Relationships between groundwater composition and stimulation of the cyanobacterium Lyngbya majuscula

The Pumicestone Passage/Deception Bay region of southeast Queensland, Australia, has experienced increased frequency and severity of blooms of the toxic benthic cyanobacterium Lyngbya majuscula. It is hypothesised that blooms are the result of landuse changes in the surrounding catchments leading to increased nutrient and organic matter loads to waterways. Previous studies investigating the response of L. majuscula to diluted groundwaters from across Deception Bay/Pumicestone Passage showed groundwater from acid sulfate soils, exotic pine plantations and Melaleuca vegetation significantly stimulated L. majuscula photo - synthetic response in laboratory bioassays. The results of the previous study are expanded by investigating the composition of these 74 groundwaters to ascertain what factors contribute to the observed differences in L. majuscula response. A multiple regression analysis showed the total iron, pH, conductivity, total phosphorus and dissolved organic carbon contents in groundwater accounted for 58% of the variation in L. majuscula response. Total iron content of the groundwater had the highest correlation accounting for 28% of the variation in response. Other significant correlations included ammonium nitrogen, total phosphorus and electrical conductivity. Significant responses to iron, phosphorus and nitrogen concentrations in experiments involving addition of pure chemicals has previously been found for both laboratory based bioassays and in situ field experiments. The response to electrical conductivity is probably the result of a correlation with acid sulfate soils whose groundwater has been shown to significantly stimulate L. majuscula response. As landholders commonly identify and manage land through vegetation, soils, geology and landuse, these categories were used to statistically assess groundwaters. Based on the groundwater relationships, land with Melaleuca, pine or Casuarina vegetation, or with Hydrosols, Podosols or acid sulfate soils present, or formed from marine sediments, needs to be carefully managed to limit nutrient export that could boost L. majuscula growth Our conclusions can be used to confirm or adjust hazard ratings in the Nutrient Hazard Model. q cyanobacteria, groundwater, growth, landuse, Lyngbya majuscula, Moreton Bay, nutrients