Salinity Intrusion and Seasonal Water Quality Variations in the Tidal ...

DIN.
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4.2.1.5 Stoichiometric derivations from nonconservative fluxes
In order to gain insight into processes, two variables are derived from DIP and
The first of these is primary production minus respiration (p-r), sometimes also
designated as net ecosystem metabolism (NEM): This is derived as -(C: P) part X DIP, where
le: P) part is the molar composition ratio of locally reacting organic matter. The assumption
behind this calculation is that net system production or oxidation of organic matter is the
primary nonconservative uptake (flux from the system, so -) or release (+) pathway for DIP
within the system.
The second such derived variable is the difference between nitrogen fixation and
denitrification (nfix-denit) and is calculated as DINobs - DINexp. DINobs is the observed
nonconservative flux of DIN, and DINexpis the flux that would be expected ifthe only flux
pathway were the production or consumption oforganic matter with an N:P ratio represented
by (N:P)part. Thus: (nfix-denit) = DINobs - DIP x (N: P) part. In general, the C: N: P ratio of
plankton (C: N: P = 106:16:1) is used for both of the above calculations, although this ratio
may be modified for systems for which more appropriate ratios are known. The assumptions
behind these calculations are discussed at length in Gordon et al. (1996).
The initial units follow from the hydrographic fluxes and are therefore most
conveniently reported as moles/time. Because the data are used for comparisons among
systems, it is usually useful to divide the initial units by system area, yielding mol length"
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tIme.
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