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（St. Lawrence River）流域记录的同位素时间序列，探究了δ¹⁸O–δ²H与水文过程之间的关联。研究于1997年至2008年间对三个站点进行监测，三个站点分别为渥太华河（Ottawa River）、位于蒙特利尔的圣劳伦斯干流河道以及圣劳伦斯河河口感潮段。所有站点均呈现季节性同位素循环特征：融雪期为重同位素贫化时段，无冰期则为重同位素富集时段。拟合得到的δ²H–δ¹⁸O回归直线均位于大气降水线（meteoric water line）下方。针对渥太华河的计算结果表明，该流域总入流量中约有8%通过蒸发作用损耗。圣劳伦斯干流河道的季节性同位素波动，大概率反映了五大湖（Great Lakes）内部的水文过程以及下游支流的水体混合作用。在圣劳伦斯河河口感潮段，同位素数据可用于分割径流组分，结果显示观测到的季节性变化主要由水体混合过程主导。