NPZ-model/State-Variables.md

@@ -11,6 +11,15 @@ The NPZ (Nutrients, Phytoplankton, Zooplankton) model is based on the model that
 ## Dissolved inorganic nitrogen (DIN)
 Dissolved inorganic nutrients (DIN) is the sum of NO<sub>2</sub>, NO<sub>3</sub> and NH<sub>4</sub>. The unit is mmol-N m<sup>-3</sup>. DIN is used by phytoplankton and microphytobenthos for primary production (DINuptake and DINupMPB, respectively). DIN is released by mineralization of detritus in the water column (Mineralization) and in the bottom (BotMin) and respiration by zooplankton (ZooExcretion) and shellfish (DINprod). 
 
+```mermaid
+graph TD;
+  A-->B;
+ DIN -- DINuptake --> Phyto
+  A-->C;
+  B-->D;
+  C-->D;
+```
+
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 ## Phytoplankton (Phyto)
 Phytoplankton is composed of microalgae in the water column that are transported by tidal currents. The unit of phytoplankton is mmol-N m<sup>-3</sup>. Phytoplankton increases by primary production (DINuptake). Phytoplankton is consumed by zooplankton (ZooGrazing) and shellfish (GrazingPhy). Also phytoplankton can sink to the bottom (SinkPhy), where it becomes part of the bottom detritus (Bot_Det).
@@ -38,4 +47,3 @@ Three shellfish species are included in the model, mussels (Mus), Pacific oyster
 The shellfish populations are controlled by a variable mortality (MortShellfish) which is a function of the total stock and the carrying capacity. 
 
 [top](NPZ model)
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