Characteristics of the bedrock groundwater in the southwestern (SW) Ivory Coast (IC) (5–6°N, 4–7°W) are geochemically less known compared to those in the eastern part of the country. Several main cash crops, such as cocoa, coffee, rubber and palm oil, started being grown in this area twenty years ago because of the migration of agricultural activities from the East to the West of IC; this migration of agricultural activites was tied to climate variability. Within these large land use areas, food crops such as plantain bananas, yams, rice, maize, and vegetables are also grown. In this work, the mineralisation and groundwater pollution from East IC to West IC are studied within groundwater of the Archean and Paleoproterozoïce bedrock aquifers located in the SW IC. Stable isotopes ratios (δ¹⁸O, δ²H and δ¹³C), radiocarbon activity (A¹⁴C) and chemical contents (major ions) were measured on a set of 23 groundwater samples. In SW IC, the residence times calculated by an exponential mixing model (EMM) and a dispersion model (DM) with Dispersion Parameter values of 0.05 and 0.5 reveal that the oldest groundwater is located in the aquifer of migmatitic and granulitic gneiss (MiGn aquifer). Recent groundwater is located in the metagranitoid (MetGr) and the metasedimentary rocks (MetSe) aquifers. The most appropriate model to compute residence times is EMM because of the highest proportion of recharge in accordance with the nitrate content in groundwater after 1958, the beginning of Ivorian deforestation. However, this model lead to an overestimate of the residence time of groundwater particularly high in NO₃. The oldest age of MiGn groundwater according to EMM calculation is ∼5 ka BP. The MiGn aquifer is less renewed (mean annual renewal rate of 0.03%) followed by those of MetSe (∼2.5 ka BP) and MetGr (∼2 ka BP), with mean annual renewal rates of 0.09% and 0.012%, respectively. Groundwater mineralisation is mainly governed by the hydrolysis of Al-silicates minerals and cultivation practice linked to K and N-fertilisers use, which leads to an increase of Ca, Mg and Na content. The values of TDS ranged from 49.4 to 720.4 mg L⁻¹, which indicates the chemical characteristics of fresh water in SW IC. Most of the studied area groundwater are evaporated, likely due to both climate variability since the last 5 ka BP, delayed infiltration of rainwater which would be caused by impervious sediments covering the hard rock aquifers and agricultural practices affecting the most recently recharged groundwater. River water recharge from irrigation in cultivated areas may be possible. The groundwater with low ¹⁴C activities (64.33 pMC) has high residence times and is depleted in ¹³C content, while that with high ¹⁴C activities (99.58 pMC) is enriched in ¹³C content. This demonstrates that vegetation cover changed from C₃ plants or forest (−23.9‰) to C₄ plants, savannah or cultivation plants (−12.5‰) similar to those found in the southeastern IC.

与该国东部地区相比，科特迪瓦西南部 (SW) 的基岩地下水特征 (5–6°N, 4–7°W) 在地球化学上鲜为人知。二十年前，由于农业活动从 IC 东部向西部迁移，可可、咖啡、橡胶和棕榈油等几种主要经济作物开始在该地区种植；这种农业活动的迁移与气候变化有关。在这些大面积的土地利用区域内，还种植大蕉香蕉、山药、水稻、玉米和蔬菜等粮食作物。在这项工作中，研究了位于西南 IC 的太古代和古元古代基岩含水层地下水中从东 IC 到西 IC的矿化和地下水污染。稳定的对一组 23 个地下水样品测量了同位素比（δ ¹⁸O、δ²H 和 δ¹³C）、放射性碳活性（A¹⁴ C）和化学成分（主要离子）。在 SW IC 中，通过指数混合模型 (EMM) 和离散参数值分别为 0.05 和 0.5 的离散模型 (DM) 计算的停留时间表明，最古老的地下水位于混合和粒状片麻岩含水层 (MiGn 含水层) . 最近的地下水位于变花岗岩（MetGr）和变质沉积岩 (MetSe) 含水层。计算停留时间最合适的模型是 EMM，因为根据 1958 年科特迪瓦森林砍伐开始后地下水中硝酸盐含量的补给比例最高。然而，该模型导致高估了 NO ₃含量特别高的地下水的停留时间. 根据 EMM 计算，MiGn 地下水的最古老年龄为~5 ka BP。MiGn 含水层更新较少（平均年更新率为 0.03%），其次是 MetSe（~2.5 ka BP）和 MetGr（~2 ka BP），平均年更新率分别为 0.09% 和 0.012%。地下水矿化主要受铝硅酸盐矿物的水解以及与 K 和 N 肥料使用相关的栽培实践控制，这导致 Ca、Mg 和 Na 含量增加。TDS 值范围为 49.4 至 720.4 mg L ^-1，表示 SW IC 中淡水的化学特性。大多数研究区域的地下水都被蒸发了，这可能是由于自上次 5 ka BP 以来的气候变化、由覆盖硬岩含水层的不透水沉积物引起的雨水渗透延迟以及影响最近补给地下水的农业实践。从耕地灌溉中补给河流水是可能的。¹⁴ C活性低(64.33 pMC)的地下水滞留时间长，¹³ C含量枯竭，而¹⁴ C活性高(99.58 pMC)的地下水富含¹³ C。这表明植被覆盖从 C ₃植物或森林 (-23.9‰) 到 C ₄植物、稀树草原或栽培植物 (-12.5‰) 类似于在东南 IC 发现的那些。