Over the past three years, the University of Western Australia (UWA) has carried out stormwater and groundwater sampling projects around Broome’s Roebuck Bay to assess their link to toxic blue-green algae growth.
Lyngbya Majuscula (blue-green algae) is known to have impacts on human health and scientists are beginning to better understand its impact on biodiversity.
The data gathered in these projects is informing the development of a modelling tool for the key ecological processes involved in the dynamics of Lyngbya biomass in coastal waters.
Rangelands NRM through funding from the National Landcare Program and the Department of Parks and Wildlife supported the work of UWA scientists on the modelling tool which will help to better understand the catchment and manage its health, in particular the interplay between nutrients entering the bay, environmental factors and Lyngbya growth.
Long-term monitoring, at least two years of detailed spatially extensive Lyngbya biomass data along with nutrient, catchment and environment data, would be desirable to validate the model.
The initial sampling work received logistical support from the Shire of Broome and local community volunteers, particularly the Roebuck Bay Working Group and Yawuru Rangers.
The data suggests that Roebuck Bay’s intertidal zone is a suitable ecological niche for Lyngbya blooms and that existing levels of anthropogenic nutrients can create blooms (Fig.1). In fact, UWA scientists (Assoc. Prof Ryan Vogwill, Assoc. Prof Matt Hipsey and PhD student Gayan Gunaratne) conclude that nutrients from groundwater and stormwater, combined with Roebuck Bay’s hydrodynamics, facilitates the observed Lyngbya blooms.
Preliminary modelling results are helping to understand why Lyngbya growth begins before the first stormwater flows. A number of factors may be contributing, in particular, groundwater discharge.
The intertidal zone is typically covered with a film of water during tidal exposure. This occurs as much of the intertidal zone is receiving submarine groundwater discharge all year round, which is likely rich in nutrients in places located immediately down gradient from the Broome peninsula’s wastewater treatment plant and golf course irrigated with treated wastewater (Fig 2).
This is creating an appropriate habitat for Lyngbya growth. It is also likely that enhanced biomass growth as continuous submarine groundwater discharge and episodic stormwater runoff would deliver elevated nutrient concentrations during the wet season sufficient to facilitate blooms.
The research is still a work in progress, but this preliminary stage will conclude shortly.
From it UWA are expected to highlight the data limitations so ongoing investigations into Lyngbya dynamics can be better targeted.
For now, catchment management will focus on reducing groundwater and/or surface water nutrient loads and the impact to Lyngbya distribution and biomass.
Lyngbya majuscula. Courtesy of WA Department of Parks and Wildlife.
Figure 1 - Roebuck Bay Lyngbya sampling sites showing biomass densities.
Figure 2 - Groundwater discharge in Roebuck Bay. Figures courtesy of UWA.