『Abstract
There is a vast body of knowledge that eutrophication of lakes
may cause algal blooms. Among lakes, shallow lakes are peculiar
systems in that they typically can be in one of two contrasting
(equilibrium) states that are self-stabilizing: a ‘clear’ state
with submerged macrophytes or a ‘turbid’ state dominated by phytoplankton.
Eutrophication may cause a switch from the clear to the turbid
state, if the P loading exceeds a critical value. The ecological
processes governing this switch are covered by the ecosystem model
PCLake, a dynamic model of nutrient cycling and the biota in shallow
lakes. Here we present an extensive analysis of the model, using
a three-step procedure. (1) A sensitivity analysis revealed the
key parameters for the model output. (2) These parameters were
calibrated on the combined data on total phosphorus, chlorophyll-a,
macrophytes cover and Secchi depth in over 40 lakes. This was
done by a Bayesian procedure, giving a weight to each parameter
setting based on its likelihood. (3) These weights were used for
an uncertainty analysis, applied to the switchpoints (critical
phosphorus loading levels) calculated by the model. The model
was most sensitive to changes in water depth, P and N loading,
retention time and lake size as external input factors, and to
zooplankton growth rate, setting rates and maximum growth rates
of phytoplankton and macrophytes as process parameters. The results
for the ‘best run’ showed an acceptable agreement between model
and data and classified nearly all lakes to which the model was
applied correctly as either ‘clear’ (macrophyte-dominated) or
‘turbid’ (phytoplankton-dominated). The critical loading levels
for a standard lake showed about a factor two uncertainty due
to the variation in the posterior parameter distribution. This
study calculates in one coherent analysis uncertainties in critical
phosphorus loading, a parameter that is of great importance to
water quality managers.
Keywords: Shallow lakes; Ecosystem model; Hysteresis; Sensitivity
analysis; Uncertainty analysis; Bayesian inference; Phosphorus;
Critical loading; Alternative stable states』
1. Introduction
1.1. Eutrophication of lakes
1.2. Uncertainty
2. Methods
2.1. Model description
2.2. Analysis set-up
2.3. Sensitivity analysis
2.4. Bayesian calibration
2.5. Uncertainty analysis
3. Results
3.1. Sensitivity analysis
3.2. Bayesian calibration
3.3. Comparison for some other lakes
3.4. Uncertainty analysis
4. Discussion
4.1. Model structure and model analysis
Acknowledgements
References