Recovery of arctic tundra from thermal erosion disturbance is constrained by nutrient accumulation: a modeling analysis

Abstract

Abstract. We calibrated the Multiple Element Limitation (MEL) model to Alaskan arctic tundra to simulate recovery of thermal erosion features (TEFs) caused by permafrost thaw and mass wasting. TEFs could significantly alter regional carbon (C) and nutrient budgets because permafrost soils contain large stocks of soil organic matter (SOM) and TEFs are expected to become more frequent as the climate warms. We simulated recovery following TEF stabilization and did not address initial, short-term losses of C and nutrients during TEF formation. To capture the variability among and within TEFs, we modeled a range of post-stabilization conditions by varying the initial size of SOM stocks and nutrient supply rates. Simulations indicate that nitrogen (N) losses after the TEF stabilizes are small, but phosphorus (P) losses continue. Vegetation biomass recovered 90% of its undisturbed C, N, and P stocks in 100 years using nutrients mineralized from SOM. Because of low litter inputs but continued decomposition, younger SOM continued to be lost for 10 years after the TEF began to recover, but recovered to about 84% of its undisturbed amount in 100 years. The older recalcitrant SOM in mineral soil continued to be lost throughout the 100-year simulation. Simulations suggest that biomass recovery depended on the amount of SOM remaining after disturbance. Recovery was initially limited by the photosynthetic capacity of vegetation but became co-limited by N and P once a plant canopy developed. Biomass and SOM recovery was enhanced by increasing nutrient supplies, but the magnitude, source, and controls on these supplies are poorly understood. Faster mineralization of nutrients from SOM (e.g., by warming) enhanced vegetation recovery but delayed recovery of SOM. Taken together, these results suggest that although vegetation and surface SOM on TEFs recovered quickly (25 and 100 years, respectively), the recovery of deep, mineral soil SOM took centuries and represented a major ecosystem C loss.

Ecosystem responses to climate change at a Low Arctic and a High Arctic long-term research site

“…8) indicate that this biomass increase is largely the result of increased growth by deciduous shrubs (e.g., dwarf birch, willows, and alder) in response to multi-year warming, but this response is shared with graminoids and forbs. Several researchers attribute the slow increase in biomass to a slow increase in the availability of N to plants (Shaver et al 1992, 2014; Pearce et al 2015; Jiang et al 2015). It is well known through warming and fertilization experiments that the N supply strongly limits plant growth in northern Alaska and that warming increases the microbial mineralization of organic nitrogen in the soil, the major source of N to plants in the tundra.…”

Modeling long‐term changes in tundra carbon balance following wildfire, climate change, and potential nutrient addition

“…Although climate warming increases soil respiration, MEL predicts that the greater increase in photosynthesis drives the arctic tundra ecosystem to become a strong C sink. Using the MEL model, Pearce et al (2015) conducted a sensitivity analysis for a wide range of nutrient supply and initial soil properties. MEL also indicates stronger stimulation of mineralization rates with warmer temperature.…”

“…Because the tussocks retained dead leaves for several years, we included standing dead litter in the debris pool, which did not decay directly but represented a short-term storage pool that was gradually converted to Phase I material where it began to decompose (Hyvönen andÅgren 2001, Pearce et al 2015). The calibration and spin-up procedures for the model are fully presented in Pearce et al (2015) and Jiang et al (2015a). We also ignore the denitrification process in the model because in arctic tundra the concentration of nitrate in soil is extremely low for two reasons.…”

“…Although effects of N and P additions have been examined in field studies, most studies either conducted a single treatment (Shaver and Chapin 1980, Wookey et al 1995, Robinson et al 1998 or put extremely high factorial N and P additions (e.g., Henry et al 1986, Shaver andChapin 1995). To constrain these uncertainties and investigate the underlying mechanisms that control long-term recovery of tundra ecosystems from disturbance, this study employed the multiple element limitation (MEL) model (Rastetter et al 2013, Jiang et al 2015a, Pearce et al 2015 to simulate long-term C and nutrient cycles along a burn severity gradient of the Anaktuvuk River fire scar with varied future climate scenarios. To constrain these uncertainties and investigate the underlying mechanisms that control long-term recovery of tundra ecosystems from disturbance, this study employed the multiple element limitation (MEL) model (Rastetter et al 2013, Jiang et al 2015a, Pearce et al 2015 to simulate long-term C and nutrient cycles along a burn severity gradient of the Anaktuvuk River fire scar with varied future climate scenarios.…”

Reviews and syntheses: Effects of permafrost thaw on Arctic aquatic ecosystems

“…While these features can be numerous in impacted areas (Lacelle et al, 2015) they take up a relatively small percentage of the total landscape area (1.5 % in Alaska; Krieger, 2012). Individual TEFs have lifecycles on the order of decades Pearce et al, 2014), and -while they are active -may have intense local impacts on sediment and ionic fluxes to freshwater systems (see below). They also seem likely to act as a population of features, however, only a small portion of which will be active at any one time within the landscape.…”