Comparison of dissolved inorganic and organic carbon export in the rivers of tropical volcanic island; example from Guadeloupe, French West Indies
Comparison of dissolved inorganic and organic carbon export in the rivers of tropical volcanic island; example from Guadeloupe, French West Indies
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热带火山岛河流溶解性无机碳和有机碳输出比较
DOI：
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发表时间：
2010
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影响因子：
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通讯作者：
M. Benedetti
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作者：
E. Lloret;C. Dessert;J. Gaillardet;P. Albéric;O. Crispi;C. Chaduteau;M. Benedetti
在考虑全球碳循环时，有机质是一个不可忽视的重要因素。需要新的数据，包括在小流域尺度上的有机物质地球化学，来制定更受限制的碳动态和气候模型。其目标是在约束良好的热带小河流地球化学系统中估计DOC和DIC通量，并表征和确定在不同水文制度（即低水位与洪水水位）下输出的有机碳的不同来源。为了回答这些问题，我们研究了法属西印度群岛Basse-Terre岛周围11个小流域在2006年至2008年不同水文制度下的地球化学。结合水体排放，测定了DOC、DIC浓度及其同位素组成（δ13CDOC和δ13CDIC）。有机物质性质的光谱指标被用来表征河流中DOC的来源。DOC/DIC值在0.070 ~ 1.971之间变化，与洪涝条件对应的值最高，表明洪涝条件下这些河流输出的有机质较多。枯水期DOC的同位素组成在-33.5‰~ -29.5‰之间，枯水期在-30.1‰~ -27.2‰之间，表明这两个水文阶段河流的补给来源不同。在低水位时，河流主要由常年地下水补给，而在洪水位时，河流主要由表层土溶液的浸出补给。DOC的年平均通量为2.5 ~ 5.7 t km-2年-1，DIC的年平均通量为4.8 ~ 19.6 t km-2年-1。DOC/DIC比值与流域坡度呈非线性关系。我们的研究结果强调了DOC通量在热带小河流碳质量平衡中的重要性。
Organic matter is an important factor that cannot be neglected when considering global carbon cycle. New data including organic matter geochemistry at the small watershed scale are needed to elaborate more constrained carbon dynamic and climatic models. The objectives are to estimate the DOC and DIC fluxes in well constrained geochemical systems that are small tropical rivers and to characterize and identify the different sources of the organic carbon exported under different hydrological regime (i.e. low water level vs flood level). To answer these questions, we have studied the geochemistry of eleven small watersheds around Basse-Terre Island in the French West Indies during different hydrological regime from 2006 to 2008. Together with water discharge, DOC concentrations, DIC concentrations were measured as well as their isotopic composition (δ13CDOC and δ13CDIC). Spectroscopic indicators of the nature of the organic matter are used to characterize the sources of DOC in the rivers. The ratio DOC/DIC varied between 0.070 and 1.971, with the highest values corresponding to flood conditions, indicating that these rivers export more organic matter during the flood events. The isotopic composition of DOC, ranged from -33.5 to -29.5 ‰ during low water level and from -30.1 to -27.2 ‰ during flood levels, indicates that rivers are fed by different sources during these two hydrological stages. During low water level the rivers were mainly fed by perennial groundwater flow, while during flood level the rivers were fed by lixiviation of top soil solutions. The mean annual fluxes ranged from 2.5 to 5.7 t km-2 yr-1 for the DOC and from 4.8 to 19.6 t km-2 yr-1 for the DIC. The DOC/DIC ratios exhibit a non-linear relationship with the slopes of watershed. Our results emphasize the importance of DOC fluxes in the carbon mass balance in small tropical rivers.