Carbon-Nutrient Balance Model

Several studies have tested hypotheses derived from the CNBM by manipulating the availability of resources (nutrients or light) either in laboratory or in field experiments (Table 7.3). The phlorotannin content in F. vesiculosus at sites with naturally low nitrogen levels was decreased when seaweeds were fertilized in the 

Reference Species Order Treatment Dependent variable 

Ilvessalo and Fucus vesiculosus Fucales Observation Phlorotannins 

Cronin and Hay 1996c Dictypta ciliolata Dictyotales N Terpenoids 

Puglisi and Paul 1997 Portieria homemanmi Gigartinales N, P, K Monoterpenes 

---

Table 7.3 Published studies explicitly testing hypotheses derived from the Carbon-Nutrient Balance Model concerning variation in the concentration of secondary metabolites in different macroalgal species...

Since there are no standards for flux determinations, as there are for chemical concentration measurements in water or sediments, evaluating their accuracy is difficult. One is forced to rely on comparison of different anal5dical approaches and modeling of nutrient and oxygen distributions to achieve a consensus. Of the different methods used to determine the organic carbon export presented in the following section, the first two (sediment traps and thorium isotope disequilibria) are used to evaluate the POC flux only. They must be combined with estimates of the DOC flux to achieve the total. The second two methods, molecular oxygen and carbon isotope mass balance, determine the sum of DOC and POC export. 

The present model is based on mass balances for three main components representing phytoplankton (A), nutrients (E), and organic phosphorus (C), which can describe phosphorus cycle within a water body as follows. Phytoplankton biomass is produced by the photosynthesis reaction, consuming nutrients (in lakes and reservoirs, the limiting nutrient is phosphorus) and dissolved carbon dioxide, with solar radiation and adequate temperature. Upon death, phytoplankton biomass increases the pool of organic phosphorus, which is in turn converted to phosphate by mineralization bacteria. The model has several kinetic parameters that have to be estimated based on collected data from the specific reservoir under study. 

---