ON THE SALINIZATION VULNERABILITY OF SOIL AND GROUNDWATER IN ESTUARINE ZONES

Abstract

Increased storminess, drought, and sea-level rise caused by climate change are expected to lead to surface water salinization in many estuaries. Groundwater and soil near estuaries are also increasingly vulnerable, as variations in estuarine surface water conditions may result in the salinization of freshwater resources and soils in areas not previously at risk of saltwater contamination. In marine settings, soil and groundwater salinization may occur vertically during seawater flood events, which inundate previously freshwater areas, or laterally, as more dense seawater intrudes in the subsurface due to changes in land-sea hydraulic gradients. Surface water-groundwater interactions in estuarine settings are complicated due to the spatiotemporal distribution of surface water salinities and levels. This research explores how previously fresh soil and groundwater will be impacted following exposure to salinized water due to increased estuarine flooding and surface water salinization. A managed realignment site adjacent to an estuary in Nova Scotia, Canada, provided an engineered analog of low-elevation agricultural land that may experience more frequent saline flooding events due to climate impacts. Baseline characterization was completed to identify the groundwater and soil response to changing surface water dynamics. Field data and numerical modeling were used to investigate how varying surface water conditions may impact groundwater resources. Surface water and groundwater monitoring, geophysical surveys, geomorphological (LiDAR) surveys, and sediment sampling and analysis were used to observe the short- and medium-term effects of inundation, while numerical modeling was used to identify the salinization potential based on projected scenarios. This research suggests that coastal defense structures (dikes) may be adequate to prevent lateral saltwater intrusion following surface water salinization; however, overland flooding by even low salinity brackish water was shown to affect soil and groundwater conditions after only a few floods, potentially rendering the land unsuitable for agricultural use. Additionally, flood-derived marine sediments were found to be a concentrated source of salinity, making geomorphological variation a key driver in soil and groundwater salinization potential. The research presented here has provided insight into how climate-driven estuarine surface water variations may impact near-estuary soil and groundwater in areas not previously at risk of salinization.