Seasonal connections between meteoric water and streamflow generation along a mountain headwater stream,Hydrological Processes

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Seasonal connections between meteoric water and streamflow generation along a mountain headwater stream
Hydrological Processes ( IF 2.8 ) Pub Date : 2021-01-02 , DOI: 10.1002/hyp.14029
Sam J. Leuthold _{1,

2} , Stephanie A. Ewing ₁ , Robert A. Payn _{1,

2} , Florence R. Miller ₁ , Stephan G. Custer ₃

Affiliation

In snowmelt‐driven mountain watersheds, the hydrologic connectivity between meteoric waters and stream flow generation varies strongly with the season, reflecting variable connection to soil and groundwater storage within the watershed. This variable connectivity regulates how streamflow generation mechanisms transform the seasonal and elevational variation in oxygen and hydrogen isotopic composition (δ¹⁸O and δD) of meteoric precipitation. Thus, water isotopes in stream flow can signal immediate connectivity or more prolonged mixing, especially in high‐relief mountainous catchments. We characterized δ¹⁸O and δD values in stream water along an elevational gradient in a mountain headwater catchment in southwestern Montana. Stream water isotopic compositions related most strongly to elevation between February and March, exhibiting higher δ¹⁸O and δD values with decreasing elevation. These elevational isotopic lapse rates likely reflect increased connection between stream flow and proximal snow‐derived water sources heavily subject to elevational isotopic effects. These patterns disappeared during summer sampling, when consistently lower δ¹⁸O and δD values of stream water reflected contributions from snowmelt or colder rainfall, despite much higher δ¹⁸O and δD values expected in warmer seasonal rainfall. The consistently low isotopic values and absence of a trend with elevation during summer suggest lower connectivity between summer precipitation and stream flow generation as a consequence of drier soils and greater transpiration. As further evidence of intermittent seasonal connectivity between the stream and adjacent groundwaters, we observed a late‐winter flush of nitrate into the stream at higher elevations, consistent with increased connection to accumulating mineralized nitrogen in riparian wetlands. This pattern was distinct from mid‐summer patterns of nitrate loading at lower elevations that suggested heightened human recreational activity along the stream corridor. These observations provide insights linking stream flow generation and seasonal water storage in high elevation mountainous watersheds. Greater understanding of the connections between surface water, soil water and groundwater in these environments will help predict how the quality and quantity of mountain runoff will respond to changing climate and allow better informed water management decisions.

中文翻译：

山区水源流与流水之间的季节性联系

在融雪驱动的山区流域中，随着季节的变化，流域水和河流水流之间的水文连通性变化很大，这反映了与流域内土壤和地下水存储的可变联系。此变量连接水流的调节作用产生机构如何变换季节和正视变化氧和氢同位素组成（δ ¹⁸ O和δD）大气降水的。因此，溪流中的水同位素可以指示即时连通性或更长时间的混合，特别是在高起伏的山区流域。我们的特点δ ¹⁸蒙大拿州西南部山头流域的溪流水中O和δD值沿海拔梯度变化。二月和三月之间有关最强烈的高程数据流的水同位素组成，表现出较高的δ ^18个随海拔O和δD值。这些海拔同位素流失率可能反映了溪流与严重受海拔同位素影响的近端雪源水之间的联系增加。这些模式夏季采样期间失踪，当始终较低δ ¹⁸ O和溪水的δD值反映融雪或更冷降雨贡献，尽管更高δ ¹⁸季节性暖雨中预期的O和δD值。同位素值一贯较低，并且在夏季没有升高的趋势，这表明由于土壤干燥和蒸腾作用，夏季降水和水流产生之间的连通性较低。作为溪流与相邻地下水之间断续的季节性连通性的进一步证据，我们观察到冬季后期硝酸盐在较高的海拔高度冲入溪流中，这与河岸湿地中矿化氮积累的联系增加有关。这种模式与仲夏硝酸盐负荷在较低海拔的模式不同，后者表明沿河道的人类娱乐活动增加。这些观测结果提供了将高海拔山区流域的水流产生与季节性储水联系起来的见解。进一步了解这些环境中地表水，土壤水和地下水之间的联系将有助于预测山区径流的质量和数量将如何响应不断变化的气候并做出更明智的水管理决策。

更新日期：2021-02-19

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