Ice Wedge Degradation and Stabilization Impact Water Budgets and Nutrient Cycling in Arctic Trough Ponds

Abstract

Trough ponds are ubiquitous features of Arctic landscapes and an important component of freshwater aquatic ecosystems. Permafrost thaw causes ground subsidence, creating depressions that gather water, creating ponds. Permafrost thaw also releases solutes and nutrients, which may fertilize these newly formed ponds. We measured water budget elements and chloride, ammonium, and dissolved organic nitrogen (DON) across a chronosequence of trough ponds representing different stages of ice wedge degradation and stabilization. We developed a coupled hydrologic and biogeochemical model to explore how ice wedge degradation affects hydrology and nutrient availability in trough ponds in the advanced degradation stages (DAs), which are characterized by deep troughs with warmer temperatures relative to the other stages. DAs experienced greater evaporation than the other stages, and subsurface inflows entered the DAs from a wide area. Chloride accumulated in the ponds with time since thaw, implying that subsurface fluxes are delivering solutes from the thawing permafrost. Ammonium accumulated at high rates in the initial degradation stage and was seasonally depleted over the summer in all degradation stages. Ammonium trends in the DAs were consistent with high concentration inflows and in‐pond assimilation at rates between 0.37 and 2.0 mg N m−2 day−1. Seasonal DON trends indicated that the accumulation of recalcitrant organic matter may eventually limit aquatic ecosystem production and foster pond infilling. These results provide direct evidence of nutrient release from thawing permafrost and the utilization of these nutrients by Arctic trough pond ecosystems and highlight infilling as a mechanism by which Arctic surface waters may be lost.

Feedbacks Between Surface Deformation and Permafrost Degradation in Ice Wedge Polygons, Arctic Coastal Plain, Alaska

“…This process systematically reshapes the overlying microtopography in a way that tends to improve soil aeration (Liljedahl et al, 2016), thereby altering rates of aerobic and anaerobic microbial respiration (Grosse et al, 2011;Lipson et al, 2012;Lara et al, 2015;Wainwright et al, 2015). Ice wedge degradation across the Arctic has accelerated abruptly in the last three decades in response to above-average summer temperatures (Farquharson et al, 2019;Fraser et al, 2018;Jorgenson et al, 2006Jorgenson et al, , 2015Koch et al, 2018;Liljedahl et al, 2016;Raynolds et al, 2014). However, predicting rates of ice wedge melting in a still warmer future is challenging, as thawing processes are influenced by a complex set of positive and negative feedbacks related to hydrology, geomorphology, and vegetation (Jorgenson et al, 2006(Jorgenson et al, , 2015Kanevskiy et al, 2017).…”

Regional Patterns and Asynchronous Onset of Ice-Wedge Degradation since the Mid-20th Century in Arctic Alaska

“…Seasonally, water levels and extent on the North Slope peak after spring snowmelt, draw down in midsummer due to evapotranspiration and thawing of the active-layer, and then usually increase in late summer due to rainfall and reduced evapotranspiration [40][41][42]. For example, in flat terrain with mixed low-and high-centered polygons at Prudhoe Bay, Koch et al [43] estimated that surface water temporarily covered 49% of the land during snowmelt, but only 5% during midsummer (primarily in thermokarst troughs). Thermokarst pits and troughs tend to have steep banks, such that incremental changes in water depth have limited effects on surface water extent; for example, Jorgenson and others [18] estimated that the effects of seasonal and interannual variation in water levels are small (≈1% of area) when using midsummer (i.e., July) imagery.…”

A distributed analysis of lateral inflows in an Alaskan Arctic watershed underlain by continuous permafrost

“…Second, lateral inflows on the coastal plain have historically only been considered significant for ponded surface waters (Boike etal., ; Bowling, Kane, Gieck, Hinzman, & Lettenmaier, ; Helbig etal., ; Jorgenson etal., ; Koch, ; Koch etal., ), whereas contributions to river discharge have been shown or assumed to be negligible (Arp etal., ; Bowling etal., ; Kane etal., ; Kane etal., ; Rovansek, Hinzman, & Kane, ). The contribution of coastal plain lateral inflows to river discharge has not been testable for the Kuparuk River until now, as previous studies have compared water balances for the entire basin against those with the foothill basins.…”

“…The fate of carbon in surface waters depends, in part, on the exposure history to sunlight (Cory, Harrold, Neilson, & Kling, ; Cory, Ward, Crump, & Kling, ; Li etal., ), which can be related to travel time distributions and therefore the spatial and temporal organization of lateral inflows (Snell & Sivapalan, ). Additionally, lateral inflows are important in the hydrologic (Boike, Wille, & Abnizova, ; Helbig etal., ; Koch, ) and nutrient (Koch, Jorgenson, Wickland, Kanevskiy, & Striegl, ) budgets for surface water bodies on the Arctic coastal plain. As a result, understanding the spatial distribution of lateral inflows is important for determining the degree to which carbon released from thawing permafrost may be mineralized and evaded to the atmosphere and the spatial distribution of nutrients.…”