Pit lake oxygen and hydrogen isotopic composition in subarctic Sweden: A comparison to the local meteoric water line

Abstract

A local meteoric water line based on rainwater and snow core samples was developed for an area comprising parts of eastern Norrbotten and Västerbotten in northern Sweden. The oxygen and hydrogen isotopic composition of groundwater and water from four pit lakes was compared to the local meteoric water line by line-conditioned excess. The isotopic mass balance method was used to estimate the evaporation over inflow ratio and the residence time of the lakes. The results show that the local meteoric water line for the study area is: δ2H = (7.80 ± 0.09) δ18O + (4.35 ± 1.35) ‰, which is close to the global meteoric water line. The surface water of the four pit lakes all have negative line-conditioned excess values which indicate that they have been affected by evaporation. The groundwater plots on the local meteoric water line making it hard to utilize in a mixing model for a lake where precipitation and groundwater are treated as two different sources. Two scenarios were used to estimate the starting composition of the lakes for the isotopic mass balance method. One was based on the intersection point of the local meteoric water line and the local evaporation line and gave evaporation over inflow ratios ranging from 0.23 to 0.74 and residence times ranging from 7.2 to 44.9 years. The second scenario was based on the weighted average composition of precipitation and gave evaporation over inflow ratios ranging from 0.07 to 0.32 and residence times ranging from 2.8 to 14.9 years.