Modelling the spatial and temporal variability of diatoms in the River Murray

We have developed a simple mechanistic model, which simulates the temporaland spatial variability of concentrations of the diatomAulacoseira granulata in the River Murray, NSWAustralia, over large distances under different flow conditions. The modelincorporates a simple growth function determined by the availabilities ofsilica and light, and by temperature. It also includes losses due tosinking and downstream advection. The model is tested against weeklymeasurements for the period 1981-1990, at three sites separated by 1100 km.The seasonal cycle of Aulacoseira concentrations alongthe river is well represented by the model. During times of high flow, theconcentrations of Aulacoseira remain fairly uniformalong the river as the diatoms have insufficient time to grow before beingadvected downstream.