Oral Presentation Australian Freshwater Sciences Society Conference 2022

Testing microalgae responses to point and non-point sources of nutrient pollution to enhance nutrient offsetting schemes (#84)

Jing Lu 1 , Alexandra Garzon-Garcia 2 , Jo Burton 2 , Cameron Jackson 3 , Ann Chuang 1 , Michael Newham 2 , Philip Bloesch 2 , Ian Ramsay 2 , Jenny Rogers 4 , Merran Griffith 4 , Emily Saeck 5 , Michele Burford 1
  1. Australian Rivers Institute, Nathan, Queensland, Australia
  2. Department of Environment and Science, Brisbane, Queensland, Australia
  3. Urban Utilities, Brisbane, Queensland, Australia
  4. Sydney Water, Sydney, New South Wales, Australia
  5. Healthy Land and Water, Brisbane, Queensland, Australia

Population growth of Australian cities and increasing development of water-intensive industries is driving an increase in point source nutrient discharges. Upgrading wastewater treatment works and improving treatment technologies can mitigate only part of this increasing nutrient load. Nutrient offsetting provides a mechanism for mitigating the impact of nutrients from point sources, where nutrient load from a point source can be offset by non-point source (catchment) interventions. However, it is difficult to directly compare the environmental impacts of point source and non-point source nutrients on receiving waters as they enter waterways with different concentrations and proportions of nutrient fractions, which will be assimilated into the environment in different ways. We, therefore, developed a standardized bioassay to compare the algal photosynthetic response to point (sewage treatment plants, aquaculture ponds) and non-point sources (soil erosion) of nutrients to develop better metrics for comparing the assimilation of different nutrient sources. Our key findings are: 1) discharge from the two types of point sources, i.e. sewage treatment plants and aquaculture ponds, had a higher proportion of dissolved inorganic nutrients compared to soil erosion, which had a higher proportion of particulate nutrients; 2) total nutrient or dissolved inorganic nutrient concentrations alone did not correlate well with algal photosynthesis measures; 3) a combination of organic and inorganic nutrients with organic carbon concentrations were found to be highly correlated with algal responses. This suggests that bacterial mediation, via the transformation of organic nutrients to more bioavailable forms, may also be important. Our study has improved our understanding of the difference in ecosystem response to point and non-point sources of nutrients (often referred to as a metric). This is important information for implementing a scientifically robust and defensible nutrient offset program to achieve improved water quality outcomes for waterways.