Mechanisms Underlying Near-Universal Export Patterns of Dissolved Carbon From Land to Rivers

IF 5.5 2区 地球科学 Q1 ENVIRONMENTAL SCIENCES
Bryn Stewart, Li Li
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引用次数: 0

Abstract

Land-to-river exports of dissolved carbon, characterized through concentration-discharge (CQ) relationships, follow strikingly consistent, near-universal patterns: dissolved organic carbon (DOC) typically exhibits a flushing pattern (C increases with Q), while dissolved inorganic carbon (DIC) exhibits a dilution pattern (C decreases with Q). Another, albeit sparsely documented, universal pattern is their contrasting vertical distributions in subsurface water—DOC concentrations generally decrease with subsurface depth, whereas DIC concentrations increase. These observations prompt intriguing questions: What mechanisms underlie these near-universal patterns, and how are they interconnected? Here, we address these questions by carrying out numerical experiments across a wide range of conditions using a data-grounded, catchment-scale reactive transport model (BioRT-HBV). Results reveal that biogeochemical reactions governing the production and consumption of dissolved carbon dictate the direction of export patterns (flushing or dilution) by establishing vertical concentration gradients—quantified as the concentration ratios between shallow and deep waters (Cratio). When biogeochemical reactions lead to higher concentrations in shallow soil waters than in deep waters (Cratio > 1), solutes exhibit flushing patterns, and vice versa. Meanwhile, the relative contributions of shallow and deep flow regulate stream concentration variability, where greater deep flow inputs dampen fluctuations and push CQ relationships toward near-zero slopes. These distinct roles of depth-dependent flow paths and biogeochemical processes indicate the importance of subsurface physical and biogeochemical structures in shaping export patterns of dissolved carbon from land to rivers. As climate extremes and human activities intensify, subsurface structure and processes can change, reshaping the future of carbon cycling, water quality, and ecosystem health.

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溶解碳从陆地向河流几乎普遍输出模式的机制
陆地到河流的溶解碳输出,通过浓度-排放量(CQ)关系来表征,遵循惊人一致的、近乎普遍的模式:溶解有机碳(DOC)通常表现为冲洗模式(C随Q增加),而溶解无机碳(DIC)表现为稀释模式(C随Q减少)。另一个虽然文献很少,但普遍的模式是它们在地下水中的垂直分布,doc浓度通常随着地下深度而降低,而DIC浓度则增加。这些观察结果引发了一些有趣的问题:这些近乎普遍的模式背后的机制是什么?它们是如何相互联系的?在这里,我们通过使用基于数据的流域尺度反应性转运模型(BioRT-HBV)在广泛的条件下进行数值实验来解决这些问题。结果表明,控制溶解碳生产和消耗的生物地球化学反应通过建立垂直浓度梯度(量化为浅水和深水之间的浓度比(ratio))来决定出口模式(冲洗或稀释)的方向。当生物地球化学反应导致浅水土壤中的浓度高于深水时(比值>;1)溶质呈现冲刷模式,反之亦然。同时,浅流和深流的相对贡献调节了水流浓度的变化,其中更大的深流输入抑制了波动,并将CQ关系推向接近零的斜率。这些依赖深度的流动路径和生物地球化学过程的不同作用表明,地下物理和生物地球化学结构在塑造陆地到河流的溶解碳输出模式中的重要性。随着极端气候和人类活动的加剧,地下结构和过程可能发生变化,重塑碳循环、水质和生态系统健康的未来。
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来源期刊
Global Biogeochemical Cycles
Global Biogeochemical Cycles 环境科学-地球科学综合
CiteScore
8.90
自引率
7.70%
发文量
141
审稿时长
8-16 weeks
期刊介绍: Global Biogeochemical Cycles (GBC) features research on regional to global biogeochemical interactions, as well as more local studies that demonstrate fundamental implications for biogeochemical processing at regional or global scales. Published papers draw on a wide array of methods and knowledge and extend in time from the deep geologic past to recent historical and potential future interactions. This broad scope includes studies that elucidate human activities as interactive components of biogeochemical cycles and physical Earth Systems including climate. Authors are required to make their work accessible to a broad interdisciplinary range of scientists.
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