Evaluating the Hypotheses of the Steady-state Phosphorus Models for Lakes

Abstract:

Lake eutrophication is one of the most pressing global water issues due to increased levels of nutrients. Phosphorus (P) is considered as the key nutrient and modeling P in lakes provides a valuable decision-making support tool for lake eutrophication management. During the past half a century, different hypotheses have been used for steady-state (Vollenweider-type) models of P concentration in lakes. Four main competing hypotheses are: (i) modeling P loss as a decay process in the volume of the lake vs. a sedimentation process over the area of the sediments, (ii) modeling the lake as a continuously mixed-flow reactor vs. a plug-flow reactor, and (iii) modeling P loss as a first-order reaction vs. a second-order reaction, and (iv) considering a fraction of P as fast sedimentation particles or not. We combine these hypotheses to develop 16 models. Combining a large database (n=738) from literature, we calibrate the models and compare the hypotheses of the models. The best-performing model considers the lake as a mixed-flow reactor and the P loss as a decay process over the volume of the lake. It also combines the second-order reaction hypothesis with the hypothesis that a constant fraction of P is associated with fast settling particles. Each of the hypotheses underlying the best model outperforms the competing hypotheses in the pairwise comparison of them as well.