Back to Search
Start Over
Combining resistivity and frequency domain electromagnetic methods to investigate submarine groundwater discharge in the littoral zone
- Source :
- Hydrology and Earth System Sciences, Vol 24, Pp 3539-3555 (2020), HYDROLOGY AND EARTH SYSTEM SCIENCES
- Publication Year :
- 2020
- Publisher :
- Copernicus GmbH, 2020.
-
Abstract
- Submarine groundwater discharge (SGD) is an important gateway for nutrients and pollutants from land to sea. While understanding SGD is crucial for managing nearshore ecosystems and coastal freshwater reserves, studying this discharge is complicated by its occurrence at the limit between land and sea, a dynamic environment. This practical difficulty is exacerbated by the significant spatial and temporal variability. Therefore, to capture the magnitude of SGD, a variety of techniques and measurements, applied over multiple periods, is needed. Here, we combine several geophysical methods to detect zones of fresh submarine groundwater discharge (FSGD) in the intertidal zone, upper beach, dunes, and shallow coastal area. Both terrestrial electrical-resistivity tomography (ERT; roll-along) and marine continuous resistivity profiling (CRP) are used from the shallow continental shelf up to the dunes and combined with frequency domain electromagnetic (FDEM) mapping in the intertidal zone. In particular, we apply an estimation of robust apparent electrical conductivity (rECa) from FDEM data to provide reliable lateral and vertical discrimination of FSGD zones. The study area is a very dynamic environment along the North Sea, characterized by semi-diurnal tides between 3 and 5 m. CRP is usually applied in calmer conditions, but we prove that such surveys are possible and provide additional information to primarily land-bound ERT surveying. The 2D inversion models created from ERT and CRP data clearly indicate the presence of FSGD on the lower beach or below the low-water line. This discharge originates from a potable freshwater lens below the dunes and flows underneath a thick saltwater lens, present from the dunes to the lower sandy beach, which is fully observed with ERT. Freshwater outflow intensity has increased since 1980, due to a decrease of groundwater pumping in the dunes. FDEM mapping at two different times reveals discharge at the same locations, clearly displays the lateral variation of the zone of discharge, and suggests that FSGD is stronger at the end of winter compared to the beginning of autumn. ERT, CRP, and FDEM are complementary tools in the investigation of SGD. They provide a high-resolution 3D image of the saltwater and freshwater distribution in the phreatic coastal aquifer over a relatively large area, both off- and onshore.
- Subjects :
- DYNAMICS
0208 environmental biotechnology
Intertidal zone
02 engineering and technology
010502 geochemistry & geophysics
lcsh:Technology
01 natural sciences
lcsh:TD1-1066
SALINITY
SALINIZATION
Littoral zone
lcsh:Environmental technology. Sanitary engineering
Geomorphology
COASTAL AQUIFERS
2D
lcsh:Environmental sciences
Phreatic
0105 earth and related environmental sciences
lcsh:GE1-350
geography
SEA
geography.geographical_feature_category
FRESH-WATER
lcsh:T
Continental shelf
Lens (hydrology)
lcsh:Geography. Anthropology. Recreation
SALT-WATER INFILTRATION
SEAWATER INTRUSION
Submarine groundwater discharge
TIME
020801 environmental engineering
lcsh:G
Earth and Environmental Sciences
Outflow
Groundwater
Geology
Subjects
Details
- ISSN :
- 16077938 and 10275606
- Volume :
- 24
- Database :
- OpenAIRE
- Journal :
- Hydrology and Earth System Sciences
- Accession number :
- edsair.doi.dedup.....97caea2ef19f1638edfa7b2d993f2797