Title

Groundwater and Electrical Resistivity Surveys of Marsh Dieback Locations in Coastal Georgia

Document Type

Presentation

Publication Date

3-31-2016

Abstract

Marsh dieback is a long-term concern for coastal communities as this phenomenon is characterized by a rapid senescence of salt marsh vegetation leading to plant death and loss of valuable coastal ecosystems. Proposed causes of marsh dieback have varied. In Georgia, a multi-stressor hypothesis is the most widely accepted, with drought likely the primary cause. However, little work to date has been conducted regarding the role of groundwater during dieback events. We therefore have been measuring basic water quality parameters of the groundwater and conducting electrical resistivity surveys at three dieback locations in coastal Georgia three times per year. Groundwater depth profiles were collected at 10-cm intervals to a depth of 90 cm using a push-point piezometer and peristaltic pump at nine dedicated monitoring plots at each of the three marsh locations. Generally speaking for each marsh location, groundwater salinity was quite variable across the plots and throughout the seasons. At each plot, however, the measured groundwater salinity near the top of the depth profile was very similar to the measured salinity at all other depths within the profile. A ~170 m electrical resistivity cable was deployed in a shore-perpendicular orientation through the center of each dieback location. Time-series images were collected using a dipole-dipole configuration and inverted using EarthImager 2D (Advanced Geosciences, Inc.) With this configuration, resistivity data were collected up to a maximum depth of 39 m. Generally speaking, we found no large difference in resistivity across the dieback area, but did see pockets of groundwater moving underneath the marsh. The water quality and electrical resistivity data will be combined with vegetation and soil characterization data that were collected at the same time as the groundwater data. These data sets will also be combined with high resolution mapping of marsh dieback extent and ground elevation surveys that were also collected at the same time as the groundwater data to enhance the current understanding of marsh dieback stressors and recovery.

Sponsorship/Conference/Institution

Geological Society of American Southeastern Section Annual Meeting (GSA)

Location

Columbia, SC