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Lake Michigan Mass Balance
Eutrophication/Sorbent Dynamics
The eutrophication/sorbent dynamics (ESD) model predicts the production,
transformation, and decay of plankton biomass in response to seasonal
dynamics of temperature, light, and nutrient concentrations. In the open
lake, living and dead plankton comprise the majority of suspended particles
and generate significant autochthonous loads of particulate and dissolved
carbon (POC and DOC) to which PCBs and other contaminants preferentially
partition (Richardson et al., 1983; DePinto et al., 1993). The ESD model
simulates the non-conservative, seasonally-variable dynamics of the biotic
organic carbon pool, which has a significant influence upon partitioning of
HOCs (Dean et al., 1993). Such a model was applied to simulate the
dynamics of organic carbon states in Green Bay as part of the GBMBS (De
Pinto et al., 1993). However, a more resolute, multi-class eutrophication
model (Bierman and McIlroy, 1986) will be applied to Lake Michigan, and the
linkage between plankton and organic carbon states will be refined. Model
outputs include autochthonous solids loads (primary production), and transformation
and decay rates, that will be used as input for the sediment transport and the
contaminant transport and fate models. The biomass growth rates may also be
linked to the plankton bioconcentration submodel of the food web bioaccumulation model
(Richardson et al., 1983; DePinto et al., 1993; Dean et al., 1993;
De Pinto et al., 1993).
The eutrophication/sorbent dynamics model is an important component of the
mass balance model for hydrophobic contaminants, because it simulates the
dynamics of a significant sorbent particle class (phytoplankton) in the
water column. The dynamics of phytoplankton production and loss cannot be
adequately described by seasonal EMP limnological monitoring, which will
occur too infrequently to observe major events such as blooms, assemblage
shifts, and die-offs. Furthermore, the ESD model component will allow
forecasting for integrated toxics and nutrient management options, because
mass balances for toxics and nutrients are coupled via eutrophication/sorbent
dynamics processes. Finally, the ESD model is the appropriate framework
for inclusion of zebra mussels in the mass balance model. Zebra mussels,
which at high density can impact the lower food web and alter sediment and
contaminant transport, are currently (1994) infesting Lake Michigan and
are reaching high densities in areas of suitable habitat such as Green Bay.
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