Biogeochemical responses of arctic hillslopes to storms and seasonal thaw

Abstract:

Resilience of watersheds includes maintenance of biogeochemical functions, including retention and transport of solutes, following perturbations. In the arctic, important perturbations that may result in departure from the current state of watersheds include gradual or catastrophic loss of permafrost, increasing temperature, and increased intensity of storms. However, these long-term changes are occurring against the backdrop of variation introduced by seasonality and storms. Thus, establishing baselines that capture temporal patterns is an essential step in predicting vulnerability of arctic watersheds to climate-induced change. We have documented temporal patterns in solute concentrations of six water tracks, zero-order channels that drain arctic hillslopes. Temporal patterns were typically site-specific, underscoring the value of watershed monitoring for predicting responses to perturbations. In some catchments, peak export of organic carbon, nitrogen, and phosphorus occurred during snowmelt, whereas in others, flushing during storms yielded greater export. Concentrations of non-limiting inorganic solutes (e.g., sulfate, calcium) increased through the thaw period in some catchments, suggesting that these solutes may serve as indicators of degrading permafrost. We observed a decrease in the magnitude of flushing of biolabile solutes (e.g., ammonium, organic carbon) during storms through the thaw season, reflecting hydrologic disconnection of upper, organic soils as thaw depth increases and flowpaths deepen. The observed patterns establish a template of temporal variation against which future observations may be assessed to evaluate departures from a stable state.