N.2 Hydrolysis

Hydrolysis is the pelagic biological conversion of labile particulate organic matter to labile dissolved organic matter. It is therefore a source of dissolved carbon, nitrogen and phosphorus, and a sink of the corresponding particulates. Hydrolysis neither consumes or produces dissolved oxygen or bioavailable inorganic nutrients. Hydrolysis is implemented within the labile organics constituent model of the WQ Module, and the term organic matter in this section therefore refers to labile organic matter. Refractory organic matter processes are described elsewhere.

The pelagic hydrolysis rate is computed within the labile organics constituent model via Equation (N.2).

\[\begin{equation} \left.\begin{aligned} R_{hyd\langle computed\rangle}^{POC} =& R_{hyd}^{POC} \times \frac{\left[DO\right]}{K_{hyd-O_2}^{POM} + \left[DO\right]} \times \hphantom{\text{ab}} \left[\theta_{hyd}^{POM}\right]^{\left(T-20\right)} \\ \\ R_{hyd\langle computed\rangle}^{PON} =& R_{hyd}^{PON} \times \frac{\left[DO\right]}{K_{hyd-O_2}^{POM} + \left[DO\right]} \times \hphantom{\text{ab}} \left[\theta_{hyd}^{POM}\right]^{\left(T-20\right)} \\ \\ R_{hyd\langle computed\rangle}^{POP} =& R_{hyd}^{POP} \times \underbrace{\frac{\left[DO\right]}{K_{hyd-O_2}^{POM} + \left[DO\right]}}_{\text{Influence of oxygen}} \times \underbrace{\vphantom{\frac{\left[DO\right]}{K_{sed-O_2}^{NO_3} + \left[DO\right]}} \hphantom{\text{ab}} \left[\theta_{hyd}^{POM}\right]^{\left(T-20\right)}}_{\text{Influence of temperature}} \end{aligned}\right\} \tag{N.2} \end{equation}\] \(R_{hyd}^{POC}\), \(R_{hyd}^{PON}\) and \(R_{hyd}^{POP}\) are the user specified particulate organic carbon, nitrogen and phosphorus hydrolysis rates at 20\(^o\)C without the influence of dissolved oxygen, \(\left[DO\right]\) is the ambient dissolved oxygen concentration, \(K_{hyd-O_2}^{POM}\) is the user specified half saturation concentration of dissolved oxygen for particulate organic matter hydrolysis, \(\theta_{hyd}^{POM}\) is the corresponding temperature coefficient, and \(T\) is ambient water temperature. As per sediment fluxes, the values of \(K_{hyd-O_2}^{POM}\) and \(\theta_{hyd}^{POM}\) are intentionally applied equally to particulate organic carbon, nitrogen and phosphorus hydrolysis. This is because there is one (not three) biological consumption process that generates these constituents: \(K_{hyd-O_2}^{POM}\) and \(\theta_{hyd}^{POM}\) apply to this single process. In a similar vein, the user specifications for \(R_{hyd}^{POC}\), \(R_{hyd}^{PON}\) and \(R_{hyd}^{POP}\) should not vary significantly in their relative proportions from the ratio that these typically occur in the organic matter being consumed (e.g. the Redfield ratio).

N.2.1 Consumption

The hydrolysis rates from Equation (N.2) are multiplied by their respective ambient particulate organic matter concentrations to compute their respective consumptive fluxes (losses) at each model timestep in each model cell via Equation (N.3).

\[\begin{equation} \left.\begin{aligned} \href{AppDiags.html#WQDiagPOCHydrol}{F_{hyd\langle computed\rangle}^{POC}} =& R_{hyd\langle computed\rangle}^{POC} \times \left[ POC \right] \\ \\ \href{AppDiags.html#WQDiagPONHydrol}{F_{hyd\langle computed\rangle}^{PON}} =& R_{hyd\langle computed\rangle}^{PON} \times \left[ PON \right] \\ \\ \href{AppDiags.html#WQDiagPOPHydrol}{F_{hyd\langle computed\rangle}^{POP}} =& R_{hyd\langle computed\rangle}^{POP} \times \left[ POP \right] \end{aligned}\right\} \tag{N.3} \end{equation}\]

N.2.2 Production

The consumptive fluxes from Equation (N.3) result in the dissolved organic productive fluxes in Equation (N.4).

\[\begin{equation} \left.\begin{aligned} F_{hyd\langle computed\rangle}^{DOC} =& F_{hyd\langle computed\rangle}^{POC} \\ \\ F_{hyd\langle computed\rangle}^{DON} =& F_{hyd\langle computed\rangle}^{PON} \\ \\ F_{hyd\langle computed\rangle}^{DOP} =& F_{hyd\langle computed\rangle}^{POP} \end{aligned}\right\} \tag{N.4} \end{equation}\]