Role of aquifer heterogeneity in fresh groundwater discharge and seawater recycling: An example from the Carmel coast, Israel

Abstract

[1] A case study is shown in which the pattern of submarine groundwater discharge and of seawater recycling is controlled by local hydrogeological variability. The coastal aquifer in Dor Bay is composed of two units: a partly confined calcaranitic sandstone (Kurkar) and an overlying loose sand. Groundwater in the Kurkar has elevated activities of 222 Rn ($390 dpm/L) and relatively low 224 Ra/ 223 Ra activity ratios (3-4), while the sand groundwater is significantly less radiogenic (6-90 dpm/L) and shows higher 224 Ra/ 223 Ra ratios. Groundwater discharging from sand-covered areas of the bay has salinities of 16-31 and an average 222 Rn activity of 168 dpm/L, which lies on a mixing line between Rn-rich Kurkar fresh water and Rn-poor seawater. Another key observation is that seawater infiltrates to some extent into onshore sand groundwater, while the fresh water within the submarine Kurkar can be traced up to 40 m offshore. This implies that while fresh water mainly discharges from the Kurkar unit, seawater recycling is limited to the loose sand, and that the discharge from sand-covered areas is a mixture of Kurkar water with recycled seawater. Advection rates from the bay floor were calculated from Rn time series and found to vary between 0 and 36 cm/d, correlating negatively with bay water depth. The average flux was 8.1 cm/d, and it did not seem to change much during March, May, and July 2006. The average amount of fresh water discharging to the bay was 5.0 m 3 /d per meter of shoreline. Radon activity in the sand groundwater also fluctuates due to influx of Kurkar-type groundwater.

Application of radon and radium isotopes to groundwater flow dynamics: An example from the Dead Sea

“…These values are indeed evident in southern Jordan, away from the Dead Sea, where 222 Rn activities in the sandstone Disi aquifer groundwater are only ∼400-700 dpm/L (Vengosh et al, 2009), which is similar to the activities found in sandstone aquifers elsewhere (e.g. Krishnaswami et al, 1982;Tricca et al, 2001;Weinstein et al, 2007). Given the 10% limit of 222 Rn contribution from the rock into the groundwater, also the radon activities of thousands of dpm/L observed in the TZG and KS groundwater (Appendix A, Fig.…”

“…Similarly, 222 Rn activities in the thermal springs of the eastern catchment (EC, Salameh, 1996, Appendix A) vary between ∼6000 and 60,000 dpm/L, while the activity that could be produced by the rocks is no more than 6000 dpm/L (assuming U concentration of 0.5-1 ppm in the sandstone rock and porosity of 0.2). Moreover, the above activities are a maximum estimate, since usually no more than 10% of the radon is effectively ejected to the pore space fluid (Kigoshi, 1971;Krishnaswami et al, 1982;Tricca et al, 2001;Weinstein et al, 2007), which reduces the expected 222 Rn activities to less than 600-1200 dpm/L in both aquifers. These values are indeed evident in southern Jordan, away from the Dead Sea, where 222 Rn activities in the sandstone Disi aquifer groundwater are only ∼400-700 dpm/L (Vengosh et al, 2009), which is similar to the activities found in sandstone aquifers elsewhere (e.g.…”

“…226 Ra/ 223 Ra secular equilibrium ratios are not very common in groundwater (e.g. Davidson and Dickson, 1986;Weinstein et al, 2007;Michael et al, 2011) due to the long time it takes for 226 Ra to attain steady-state activities. The common occurrence of secular equilibrium ratios in the Dead Sea groundwaters suggests that the groundwater system around the Dead Sea did not change much during the past 8000 years.…”

Deep Submarine Groundwater Discharge—Evidence From Achziv Submarine Canyon at the Exposure of the Judea Group Confined Aquifer, Eastern Mediterranean

“…Submarine groundwater discharge (SGD) is a global phenomenon observed in numerous shallow water sites (Burnett et al, 2001;Li et al, 1999;Moore, 1996;Swarzenski et al, 2006;Taniguchi & Iwakawa, 2004;Weinstein et al, 2007). SGD is a path for groundwater outflow that may have a substantial effect on water budget of coastal aquifers (e.g., Moore, 2010), as well as coastal water quality (e.g., Johannes, 1980;Moore, 2010) and seafloor morphology (e.g., Orange et al, 1994).…”

Aquifer Response to Estuarine Stream Dynamics

“…Optimal management of coastal aquifers is becoming increasingly important due to population growth and climate change, which potentially affects water quality, ecosystem health and diversity, and water-supply reliability [1][2][3][4][5]. Surface water and groundwater are intrinsically linked systems [6][7][8][9]. Areas around streams, rivers, lakes and coastal environments represent zones of interaction and transition between the two systems, where dissolved constituents such as pollutants can be diluted, exchanged, transformed, or degraded.…”