Phosphorus retention as a function of external loading, hydraulic turnover time, area and relative depth in 54 lakes and reservoirs

Abstract

We analysed phosphorus retention as a function of external loading, hydraulic turnover time, area and relative depth on the basis of published data from 54 lakes and reservoirs in different climate regions around the world. Our analysis demonstrated that reservoirs and lakes that received higher areal loading of phosphorus (TPin) also retained more P per m2 but the proportion of the external P loading retained in the waterbody (retention coefficient, R P) remained generally independent of TPin. The waterbodies with longer hydraulic residence times (T R) retained larger proportions of external P and the correlation between R P and T R was much stronger in lakes with areas larger than 25 km2 than in the whole data set. TPin and T R together determined 78% of the variation in R P in large lakes. We also partially confirmed our hypothesis that waterbodies with bigger relative depths (Z R) retain more of the external phosphorus than larger and shallower waterbodies with lower Z R. The hypothesis was, however, validated only for lakes larger than 25 km2 and for those with T R <0.3 year, where R P increased significantly with increasing Z R. In stratified lakes, increasing relative depth correlated with reduced P retention capacity, demonstrating the complex nature of phosphorus biogeochemistry in lake ecosystems.