Alluvial plains are transition areas between terrestrial and aquatic environments where groundwater (GW) and surface water (SW) interactions occur. They are the subject of our present study, using hydrochemistry and environmental isotopes. Two water sampling campaigns in dry and wet seasons for studying physicochemical and natural isotope analysis provided 44 groundwater samples and watertable level measurements from monitoring wells and eight water samples from river, creek, and lake. In the dry season, lake and creek waters presented TDS (<3.64 mg L⁻¹) and high values of TDS in groundwater and river (average 47.71 and 108.7 mg L⁻¹, respectively), showing CaMgHCO₃, NaHCO₃, and NaHCO₃Cl types and precipitation prevalence. However, GW–SW interaction occurred in CaMgCl and CaMgSO₄ groundwater with TDS varying from 93.8 to 164.7 mg L⁻¹ and weathering dominance close to riverbanks. The TDS, sulfate, and sodium were monitoring markers of this interaction. In the wet season, superficial waters and groundwater were more diluted, presenting CaMgHCO₃, NaHCO₃, and NaHCO₃Cl types and precipitation dominance. Overall, the ion exchange was the main hydrochemical process. The δ¹⁸O, δ²H, and d-excess indicated groundwater recharge with a weak evaporation process, rainwater mixture, and water–rock interaction. Maps of the distribution of ions, isotopes, and d-excess showed GW–SW interaction along the riverbanks and depleted groundwater in a large portion of the alluvial plain. The alluvial plains are susceptible areas to precipitation changes due to fast and direct infiltration. Their monitoring can be essential to understand the climate variability and reduce impacts on the shallow aquifer that sustain forests and human life.

中文翻译：

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巴西东南部冲积平原地下水和地表水相互作用的水文地球化学评价

冲积平原是发生地下水 (GW) 和地表水 (SW) 相互作用的陆地和水生环境之间的过渡区域。它们是我们目前研究的主题，使用水化学和环境同位素。为研究物理化学和天然同位素分析而在旱季和雨季进行的两次水采样活动提供了来自监测井的 44 个地下水样品和地下水位测量值以及来自河流、小溪和湖泊的 8 个水样。在旱季，湖水和溪水的 TDS（<3.64 mg L ^-1）和地下水和河流的高 TDS 值（分别为平均 47.71 和 108.7 mg L ^-1），显示 CaMgHCO ₃、NaHCO ₃和 NaHCO ₃Cl 类型和降水流行。然而，GW-SW 相互作用发生在 CaMgCl 和 CaMgSO ₄地下水中，TDS 从 93.8 到 164.7 mg L ^-1不等，靠近河岸的风化占优势。TDS、硫酸盐和钠是这种相互作用的监测标志物。雨季地表水和地下水较稀薄，表现为CaMgHCO ₃、NaHCO ₃和NaHCO ₃ Cl类型和降水优势。总的来说，离子交换是主要的水化学过程。δ ¹⁸ O、δ ²H 和 d-过量表明地下水补给具有弱蒸发过程、雨水混合和水-岩相互作用。离子、同位素和 d-过量的分布图显示了沿河岸的 GW-SW 相互作用并耗尽了大部分冲积平原的地下水。由于快速和直接的渗透，冲积平原是易受降水变化影响的地区。它们的监测对于了解气候变化和减少对维持森林和人类生命的浅层含水层的影响至关重要。