How landscape heterogeneity governs stream water concentration-discharge behavior in carbonate terrains (Konza Prairie, USA)
How landscape heterogeneity governs stream water concentration-discharge behavior in carbonate terrains (Konza Prairie, USA)
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DOI：
10.1016/j.chemgeo.2018.12.002
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发表时间：
2019-11
期刊：
影响因子：
3.9
通讯作者：
P. Sullivan;Marvin Wes Stops;G. Macpherson;Li Li-Li;D. Hirmas;W. Dodds
中科院分区：
文献类型：
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作者：
P. Sullivan;Marvin Wes Stops;G. Macpherson;Li Li-Li;D. Hirmas;W. Dodds
越来越多的证据表明，改变碳酸盐地区地下水通量和二氧化碳浓度的生态系统变化，可能会在人类时间尺度上推动化学风化速率、溪水化学和流动路径演变的可测量变化。我们通过探索Konza Prairie(KS，美国)碳酸盐地形景观中木本植物对草原的侵蚀是否导致景观-溪流连通性的差异，从而导致溪水溶质的行为，来检验这一观点。在Konza观察到了伍迪侵蚀(高达60%的覆盖率)的分水岭，特别是那些经历四年或更长时间火灾回归的分水岭。我们以三个水源流域(两个草原和一个木本侵蚀)和一个下游汇流为重点，分析了2015-2016年间的径流流量和化学成分(主要阴离子、阳离子和溶解营养物质)。我们观察到，与较少侵蚀的草原流域相比，木本侵蚀的流域表现出更大的面积归一化溶质通量和更大程度的地源物种的化学动力行为。与低阶分水岭相比，下游汇流对这些相同溶质表现出最强的化学稳定行为。我们解释说，木本侵蚀的流域的化学动力学行为是由更多不同的流动路径和溶质来源引起的，这些物质来源对这条河流有贡献。端元混合分析(EMMA)支持这一假说，但也指出了可能的“缺失”端元，我们解释为可能是来自沿石灰岩-泥岩边界的粘土风化的溶质。我们援引草本植物和木本植物之间生根系统的差异来解释这些源地之间在流动路径和溶质生成方面的差异，因为它们毗邻而坐，解剖了相同的近水平(倾角0.1-0.21°NW)的岩性单位，并经历了相同的气候。如果这些过程在其他地点也适用，那么全球观察到的木本植物对草原的侵蚀可能会加深流动路径，增强来自生态系统的化学风化通量，并在长期内改变土壤发展和景观演变的轨迹。
Mounting evidence suggests ecosystem changes that alter subsurface water fluxes and carbon dioxide concentrations in carbonate terrains may drive measurable changes in chemical weathering rates, stream water chemistry, and flow path evolution on human timescales. We test this idea by exploring if the encroachment of woody vegetation into grasslands in a carbonate terrain landscape at the Konza Prairie (KS, USA) has resulted in differences in landscape-stream connectivity and, thus, the behavior of stream water solutes. Woody encroachment (up to 60% cover) at Konza has been observed on watersheds, particularly those that experience a fire return interval of four years or greater. We focus on three headwater catchments (two grassland and one woody-encroached) and a downstream confluence, and analyze stream water discharge and chemistry (major anions, cations, and dissolved nutrients) measured from 2015 to 2016.We observe that the woody-encroached watershed exhibits a greater area-normalized solute flux and greater degree of chemodynamic behavior for most geogenic species compared to the less encroached grassland watersheds. The downstream confluence exhibits the most chemostatic behavior for these same solutes compared to the low order watersheds. We interpret the chemodynamic behavior of the woody-encroached watersheds to arise from a greater diversity of flow paths and solute sources that contribute to this stream. End member mixing analysis (EMMA) supports this hypothesis but also indicates a possible “missing” end member which we interpret to be solutes likely derived from clay weathering along limestone-mudstone boundaries. We invoke differences in rooting systems between grass and woody species to explain the differences in flow paths and solute generation between these headwater sites given that they sit adjacent to each other, dissect the same nearly horizontal (dip 0.1–0.21°NW) lithologic units, and experience the same climate. If these processes hold true at other sites, then the globally observed encroachment of woody vegetation into grasslands may deepen flow paths and enhance chemical weathering fluxes from ecosystems, and over long-time periods alter the trajectory of soil development and landscape evolution.