PE EIE[R-Rg RESEARCH ON - HJ Andrews Experimental Forest

The net rate of primary production at any
particular depth depends upon the temperature,
light intensity, essential nutrient concentration,
and zooplankton grazing pressure a t
that depth. The vertical distribution an d
abundance of phytoplankton is thus a functio n
of varying net production, sinking rates of algae
and mixing dynamics of the water column . Th e
total production per unit area of lake surfac e
may be obtained by integrating the concentration
of phytoplankton from top to bottom .
The next step is to incorporate the size selective
feeding of zooplankton and determine it s
effect upon production (since algal cells o f
different sizes possess varying capacities t o
absorb nutrients) .
The effective grazing rate by zooplankto n
is modeled as a function of the phytoplankton
density (at high densities the zooplanktons
feeding structures become saturated) .
The efficiency of assimilation of phytoplankton
by zooplankton is also allowed to depen d
upon algae abundance (efficiency decrease s
with increasing abundance) .
The overall model relating the phytoplankton,
zooplankton, and nutrients is a system o f
partial differential equations (in time and
depth) .
The submodel describing the physical
cycling of nutrients (developed in the botto m
related processes group) is an integral part of
the phytoplankton, zooplankton submodels .
The number and kinds of heterotrophi c
bacteria will be assessed to give some information
on the constancy of community structure
of the decomposers . The utilization an d
ultimate destruction of fixed organic material
for the entire system will be estimated by
respiration studies and verified by substrat e
disappearance . The respiration an d
heterotroph abundance values will also be correlated
with the regeneration of nutrients .
The nutrient budget and effective concentrations
will be assessed . All of the above studie s
will be carried out in units of biomass or wil l
be convertible to biomass and units of carbo n
by calculation of size distribution. Determinations
of the magnitude of nitrogen transformation
within each of the above compartments,
as well as the search for evidence nitrogen
fixation and its opposite process, denitri -
fication, will be made .
The detailed carbon cycle through th e
phytoplankton, zooplankton, bacteria and
pools of dissolved inorganic carbon, dissolved
organic carbon, and detritus are bein g
modeled initially with a varying rate compartment
system. The rates of flow between th e
compartments are to be functions of light ,
temperature, and P0 4 and NO 3 concentrations.
Later the rates will also be modeled a s
functions of 0 2 and Si concentration. Thi s
model will allow an analysis of what paths o f
the cycling process limit the rate of
production .
Bottom Related Process Studie s
The compartments are shown in figure 9 .
The necessary chemical analyses to assess thi s
aspect of the nutrient budget will also be
done. Inputs of detrital materials to the sediments
and their potential incorporation int o
higher food chains via bottom invertebrates t o
the fish will be assessed . The oxidation of
organic material will be assessed by respiration
rates of the sediments. The disappearanc e
of substrates such as cellulose and chitin an d
information on the bacteria associated wit h
Figure 9 . Categories and relationships of sub-syste m
(C)b ; bottom related processes.
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