Search

Changes in soil nutrient availability attributed to climate change and associated permafrost degradation have been reported in several ecosystems. However, little is known about the changes of soil nutrient availability in alpine grassland ecosystems. Based on a comprehensive dataset and random forest models, we investigated soil available nutrients changes and their relationships with environmental factors for the top 10 cm soils across Tibetan grassland between the 1980s and 2010s. During this period, topsoil available nitrogen stocks increased significantly by 24%, while available phosphorus and potassium stocks decreased significantly by 3% and 23%, respectively. Topsoil nutrient availability dynamics varied substantially among vegetation types. Initial nutrient stocks explained the largest proportions of available nutrients changes, though climate, permafrost, vegetation, soil properties, and their interactions also had significant contributions. The increasing rate of active layer thickness was negatively related to soil available nitrogen dynamics but did not significantly change available phosphorus and potassium, indicating that the increase in the annual depth of surface thaw of the permafrost was associated with an increase in soil nitrogen availability but no significant changes in available phosphorus and potassium. These results suggest that the Tibetan alpine grassland ecosystems may shift from nitrogen-limited to phosphorus or potassium-limited in the future.

Vast amounts of soil organic matter (SOM) have been preserved in arctic soils over millennia time scales due to the limiting effects of cold and wet environments on decomposer activity. With the increase in high latitude warming due to climate change, the potential decomposability of this SOM needs to be assessed. In this study, we investigated the capability of mid infrared (MIR) spectroscopy to quickly predict soil carbon and nitrogen concentrations and carbon (C) mineralized during short-term incubations of tundra soils. Active layer and upper permafrost soils collected from four tundra sites on the North Slope of Alaska were incubated at 1, 4, 8 and 16 °C for 60 days. All incubated soils were scanned to obtain the MIR spectra and analyzed for total organic carbon (TOC) and total nitrogen (TN) concentrations, and salt-extractable organic matter carbon (SEOM). Partial least square regression (PLSR) models, constructed using the MIR spectral data for all soils, were excellent predictors of soil TOC and TN concentrations and good predictors of mineralized C for these tundra soils. We explored whether we could improve the prediction of mineralized C by splitting the soils into the groups defined by the influential factors and thresholds identified in a principal components analysis: (1) TOC >10%, (2) TOC 0.6%, (5) acidic tundra, and (6) non-acidic tundra. The best PLSR mineralization models were found for soils with TOC

Heterogeneous environmental controls on permafrost region soil organic carbon stocks can now be quantified with spatial modeling., Large stocks of soil organic carbon (SOC) have accumulated in the Northern Hemisphere permafrost region, but their current amounts and future fate remain uncertain. By analyzing dataset combining >2700 soil profiles with environmental variables in a geospatial framework, we generated spatially explicit estimates of permafrost-region SOC stocks, quantified spatial heterogeneity, and identified key environmental predictors. We estimated that Pg C are stored in the top 3 m of permafrost region soils. The greatest uncertainties occurred in circumpolar toe-slope positions and in flat areas of the Tibetan region. We found that soil wetness index and elevation are the dominant topographic controllers and surface air temperature (circumpolar region) and precipitation (Tibetan region) are significant climatic controllers of SOC stocks. Our results provide first high-resolution geospatial assessment of permafrost region SOC stocks and their relationships with environmental factors, which are crucial for modeling the response of permafrost affected soils to changing climate.

In this contribution, we examined a latitudinal soil transect from interior Alaska, focusing on morphological, physical and chemical characteristics of permafrost affected soils. The aim of this work was to evaluate if latitude (a proxy for temperature change) or other soil forming factors may affect organic layer thickness and, consequently, permafrost depth along the latitudinal gradient of 65° to 69°. Along this gradient, the plant community changed from boreal forest to moist tundra, but this change did not affect the amount of C stored in the organic horizons and the permafrost depth. Hence, we suspected that, at latitudes higher than the 65° degree, the formation of thick and thermally insulating organic layers is controlled mostly by the extent of the pedoturbations produced by the permafrost dynamics and the soil parent material.

We investigated the influence of site characteristics and soil properties on the chemical composition of organic matter in soils collected from a latitudinal transect across northern cold-region through analysis of diffuse reflectance Fourier transform mid infrared (DRIFT) spectra of bulk soils. The study included 119 soil samples collected from 28 sites including tundra, boreal forest, grassland, and coastal rainforest ecosystems. Organic, mineral, and cryoturbated soil horizons, both seasonally and perennially frozen, representing a variety of depths and edaphic conditions were examined. The amount and chemical composition of organic matter, as well as site and soil properties, exerted a strong influence on the DRIFT spectra. The spectra were highly sensitive to the extent of organic matter decomposition, enabling the ordination of organic (Oi, Oe and Oa) horizons. Differences in absorbance intensity for several spectral bands indicated that Oi horizons contained greater abundance of relatively fresh residues, phenolic-OH compounds, aliphatic compounds, and carbohydrates. In contrast, Oa horizons had a greater presence of amide groups, aromatics, CC bonds, carboxylates and carboxylic acids. Another significant factor differentiating these horizons was the incorporation of clays and silicates into the Oa horizons. Calculated ratios of characteristic spectral bands showed a clear trend of increasing decomposition from Oi to Oe to Oa. The DRIFT spectra were related to many site/soil attributes including land cover type, parent material, and associated factors, such as permafrost presence/absence, drainage class, horizon depth, bulk density, cation exchange capacity, and pH. A single DRIFT spectral band was identified that might be used in future studies to quickly estimate the organic carbon, total nitrogen, and carbon:nitrogen ratios of northern soils. Our results demonstrate that the information contained in DRIFT spectra of soil integrates the quantity and chemical composition of soil organic matter with soil properties and highlights the potential for using this information to assess the degradation state of organic matter stored in northern cold-region soils.

Northern circumpolar permafrost soils contain more than a third of the global Soil Organic Carbon pool (SOC). The sensitivity of this carbon pool to a changing climate is a primary source of uncertainty in simulation-based climate projections. These projections, however, do not account for the accumulation of soil deposits at the base of hillslopes (hill-toes), and the influence of this accumulation on the distribution, sequestration, and decomposition of SOC in landscapes affected by permafrost. Here we combine topographic models with soil-profile data and topographic analysis to evaluate the quantity and uncertainty of SOC mass stored in perennially frozen hill-toe soil deposits. We show that in Alaska this SOC mass introduces an uncertainty that is >200% than state-wide estimates of SOC stocks (77 PgC), and that a similarly large uncertainty may also pertain at a circumpolar scale. Soil sampling and geophysical-imaging efforts that target hill-toe deposits can help constrain this large uncertainty.

Ecosystem shifts related to climate change are anticipated for the next decades to centuries based on a number of conceptual and experimentally derived models of plant structure and function. Belowground, the potential responses of soil systems are less well known. We used geochemical steady state models, soil density fractionation, and soil radiocarbon data to constrain changes in soil carbon based on measurements from detrital (free light), aggregate-bound (occluded) and complexed or chemically bound (mineral associated) carbon pools and for bulk soil. We explored a space-for-time sequence of soils along a cold-to-warm climatic gradient from Alaskan Black Spruce forest soil with permafrost (Gelisols; 50 cm Mean Annual Temperature −1.5 ºC), Alaskan White Spruce forest soil lacking permafrost (Inceptisols; 50 cm MAT +3 ºC ), and Iowa Grassland soil lacking permafrost (Mollisols; 50 cm MAT +9 ºC) developed on similar geologic substrates (wind-blown loess deposits). These temperature ranges were also representative of temperatures at 50 cm soil depth from model output by the Community Land Model for the years 2014, 2100, and 2300 for Interior Alaska. Fitting an exponential equation to depth trends in soil C down to 2 m depths, we found that depth distributions of organic C were related mainly to depths of rooting and changes in bulk density. Using output from the geochemical steady state model, the direction and magnitude of the C loss or gain upon ecosystem shift was dictated by the C stocks of initial and final ecosystems. Radiocarbon measurements specific to each soil fraction (free light, occluded, and mineral associated) allowed us to constrain the timing of the potential loss or gain of C in each fraction driven by climatic shifts. Thawing from the Gelisol to Inceptisol in loess parent materials from present day to year 2100 resulted in small net gains to soil C, reflecting the net balance between loss of detrital and gain into occluded and mineral associated C. Greater warming and shifts from Inceptisol to Mollisol analogous to predicted warming from circa 2100 to 2300 resulted in net C losses from both occluded and mineral associated C, although small gains to the free light C fraction occurred throughout the depth profile. Gains to occluded and mineral associated C post- thaw likely reflect aggregate formation and physical protection of C as well as formation of organo-mineral compounds that accompany microbial processing. Greater warming and shifts from Inceptisol to Mollisol, which are analogous to predicted warming circa 2100 to 2300, resulted in net C losses from both occluded and mineral associated C resulting from enhanced decomposition, small gains to the free light C fraction occurred throughout the transition to Mollisol reflecting deeper rooting of the tallgrass prairie system.

Frozen soils or those with permafrost cover large areas of the earth's surface and support unique vegetative ecosystems. Plants growing in such harsh conditions have adapted to small niches, which allow them to survive. In northern Alaska, USA, both moist acidic and non-acidic tundra occur, yet determination of frozen soil pHs currently requires thawing of the soil so that electrometric pH methods can be utilized. Contrariwise, a portable X-ray fluorescence (PXRF) spectrometer was used in this study to assess elemental abundances and relate those characteristics to soil pH through predictive multiple linear regressions. Two operational modes, Soil Mode and Geochem Mode, were utilized to scan frozen soils in-situ and under laboratory conditions, respectively, after soil samples were dried and ground. Results showed that lab scanning produced optimal results with adjusted coefficient of determination (R2) of 0.88 and 0.33 and root mean squared errors (RMSEs) of 0.87 and 0.34 between elemental data and lab-determined pH for Soil Mode and Geochem Mode, respectively. Even though the presence of ice attenuated fluoresced radiation under field conditions, adjusted R2 and RMSEs between the datasets still provided reasonable model generalization (e.g., 0.73 and 0.49 for field Geochem Mode). Principal component analysis qualitatively separated multiple sampling sites based on elemental data provided by PXRF, reflecting differences in the chemical composition of the soils studied. Summarily, PXRF can be used for in-situ determination of soil pH in arctic environments without the need for sample modification and thawing. Furthermore, use of PXRF for determination of soil pH may provide higher sample throughput than traditional eletrometric-based methods, while generating elemental data useful for the prediction of multiple soil parameters.

Soil microbial communities in the Arctic play a critical role in regulating the global carbon (C) cycle. Vast amounts of C are stored in northern high latitude soils, and rising temperatures in the Arctic threaten to thaw permafrost, making relatively inaccessible C sources more available for mineralization by soil microbes. Few studies have characterized how microbial community structure responds to thawing permafrost in the context of varying soil chemistries associated with contrasting tundra landscapes. We subjected active layer and permafrost soils from upland and lowland tundra sites on the North Slope of Alaska to a soil-warming incubation experiment and compared soil bacterial community profiles (obtained by 16S rRNA amplicon sequencing) before and after incubation. The influence of soil composition (characterized by mid-infrared [MIR] spectroscopy) on bacterial community structure and class abundance was analyzed using redundancy and correlation analyses. We found increased abundances of Alphaproteobacteria, Gammaproteobacteria, and Bacteroidetes [Sphingobacteriia] post incubation, particularly in permafrost soils. The categorical descriptors site and soil layer had the most explanatory power in our predictive models of bacterial community structure, highlighting the close relationship between soil bacteria and the soil environment. Specific soil chemical attributes characterizing the soil environments that were found to be the best predictors included MIR spectral bands associated with inorganic C, silicates, amide II (C N stretch), and carboxylics (C–O stretch), and MIR peak ratios representing C substrate quality. Overall, these results further characterize soil bacterial community shifts that may occur as frozen environments with limited access to C sources, as is found in undisturbed permafrost, transition to warmer and more C-available environments, as is predicted in thawing permafrost due to climate change.

Soil nutrient stoichiometry and its environmental controllers play vital roles in understanding soil-plant interaction and nutrient cycling under a changing environment, while they remain poorly understood in alpine grassland due to lack of systematic field investigations. We examined the patterns and controls of soil nutrients stoichiometry for the top 10 cm soils across the Tibetan ecosystems. Soil nutrient stoichiometry varied substantially among vegetation types. Alpine swamp meadow had larger topsoil C:N, C:P, N:P, and C:K ratios compared to the alpine meadow, alpine steppe, and alpine desert. In addition, the presence or absence of permafrost did not significantly impact soil nutrient stoichiometry in Tibetan grassland. Moreover, clay and silt contents explained approximately 32.5% of the total variation in soil C:N ratio. Climate, topography, soil properties, and vegetation combined to explain 10.3–13.2% for the stoichiometry of soil C:P, N:P, and C:K. Furthermore, soil C and N were weakly related to P and K in alpine grassland. These results indicated that the nutrient limitation in alpine ecosystem might shifts from N-limited to P-limited or K-limited due to the increase of N deposition and decrease of soil P and K contents under the changing climate conditions and weathering stages. Finally, we suggested that soil moisture and mud content could be good predictors of topsoil nutrient stoichiometry in Tibetan grassland.

Soil–landscape models serve as a basis for understanding the relationships between soils and landscape, and such models also allow us to study soil distribution, and classification. To understand the distribution of soils and landform relationships in permafrost regions, we developed a soil–landscape model by using See5.0 decision tree software in the Wenquan region of Xinghai County, in the eastern part of permafrost regions of Qinghai–Xizang (Tibetan) Plateau (QTP). The model was based on soil pedon data from 2009. Nine environmental factors closely related to permafrost-affected-soil formation were selected as variables for the model: land surface temperature for warm season and cool season, elevation, slope gradient, slope aspect, planform and profile curvatures, wetness index and NDVI. A 5-fold cross-validation method was applied to verify the effectiveness of the soil–landscape model. The model results were consistent with field observations, and the slope was the most strongly correlated factor with soil type of the nine environmental variables. The soils in the modeled area are mainly Ustic Cambosols and Ustic Isohumisols, which cover about 60.0% and 25.6% of the total area, respectively. Gelic cambosols occur mainly in permafrost region, while Ustic isohumosols occur in the transition region between permafrost and seasonally frozen ground. Further studies are required to utilize the soil–landscape model to predict the spatial distribution of soil types over the QTP.

Field portable X-ray fluorescence (PXRF) spectrometry has become an increasingly popular technique for in-situ elemental characterization of soils. The technique is fast, portable, and accurate, requiring minimal sample preparation and no consumables. However, soil moisture > 20% has been known to cause fluorescence denudation and error in elemental reporting and few studies have evaluated the presence of soil moisture in solid form as ice. Gelisols (USDA Soil Taxonomy), permafrost-affected soils, cover a large amount of the land surface in the northern and southern hemispheres. Thus, the applicability of PXRF in those areas requires further investigation. PXRF was used to scan the elemental composition (Ba, Ca, Cr, Fe, K, Mn, Pb, Rb, Sr, Ti, Zn, and Zr) of 13 pedons in central and northern Alaska, USA. Four types of scans were completed: 1) in-situ frozen soil, 2) re-frozen soil in the laboratory, 3) melted soil/water mixture in the laboratory, and 4) moisture-corrected soil. All were then compared to oven dry soil scans. Results showed that the majority of PXRF readings from in-situ, re-frozen, and melted samples were significantly underestimated, compared to the readings on oven dry samples, owing to the interference expected by moisture. However, when the moisture contents were divided into > 40% and < 40% groups, the PXRF readings under different scanning conditions performed better in the group with < 40% moisture contents. Most elements of the scans on the melted samples with < 40% moisture contents acceptably compared to those of the dry samples, with R 2 values ranging from 0.446 (Mn) to 0.930 (Sr). However, underestimation of the melted samples was still quite apparent. Moisture-corrected sample PXRF readings provided the best correlation to those of the dry, ground samples as indicated by higher R2 values, lower root mean square errors (RMSEs), and slopes closer to 1 in linear regression equations. However, the in-situ (frozen) sample scans did not differ appreciably from the melted sample scans in their correlations to dry sample scans in terms of R 2 values (0.81 vs. 0.88), RMSEs (1.06 vs. 0.85), and slopes (0.88 vs. 0.92). Notably, all of those relationships improved for

We combined C and N related pedon data from the USDA-NRCS National Cooperative Soil Survey Soil Characterization Database with data from the University of Alaska Fairbanks (UAF) northern soils research program, representing 58 and 30 years of field work, respectively. Carbon and N data from 117 UAF pedons were added to 541 pedons from the USDA-NRCS data set for a total of 658. Missing carbon (C), nitrogen (N) and related data were added to nearly all of the USDA-NRCS Arctic region pedons from unpublished UAF data. We present relationships among soil parameters of the data set that are necessary for calculation of pedon soil organic C and N stores. These new relationships are necessary for better estimating missing soil bulk density (Db) from measured soil organic C by high-temperature combustion (SOCHTC) and for conversion of acid chromate reduction soil organic carbon (SOCACR) to SOCHTC. For the USDA-NRCS data, missing Db data were estimated and SOCACR corrected to SOCHTC using the new functional relationships developed. This allowed for pedon SOC and N stores to be calculated for 609 and 468 Alaska pedons respectively, the most available to-date. Additionally, functional relationships were developed for data within soil orders to estimate total SOCHTC and N stores in pedons with missing surface organic horizons where only thicknesses were known. These relationships are presented in order to fill-in missing data and to better define the existing data set for future use. Some 1904 missing Db data points and 1612 corrected SOCHTC data points were added to the total of 4240 points in the 609 pedons that constitute the updated dataset. When O-layer thickness functions developed here were used, SOC and N stores were calculated for an additional 137 and 184 pedons respectively.

Differentiation of horizons in soils formed in volcanic ash can be problematic as recent ash deposits often have the same morphological appearance as eluvial albic horizons. Furthermore, differentiation of spodic horizons can be difficult as multiple horizons can appear homogeneous. A portable x-ray fluorescence (PXRF) spectrometer was utilized to scan volcanic ash-derived Spodosols, Andisols, and Inceptisols in northern Idaho and southern Alaska. Distinct patterns of elemental concentrations were identified in soil profiles. These data can be used to quantitatively differentiate seemingly nondescript horizons. Organic carbon variability within soil profiles was found to significantly correlate to elemental concentrations as evidenced by strong regression r2 and low root mean squared errors (RMSEs). Specifically, Fe/Zr ratios proved useful for documenting spodic horizons in the studied profiles, and showed some potential for differentiating volcanic ash from true E horizons. In areas of frequent saturation or inundation, the PXRF also demonstrated the ability to distinguish depleted soil matrix materials from reduced Fe. Summarily, the PXRF proved to be a useful instrument for rapid, on-site analysis of volcanic ash soils.

Peatlands are a subset of wetlands that have accumulated significant amounts of soil organic matter. Soils of peatlands are colloquially known as peat, with mucks referring to peats that are decomposed to the point that the original plant remains are altered beyond recognition (Chapter 6, SSSA 2008). Generally, soils with a surface organic layer >40 cm thick have been classified as Histosols in the U.S. soil classification system—Soil Taxonomy (Soil Survey Staff 2014). Permafrost-affected organic soils are classified as the Histels suborder in the Gelisols order (Soil Survey Staff 2014). Based on current calculations of earth’s land surface of 148,940,000 km2 and our estimate of peatland area (or the combined area of Histosols and Histels) (Table 10.1), peatlands occupy about 2.7% of the earth’s surface.

Small patterned-ground features (PGFs) in the Arctic have unique soil properties that vary with latitude and may greatly affect tundra biogeochemistry. Because nitrogen availability can strongly limit arctic vegetation growth, we examined how soil nitrogen transformations differ between PGFs and the surrounding inter-PGF tundra along an arctic latitudinal gradient. We collected soils at eight sites from the Alaskan Low Arctic to the Canadian High Arctic. The soils were incubated for 21days at 9 C and 15 C and analysed for changes in total inorganic nitrogen, nitrate and extractable organic nitrogen (EON). We found greater nitrogen immobilisation in the surrounding inter-PGF soils than in the PGF soils. Along the latitudinal gradient, differences in net nitrogen mineralisation and EON cycling between PGF and inter-PGF soils were strongly influenced by the presence of a pH boundary within the Low Arctic and the transition between the High and Low Arctic, with greater immobilisation in the nonacidic and Low Arctic sites, respectively. Incubation temperature affected EON flux but did not affect net nitrogen mineralisation or nitrification. These results show that spatial heterogeneity at several scales can influence soil nitrogen dynamics, and is therefore an important influence on arctic ecosystem function. Copyright © 2012 John Wiley & Sons, Ltd.

Coastal erosion plays an important role in the terrestrial–marine–atmosphere carbon cycle. This study was conducted to explore the spatial variation of soil organic carbon (SOC) and other soil properties along the coastline of northern Alaska. A total of 769 soil samples, from 48 sites along over 1800-km of coastline in northern Alaska, were collected during the summers of 2005 and 2006. A geological information system (GIS) and a geostatistical method (ordinary kriging) were coupled to investigate the spatial variation of SOC along the coastline. SOC have a big variation ranging from 0.8 to 187.4 kg C m− 2 with the greatest value observed in the middle and lowest in the northeastern coastline. Compared to the 1-D model or the 1-D model with shortcut distance, the 2-D model was more reasonable to describe SOC along the coastline. The Gaussian correlation structure model had less prediction error than other examined geostatistical models. All mapping results also indicate that soils of the northwestern coastline stored greater SOC than those of the northeastern coastline. The estimation of total SOC along the coastline of northern Alaska was 6.86 ∗ 107 kg m− 1. The prediction errors indicated that greater errors were observed in both ends of the coastline than were observed in other fractions, although the range was from 0.739 to 0.779. Our study suggests that the isotropic 2-D model without a trend, with the nugget effect and the Gaussian correlation structure is a useful tool to investigate SOC in large scale. Results of stable isotope of organic matter indicate that SOC are mainly derived from C3 plant, which ranged from − 30‰ to − 22‰.

Soil organic carbon (SOC) accumulated in the Arctic regions has been subject to impacts of climate warming, but the interactions of SOC with aquatic environments and their biogeochemical consequences remain poorly understood. Arctic tundra soil samples were collected from the upper permafrost of arctic Alaska and size-fractionated into the > 2000 µm, 250–2000 µm, 53–250 µm and 3 kDa) and low-molecular-weight (LMW, 250–2000 µm > less than 53 µm. In both acidic and non-acidic soils, DOC yields increased with decreasing soil particle size, while TOC content increased with increasing particle size. Soil DOC released from bulk acidic soils contains 65% of HMW-DOC and 35% of LMW-DOC, but 44% and 56% respectively in non-acidic soil DOC. Acidic soils seemed to have higher potential of releasing DOC than non-acidic soils. On average, up to 2% of arctic SOC could be potentially released into aquatic systems during soil/water interactions. The fate of this newly released soil DOC and its biogeochemical impacts on aquatic systems needs further investigation.

The Arctic soil organic-carbon pool is a significant, but poorly constrained, carbon store. The most cited pool size estimates are based on a study that severely undersamples Arctic soils, with only five out of the 48 soils examined actually from the Arctic region. Furthermore, previous measurements have been confined to the top 40 cm of soil. Here, we present 1-m-deep measurements of soil organic carbon obtained at 117 locations in the North American Arctic region. To this dataset we add previously published measurements to generate a total sample size of 139 North American Arctic soils. We show that soil organic-carbon stores are highly dependent on landscape type, being highest in lowland and hilly upland soils, where values average 55.1 and 40.6 kg soil organic carbon m−2 respectively, and lowest in rubbleland and mountain soils, where values average 3.4 and 3.8 kg soil organic carbon m−2 respectively. Extrapolating our measurements using known distributions of landscape types we estimate that the total organic carbon pool in North American Arctic soils, together with the average amount of carbon per unit area, is considerably higher than previously thought. Our estimates of the depth distribution and total amount of organic carbon in North American Arctic soils will form an important basis for studies examining the impact of climate warming on CO2 release in the region. The Arctic soil organic-carbon pool is poorly constrained. Measurements of soil organic carbon in the North American Arctic reveal that the carbon store in this region is larger than previous estimates suggest, and highly dependent on landscape type.

Volcanic soils form by weathering of volcanogenic materials. Their distribution on the Earth parallels that of terrestrial volcanoes, and they are found across various climates, but most of them are classified as Andisols. This soil group shares unique physical and chemical properties largely attributable to the formation of poorly crystalline and noncrystalline minerals, and the accumulation of organic matter. The presence of rapidly weatherable silicate glass in the volcanic parent material strongly dictates the genesis of Andisols, whereas environmental factors, principally climate, influence their evolution with time. In active volcanic areas, the intermittent deposition of fresh tephra onto land helps to maintain the Andisols' attributes. Volcanic soils, and Andisols in particular, generally possess good fertility and support the livelihood of millions of people. However, improper use of these soils may result in severe degradation of their intrinsic qualities and consequent negative environmental effects, thus emphasizing the need for effective soil management.

Microbial activity in arctic tundra soils has been evaluated through both lab incubations and field flux measurements. To determine whether these different measurement approaches can be directly linked to each other, we developed a simple model of soil microbial CO2 production during the cold season in tussock tundra, moss tundra, and wet meadow tundra in the Alaskan Arctic. The model incorporated laboratory-based estimates of microbial temperature responses at sub-zero temperatures with field measurements of C stocks through the soil profile and daily temperature measurements at the sites. Estimates of total CO2 production overestimated in situ cold season CO2 fluxes for the studied sites by as much as two- to threefold, suggesting that either CO2 produced in situ does not efflux during the cold season or that microbial respiration potentials are constrained by some other factor in situ. Average estimated winter CO2 production was near 120 g C m−2 in moist tundra and 60 g C m−2 in wet meadow tun...

In the past 30 years, the arctic climate has warmed appreciably. Mounting evidence suggests that climate warming is being amplified at the earth's polar regions. A warmer Arctic could lead to the gradual loss of circumpolar permafrost. Northern soils are estimated to contain 25–33% of the world's soil carbon, much of which is frozen in permafrost as poorly decomposed plant remains. A warming and thawing of northern permafrost would result in an increase in soil organic matter (SOM) exposed to decomposition. Carbon dioxide (CO2) or methane (CH4) released from decomposing SOM would likely result in a positive feedback to climate warming. The rate that SOM decomposes in soil depends on many variables, including temperature, soil moisture, nutrient availability, pH, oxidation–reduction potential, and chemical composition of the SOM. This paper addresses the effect of regional scale ecosystem differences on SOM composition and the potential for CO2 to be respired from these soils under SOM-limiting conditions. In previous research, an empirical model was developed to predict CO2 flux from arctic soils based on specific compounds in the SOM. The model was built using an incubation designed to create SOM-limiting conditions and pyrolysis-gas chromatography/mass spectrometry (py-GC/MS) analysis of SOM. SOM-limiting conditions were defined as the state in which microbial respiration was limited only by the SOM quality. That is, during the incubation, ample nutrients were available to microorganisms, the pH was neutral, and the system was kept aerobic, mixed, and at 20 °C. SOM that was rapidly mineralized was defined as being of high quality. SOM that was slowly mineralized was defined as being of low quality. With an understanding of SOM quality in different soil types, one can better understand the relative potential for different soils to contribute to atmospheric CO2 in a warmer, drier arctic environment. In the research described herein, soils from across the Western and Northern Alaska transects were analyzed to determine if SOM quality could be tied to cover class, a parameter that can be remotely sensed. In nearly all cases, SOM quality under similar cover classes was of similar quality regardless of its geographic origin. The clearest trend observed was that SOM quality was highest in soil under moist acidic tundra, followed by tussock tundra and tundra/shrub transitions, shrubs, and nonacidic tundra, respectively.

In the past 30 years, the arctic climate has warmed appreciably and there is evidence for a significant polar amplification of global warming in the future. A warming and drying of northern soils could result in an increase in organic matter decomposition and positive feedback to future climate warming. Northern ecosystems have accumulated 25–33% of the world's soil carbon, much of which is preserved as poorly decomposed plant remains. The soil organic matter (SOM) decomposition rate, however, depends on many variables such as temperature, nutrient availability, pH, oxidation/reduction potential, and chemical composition of the SOM. This paper addresses the effect of SOM composition on CO2 respiration in arctic soil. In order to isolate the effect of SOM composition on respiration rate, 19 soils from the circumpolar arctic were incubated in a 25 °C, nutrient-rich, pH neutral, constantly mixed environment. The SOM composition was studied using pyrolysis-gas chromatography/mass spectrometry (py-GC/MS), an analytical technique that produces a “fingerprint” of SOM. Correlations were made between SOM composition and CO2 respiration rate for the 19 soils. From these data, a model was built to predict respiration rates in soil subjected to similar incubation conditions using py-GC/MS fingerprints. Results go on to compare model predictions of measured respiration in laboratory incubations of 15 soils from four different locations in the Northern and Western Alaska Transects. Predictions for cumulative respiration over a 70-day laboratory respiration test were within 20% of measured values.

Soils and other unconsolidated deposits in the northern circumpolar permafrost region store large amounts of soil organic carbon (SOC). This SOC is potentially vulnerable to remobilization following soil warming and permafrost thaw, but stock estimates are poorly constrained and quantitative error estimates were lacking. This study presents revised estimates of the permafrost SOC pool, including quantitative uncertainty estimates, in the 0–3 m depth range in soils as well as for deeper sediments (>3 m) in deltaic deposits of major rivers and in the Yedoma region of Siberia and Alaska. The revised estimates are based on significantly larger databases compared to previous studies. Compared to previous studies, the number of individual sites/pedons has increased by a factor ×8–11 for soils in the 1–3 m depth range,, a factor ×8 for deltaic alluvium and a factor ×5 for Yedoma region deposits. Upscaled based on regional soil maps, estimated permafrost region SOC stocks are 217 ± 15 and 472 ± 34 Pg for the 0–0.3 m and 0–1 m soil depths, respectively (±95% confidence intervals). Depending on the regional subdivision used to upscale 1–3 m soils (following physiography or continents), estimated 0–3 m SOC storage is 1034 ± 183 Pg or 1104 ± 133 Pg. Of this, 34 ± 16 Pg C is stored in thin soils of the High Arctic. Based on generalised calculations, storage of SOC in deep deltaic alluvium (>3 m to ≤60 m depth) of major Arctic rivers is estimated to 91 ± 39 Pg (of which 69 ± 34 Pg is in permafrost). In the Yedoma region, estimated >3 m SOC stocks are 178 +140/−146 Pg, of which 74 +54/−57 Pg is stored in intact, frozen Yedoma (late Pleistocene ice- and organic-rich silty sediments) with the remainder in refrozen thermokarst deposits (±16/84th percentiles of bootstrapped estimates). A total estimated mean storage for the permafrost region of ca. 1300–1370 Pg with an uncertainty range of 930–1690 Pg encompasses the combined revised estimates. Of this, ≤819–836 Pg is perennially frozen. While some components of the revised SOC stocks are similar in magnitude to those previously reported for this region, there are also substantial differences in individual components. There is evidence of remaining regional data-gaps. Estimates remain particularly poorly constrained for soils in the High Arctic region and physiographic regions with thin sedimentary overburden (mountains, highlands and plateaus) as well as for >3 m depth deposits in deltas and the Yedoma region.

Soils and other unconsolidated deposits in the northern circumpolar permafrost region store large amounts of soil organic carbon (SOC). This SOC is potentially vulnerable to remobilization following soil warming and permafrost thaw, but SOC stock estimates were poorly constrained and quantitative error estimates were lacking. This study presents revised estimates of permafrost SOC stocks, including quantitative uncertainty estimates, in the 0–3 m depth range in soils as well as for sediments deeper than 3 m in deltaic deposits of major rivers and in the Yedoma region of Siberia and Alaska. Revised estimates are based on significantly larger databases compared to previous studies. Despite this there is evidence of significant remaining regional data gaps. Estimates remain particularly poorly constrained for soils in the High Arctic region and physiographic regions with thin sedimentary overburden (mountains, highlands and plateaus) as well as for deposits below 3 m depth in deltas and the Yedoma region. While some components of the revised SOC stocks are similar in magnitude to those previously reported for this region, there are substantial differences in other components, including the fraction of perennially frozen SOC. Upscaled based on regional soil maps, estimated permafrost region SOC stocks are 217 ± 12 and 472 ± 27 Pg for the 0–0.3 and 0–1 m soil depths, respectively (±95% confidence intervals). Storage of SOC in 0–3 m of soils is estimated to 1035 ± 150 Pg. Of this, 34 ± 16 Pg C is stored in poorly developed soils of the High Arctic. Based on generalized calculations, storage of SOC below 3 m of surface soils in deltaic alluvium of major Arctic rivers is estimated as 91 ± 52 Pg. In the Yedoma region, estimated SOC stocks below 3 m depth are 181 ± 54 Pg, of which 74 ± 20 Pg is stored in intact Yedoma (late Pleistocene ice- and organic-rich silty sediments) with the remainder in refrozen thermokarst deposits. Total estimated SOC storage for the permafrost region is ∼1300 Pg with an uncertainty range of ∼1100 to 1500 Pg. Of this, ∼500 Pg is in non-permafrost soils, seasonally thawed in the active layer or in deeper taliks, while ∼800 Pg is perennially frozen. This represents a substantial ∼300 Pg lowering of the estimated perennially frozen SOC stock compared to previous estimates.

Soils along an elevational gradient in the Himalayas from the Lhasa River Valley bottom at 3700 m in elevation through subalpine (4200 to 4600 m) and alpine (>4600 m elevation) vegetation zones were described, sampled and classified according to the USDA soil taxonomy. Active flood plain soils were classified as Aridic Ustifluvents or, on more stable valley slopes and stream terraces, as Aridic Ustochrepts. Limited soil temperature data suggest these temperate valley bottom and lower valley slope soils have a mesic soil temperature regime. Soils within the subalpine zone were estimated to have a frigid temperature regime and sample sites were classified as Typic Haploborolls or Typic Ustochrepts, depending on parent material and degree of aeolian influence on epipedon properties. At elevations above 4600 m elevation under alpine sedge and forb turf, soils were classified as Typic Cryumbrepts. Soils above 4600 m elevation showed evidence of cryogenic soil structures (platy and fine subangular blocky) presumably formed as the result of extended periods (more than 300 days per year) of freezing and thawing and vein ice formation. Although permafrost may be expected to occur at depth at these elevations, no permafrost was observed within 2 m of the soil surface within the elevational range sampled. Copyright © 1999 John Wiley & Sons, Ltd. Dans un secteur allant depuis le fond de la vallee de Lhasa, a 3700 m d'altitude, jusqu'aux zones subalpine (4200 a 4600 m) et alpine (>4600 m), les sols de l'Himalaya ont ete decrits, echantillonnes et classes en utilisant la nomenclature des sols USDA. Les sols des plaines d'inondation actuelles ont ete classes comme Aridic Ustifluvents ou, sur les pentes plus stables de la vallee et les terrasses fluviatiles, comme Aridic Ustochrepts. Des donnees limitees de temperature des sols suggerent que ces fonds de vallee et les sols des pentes inferieures des vallees ont un regime moyen tempere de temperature des sols. Des sols dans la zone subalpine ont ete estimes comme ayant un regime de temperature froid et des sites echantillons ont ete classes comme Typic Haploborolls ou Typic Ustochrepts, suivant le materiau d'origine et le degre d'influence eolienne sur les proprietes epipedons. A des altitudes superieures a 4600 m, sous la pelouse et prairie alpine, les sols on ete classes comme Typic Cryumbrepts. Des sols au dessus de 4600 m montrent des evidences de structures cryogeniques (lamellaires et en blocs subanguleux fins) probablement formees au moment de periodes importantes (plus de 300 jours par an) de gel et de degel avec formation de lentilles de glace. Quoiqu'on puisse s'attendre a ce que le pergelisol soit present en profondeur a ces altitudes, il n'a ete observe nulle part jusqu'a 2 m de profondeur dans la zone qui a ete etudiee. Copyright © 1999 John Wiley & Sons, Ltd.

The morphological, chemical, and physical properties of arctic tundra soils were examined along a 200-km latitudinal gradient in northern Alaska which includes two major physiographic provinces; the Arctic Coastal Plain and the Arctic Foothills. Annual air temperature and precipitation increase along the gradient from north to south. Soils on the Arctic Coastal Plain support wet, nonacidic tundra vegetation and have high carbonate contents. Soil on the Arctic Foothills support moist, nonacidic tundra in the northern part and moist acidic tundra in the southern part. Most arctic tundra soils are characterized by medium texture, poor drainage, and high organic matter content. From north to south along the transect, the base saturation of the active layer decreases and exchangeable aluminum increases from north to south. Most soils have strongly developed cryogenic features, including warped and broken horizons, ice lenses, thin platy structure, and organic matter frost-churned into the ice-rich upper permafrost horizons.

The brief spring thaw period in the arctic is an important time when carbon is transferred from terrestrial to aquatic systems as melting snow and soil waters run off into the streams, lakes, and ocean. Measurements were made of the quantity and quality of dissolved organic carbon (DOC) in thawing soil and runoff waters in the foothills region of the Kuparuk River basin of arctic Alaska, during the thaw of May 1996. Incubations were performed using DOC and soil cores at the time of thaw from the surface layers of two major tundra types of the region, nonacidic and acidic tundra. Results indicated that there are major changes in both the quantity and quality of DOC as soil waters thaw and move to the streams and lakes. DOC concentrations were found to be reduced up to 90% as soil waters thawed and became free-flowing soil waters with leachates from thawed soil cores averaging 116 mg DOC/L at thaw and soil waters averaging 20 mg DOC/L. Stream and inlet to Toolik Lake DOC concentrations averaged 12 and 10 mg DOC/L respectively indicating further dilution of DOC. Quality differences elucidated by XAD-8/4 resin fractionation of DOC were observed for waters at various points in the ecosystem. The hydrophilic neutral fraction (HIN) accounted for 71% of the DOC in waters of thawing soil cores, but was only 23% in flowing waters of soils, and 9-20% in stream waters. A 14 day 4°C incubation of DOC from thawing soil core waters reduced DOC an average of 39%, with 80% of that reduction occurring in the HIN fraction. Soil waters and stream waters were similar in DOC fraction composition, and fulvic acid fractions were dominant. Initial 14 day DOC respiration rates with high HIN waters were 10 mg CO 2 -C/g DOC/d, and reduced to 1.2-1.7 mg CO 2 -C/g DOC/d after 34 days incubation. Respiration rates of thawed cores ranged from 0.12 to 0.06 and 0.03 mg CO 2 -C/g C/d for nonacidic and acidic cores, respectively.

Soil processes in permafrost regions differ markedly from those of the mid and low latitudes. Permafrost soils are cold during the short growing season and frozen the rest of the year. This study was conducted to describe permafrost soils on the tundra coastal plain of northern Seward Peninsula with emphasis on soil characteristics below the active layer and cryogenic structures, both aspects which were widely neglected in previous studies of permafrost soils. We used cryogenic structures to determine active layer depths. In describing these soils, we applied the previous soil taxonomy and tested the utility of the new Gelisol order. Seven pedons were excavated and described in different topographic positions. Most pedons are influenced by frost action, as evidenced by irregular and broken horizons and weakly developed soils. Mineral horizons have predominantly reduced colors. Organic horizons of 7- to 50-cm thickness occur in the study area. All soils contain segregated ice and ice wedges. Segregated ice includes ice lenses, ice nets, and ataxitic ice concentrations at the base of the active layer. With the identification of these cryogenic features, it was possible to determine active layer depths independently of thaw season. For describing the properties of permafrost soils, the new Gelisol order is shown to he a significant improvement on the previous soil taxonomy.

Studies and models of trace-gas flux in the Arctic consider temperature and moisture to be the dominant controls over land–atmosphere exchange1,2, with little attention having been paid to the effects of different substrates. Likewise, current Arctic vegetation maps for models of vegetation change recognize one or two tundra types3,4 and do not portray the extensive regions with different soils within the Arctic. Here we show that rapid changes to ecosystem processes (such as photosynthesis and respiration) that are related to changes in climate and land usage will be superimposed upon and modulated by differences in substrate pH. A sharp soil pH boundary along the northern front of the Arctic Foothills in Alaska separates non-acidic (pH > 6.5) ecosystems to the north from predominantly acidic (pH < 5.5) ecosystems to the south. Moist non-acidic tundra has greater heat flux, deeper summer thaw (active layer), is less of a carbon sink, and is a smaller source of methane than moist acidic tundra.

High-latitude terrestrial ecosystems are key components in the global carbon cycle. The Northern Circumpolar Soil Carbon Database (NCSCD) was developed to quantify stocks of soil organic carbon (SOC) in the northern circumpolar permafrost region (a total area of 18.7 × 106 km2). The NCSCD is a geographical information system (GIS) data set that has been constructed using harmonized regional soil classification maps together with pedon data from the northern permafrost region. Previously, the NCSCD has been used to calculate SOC storage to the reference depths 0–30 cm and 0–100 cm (based on 1778 pedons). It has been shown that soils of the northern circumpolar permafrost region also contain significant quantities of SOC in the 100–300 cm depth range, but there has been no circumpolar compilation of pedon data to quantify this deeper SOC pool and there are no spatially distributed estimates of SOC storage below 100 cm depth in this region. Here we describe the synthesis of an updated pedon data set for SOC storage (kg C m−2) in deep soils of the northern circumpolar permafrost regions, with separate data sets for the 100–200 cm (524 pedons) and 200–300 cm (356 pedons) depth ranges. These pedons have been grouped into the North American and Eurasian sectors and the mean SOC storage for different soil taxa (subdivided into Gelisols including the sub-orders Histels, Turbels, Orthels, permafrost-free Histosols, and permafrost-free mineral soil orders) has been added to the updated NCSCDv2. The updated version of the data set is freely available online in different file formats and spatial resolutions that enable spatially explicit applications in GIS mapping and terrestrial ecosystem models. While this newly compiled data set adds to our knowledge of SOC in the 100–300 cm depth range, it also reveals that large uncertainties remain. Identified data gaps include spatial coverage of deep (> 100 cm) pedons in many regions as well as the spatial extent of areas with thin soils overlying bedrock and the quantity and distribution of massive ground ice. An open access data-portal for the pedon data set and the GIS-data sets is available online at http://bolin.su.se/data/ncscd/. The NCSCDv2 data set has a digital object identifier (doi:10.5879/ECDS/00000002).

Soils on Seward Peninsula, northwest Alaska, that were buried about 17,500 years ago and froze after burial present a unique opportunity to study soil development under the conditions of the last glacial maximum. Stratigraphic sections were excavated during the summers of 1993 and 1994. Study sites were located on steep banks of thaw lakes. We described soil morphology (including cryogenic features) and sampled for chemical and physical analyses. All paleosols are permafrost soils that developed in calcareous loess and have roots present throughout. Colors are predominantly grayish and either reflect original loess color or periodic saturation of the soils (possibly caused by the permafrost environment). Active layer thicknesses before burial ranged from 32 to 64 cm. Organic carbon contents average 3.0%, carbon/nitrogen ratios average 9, cation exchange capacities average 19.1 cmol/kg, and base saturations generally exceed 100%. There is no evidence of leaching in the profile. Soil formation occurred simultaneously to the deposition of the parent material loess. Morphological and chemical data suggest that soil development was weak and confined to organic matter accumulation, and hydrolysis of iron. All studied soils show similar morphological, chemical, and physical properties, which suggests a relatively uniform mode of soil formation in the study area. Soil-forming conditions on northern Seward Peninsula during the last glacial maximum were severe, and combined with fairly continuous loess deposition they resulted in weakly developed, nutrient-rich soils.

[1] Carbon, nitrogen, and material fluxes were quantified at 48 sampling locations along the 1957 km coastline of the Beaufort Sea, Alaska. Landform characteristics, soil stratigraphy, cryogenic features, and ice contents were determined for each site. Erosion rates for the sites were quantified using satellite images and aerial photos, and the rates averaged across the coastline increased from 0.6 m yr−1 during circa 1950–1980 to 1.2 m yr−1 during circa 1980–2000. Soils were highly cryoturbated, and organic carbon (OC) stores ranged from 13 to 162 kg OC m−2 in banks above sea level and averaged 63 kg OC m−2 over the entire coastline. Long-term (1950–2000) annual lateral fluxes due to erosion were estimated at −153 Gg OC, −7762 Mg total nitrogen, −2106 Tg solids, and −2762 Tg water. Total land area loss along the Alaska Beaufort Sea coastline was estimated at 203 ha yr−1. We found coastal erosion rates, bank heights, soil properties, and material stores and fluxes to be extremely variable among sampling sites. In comparing two classification systems used to classifying coastline types from an oceanographic, coastal morphology perspective and geomorphic units from a terrestrial, soils perspective, we found both systems were effective at differentiating significant differences among classes for most material stores, but the coastline classification did not find significant differences in erosion rates because it lacked differentiation of soil texture.

[1] Soil CH4 and CO2 gas contents were determined at 39 sites located along the 1957 km coastline of the Beaufort Sea of northern Alaska. Average soil CH4 concentrations increased with depth into the upper frozen layers, while the CO2 decreased with depth. Over 80% of the CH4 and 46% of the total CO2 were contained in the permafrost portion of the profiles. Overall, average concentrations of CH4 within the soil profiles were correlated to water content (R2 = 0.66, p ≤ 0.01). Concentrations of CO2 were correlated to total organic carbon (R2 = 0.76, p ≤ 0.001) and negatively correlated to water content (R2 = 0.61, p ≤ 0.01). The highest total bank gas concentrations for both gases were found in ice-rich permafrost (average volumetric H2O ≥ 70%). Soils eroded across the coast annually were estimated to contain 3.61 ± 1.35 t CH4 (average 1.86 ± 0.70 g m−2) and 469 ± 128 t CO2 (average 240 ± 65 g m−2). Gas amounts present in annually eroding banks were on the same order of magnitude as amounts emitted per year on an area basis from undisturbed tundra and lakes reported by others for the Arctic and smaller than previous estimates for local coastal anthropogenic sources. Soil stocks of gases, water and total organic carbon indicate that with coastal permafrost degradation gas release is minor in magnitude and importance to C-dynamics when compared to the TOC stocks of the coastline.

The production of water-extractable organic carbon (WEOC) during arctic coastal erosion and permafrost degradation may contribute significantly to C fluxes under warming conditions, but it remains difficult to quantify. A tundra soil collected near Barrow, AK, was selected to evaluate the effects of soil pretreatments (oven drying vs. freeze drying) as well as extraction solutions (pure water vs. seawater) on WEOC yields. Both oven drying and freeze drying significantly increased WEOC release compared with the original moist soil samples; dried samples released, on average, 18% more WEOC than did original moist samples. Similar results were observed for the production of low-molecular-weight dissolved organic C. However, extractable OC released from different soil horizons exhibited differences in specific UV absorption, suggesting differences in WEOC quality. Furthermore, extractable OC yields were significantly less in samples extracted with seawater compared with those extracted with pure water, likely due to the effects of major ions on extractable OC flocculation. Compared with samples from the active horizons, upper permafrost samples released more WEOC, suggesting that continuously frozen samples were more sensitive than samples that had experienced more drying-wetting cycles in nature. Specific UV absorption of seawater-extracted OC was significantly lower than that of OC extracted using pure water, suggesting more aromatic or humic substances were flocculated during seawater extraction. Our results suggest that overestimation of total terrestrial WEOC input to the Arctic Ocean during coastal erosion could occur if estimations were based on WEOC extracted from dried soil samples using pure water.

[1] We studied soil properties of frost boils at nine zonal-vegetation locations across the North American Arctic Transect (NAAT) in order to better understand arctic soils and their interaction with other biogeophysical components of frost boil ecosystems. Soil genetic horizons were analyzed for particle size, pH, electrical conductivity, total organic carbon (OC) and nitrogen (N), bulk density and volumetric water content. Surface soils (0–5 cm) across frost boil patterns were analyzed for of pH, OC, water content, extractable N and P, and exchangeable K, Ca and Na. Our results revealed that soil texture, pH, EC, P, Na and Ca contents are strongly influenced by local parent materials. Soil pH was acidic in the north going to alkaline in the midtransect and then again back to acidic in the south. Simple correlations between soil analytical data and observed frost boil properties across the NAAT support and are consistent with the laboratory and theoretical-conceptual models of pattern ground dynamics that have been developed by others. Soil water related well to texture. Soil horizon %OC and profile OC stocks under the pattern corresponded well to biomass and frost heave, respectively. Also soil water was closely related to biomass and heave. Nutrients in surface soils at sites corresponded to OC stocks. An interaction between soil water and segregation of Na and Ca between the pattern and interpattern was found for locations with high cation availability. At these sites, chemical as well as physical disruption of the pattern area could affect plant establishment. Overall there was a good linkage between properties relating to frost boil pattern dynamics and soil biogeochemical properties. Our study offers insight into the important process of cryoturbation for carbon sequestration in Gelisols across the Arctic.

Permafrost is defined as a thickness of soil or other superficial deposit, even bedrock, that remains frozen for consecutively two years or more (Muller, 1947). Permafrost, or perennially frozen ground, underlies 2.15x106 km2 or 22.4% of the territory of China (Qui and Cheng, 1995) and can be divided into two broad categories, high-latitude permafrost in northeastern China (0.38x106 km2) and high-altitude permafrost in the Qinghai-Xizang Plateau and some alpine regions in western and eastern China (1.76x106 km2) (Figure 2.11.1). The total area of soils affected by permafrost in China is third in the world, after Russia and Canada, but the area of high-altitude perennially frozen soils is the largest in the world.

[1] Carbon dioxide respiration rates were measured in the laboratory at −2°C for 88 arctic Alaska soil horizon samples. Soil horizon samples represented most ATLAS C-flux study sites to a 1-m depth. Sites represented extend across the Alaska Arctic, from tundra at Prudhoe Bay (70°N, 149°W) in the northeast to the tundra–forest transition zone of the Seward Peninsula (64°N, 163°W) in the southwest, a range of nearly 1000 km. Results of an initial temperature sensitivity study indicated that at 4°C, organic horizons (>20% organic carbon [OC]) have average respiration rates that are twice as high as those found for the mineral horizons. However, as temperature dropped to −2°C, respiration in organic horizons was about the same as that for the low OC mineral horizons (with

The vast amount of organic carbon (OC) stored in soils of the northern circumpolar permafrost region is a potentially vulnerable component of the global carbon cycle. However, estimates of the quan ...

In the Arctic tundra and boreal regions, permafrost-affected soils (Gelisols) have segregated ice that accumulates and thaws during freeze–thaw cycles resulting in cryoturbated soils. These cryoturbated soils (Turbels) have warped, broken, or involuted horizons and cryostructures that require sampling protocols different than soils not affected by permafrost. We provide a general overview of the cryoturbated soil profi les associated with different cryogenic landscapes and landforms and a specifi c protocol for description and sampling pedons with permafrost. Peer Reviewed Papers

Tundra soil carbon stores ranged from a low of 16 kg C m-3 for a northern foothills ridge top site to a high of 94 kg C m-3 for a Barrow coastal plain tundra. Relatively low carbon stores were found in riparian shrubland, barren mountain slope, and alpine slope soils (3, 4 and 10 kg C m-3, respectively). Coastal plain and foothills tundra soils averaged 62 and 44 kg C m-3, respectively. Active layer to permafrost partitioning of carbon stores varied, but when the carbon stores of the permafrost (to 1 m) were considered along with those of the active layer, carbon store estimates for the tundra are nearly doubled. Cryoturbation played a key role in the distribution of soil carbon stocks. Carbon stores over the pattern cycle of three coastal plain polygon types were found to be similar (59-60 kg C m-3). However, the carbon stores of coastal plain thaw lake basin soils ranged widely from 16 to 64 kg C m-3. In the foothills, carbon stores increased from ridge top to down-slope positions, and increased or stayed nearly constant from midslope to watertrack positions. On the average, the largest carbon stores were in the Cf, Oa, and Bg/Oa soil genetic horizons with average stores to 1 m of 15, 13, and 13 kg C m-2, respectively. Carbon stores for the Kuparuk River drainage were calculated for the pedon (1 m) and for the active layer only, the results were 2.5 and 1.4 times higher, respectively, than if generalized tundra carbon stores from the literature were used in the calculation. The results of this study indicate that the Arctic terrestrial carbon pool size estimates that have been used recently could be low by a factor of 2 or more if the lower soil horizon stores are ignored.

We studied properties and classification of selected volcanic ash soils formed under different vegetations on Kenai Peninsula, southcentral Alaska. Spruce (Sitka spruce) and alder soils had well-developed eluvial and spodic horizons common to most Spodosols. Fescue soil, developed under fescue-liche

Forage barley dry matter yield and quality, as well as soil pH, Al, and Mn were monitored in response to P, K, and lime application on a newly cleared Typic Cryorthod (Orthid Podzol). The overall yearly yield level was affected by precipitation. Without liming soil acidification occurred after three years of production. The liming rate of 2.2 Mg.ha−1 was found optimal for maintaining initial pH levels (5.66) and increasing forage barley yields. It was also found optimum for K and P utilization for these first years of production. Soil pH dropped an average of 0.33 units over the three years on unlimed P plots and 0.46 units over 4 years on K plots. Phosphorus and K fertilization increased N utilization and resulted in decreased soil acidification. Phosphorus availability was greater in the first year of cropping than in subsequent years, this was likely due to the effects of higher available moisture, liming release of native P, and effects of initial fertilization. There was a 148% increase in total dry matter yield and an 85% increase in protein yield of forage barley with P application. Liming increased total forage barley yields an average of 69% and total protein yields 48%. Reduced barley yields in unlimed plots were due to low soil pH. After two years of cultivation, unlimed plots contained exchangeable Al and soluble Mn levels reported toxic for other soils. The higher liming rates of 4.4 and 6.6 Mg.ha−1 reduced soluble Mn to near critically low levels. soil Al and Mn were highly correlated to pH. Soil exchangeable Al, Mn, and soluble Mn along with tissue Al were inversely correlated to percentage yield. The average yield respone to three levels of applied K, increased from zero initially to 67% by the fourth year. Total dry-matter production increased 32% and total protein yield increased an average of 32% and total protein yield increased an average of 15% with K fertilization over four years. About 60% of the yield response occurred between the 0 and 22kg K.ha−1 rates. Initial soil exchangeable K levels were not maintained even at the highest 66kg K.ha−1 treatment. Soil exchangeable Al and soluble Mn were elevated with dropping pH. Soil K reserves and resupply of exchangeable K in these soils over the long term will be an important factor in crop production.

Approximately 1700 Pg of soil carbon (C) are stored in the northern circumpolar permafrost zone, more than twice as much C than in the atmosphere. The overall amount, rate, and form of C released to the atmosphere in a warmer world will influence the strength of the permafrost C feedback to climate change. We used a survey to quantify variability in the perception of the vulnerability of permafrost C to climate change. Experts were asked to provide quantitative estimates of permafrost change in response to four scenarios of warming. For the highest warming scenario (RCP 8.5), experts hypothesized that C release from permafrost zone soils could be 19-45 Pg C by 2040, 162-288 Pg C by 2100, and 381-616 Pg C by 2300 in CO2 equivalent using 100-year CH4 global warming potential (GWP). These values become 50 % larger using 20-year CH4 GWP, with a third to a half of expected climate forcing coming from CH4 even though CH4 was only 2.3 % of the expected C release. Experts projected that two-thirds of this release could be avoided under the lowest warming scenario (RCP 2.6). These results highlight the potential risk from permafrost thaw and serve to frame a hypothesis about the magnitude of this feedback to climate change. However, the level of emissions proposed here are unlikely to overshadow the impact of fossil fuel burning, which will continue to be the main source of C emissions and climate forcing. © 2013 The Author(s).