in lakes arc summarized and reported in different ways. Annual whole lake P (Pann), epilimnetic summer P (Pepi), and mixed water column P during fall turnover after summer stratification (Pfall) were investigated with data from up to 150 lakes. Differences between P averages are caused by temporal variation in thermal stratification and the size of internal P sources. To predict various P averages in specific lake types, I combined a P retention model that predicts annual retention due to sedimentation (Rpred) with external and internal load estimates (Lext, Lint) in a steady-state, P mass balance approach. Retention of internal and external loads in stratified and polymictic lakes can be predicted by the same model, Rpred = 15/(18 + qs), where qs is annual water load (m yr-1). However, lakes with chemically enhanced P coprecipitation (e.g., with calcium) are an exception. P averages can be predicted in stratified lakes, as [Equations 1 and 2] although Pepi is overestimated in lakes with oxic hypolimnia. P concentrations can be approximately predicted in polymictic lakes as [Equation 3].

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