A significant portion of the disproportionally high chemical weathering flux in volcanic island arcs may originate from hydrothermal fluid-rock interaction, thereby compromising the accurate estimate of atmospheric CO₂ consumption rates. The objective of this study is to evaluate how the riverine Ge/Si ratio and Si isotopes, two well-established tracers of weathering, respond to hydrothermal inputs. The work took place in Basse-Terre, Guadeloupe, a tropical volcanic island with a dense river network, high chemical weathering fluxes and various hydrothermal surface manifestations. We characterized the Ge/Si ratio and δ³⁰Si of 15 thermal springs, nine non-impacted (NI) rivers and 13 hydrothermally-impacted (HI) rivers. The soil solution from a highly weathered soil profile (Ferralsol) and a clayey-rock corresponding to the material exposed in an extinct hydrothermal system were also measured. A new purification method was successfully developed in order to allow the reliable measurement of Si isotopes in SO₄²⁻- and Cl⁻-rich thermal spring and HI river waters by mass spectrometry. Basse-Terre's thermal springs have variable Ge/Si ratios (0.05–21.03 μmol.mol⁻¹) and δ³⁰Si (0.71–1.50‰), but with no apparent relationship to the water compositional type. The Ge/Si ratio (0.15–2.57 μmol.mol⁻¹) and Si isotope composition (0.26–1.21‰) values of the NI rivers reveal differences in the watersheds' weathering degree. Dissolution of Ge- and ²⁸Si-rich secondary minerals explains the high Ge/Si and isotopically light composition of the northern NI rivers draining strongly weathered terranes. The Ge/Si ratio and δ³⁰Si values measured for the NI and HI rivers overlap, implying that they cannot be used to diagnose hydrothermal contributions to river basins unambiguously. However, when combined with the Cl⁻ and SO₄²⁻ concentrations, the analysis of Ge and Si in the HI rivers suggests that water seeping through an extinct hydrothermal system produces SO₄-rich drainages with distinctively lower Ge/Si ratios than those inferred for watersheds receiving thermal spring discharges associated with an active hydrothermal system. Overall, our results provide new constraints for applying and interpreting Ge/Si and Si isotope measurements to study weathering in volcanic environments.

火山岛弧中不成比例的高化学风化通量的很大一部分可能源自水热流体-岩石相互作用，从而损害了对大气CO ₂消耗率的准确估算。这项研究的目的是评估河流中锗/硅比和硅同位素（两种公认的风化示踪剂）对热液输入的响应。这项工作在瓜德罗普岛的巴斯特尔（Basse-Terre）进行，瓜德罗普岛是一个热带火山岛，拥有密集的河网，高化学风化通量和各种热液面表现。我们的特点在Ge / Si比和δ ³⁰共有15个温泉，9条非影响（NI）河流和13条热液影响（HI）河流。还测量了来自高度风化土壤剖面（Ferralsol）的土壤溶液和对应于已灭绝热液系统中暴露物质的黏土岩石。一种新的纯化方法，以允许Si的可靠的测量同位素在SO研制成功₄ ^2-和Cl - ^-通过质谱法富热弹簧和HI河水。巴斯特尔的热弹簧具有可变锗/硅比（0.05-21.03μmol.mol ^-1）和Δ ³⁰的Si（0.71-1.50‰），但与去水组成型没有明显的关系。Ge / Si比（0.15–2.57μmol.mol- ¹）和NI河流的Si同位素组成（0.26-1.21‰）值揭示了流域风化程度的差异。富含Ge和^28种Si的次生矿物的溶解解释了北NI河中高Ge / Si和同位素轻的成分，这些河流排出了强烈风化的地层。在Ge / Si比和δ ^30个为NI和HI河流测量的Si值重叠，这意味着它们不能被用于诊断对流域明确地热液贡献。然而，当与氯结合^-和SO _4倍^2-的浓度，Ge和Si在HI河流的分析表明，水通过水热灭绝系统渗出产生SO ₄丰富的排水系统，Ge / Si比明显低于那些接收与活跃水热系统相关的温泉排放的流域的锗/硅比率。总体而言，我们的结果为应用和解释Ge / Si和Si同位素测量值以研究火山环境中的风化提供了新的限制。