A Dynamic Model of Primary Production and Plant Coverage in an Oligotrophic Tropical River

Many of Australia's tropical rivers are amongst the most ecologically intact inthe world, but have been relatively little studied. Now, however, there is pressure forfurther development of these tropical land and water resources. To avoid repeatingmanagement mistakes that have been made elsewhere, it is essential to improve ourunderstanding of how these rivers function. As part of the Tropical Rivers and CoastalKnowledge Research hub, we studied flow, nutrients, and primary production in the DalyRiver (N.T.), a perennial tropical river maintained in the dry season by ground-water anddeveloped a dynamic simulation model to predict the coverage and biomass of each of fivekey plant and algae groups in the river. Flow is the key driver in this model, controllingboth loss and growth terms for plants. When flow (and hence shear stress) is high,sloughing and bed-scouring contribute to loss of biomass, while shear stresses (and hencehigher boundary layer thickness) limit the rate of transfer of nutrients to benthic plants.This paper will describe work to understand and model these dynamics, and will discusswhat this might mean for the river's future.