A mathematical model of the phosphorus cycle in Lake Loosdrecht and simulation of additional measures

Abstract

The phosphorus cycle in the ecosystem of the shallow, hypertrophic Loosdrecht lakes (The Netherlands) was simulated by means of the dynamic eutrophication model PCLOOS. The model comprises three algal groups, zooplankton, fish, detritus, zoobenthos, sediment detritus and some inorganic phosphorus fractions. All organic compartments are modelled in two elements, carbon and phosphorus. Within the model system, the phosphorus cycle is considered as completely closed. Carbon and phosphorus are described independently, so that the dynamics of the P/C ratios can be modelled. The model has been partly calibrated by a method based on Bayesian statistics combined with a Range Check procedure.Simulations were carried out for Lake Loosdrecht for the periods before and after the restoration measures in 1984, which reduced the external phosphorus loading to the lake from ca. 2 mgP m-* d-' to lmgPm-*d-l.The model outcome was largely comparable with the measured data. Total phosphorus has slowly decreased from an average 130 PgP l-' to ca. 80 PgP l-', but chlorophyll-a (ca. 15opg1-', summer-averaged) and seston concentrations (8-15 mgC l-') hardly changed since the restoration measures. About two-thirds of the seston consisted of detritus, while the phytoplankton remained dominated by filamentous cyanobacteria. The P/C ratio of the seston decreased from ca. 1.0% to 0.7 %, while the P/C ratios of zooplankton, zoobenthos and fish have remained constant and are much higher. The system showed a delayed response to the decreased phosphorus loading until a new equilibrium was reached in ca. five years. Major reasons for the observed resilience of the lake in responding to the load reduction are the high phosphorus assimilation efficiency of the cyanobacteria and the high internal recycling of phosphorus. A further reduction of nutrient loading, perhaps in combination with additional measures like biomanipulation, will be the most fruitful additional restoration measure.

The dynamics and role of limnetic zooplankton in Loosdrecht lakes (The Netherlands)

“…Lake Tjeukemeer which has a net P-retention of about 10% of the external-P load of 25-50 mg P m -2 d-' (Van Huet, 1991). This is more than an order-of-magnitude higher than the net daily retention calculated for the Lake Loosdrecht by Janse et al (1992). Moreover, the total-P concentration in the Tjeukemeer is also much higher (Lammens et al, 1992).…”

Restoration and resilience to recovery of the Lake Loosdrecht ecosystem in relation to its phosphorus flow

“…A conceptual model of phosphorus cycling through various ecosystem compartments was made as presented below. Using various parameters measured in water and various compartments of the ecosystem, a mathematical model was developed (Janse & Aldenberg, 1990). This model output was compared with empirical data, in order to test its possibilities to simulate further water management measures in L. Loosdrecht (Janse et al, 1992).…”

“…Using various parameters measured in water and various compartments of the ecosystem, a mathematical model was developed (Janse & Aldenberg, 1990). This model output was compared with empirical data, in order to test its possibilities to simulate further water management measures in L. Loosdrecht (Janse et al, 1992). The needs for further (and additional) measures to restore Loosdrecht lakes are indicated.…”

Making eco logic and models work : an integrative approach to lake ecosystem modelling

“…PCLake has originally been developed to describe the nutrient cycles of Lake Loosdrecht in the Netherlands as part of the WQL project (Water Quality research Loosdrecht Lakes; Janse and Aldenberg, 1990;Janse et al, 1992). The WQL project was basically a comprehensive system analysis aimed at understanding the mechanisms of the eutrophication process, and evaluating the effect of recovery measures (Fig.…”

“…PCLake is originally the product of large multidisciplinary research program on the eutrophication and restoration of the Loosdrecht Lakes in the Netherlands (Janse and Aldenberg, 1990;Janse et al, 1992). This WQL project ran from 1979 to 1990 and resulted in the publication of more than 130 scientific papers (Van Liere, 1992).…”