Origins and processes of groundwater salinization in the urban coastal aquifers of Recife (Pernambuco, Brazil): A multi-isotope approach

Abstract

In the coastal multilayer aquifer system of a highly urbanized southern city (Recife, Brazil), where groundwaters are affected by salinization, a multi-isotope approach (Sr, B, O, H) was used to investigate the sources and processes of salinization. The high diversity of the geological bodies, built since the Atlantic opening during the Cretaceous, highly constrains the heterogeneity of the groundwater chemistry, e.g. Sr isotope ratios, and needs to be integrated to explain the salinization processes and groundwater pathways. A paleoseawater intrusion, most probably the 120 kyB.P. Pleistocene marine transgression, and cationic exchange are clearly evidenced in the most salinized parts of the Cabo and Beberibe aquifers. All (87)Sr/(86)Sr values are above the past and present-day seawater signatures, meaning that the Sr isotopic signature is altered due to additional Sr inputs from dilution with different freshwaters, and water-rock interactions. Only the Cabo aquifer presents a well-delimitated area of Na-HCO3 water typical of a freshening process. The two deep aquifers also display a broad range of B concentrations and B isotope ratios with values among the highest known to date (63-68.5‰). This suggests multiple sources and processes affecting B behavior, among which mixing with saline water, B sorption on clays and mixing with wastewater. The highly fractionated B isotopic values were explained by infiltration of relatively salty water with B interacting with clays, pointing out the major role played by (palaeo)-channels for the deep Beberibe aquifer recharge. Based on an increase of salinity at the end of the dry season, a present-day seawater intrusion is identified in the surficial Boa Viagem aquifer. Our conceptual model presents a comprehensive understanding of the major groundwater salinization pathways and processes, and should be of benefit for other southern Atlantic coastal aquifers to better address groundwater management issues.

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

“…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).…”

Hydrochemistry and Isotope Hydrology for Groundwater Sustainability of the Coastal Multilayered Aquifer System (Zhanjiang, China)

“…To address the possibility of seawater intrusion in Naozhou island, we referred to the hydrochemistry data of Naozhou island investigated by Zhang et al [34] in March 2011 (Table 5). These hydrochemical data showed that the confined groundwater in the southern and eastern coastal area (e.g., samples 26,22,20, and 14 in Figure 1(d)) has been saline with TDS value of 1.39-10.28 g/L. This means that freshwater-seawater mixing zones in the confined aquifers of Naozhou island have extended landward.…”

“…The application of chemistry and hydrogen-oxygen isotopes can be used also to identify processes of groundwater salinization induced by seawater intrusion [21][22][23][24][25]. In addition, many 2 Geofluids other isotopes (e.g., radium, carbon, chlorine, boron, and strontium) have been used as tracers for characterizing the hydrogeological conditions and hydrochemical processes in coastal aquifers, specifically identifying submarine groundwater discharge and describing seawater intrusion [10,13,26,27].…”

Delineating multiple salinization processes in a coastal plain aquifer, northern China: hydrochemical and isotopic evidence

“…Overexploitation of groundwater can therefore result in seawater intrusion, as well as related environmental issues such as land subsidence. Seawater intrusion has become a global issue and related studies can be found from coastal aquifers around the world, including Israel (Sivan et al, 2005;Yechieli et al, 2009;Mazi et al, 2014), Spain (Price and Herman, 1991;Pulido-Leboeuf, 2004;Garing et al, 2013), France (Barbecot et al, 2000;de Montety et al, 2008), Italy (Giambastiani et al, 2007;Ghiglieri et al, 2012), Morocco (Bouchaou et al, 2008;El Yaouti et al, 2009), the USA (Gingerich and Voss, 2002;Masterson, 2004;Langevin et al, 2010), Australia (Zhang et al, 2004;Narayan et al, 2007;Werner, 2010), China (Xue et al, 2000;Han et al, 2011Han et al, , 2015, Vietnam , Indonesia (Rahmawati et al, 2013), India (Radhakrishna, 2001;Bobba, 2002) and Brazil (Montenegro et al, 2006;Cary et al, 2015). Werner et al (2013) provides a comprehensive review of seawater intrusion processes, investigation and management.…”

“…Relatively few studies have focused on delineating complex interactions among the surface-groundseawater continuum in estuarine environments, including the effects of vertical infiltration of seawater into aquifers through river channels, compared to subsurface lateral landward migration of the freshwater-saltwater interface. Recent data indicate that such processes may be more important in causing historical salinization of coastal groundwater than previously appreciated (e.g., Cary et al, 2015;Lee et al, 2016;Larsen et al, 2017).…”