Session 2B: Water Use and Management and SWI
June 11
2:15 - 3:45 pm
Chesapeake Salon EF
Mechanisms of salinization of coastal water resources and ecosystems: Insights from observations across the Mid-Atlantic
Holly Michael
University of Delaware
Coastlines around the world are rapidly changing as sea level rises and coastal storms become more frequent and intense. Coastal water resources are vulnerable to salinization, exacerbated by overuse. As salinity increases and flooding becomes more frequent, marshes migrate inland, displacing trees and croplands. Understanding the primary factors that affect aquifer vulnerability to changes in salinity and groundwater flow patterns is critical to developing effective management plans in coastal zones. We present examples of salinization mechanisms in coastal systems around the Mid-Atlantic. The examples span different land use and ecosystems, and consider both surface and subsurface pathways for salinization. We address effects on water resources, agriculture, and ecosystems that span the land-sea margin.
The potential benefit of coastal wetland migration to agricultural land subject to storm surge inundation
Julia Guimond
Woods Hole Oceanographic Institution
Low-lying coastlines are vulnerable to storm surge inundation and salinization. In the mid-Atlantic, as well as other regions of the world, agricultural fields exist at low elevations and close to the ocean, putting them at a heightened risk of storm surge salinization. Given the salinity intolerance of most crops, minimization of saltwater intrusion is critical to sustained utilization of agricultural land. Coastal wetlands often exist at the interface between agricultural fields and the ocean and have been shown to dissipate wave energy and attenuate storm surges. However, most research studying protection by coastal wetlands only focuses on overland flow dissipation and present-day conditions, neglecting consideration of subsurface salinization and the landward migration of coastal wetlands. Using two-dimensional, variable-density, coupled surface-subsurface hydrological models, we explore how coastal wetlands, and their landward migration, affect the extent of saltwater flooding and groundwater salinization due to storm surges. We find that along topographically low coastlines, coastal wetland migration into agricultural fields prolongs the use of landward agricultural fields while also protecting the water quality of the unconfined aquifer. Coastal wetland migration may also benefit farmers financially through maintained productivity in the fields landward of the wetland. However, there is a tipping point at which the reduction in saltwater intrusion due to coastal wetland migration does not compensate for the loss of arable land. Our study highlights the environmental and potential financial benefit of marsh migration along topographically low coastlines.
Spaceborne Lidar Observations Reveal Impacts of Inundation on Coastal Forest Structure Across the U.S. Mid-Atlantic
Elisabeth Powell
University of Maryland
The impacts of accelerated sea level rise (SLR) due to climate change on coastal ecosystems has yet to be fully realized. SLR, combined with increasing storm surges, are driving significant regime shifts in vegetation across coastal landscapes, leading to marsh migration and upland forest mortality. However, the specific effects of tidal inundation, stemming from elevated water levels and soil salinity, on forest vertical structure remain poorly understood. In this study, we use spaceborne light detection and ranging (lidar) data from the Global Ecosystem Dynamics Investigation (GEDI) to explore the response of vertical forest structural dynamics in areas highly vulnerable to increased inundation across the U.S. Mid-Atlantic region. We analyzed the impact of inundation on three GEDI-derived forest structural traits, identified elevation thresholds for these impacts, and examined the environmental factors influencing these thresholds. We discovered that watersheds with a high proportion of area below Mean Higher High Water (MHHW) exhibited higher elevation thresholds, indicating a greater susceptibility to forest conversion into marshes. Conversely, watersheds characterized by higher slopes and drainage densities tended to have lower elevation thresholds, suggesting increased forest resistance to marsh migration. These findings highlight the importance of monitoring forest structural dynamics for early detection of upland marsh expansion, with lidar technology offering a potential tool for enhancing our understanding of ecological shifts in coastal environments. Such insights may be essential for evaluating ecosystem responses to SLR and may foster a more comprehensive understanding how SLR and other climate change-induced disturbances will affect the coastal carbon sink.
Application of geophysical methods to investigate the role of drainage ditches in facilitating saltwater intrusion
Alex Manda
East Carolina University
Innovative geophysical methods are used to investigate the role of drainage ditches in facilitating saltwater intrusion in the low-lying coastal regions of eastern North Carolina. The geophysical methods were applied in agricultural fields in coastal North Carolina that are currently experiencing saltwater intrusion and soil salinization problems. Electromagnetic induction (EMI) and electrical resistivity tomography (ERT) are used in conjunction with traditional field techniques to characterize field sites. EMI is used here to generate maps of the conductivity distribution across fields that are traversed by multiple drainage ditches, whereas ERT is used to generate cross-sectional 2-D images of the resistivity distribution of the subsurface across several drainage ditches. High conductivity zones in the EMI and ERT images are then used with other data and information to infer the presence and/or movement of saltwater in the subsurface or on the surface. EMI results show that some ditches are adjacent to high conductivity zones, whereas other ditches neighbor low conductivity zones. Results from ERT surveys show a variety of conductivity patterns immediately below and adjacent to the ditches. These patterns include (a) narrow, plume-shaped and well-defined high conductivity zones beneath ditches, (b) broad, laterally extensive well-defined high conductivity zones beneath and adjacent to ditches, and (c) low conductivity zones beneath ditches. Results from the geophysical techniques and other environmental data suggest that complex processes may play a greater role in facilitating saltwater intrusion processes than was previously thought. This study may therefore be useful in improving our understanding of how saltwater migrates from drainage ditches into the subsurface.