Multi-year impacts of permafrost disturbance and thermal perturbation on High Arctic stream chemistry

Abstract

Permafrost disturbances (such as active layer detachment (ALD) slides) and thermal perturbation (deep ground thaw from high soil temperatures) alter Arctic surface water chemistry. However, the potential multi-year impacts on water chemistry and the ultimate recovery time are not well understood. This study evaluates the impacts on surface waters and recovery following disturbance of a High Arctic catchment in 2007 from ALDs. We measured ion concentrations and stable isotopes in surface waters collected between 2006 and 2014 from paired catchments — one disturbed and the other not. The years 2007 and 2012 were exceptionally warm and represent unusual thermal perturbation for both catchments. Results indicate that the exposure and mobilization of soluble ions in near surface soil is a key control over dissolved ion concentrations and composition following ALDs. Runoff in the disturbed catchment shows increased total dissolved solute (TDS) concentrations and seasonal TDS fluxes and changes to the relative composition of individual ions in surface water. These impacts persisted for the 7 year study duration after disturbance and are consistent with the thawing of the solute-rich transient layer and upper permafrost. Thermal perturbation increased TDS concentrations and seasonal fluxes in runoff for up to 2 years, as ions released from ground thaw appear to be available for flushing in subsequent summers.