Assessing the role of submarine groundwater discharge as a source of Sr to the Mediterranean Sea

The Mediterranean Sea (MS) is a semienclosed basin that is considered one of the most oligotrophic seas in the world. In such an environment, inputs of allochthonous nutrients and micronutrients play an important role in sustaining primary productivity. Atmospheric deposition and riverine runoff have been traditionally considered the main external sources of nutrients to the MS, whereas the role of submarine groundwater discharge (SGD) has been largely ignored. However, given the large Mediterranean shore length relative to its surface area, SGD may be a major conveyor of dissolved compounds to the MS. Here, we used a 228Ra mass balance to demonstrate that the total SGD contributes up to (0.3–4.8)⋅1012 m3⋅y−1 to the MS, which appears to be equal or larger by a factor of 16 to the riverine discharge. SGD is also a major source of dissolved inorganic nutrients to the MS, with median annual fluxes of 190⋅109, 0.7⋅109, and 110⋅109 mol for nitrogen, phosphorous, and silica, respectively, which are comparable to riverine and atmospheric inputs. This corroborates the profound implications that SGD may have for the biogeochemical cycles of the MS. Inputs of other dissolved compounds (e.g., iron, carbon) via SGD could also be significant and should be investigated.

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Supplementary material to "Applicability of Landsat 8 Thermal Infrared Sensor to Identify Submarine Groundwater Discharge Springs in the Mediterranean Sea Basin"

10.5194/hess-2020-569-supplement ◽

2020 ◽

Author(s):

Sònia Jou-Claus ◽

Albert Folch ◽

Jordi Garcia-Orellana

Keyword(s):

Mediterranean Sea ◽

Submarine Groundwater Discharge ◽

Groundwater Discharge ◽

Thermal Infrared ◽

Landsat 8 ◽

Infrared Sensor ◽

Submarine Groundwater ◽

Supplementary Material ◽

The Mediterranean

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Applicability of Landsat 8 Thermal Infrared Sensor to Identify Submarine Groundwater Discharge Springs in the Mediterranean Sea Basin

10.5194/hess-2020-569 ◽

2020 ◽

Author(s):

Sònia Jou-Claus ◽

Albert Folch ◽

Jordi Garcia-Orellana

Keyword(s):

Mediterranean Sea ◽

Submarine Groundwater Discharge ◽

Regional Scale ◽

Groundwater Discharge ◽

Thermal Infrared ◽

Landsat 8 ◽

Infrared Sensor ◽

Hydrogeological Characteristics ◽

Submarine Groundwater ◽

The Mediterranean

Abstract. Submarine groundwater discharge (SGD) has received increasing attention over the past two decades as a source of nutrients, trace elements and pollutants to the ocean that may alter coastal biogeochemical cycles. Assessing submarine groundwater flows and their impacts on coastal marine environments is a difficult task since it is not easy to identify and measure these water flows discharging into the sea. The aim of this study is to prove the great usefulness of the freely-available thermal infrared (TIR) imagery of the Landsat 8 thermal infrared sensor (TIRS) as an exploratory tool to identify SGD springs worldwide, from local to regional scales, for long-term analysis. The use of satellite thermal data as a technique to identify SGD springs in seawater is based on the identification of thermally-anomalous plumes obtained from the thermal contrasts between groundwater and sea surface water. We propose a conceptual framework to apply this technique worldwide and also discuss the limitations of using this technique in SGD studies. The study was developed on a regional scale in karstic coastal aquifers in the Mediterranean Sea basin at different seasons and diverse meteorological conditions. Although this study demonstrates that the freely-available satellite TIR remote sensing is a useful method to identify coastal springs in karst aquifers both locally and regionally, the limiting factors include technical limitations, geological/hydrogeological characteristics, environmental and marine conditions and coastal geomorphology.

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Quantification of Submarine Groundwater Discharge in the Gaza Strip

Water ◽

10.3390/w10121818 ◽

2018 ◽

Vol 10 (12) ◽

pp. 1818 ◽

Cited By ~ 2

Author(s):

Ashraf Mushtaha ◽

Kristine Walraevens

Keyword(s):

Mediterranean Sea ◽

Seawater Intrusion ◽

Submarine Groundwater Discharge ◽

Gaza Strip ◽

Groundwater Discharge ◽

Unconfined Aquifer ◽

The North ◽

Submarine Groundwater ◽

The Mediterranean ◽

The Gaza Strip

Gaza Strip has suffered from seawater intrusion during the past three decades due to low rainfall and high abstraction from the groundwater resource. On a yearly basis, more than 170 million m3 of groundwater is abstracted, while the long-term average recharge from rainfall is 24.4 million m3/year. Submarine groundwater discharge (SGD) has never been studied in the Gaza Strip, due to lack of experience in this field, next to the ignorance of this subject due to the seawater intrusion process taking place. Continuous radon measurements were carried out in six sites along the Gaza Strip to quantify the SGD rate. The final result shows SGD to occur in all sampled sites. The range of SGD rates varies from 0.9 to 5.9 cm·day−1. High values of SGD are found in the south (Rafah and Khan Younis governorates). The high values are probably related to the shallow unconfined aquifer, while the lowest values of SGD are found in the middle of Gaza Strip, and they are probably related to the Sabkha formation. In the north of Gaza Strip, SGD values are in the range of 1.0 to 2.0 cm·day−1. Considering that SGD would occur with the measured rates in a strip of 100 m wide along the whole coast line, the results in a quantity of 38 million m3 of groundwater being discharged yearly to the Mediterranean Sea along Gaza coast. Nutrient samples were taken along Gaza Strip coastline, and they were compared to the onshore wells, 600 m away from the Mediterranean Sea. The results show that SGD has higher NO3− + NO2− than nutrient-poor seawater, and that it is close to the onshore results from the wells. This confirms that the source of SGD is groundwater, and not shallow seawater circulation. In a coastal strip of 100 m wide along the Gaza coast, a yearly discharge of over 400 tons of nitrate and 250 tons of ammonium occurs from groundwater to the Mediterranean Sea.

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Applicability of Landsat 8 thermal infrared sensor for identifying submarine groundwater discharge springs in the Mediterranean Sea basin

Hydrology and Earth System Sciences ◽

10.5194/hess-25-4789-2021 ◽

2021 ◽

Vol 25 (9) ◽

pp. 4789-4805

Author(s):

Sònia Jou-Claus ◽

Albert Folch ◽

Jordi Garcia-Orellana

Keyword(s):

Remote Sensing ◽

Mediterranean Sea ◽

Submarine Groundwater Discharge ◽

Groundwater Discharge ◽

Thermal Infrared ◽

Limiting Factors ◽

Landsat 8 ◽

Infrared Sensor ◽

Submarine Groundwater ◽

The Mediterranean

Abstract. Submarine groundwater discharge (SGD) has received increasing attention over the past 2 decades as a source of nutrients, trace elements and ocean pollutants that may alter coastal biogeochemical cycles. Assessing SGD flows and their impact on coastal marine environments is a difficult task, since it is not easy to identify and measure these water flows discharging into the sea. The aim of this study is to demonstrate the significant usefulness of the freely available thermal infrared (TIR) imagery of the Landsat 8 thermal infrared sensor (TIRS) as an exploratory tool for identifying SGD springs worldwide, from local to regional scales, for long-term analysis. The use of satellite thermal data as a technique for identifying SGD springs in seawater is based on the identification of thermally anomalous plumes obtained from the thermal contrasts between groundwater and sea surface water. In this study, we use the TIR remote sensing (TIR-RS) imagery provided by Landsat 8 at a regional scale and discuss the principle limiting factors of using this technique in SGD studies. The study was developed in karstic coastal aquifers in the Mediterranean Sea basin during different seasons and under diverse meteorological conditions. Although this study demonstrates that freely available satellite TIR remote sensing is a useful method for identifying coastal springs in karst aquifers both locally and regionally, the limiting factors include technical limitations, geological and hydrogeological characteristics, environmental and marine conditions and coastal geomorphology.

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