Holocene dynamics of the salt–fresh groundwater interface under a sand island, Inhaca, Mozambique

Marine water from mid-Holocene sea level highstand trapped in a coastal aquifer: Evidence from groundwater isotopes, and environmental significance

“…Vaeret et al, 2012;Cary et al, 2015). We propose that dating of saline water in coastal aquifers using radiocarbon, tritium and other appropriate techniques, along with a detailed examination of vertical profiles of salinity and stable isotopes, are important steps required to distinguish typical seawater intrusion modes from palaeo-marine water emplacement.…”

“…While likely to be much more localised in time and space than VMGRs, due to the current sea level position being relatively high by recent geological standards, there are examples of low lying areas where inundation by seawater in previous times (e.g. the mid-Holocene) appears evident (Giambastiani et al, 2012;Vaeret et al, 2012;Currell et al, 2014;Cary et al, 2015). Key controls on the presence of such trapped marine water in coastal aquifers are changes in relative coastline elevation due to sea level change, evolution of the aquifer water balance, and the geological structure and aquifer properties, which control the rate of re-equilibration of the interface following a sea level change (Kooi et al, 2000).…”

Cation exchange in a temporally fluctuating thin freshwater lens on top of saline groundwater

“…The RW-lens extends from the base of the mixing zone (B mix ) to the water table. At the depth of the center of the mixing zone (D mix ) the salinity is 50 % of the seepage water salinity (EC s ) (taken from De Louw et al 2013) BGH lenses in horizontal (10's of meters instead of 100's of meters) and vertical (less than a few meters instead of 10-100's of meters) planes, causing travel times of less than 5 years (De Louw et al 2013) instead of decades to centuries (Stuyfzand 1993;Vaeret et al 2011;Oude Essink 1996). Foppen and Griffioen (1995) stressed that the role of drains in hydrochemical processes needs elucidation.…”

Dynamics of rainwater lenses on upward seeping saline groundwater

“…Vaeret et al 2012, Oude Essink,1996, for thin lens systems, we expect fast responses of the position of the mixing zone to recharge variability. The main responses of interest are the thickness of the lens and of its mixing zone.…”

“…In BGH-lenses the response to recharge variations is in the order of decades (e.g. Vaeret et al, 2012;Oude Essink, 1996). Rotzoll et al (2010) observed thinning rates of 0.5 to 1.0 m y -1 in thick freshwater lenses in Hawaii due to long term groundwater withdrawal and reduced recharge.…”