Concurrent Salinization and Development of Anoxic Conditions in a Confined Aquifer, Southern Israel

Abstract

An ancient, brackish, anoxic, and relatively hot water body exists within the Yarqon-Tanninim Aquifer in southern Israel. A hydrogeological-geochemical conceptual model is presented, whereby the low water quality is the outcome of three conditions that are met simultaneously: (1) Presence of an organic-rich unit with low permeability that overlies and confines the aquifer; the confining unit contains perched horizons with relatively saline water. (2) Local phreatic/roofed conditions within the aquifer that enable seepage of the organic-rich brackish water from above. The oxidation of the dissolved organic matter in the seeping water consumes the dissolved oxygen and continues through bacterial sulfate reduction, with H S as a product. These exothermic reactions result in some heating. (3) The seeping water comprises a relatively large portion of the water volume. In the presented case study, the latter condition first developed in the Late Pleistocene following climate change, which led to a dramatic decline in recharge. Consequently, water flow in the local basin has nearly ceased, as evident by old water ages, specific isotopic composition, and nearly equipotential water levels. The continuous seepage from above into the almost stagnant water body has resulted in degraded water quality. Seepages of organic-rich brackish water exist at other sites throughout the aquifer but have limited impact on the salinity and redox conditions due to the dynamic water flow, which flushes the seeping water, that is, the third condition is not met. The coexistence of the above three conditions may explain the development of anoxic and saline groundwater in other aquifers worldwide.

Metabolic adaptations and aquifer connectivity underpin the high productivity rates in the relict subsurface water

“…Using the productivity estimates in this study, we aim to update the rates of carbon sequestration in global aquifer systems. 81 Kr ages of the sandstone and carbonate aquifer wells (orange and blue labels, respectively) follow previous studies [29][30][31], and are reported in thousands of years (kyr). (c) A schematic cross-section A-A' of the nine sampled wells along the eastern flow path (not to scale).…”

The Issue of Groundwater Salinization in Coastal Areas of the Mediterranean Region: A Review

“…Early studies in the Mediterranean area were developed in Israel [92,93], while since the year 2005, there has been a growing legacy of studies employing these techniques. Most of the studies used stable isotopes to distinguish between different GW origins [94][95][96][97][98][99][100][101][102][103][104][105][106][107][108][109][110][111][112][113], while some of them used radioactive isotopes to determine the residence time of GW [114][115][116], that is, one of the very few pieces of information allowing researchers to distinguish between actual and paleo SWI. These last elements have also been used to study surface water/groundwater interaction; for example, in a recent paper from Mayer et al [117], short-lived radioactive isotopes, such as radon-222, allowed not only for the determination of the amount of exchange between different water bodies, but also for the ability to precisely derive GW flow velocities and saturated hydraulic conductivities, which are vital parameters to constrain numerical simulations.…”

The Nubian Sandstone Aquifer in the Sinai Peninsula and the Negev Desert

“…The left section is a modification after Nativ et al (1987) and Calvo and Gvirtzman (2013), and illustrates the deeper groups in the Negev Desert based mainly on deep oil drillings. The right section is modified after Burg et al (2017) and presents the litho-stratigraphy of shallower units in the northern Negev…”

“…According to this approach, the extra heat of the Judea Group Aquifer represents exothermic reactions that occur mainly due to the oxidation of organic matter derived from the bituminous deposits found in the Mt. Scopus Group rocks (Burg et al 2017).…”