Temperature controls production but hydrology controls export of dissolved organic carbon at the catchment scale
Temperature controls production but hydrology controls export of dissolved organic carbon at the catchment scale
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DOI：
10.5194/hess-2019-310
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发表时间：
2019
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通讯作者：
H. Wen;J. Perdrial;S. Bernal;Benjamin W. Abbott;R. Dupas;S. Godsey;A. Harpold;D. Rizzo;Kristen L. Underwood;T. Adler;R. Hale;Gary Sterle;Li Li-Li
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作者：
H. Wen;J. Perdrial;S. Bernal;Benjamin W. Abbott;R. Dupas;S. Godsey;A. Harpold;D. Rizzo;Kristen L. Underwood;T. Adler;R. Hale;Gary Sterle;Li Li-Li
抽象的。通过河流网络的横向碳通量是全球碳收支的一个重要组成部分，但人们对其了解甚少。本文研究了美国宾夕法尼亚州萨斯奎汉纳页岩山临界区观测站的温度和水文条件对溶解有机碳（DOC）生成和输出的影响。应用流域尺度水文地球化学反应输运模型BioRT-Flux-PIHM模拟DOC的动态变化。我们估计了每日DOC生产率（Rp;单个建模网格单元中本地DOC生产率的总和）和每日DOC输出率（Re;在流出口处的浓度和排放的乘积）到下游生态系统。模拟表明，Rp的变化小于一个数量级，主要取决于季节性温度变化。与此相反，Re变化超过三个数量级的强烈依赖于放电和水文连通性。在夏季，高温导致高的大气需水量（和蒸散量），干燥和断开山坡流。Rp达到最大值，但Re处于最小值。该流仅输出DOC从有机质贫乏的地下水和土壤水在狭窄的有机质丰富的洼地与丰富的DOC，DOC积累在集水区。在潮湿的时期（冬季和春季），Rp达到最低值，但Re达到峰值，因为流重新连接到一个更大的上坡地区，冲洗出存储的DOC。该模型再现了所观察到的浓度排放（C-Q）的关系，其特征在于冲洗稀释模式的浓度上升到最大值（冲洗）在阈值排放，然后遵循一般稀释与浓度随排放而降低。这种模式被解释为有机贫深层地下水和土壤水的贡献，从有机丰富的沼泽在最小流量，最大化的百分比贡献的土壤水从有机丰富的沼泽在低流量制度，和增加的贡献上坡土壤水interflow从上坡DOC在高流量制度。这种模式持续不管DOC的生产率，只要更深的地下水流的贡献仍然很低（18%），冲洗稀释C-Q模式转向冲洗模式与DOC浓度随排放量增加。这项研究说明了DOC的生产，主要是由温度控制的时间序列，DOC的输出，主要是由水文流径在流域尺度。未来更温暖和更极端的水文事件的发生可能会加剧这一趋势，DOC的主要横向输出主要由几个主要的风暴事件主导，而DOC在长期干旱期间产生并储存在集水区。
Abstract. Lateral carbon flux through river networks is an important and poorly-understood component of the global carbon budget. This work investigates how temperature and hydrology control the production and export of dissolved organic carbon (DOC) in the Susquehanna Shale Hills Critical Zone Observatory in Pennsylvania, USA. We applied the catchment-scale hydro-biogeochemical reactive transport model BioRT-Flux-PIHM to simulate the DOC dynamics. We estimated the daily DOC production rate (Rp; the sum of local DOC production rates in individual modeling grid cell) and the daily DOC export rate (Re; the product of concentration and discharge at the stream outlet) to downstream ecosystems. Simulations showed that Rp varied by less than an order of magnitude and primarily hinged on seasonal temperature change. In contrast, Re varied by more than three orders of magnitude with a strong dependence on discharge and hydrological connectivity. During summer, high temperatures led to high atmospheric water demand (and evapotranspiration) that dried and disconnected hillslope to stream. Rp reached its maximum but Re was at its minimum. The stream only exported DOC from the organic-poor groundwater and from soil water in the narrow organic-rich swales with enriched DOC such that DOC accumulated in the catchment. During the wet period (winter and spring), Rp reached its minimum but Re peaked because the stream was re-connected to a greater uphill area, flushing out the stored DOC. The model reproduced the observed concentration discharge (C–Q) relationship characterized by a flushing-dilution pattern with a rise in concentrations to a maximum (flushing) at a threshold discharge and then followed a general dilution with concentrations decreasing with discharge. This pattern was explained by the comparable contribution of organic-poor deeper groundwater and soil water from organic-rich swales at the minimum flow, maximized percentage contribution of soil water from organic-rich swales at the low flow regime, and increased contribution of uphill soil water interflow from uphill with less DOC at the high flow regime. This pattern persisted regardless of DOC production rate as long as the contribution of deeper groundwater flow remained low ( 18 %, the flushing-dilution C–Q pattern shifted towards a flushing-only pattern with DOC concentrations increasing with discharge. This study illustrates the temporal asynchrony of DOC production, mostly controlled by temperature, and DOC export, primarily governed by hydrological flow paths at the catchment scale. The occurrence of warmer and more extreme hydrological events in the future could accentuate this asynchrony, with major lateral export of DOC dominated by a few major storm events whereas DOC is produced and stored in the catchment in the prolonged drought periods.