Plant biomass and nutrient dynamics: modelling blooming phenomenon

There is an increasing public awareness of the very strong pressures that aquatic ecosystems are experiencing because of direct and indirect influences from rapid population growth. The signs that there are problems in such ecosystems are already obvious: changes in biodiversity, decreased water availability, increased salinity and general deterioration in the catchment environment. In addition, such areas already experience instances of poor water quality caused by changes in chemical nutrients from the redeployment of land for urban, industrial and agricultural uses. Aquatic ecosystems such as catchments are essential for the health, wellbeing and diversity of the coastal and marine environment. Variations in the conditions in these environments from increased pollution, changing weather and long term climatic trends has altered the biodiversity and abundance of species found. Selner et al. (2003) documented the shift in climatic and pollution trends which are favourable for algae blooming. The National Land and Water Resources Audit also confirms this link in the Australian Catchment, River and Estuary Assessment. Catchments comprise dynamic estuaries which currently suffer under eutrophication due to excessive nutrients from run-off and storm water input. An increase in primary production through excessive or- ganism growth is the general outcome of an increased nutrient flux of either Phosphorus (P) or Nitrogen (N). The addition of excess nutrients to high nutrient ecosystems creates a negative response in benthic species such as seagrass because of secondary light limitation from shading due to algae blooms. In this paper, the consequences of blooming experienced in aquatic ecosystems due to changes in temperature and chemical nutrient dynamics is modelled by a Lotka-Volterra type system. The aim of this paper is to use this system to address aspects of competition between seagrass and filamentous algae. Accounting for the dynamics of species in estuaries proves to be an effective measure of the overall risk from increased nutrient and changing temperature fluxes. Integrating this component into a whole catchment model could potentially provide a useful tool in reducing the uncertainty around optimal man- agement practices for controlling excess nutrient loads from storm water and run-off.