30
The Biogeochemical Theatre - Phosphorus Cycling and Phosphorus Household in Lakes
(2.16)
This first term in Eq. (2.16) is again the dilution equation for a conservative
element, while the second term is the sum of phosphorus loss rates over all
the phyto- and zooplankton populations. By inspection of Equation (2.2), it
is seen that Eq. (2.16) is identical to the typical one-box total phosphorus
loading model if we assume the identity of net sources and sinks term (S,.)
with the terms inside brackets in Eq. (2.16):
Sp = LO'I Q G + Lc5 j B j Z j •
(2.17)
i
j
This relationship between the phosphorus cycling model and the total
phosphorus mass balance is less trivial than it might seem: several models
of nutrient cycling in the plankton community neglect the contribution of
zooplankton to total nutrients, and thereby create serious problems in
maintaining the necessary mass balances between nutrient intake, utilization, and regeneration in the grazer compartments. If zooplankton nutrient
release is modeled merely by the allometric relationships between body size
and release rate (Peters and Rigler 1973), and without any feedback from
the actual nutrient intake via ingested food (e_g., Carpenter and Kitchell
1984), then zooplankton will actually be represented as nonstoichiometric
entities with the ability to spontaneously create nutrient atoms.
2.6 Summary and Conclusions
The main features of common phosphorus mass-balance models based on
the principles of Vollenweider (1968,1976) have been briefly reviewed. It is
shown that predictions from present models, based mainly on the hydraulic
properties of lakes, contain ample amounts of residual variance both in the
predicted lake total P content at a given P loading, and in the predicted
algal biomass at a give total P level. It is proposed that both the retention of
phosphorus and the yield of algal biomass can be viewed as results of biological processes deeply connected with the dynamics of the phosphorus
cycle in the plankton community.
In an attempt to link a dynamic view of the pelagic phosphorus cycle
with the mass-balance concepts of phosphorus loading models, a dynamic
model is formulated which accounts for the partitioning of pelagic phosphorus between major compartments through the processes of uptake,
grazing, and recycling. It is shown that this modeling framework is a valid
augmentation to the single-compartment type of total phosphorus models.
Although arguments of functions have been omitted in the model description above to increase readability, it must be kept in mind that, except for
The Biogeochemical Theatre - Phosphorus Cycling and Phosphorus Household in Lakes
(2.16)
This first term in Eq. (2.16) is again the dilution equation for a conservative
element, while the second term is the sum of phosphorus loss rates over all
the phyto- and zooplankton populations. By inspection of Equation (2.2), it
is seen that Eq. (2.16) is identical to the typical one-box total phosphorus
loading model if we assume the identity of net sources and sinks term (S,.)
with the terms inside brackets in Eq. (2.16):
Sp = LO'I Q G + Lc5 j B j Z j •
(2.17)
i
j
This relationship between the phosphorus cycling model and the total
phosphorus mass balance is less trivial than it might seem: several models
of nutrient cycling in the plankton community neglect the contribution of
zooplankton to total nutrients, and thereby create serious problems in
maintaining the necessary mass balances between nutrient intake, utilization, and regeneration in the grazer compartments. If zooplankton nutrient
release is modeled merely by the allometric relationships between body size
and release rate (Peters and Rigler 1973), and without any feedback from
the actual nutrient intake via ingested food (e_g., Carpenter and Kitchell
1984), then zooplankton will actually be represented as nonstoichiometric
entities with the ability to spontaneously create nutrient atoms.
2.6 Summary and Conclusions
The main features of common phosphorus mass-balance models based on
the principles of Vollenweider (1968,1976) have been briefly reviewed. It is
shown that predictions from present models, based mainly on the hydraulic
properties of lakes, contain ample amounts of residual variance both in the
predicted lake total P content at a given P loading, and in the predicted
algal biomass at a give total P level. It is proposed that both the retention of
phosphorus and the yield of algal biomass can be viewed as results of biological processes deeply connected with the dynamics of the phosphorus
cycle in the plankton community.
In an attempt to link a dynamic view of the pelagic phosphorus cycle
with the mass-balance concepts of phosphorus loading models, a dynamic
model is formulated which accounts for the partitioning of pelagic phosphorus between major compartments through the processes of uptake,
grazing, and recycling. It is shown that this modeling framework is a valid
augmentation to the single-compartment type of total phosphorus models.
Although arguments of functions have been omitted in the model description above to increase readability, it must be kept in mind that, except for