Sediment and nutrient delivery from thermokarst features in the foothills of the North Slope, Alaska: Potential impacts on headwater stream ecosystems

Abstract

Permafrost is a defining characteristic of the Arctic environment. However, climate warming is thawing permafrost in many areas leading to failures in soil structure called thermokarst. An extensive survey of a 600 km2 area in and around the Toolik Lake Natural Research Area (TLNRA) revealed at least 34 thermokarst features, two thirds of which were new since ∼1980 when a high resolution aerial survey of the area was done. Most of these thermokarst features were associated with headwater streams or lakes. We have measured significantly increased sediment and nutrient loading from thermokarst features to streams in two well‐studied locations near the TLNRA. One small thermokarst gully that formed in 2003 on the Toolik River in a 0.9 km2 subcatchment delivered more sediment to the river than is normally delivered in 18 years from 132 km2 in the adjacent upper Kuparuk River basin (a long‐term monitoring reference site). Ammonium, nitrate, and phosphate concentrations downstream from a thermokarst feature on Imnavait Creek increased significantly compared to upstream reference concentrations and the increased concentrations persisted over the period of sampling (1999–2005). The downstream concentrations were similar to those we have used in a long‐term experimental manipulation of the Kuparuk River and that have significantly altered the structure and function of that river. A subsampling of other thermokarst features from the extensive regional survey showed that concentrations of ammonium, nitrate, and phosphate were always higher downstream of the thermokarst features. Our previous research has shown that even minor increases in nutrient loading stimulate primary and secondary production. However, increased sediment loading could interfere with benthic communities and change the responses to increased nutrient delivery. Although the terrestrial area impacted by thermokarsts is limited, the aquatic habitat altered by these failures can be extensive. If warming in the Arctic foothills accelerates thermokarst formation, there may be substantial and wide‐spread impacts on arctic stream ecosystems that are currently poorly understood.

Bacterial production in subarctic peatland lakes enriched by thawing permafrost

“…Slumping of permafrost soils into Alaskan streams increases their inorganic and organic concentrations (Bowden et al, 2008), but phosphorus adsorption onto clays may decrease SRP concentrations in some mineral permafrost environments (Breton et al, 2009). Nitrate export from the Kuparuk River catchment on the Alaska North Slope increased 5-fold between the late 1970s and early 2000s and may have been related to permafrost soil and vegetation effects (McClelland et al, 2007).…”

Transformation of terrestrial organic matter along thermokarst-affected permafrost coasts in the Arctic

“…It is of particular importance for the mobilization of OM, as it triggers its release by disturbing the frozen ground Bowden et al, 2008;Vonk et al, 2013). Thermokarst in upland, inland, sub-Arctic, and High Arctic permafrost regions, was intensively studied focusing on the lability of permafrost carbon, greenhouse gas emissions, release of nutrients (e.g., nitrogen, phosphorus, sulfur), and impacts on aquatic systems Cassidy et al, 2016;Frey et al, 2007;Turetsky et al, 2007).…”

Surface exposure to sunlight stimulates CO2release from permafrost soil carbon in the Arctic

“…Thawed soils allow for microbial respiration of previously frozen C and seem to increase the net loss of CO 2 to the atmosphere (8), further accentuating the debate on whether thawing of arctic soil C and release as greenhouse gases will create a positive feedback on global warming (9)(10)(11). Furthermore, recent increases in thermokarst failures (12) because of melting ice and soil subsidence (6) indicate that thawed soil C may not be processed in situ, but instead it will be mixed to the surface, exposed to light, and increasingly released as dissolved organic carbon (DOC) to surface waters (13,14). Once exposed, the fate of this C is unknown but will depend on its reactivity to the combined effects of sunlight and microbial processing.…”