Quantifying groundwater dependence of a sub-polar lake cluster in Finland using an isotope mass balance approach

• Published in: Hydrology and Earth System Sciences
• Main Authors: E. Isokangas, K. Rozanski, P. M. Rossi, A.-K. Ronkanen, B. Kløve
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2015
• Subjects: Technology; T; Environmental technology. Sanitary engineering; TD1-1066; Geography. Anthropology. Recreation; G; Environmental sciences; GE1-350; Northern Finland
• Online Access: https://doi.org/10.5194/hess-19-1247-2015; https://doaj.org/article/bd186563dfa94603aa64648f359fef9d

A stable isotope study of 67 kettle lakes and ponds situated on an esker aquifer (90 km 2 ) in northern Finland was carried out to determine the role and extent of groundwater inflow in groundwater-dependent lakes. Distinct seasonal fluctuations in the δ 18 O and δ 2 H values of lakes are the result of seasonal ice cover prohibiting evaporation during the winter. An iterative isotope mass balance approach was used to calculate the inflow-to-evaporation ratios ( I TOT / E ) of all 67 lakes during the summer of 2013 when the isotopic compositions of the lakes were approaching a steady-state. The balance calculations were carried out independently for 2 H and 18 O data. Since evaporation rates were derived independently of any mass balance considerations, it was possible to determine the total inflow ( I TOT ) and mean turnover time (MTT) of the lakes. Furthermore, the groundwater seepage rates to all studied lakes were calculated. A quantitative measure was introduced for the dependence of a lake on groundwater ( G index) that is defined as the percentage contribution of groundwater inflow to the total inflow of water to the given lake. The G index values of the lakes studied ranged from ca. 39 to 98%, revealing generally large groundwater dependency among the studied lakes. This study shows the effectiveness of applying an isotope mass balance approach to quantify the groundwater reliance of lakes situated in a relatively small area with similar climatic conditions.