Assessing the Impacts of Wetlands on Discharge and Nutrient Loading: Insights from Restoring Past Wetlands with GIS-Based Analysis and Modeling

Wetlands play an essential role in overland flow generation by retaining water and providing an environment for the hydrogeochemical functions of a watershed. Few studies have addressed the restoration of past wetlands using wetland-corrected land-use land-cover (LULC) datasets. We evaluated the impacts of wetlands on hydrology and nutrient (nitrogen) loading by comparing Present, Past, and Restored scenarios. A GIS-based data processing procedure was proposed for generating a wetland-corrected proxy LULC raster to mimic the past wetland distribution. This was subsequently incorporated in the Soil and Water Assessment Tool (SWAT) to simulate discharge and nitrogen loading. In addition, two models, with and without using the proxy LULC dataset, were developed to examine the impacts of the proxy LULC on the model performance. The effect of hydroclimatic variations was also assessed by comparing the simulated peak flows and nutrient loads in dry and wet years. The results demonstrated the necessity of using the wetland-corrected proxy LULC data in the water quantity and quality modeling, especially for wet years. Our modeling approach and wetland-oriented LULC correction procedure can be applied to other wetland-dominated watersheds to improve hydrologic and water quality modeling.