J.5 Silicate

Equation (J.17) is used to compute \(L_{sil}^{phy}\), if phytoplankton is configured to take up silicate. Specifying silicate limitation parameters will trigger the WQ Module to take up silicate (Section 4.7.3.5.1.6).

\[\begin{equation} L_{sil}^{phy} = \frac{\left(\left[Si\right] - \left[Si\right]_{min}\right)}{\left(\left[Si\right] - \left[Si\right]_{min}\right) + K_{lim-Si}^{phy}} \tag{J.17} \end{equation}\] \(\left[Si\right]\) is the ambient silicate concentration. \(\left[Si\right]_{min}\) is the silicate concentration below which phytoplankton no longer is permitted to uptake silicate and \(K_{lim-Si}^{phy}\) is the half saturation silicate concentration for phytoplankton uptake.

\(K_{lim-Si}^{phy}\) is specified as a silicate concentration. When this concentration is equal to the difference between the relevant ambient concentration and \(\left[Si\right]_{min}\), i.e. when

\[\begin{equation} K_{lim-Si}^{phy} = \left[Si\right] - \left[Si\right]_{min} \tag{J.18} \end{equation}\]

then \(L_{sil}^{phy}\) = 0.5. The form of \(L_{sil}^{phy}\) with varying \(\left[Si\right]_{min}\) and \(K_{lim-Si}^{phy}\) is provided in Figure J.5, for constant \(\left[Si\right]_{avail}\) = 1.0 mg/L.

Figure J.5: Move the slider to see the effect of changing \(K_{lim-Si}^{phy}\) on the computed silicate limitation function