Processes governing the stable isotope composition of water in the St. Lawrence river system, Canada

Linkages between δ¹⁸O–δ²H and hydrological processes have been investigated from isotopic time series recorded in the St. Lawrence River basin. Three stations were monitored from 1997 to 2008. They include the Ottawa River, the St. Lawrence River main channel at Montreal and the fluvial estuary. All sites depict seasonal isotopic cycles characterized by heavy isotope depletions during the snowmelt period and heavy isotope enrichments throughout the ice-free period. The data define δ²H–δ¹⁸O regression lines falling below the meteoric water line. In the Ottawa River, calculations suggest that approximately 8 % of the total inflow to the basin is lost through evaporation. In the St. Lawrence River main channel, seasonal isotopic fluctuations most likely reflect hydrological processes occurring within the Great Lakes and mixing with tributaries located downstream. In the St. Lawrence River fluvial estuary, isotopic data allow partitioning streamflow components and suggest that the recorded seasonal variations mainly respond to mixing processes.

本研究基于圣劳伦斯河流域（St. Lawrence River basin）记录的同位素时间序列，探究了氧18同位素（δ¹⁸O）与氘同位素（δ²H）和水文过程之间的关联。1997年至2008年间，研究团队对三处监测站点开展了观测，分别为渥太华河（Ottawa River）、蒙特利尔河段的圣劳伦斯干流河道以及河流型河口（fluvial estuary）。所有监测点位均呈现出季节性同位素循环特征：融雪期（snowmelt period）为重同位素贫化阶段，无冰期（ice-free period）则为重同位素富集阶段。本次数据集得到的δ²H-δ¹⁸O回归直线均位于大气水线（meteoric water line）下方。针对渥太华河的计算结果显示，该流域总径流入流中约有8%通过蒸发作用损失。在圣劳伦斯干流河道中，季节性同位素波动大概率反映了五大湖（Great Lakes）内部发生的水文过程，以及下游支流的汇入混合作用。在圣劳伦斯河河流型河口区域，同位素数据可用于径流组分（streamflow components）划分，研究结果表明所记录的季节性变化主要由混合过程主导。