Oxygen-18 study of the atmospheric-aquatic linkage in adirondack watersheds

Abstract

Twelve monthly measurements were made of the δ¹⁸O of the water and of the dissolved sulfates in inlet streams and in outlet streams of lakes in three watersheds in the Adirondack Park region of New York. The average$\delta ^{18} {\text{O}}_{{\text{H}}_{\text{2}} {\text{O}}}$ of the surface waters (streams and lakes) of the three watersheds was in the typical range of seasonally varying$\delta ^{18} {\text{O}}_{{\text{H}}_{\text{2}} {\text{O}}}$ of precipitation water, whereas the$\delta ^{18} {\text{O}}_{{\text{SO}}_{\text{4}}^{{\text{2 - }}} }$ of the surface waters was significantly lower than the typical range of seasonally varying$\delta ^{18} {\text{O}}_{{\text{SO}}_{\text{4}}^{{\text{2 - }}} }$ in precipitation water. Two possible causes for the apparent alteration of δ¹⁸O of the sulfates during percolation of the water through various strata in the ground link between the atmosphere and the watershed lakes are: (1) bacterial redox cycling, in which the sulfate is reduced, allowing isotopic equilibration between the HS0₃ ⁻ ion and associated water, and then catalytically reoxidized to sulfate; and (2) ion exchange, in which the soil strata, containing chemically fixed sulfates, behave as a “column” that is not in sulfate-ion equilibrium with sulfates in the atmospheric recharge water.