US Long-Term Ecological Research Network
Modelling phytoplankton-zooplankton interactions in Sparkling Lake, USA
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Numerical models commonly applied to simulate water quality in lakes and reservoirs range· from simple ’VOLLENWEIDER’ steady state models (OECD 1982) to more complex coupled models of hydrodynamic and ecological processes (e.g. RILEY \& STEFAN 1988). For the coupled hydrodynamic-ecological lake model applied in this study (DYRESM-WQ), no calibration of the hydrodynamics is required as there is a high degree of process representation of the major transport and mixing phenomena (HAMILTON \& SCHLADOW 1994). However, the level of process description of the major food chain interactions in DYRESM-WQ, in common with similar coupled models (e.g. RILEY \& STEFAN 1988, MRAGOUNIS et al. 1993 ), is overly simplistic and requires further development in order to improve the predictive capabilities of the model. The objective of this study was to introduce zooplankton algorithms into the DYRESM-WQ model so that interactions of phytoplankton and zooplankton could be simulated. The new version of the model has been applied to Sparkling Lake in Wisconsin, USA. This approach provides a basis for understanding the physiological importance of diurnal migration by zooplankton and the role that zooplankton play in regulating phytoplankton biomass (DESTASIO et al. 1993). DYRESM is a one dimensional, process-based hydrodynamic model thatsimulates the vertical distribution of temperature and salinity in lakes using a series of horizontal layers (IMBERGER \& PATTERSON 1981). In DYRESM-WQ the hydrodynamic component is coupled with algorithms for phytoplankton biomass (chlorophylla), nutrients (P04-P, NOrN, NH4-N, TN and TP), dissolved oxygen and BOD (HAMILTON \& SCHLADOW 1994). These state variables interact through time-varying, interdependent conservation equations that require calibration for each new lake, in contrast to the hydrodynamic equations.