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 in the world, but have been relatively little studied. Now, however, there is pressure for further development of these tropical land and water resources. To avoid repeating management mistakes that have been made elsewhere, it is essential to improve our understanding of how these rivers function. As part of the Tropical Rivers and Coastal Knowledge Research hub, we studied flow, nutrients, and primary production in the Daly River (N.T.), a perennial tropical river maintained in the dry season by ground-water and developed a dynamic simulation model to predict the coverage and biomass of each of five key plant and algae groups in the river. Flow is the key driver in this model, controlling both 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 hence higher 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 discuss what this might mean for the river's future.