Scrutinizing Relationships between Submarine Groundwater Discharge and Upstream Areas Using Thermal Remote Sensing: A Case Study in the Northern Persian Gulf

Abstract

Nutrient input through submarine groundwater discharge (SGD) often plays a significant role in primary productivity and nutrient cycling in the coastal areas. Understanding relationships between SGD and topo-hydrological and geo-environmental characteristics of upstream zones is essential for sustainable development in these areas. However, these important relationships have not yet been completely explored using data-mining approaches, especially in arid and semi-arid coastal lands. Here, Landsat 8 thermal sensor data were used to identify potential sites of SGD at a regional scale. Relationships between the remotely-sensed sea surface temperature (SST) patterns and geo-environmental variables of upland watersheds were analyzed using logistic regression model for the first time. The accuracy of the predictions was evaluated using the area under the receiver operating characteristic curve (AUC-ROC) metric. A highly accurate model, with the AUC-ROC of 96.6%, was generated. Moreover, the results indicated that the percentage of karstic lithological formation and topographic wetness index were key variables influencing SGD phenomenon and spatial distribution in the northern coastal areas of the Persian Gulf. The adopted methodology and applied metrics can be transferred to other coastal regions as a rapid assessment procedure for SGD site detection. Moreover, the results can help planners and decision-makers to develop efficient environmental management strategies and the design of comprehensive sustainable development policies.

Thermal-Based Remote Sensing Solution for Identifying Coastal Zones with Potential Groundwater Discharge

“…The relevance of Landsat 8 TIR imagery to recognize Submarine Groundwater Discharge (SGD) sites has been effectively applied in previous studies [20,22,23,38]. Here, we also confirmed the capacity of thermal remote sensing for identifying SGD sites at large regional scales.…”

“…For instance, Wilson & Rocha [20] mapped temperature anomalies in the south and west coasts of Ireland, highlighting the suitability of the approach for a regional scale survey. More recently, Samani et al [22] used Landsat 8 thermal sensor data to identify potential sites of SGD at a regional scale in the Northern Persian Gulf, Jou-Claus et al [23] used Landsat 8 imagery as an exploratory tool for identifying SGD in karstic coastal aquifers in the Mediterranean Sea basin. The inverse process-warmer groundwater discharging into colder ocean waters during the winter months-is also coherent and hydrogeologically correct.…”

“…As an initial step, pixel digital numbers (DNs) of the Landsat TIR band 10 were converted to top-of-atmosphere (TOA) spectral radiance using Equation (1). [22]:…”

“…Heat has been considered as a groundwater tracer for over a century and remote sensing-based methods for SGD detection are appropriate where temperature gradients form between discharging groundwater and the surface water bodies [35]. Hence, our analysis is based on the hypothesis that in winter months the SGD is warmer than the receiving surface-waters but in summer SGD is cooler than surface-waters [20][21][22].…”

“…Also, Tamborski et al [21], combined airborne thermal infrared overflights with shoreline radionuclide surveys to investigate SGD along the north shore of Long Island, New York. More recently, Samani et al [22] used Landsat 8 thermal sensor data to identify potential sites of SGD at a regional scale in the Northern Persian Gulf. Similarly, Jou-Claus et al [23] demonstrated the significant use of the thermal infrared imagery as an exploratory tool for identifying SGD springs in karstic coastal aquifers in the Mediterranean Sea basin.…”