Groundwater evolution and mean water age inferred from hydrochemical and isotopic tracers in a tropical confined aquifer

Abstract

The coastal confined aquifer in the Gulf of Urabá (Colombia) is an important water source for the banana agro-industry as well as for urban and rural communities. However, the main processes controlling recharge and mixing in the aquifer are still poorly understood. Hydrochemical analyses and stable isotope monitoring were conducted to (a) determine groundwater recharge origin, mean groundwater age, and the main processes governing groundwater chemistry and the potential mixing of marine water and the influence of diffusive processes from the two surrounding aquitard layers.Hydrochemical data indicate that the main processes affecting the dissolved chemical composition include cation exchange, dissolution of carbonated and CO 2 , and silicate weathering. δ 18 O and δ 2 H compositions combined with 14 C data highlight the differences in climatic conditions between the recharge zone and the confined section of the aquifer, which is close to the Atlantic Ocean. Groundwater samples with 14 C ages from recent to 28,300 years BP show a depleted isotopic trend ranging from −6.43‰ to −9.14‰ in δ 18 O and from −43.2‰ to −65.7‰ in δ 2 H. The most depleted δ 18 O and δ 2 H compositions suggest a cooler recharge climate than the current conditions (corresponding to the last glacial period of the late Pleistocene). Depleted δ 13 C values in the total dissolved inorganic carbon indicate the existence of organic material oxidation processes within the geologic formation. These results can be used or transferred to enhance groundwater modelling efforts in other confined coastal aquifers of South America where scarcity of long-term monitoring data limits water resources planification under a changing climate. KEYWORDS Colombia, confined coastal aquifer, isotope and geochemical hydrology, mean groundwater ages, recharge areas and groundwater flow

Tracer hydrology of the data‐scarce and heterogeneous Central American Isthmus

“…The results are intended to inform governmental institutions in Central America and raise awareness regarding protection and conservation (e.g., reforestation) of critical recharge zones. The present work also may contribute to the understanding of groundwater recharge mechanisms in other tropical regions where isotopically informed geospatial models are becoming robust and more widely applied tools to improve water resources planning (Dehaspe et al, 2018; Jasechko & Taylor, 2015; Munksgaard et al, 2019; Sánchez‐Murillo & Birkel, 2016; Taylor et al, 2013; Villegas, Paredes, Betancur, Taupin, & Toro, 2018).…”

The Origin and Quality of the Groundwater of the Rawadanau Basin in Serang Banten, Indonesia

“…According to the piper diagram (see Figure 8), the SO 4 2content is relatively low, not more than 14.9 mg/L, proving that groundwater is freshwater that is still original (Appelo and Postma, 2005). The SO 4 2is related to pesticides or fertilizers, besides dissolution minerals as gypsum and seawater related (Villegas et al, 2018).…”

“…Throughout the geothermal system, the processes that occur show that the dissolution of the minerals that make up the rock produces silica, which is the most stable mineral under a given set of conditions (Giggenbach, 1981). The hot springs (13S, 31S, and 33S) contain high levels of Na + and Cl -, possibly from formation water that comes out as springs or as seawater trapped in aquifers (Villegas et al, 2018).…”

Tracing Water Sources and Fluxes in a Dynamic Tropical Environment: From Observations to Modeling

“…The distinct isotopic pulses or input functions provided by rainfall in the tropics are commonly damped or modified by different ecological and hydrogeological processes across the landscape. Connectivity between groundwater and surface water compartments have been widely studied in humid tropical watersheds (Gordon et al, 2015;Lagomasino et al, 2015;Batista et al, 2018;Oiro et al, 2018;Villegas et al, 2018;Welsh et al, 2018;Tsuchihara et al, 2019); however, large scale or regional approaches are uncommon across tropical biomes. Figure 9 shows locations of groundwater (N 1,156) and surface water (N 603) sampling efforts across Costa Rica (2016-2019).…”