The Effect of Riparian Zones on Nitrate Removal by Denitrification at the River Basin Scale

At the interface between terrestrial and aquatic ecosystems, the riparian zone plays an important role in nitrogen removal, despite the minor proportion of the land area that it covers. Very limited studies are carried out in modelling these effects at the river basin scales. The Soil and Water Assessment Tool (SWAT) is a well-known river basin scale model to simulate hydrological processes and nutrient dispersal. So far, SWAT followed a lumped approach that did not take into account the effect of the particular position of the hydrological units and their interaction, which implied that SWAT could not model riparian zones as discrete units and take into account the effects from upland areas.
This thesis presents two modifications in SWAT: (i) an approach to represent landscape variability and landscape routing across different landscape units, and (ii) a Riparian Nitrogen Model that simulates the denitrification process in riparian zones. This enhanced landscape SWAT model, referred to as SWAT_LS, was tested on a hypothetical case study and then applied to the Odense river basin, an agriculture-dominated and a densely tile-drained river basin.
Case study results show that SWAT_LS is able to evaluate the effect of denitrification in riparian zones, taking into account their specific locations as interfaces between terrestrial and aquatic ecosystems. These modifications enable the SWAT model to be used for flow and nitrogen modelling in riparian zones.

Linh Hoang (31 December, 1983, Ho Chi Minh City, Vietnam) did her bachelor degree on Environmental Management in the Faculty of Environment, Ho Chi Minh City University of Technology, Vietnam. After graduation, she worked as an assistant lecturer and also joined several projects on water quality monitoring and management and Environmental Impact Assessment before winning the Huygens scholarship from the Dutch government to pursue her Master in Hydroinformatics at UNESCO-IHE Institute for Water Education, Delft, the Netherlands. She did her Master thesis using the Soil and Water Assessment Tool (SWAT) on river basin modelling integrating with water quality modelling. Then she continued to persue her PhD programme in the same Institute. In her PhD thesis, she continued to use the SWAT model, but focused on improving the model processes by adding the landscape routing process to hydrological modelling and a sub-module to simulate the denitrification in riparian zones for the SWAT model. Her research interest is related to eco-hydrological modelling and integrating hydrological models and water quality models to simulate water quality processes at large scale in consideration of calibration and validation using observations and process understanding.