Thesis
Nitrogen sources, attenuation, and management in subtropical coastal waterways
Southern Cross University
Doctor of Philosophy (PhD), Southern Cross University
2021
DOI:
https://doi.org/10.25918/thesis.176
Metrics
203 File views/ downloads
244 Record Views
Abstract
Land use modifications and disturbed drainage alter natural nitrogen pathways and the way wetlands such as mangroves remove nitrogen from estuaries. This thesis investigated nitrogen sources, attenuation and groundwater exchange in specific Australian subtropical waterways experiencing rapid land use change. The thesis was organized into four data chapters. First, I tested the efficiency of a mangrove-dominated estuary in removing dissolved nitrogen before, during and after a rain event. The results suggested a conversion of upstream nitrogen oxides (NOx) into ammonium (NH4) and dissolved organic nitrogen (DON) likely due to tidally-driven pore water exchange within the anoxic estuarine mangrove sediments. Second, I assessed groundwater exchange and associated nitrogen (N) fluxes in a coastal canal estate versus a nearby mangrove creek using time series observations of radium isotopes and dissolved nitrogen. This research revealed that mangroves were more efficient at retaining groundwater-derived nitrogen than vegetation-stripped, sandy canals. Land reclamation for canal estate development not only drives losses of ecosystem services but also modifies groundwater and related nitrogen exchange. Third, I examined spatial and temporal drivers of coastal stream nitrogen loads across a subtropical land-use gradient using the isotopic compositions of nitrate and radon (a groundwater tracer) over contrasting hydrological conditions. I found intensive agricultural land use and episodic rainfall events were the major spatial and temporal drivers of nitrogen loads. Finally, I tested whether a new woodchip bioreactor approach can attenuate the highly concentrated nitrogen effluent without producing nitrous oxide (N2O) from rapidly expanding horticultural operations. These trial bioreactors were not significantly swapping aquatic nitrogen for the greenhouse gas nitrous oxide. The bioreactor achieved one of the highest nitrate removal rates recorded in the field trial, likely due to the warm conditions and high starting nitrate concentrations. Overall this thesis exemplified the importance of land use characteristics and hydrology when assessing the chemistry of waterways. The results in this thesis determined how nitrogen loads link with land cover, fertilizer input, sewage water injected agriculture and rainfall events in subtropical Australian waterways. Both mangroves and woodchip bioreactors can play a role in mitigating nitrogen pollution reaching the coast.
Details
- Title
- Nitrogen sources, attenuation, and management in subtropical coastal waterways
- Creators
- Praktan Damodar Wadnerkar
- Contributors
- Isaac R Santos (Supervisor) - Southern Cross UniversityChristian Sanders (Supervisor) - Southern Cross University
- Awarding Institution
- Southern Cross University; Doctor of Philosophy (PhD)
- Theses
- Doctor of Philosophy (PhD), Southern Cross University
- Publisher
- Southern Cross University
- Number of pages
- 160
- Identifiers
- 991012977170902368
- Copyright
- © Praktan D. Wadnerkar 2021
- Academic Unit
- Faculty of Science and Engineering; National Marine Science Centre
- Resource Type
- Thesis