Investigating the potential for groundwater from different vegetation, soil and landuses to stimulate blooms of the cyanobacterium, Lyngbya majuscula, in coastal waters

Over the past decade, toxic blooms of the cyanobacterium Lyngbya majuscula have increased in frequency and severity in south-east Queensland, Australia, with blooms in Deception Bay linked to increased inputs of dissolved nutrients and organic carbon from land-based sources. The current study investigates the potential for groundwater from ten combinations of vegetation, soil and landuses to stimulate L. majuscula growth in Deception Bay. The photosynthetic response (C-14-bicarbonate uptake rate) of L. majuscula to diluted samples of groundwater (1 part groundwater to 19 parts seawater) was measured under laboratory conditions. The results from the present study show that groundwaters from vegetation/soil/landuse systems characterised by acid sulfate soils, exotic pine plantations and Melaleuca vegetation significantly stimulated L. majuscula photosynthesis. These areas typically have low pH and/or high dissolved organic carbon concentrations with strong iron complexation properties, favouring the bioavailability of nutrients. Data from the current study have been incorporated into models and hazard maps to identify areas most vulnerable to the export of nutrients of concern for L. majuscula growth. The hazard maps are part of the Harmful Algal Bloom Policy within the draft South-east Queensland Coastal Management Plan and are aimed at reducing the severity of L. majuscula blooms.