Hydrology and biogeochemistry of zero-order channels draining arctic hillslopes

Abstract:

Hydrologic flowpaths couple terrestrial and aquatic ecosystems and are responsive to changing climate in the arctic. However, significant uncertainty remains regarding the character and strength of links between terrestrial ecosystems and downstream aquatic ecosystems. We investigated spatial and temporal patterns in solute concentrations and stream discharge of zero-order channels, termed water tracks, draining hillslopes underlain by permafrost within the Kuparuk Basin of northern Alaska. Water tracks are ubiquitous features in this region, and may serve as a key regulator of elemental fluxes between terrestrial and aquatic ecosystems. Flow in water tracks was highly responsive to precipitation. Snowmelt dominated the annual hydrograph and in summer, rapid drying occurred between rain events. Despite widespread drying after snowmelt, isotopes of water indicated that snow-derived water contributed to flow in water tracks and the receiving river for several weeks beyond the snowmelt period, indicating capacity for storage of water in catchments even when thaw depth is shallow. In contrast, the snowmelt-derived flush of dissolved organic carbon, nitrogen, and phosphorus subsided with discharge, indicating limited supplies of these elements, or rapid uptake within catchments. After snowmelt, concentrations of nitrogen and phosphorus, the elements limiting primary production of terrestrial and aquatic ecosystems, respectively, remained low or undetectable in inorganic forms, except during large storms. Thus we expect that changes to the intensity or magnitude of precipitation will alter the availability and distribution of limiting nutrients within tundra catchments. Our observations of zero-order arctic channels indicate that changes in precipitation patterns and thaw dynamics may alter nutrient regimes of arctic ecosystems due to the key functions of nutrient delivery and distribution performed by water tracks. Strong nutrient limitation in terrestrial and aquatic ecosystems indicates potential for change in the structure and function of ecosystems under altered nutrient regimes in the arctic.