Modeling agricultural non-point source pollution at catchment scale: application, novel calibration and model advancement

Modeling agricultural non-point source pollution at catchment scale: application, novel calibration and model advancement

Agricultural non-point source pollution is the primary cause of water quality impairment around the world, with far-reaching ecological impacts on aquatic ecosystems and toxicological consequences for humans and living organisms. Especially the Great Barrier Reef (GBR)– the world's largest coral reef– is severely affected by increased sediment and nutrient loads due to agricultural intensification in its coastal catchments. Reducing pollution discharge to the reef is critically essential for reversing the decline of the reef ecosystem and maintaining its economic benefits. However, due to the heterogeneity of natural systems and anthropogenic activities, reducing the pollution discharge to the reef requires developing on-farm and off-farm strategic planning at various scales. Previous studies have investigated and documented the effectiveness of on-farm management strategies. However, on-farm management practices have not been widely adopted by landholders. Modeling studies in the region also indicate that even if all the on-farm management practices were adopted, it would still be inefficient to meet reduction targets under future climate change and land use change scenarios. Therefore, off-farm management practices, including reforestation and wetland restoration/creation, have been recently proposed as supplementary solutions for reducing pollution to the reef, but their effectiveness in reducing pollution needs to be quantified for the catchment scale implementation. My aim in this research is to investigate the impact of reforestation and wetland restoration/ creation on reducing sediment and nutrient loads to the GBR at the catchment scale. I addressed this goal by 1) quantifying the impact of reforestation on the spatiotemporal sources of sediment and soil erosion, 2) quantifying the role of groundwater and surface water in nitrate cycling necessary for implementing effective management practices, and 3) quantifying the role of wetlands restoration and creation in reducing nutrient loads to the GBR. The research also contributes to 1) developing an effective calibration technique to overcome the high dimensionality of complex hydrogeochemical models, 2) advancing a widely known hydrogeochemical model to simulate groundwater-wetland interactions in terms of exchanging flow and nitrate loads.

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