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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.

Warming thaws permafrost, releasing carbon that can cause more warming. Radiocarbon, soil carbon, and remote sensing data suggest that 0.2–2.5 Pg of carbon has been emitted from permafrost as CO2 and CH4 around Arctic lakes since the 1950s. Permafrost thaw exposes previously frozen soil organic matter to microbial decomposition. This process generates methane and carbon dioxide, and thereby fuels a positive feedback process that leads to further warming and thaw1. Despite widespread permafrost degradation during the past ∼40 years2,3,4, the degree to which permafrost thaw may be contributing to a feedback between warming and thaw in recent decades is not well understood. Radiocarbon evidence of modern emissions of ancient permafrost carbon is also sparse5. Here we combine radiocarbon dating of lake bubble trace-gas methane (113 measurements) and soil organic carbon (289 measurements) for lakes in Alaska, Canada, Sweden and Siberia with numerical modelling of thaw and remote sensing of thermokarst shore expansion. Methane emissions from thermokarst areas of lakes that have expanded over the past 60 years were directly proportional to the mass of soil carbon inputs to the lakes from the erosion of thawing permafrost. Radiocarbon dating indicates that methane age from lakes is nearly identical to the age of permafrost soil carbon thawing around them. Based on this evidence of landscape-scale permafrost carbon feedback, we estimate that 0.2 to 2.5 Pg permafrost carbon was released as methane and carbon dioxide in thermokarst expansion zones of pan-Arctic lakes during the past 60 years.

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.

In the four years after the 2008 eruption and burial of Kasatochi Island volcano, erosion and the return of bird activity have resulted in new and altered land surfaces and initiation of ecosystem recovery. We examined fertility characteristics of the recently deposited pyroclastic surfaces, patches of legacy pre-eruptive surface soil (LS), and a post-eruptive surface with recent bird roosting activity. Pyroclastic materials were found lacking in N, but P, K, and other macronutrients were in sufficient supply for plants. Erosion and leaching are moving mobile P and Fe downslope to deposition fan areas. Legacy soil patches that currently support plants have available-N at levels (10–22 mg N kg-1) similar to those added by birds in a recent bird roosting area. Roosting increased surface available N from

The Tien Shan Mountains, the largest mountain range in the Xinjiang Autonomous Region of north-western China, significantly influence the climate of central Asia. Recent permafrost changes in the region of the headwaters of the Urumqi River, as well as its relationship to climatic factors, were studied based on ground temperatures measured in a 60 m deep borehole, air temperatures and precipitation over a period from 1992 to 2011. The results showed that the maximum active-layer thickness (ALT; 1.70 m) occurred in 2009 and 2011, with an increase of 0.45 m compared with 1992. The change in ALT was related to the variation in the climatic conditions, and the increase in the deep-seated permafrost temperature. The permafrost temperature increased from −1.7°C in 1992 to −1.1°C in 2011, and the permafrost base moved upwards by approximately 14 m from 1992 to 2011. The long-term step-wise change in the air temperature may be the main cause of the permafrost warming in the headwaters of the Urumqi River. Copyright © 2015 John Wiley & Sons, Ltd.

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.

Knowledge of soils in the permafrost region has advanced immensely in recent decades, despite the remoteness and inaccessibility of most of the region and the sampling limitations posed by the severe environment. These efforts significantly increased estimates of the amount of organic carbon stored in permafrost-region soils and improved understanding of how pedogenic processes unique to permafrost environments built enormous organic carbon stocks during the Quaternary. This knowledge has also called attention to the importance of permafrost-affected soils to the global carbon cycle and the potential vulnerability of the region's soil organic carbon (SOC) stocks to changing climatic conditions. In this review, we briefly introduce the permafrost characteristics, ice structures, and cryopedogenic processes that shape the development of permafrost-affected soils, and discuss their effects on soil structures and on organic matter distributions within the soil profile. We then examine the quantity of organic carbon stored in permafrost-region soils, as well as the characteristics, intrinsic decomposability, and potential vulnerability of this organic carbon to permafrost thaw under a warming climate. Overall, frozen conditions and cryopedogenic processes, such as cryoturbation, have slowed decomposition and enhanced the sequestration of organic carbon in permafrost-affected soils over millennial timescales. Due to the low temperatures, the organic matter in permafrost soils is often less humified than in more temperate soils, making some portion of this stored organic carbon relatively vulnerable to mineralization upon thawing of permafrost.

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

The current estimate of the soil organic carbon (SOC) pool in the northern permafrost region of 1672 Petagrams (Pg) C is much larger than previously reported and needs to be incorporated in global ...

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.

Ground ice in the upper permafrost of the Beaufort Sea coast of Alaska was studied from 2005 to 2008 at 65 field sites located between Point Barrow and the Canadian border. The main terrain units in the studied area include (1) the primary surface of the coastal plain; (2) drained-lake basins; (3) low foothills (yedoma); (4) deltas and tidal flats; and (5) sand dunes. Wedge ice is the main type of massive ground ice, and ice-wedge polygons occurred on nearly all land surfaces. The volumetric content of wedge ice for the area varies from 3% to 50% between various terrain units with average value of about 11% for the entire coast. The highest content of wedge ice (about 50%) is typical of yedoma terrain, which occurred in a small segment at the coast of the Camden Bay. At the primary surface of the western region of the Arctic Coastal Plain, wedge-ice content reached almost 30%, with an average value of about 14%. Slightly smaller values were estimated for the primary surface of the eastern region of the Arctic Coastal Plain and for old drained-lake basins. Other types of massive ground ice included thermokarst-cave ice, ice cores of pingos, and a rare occurrence of folded massive ice at Barter Island. The content of segregated ice in organic and mineral soils between ice wedges was very high at most of the study sites. The total average volumetric ice content (due to wedge, segregated, and pore ice) for the whole area was 77%, ranging from 43% in eolian sand to 89% in yedoma.

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.

The direction and magnitude of soil organic carbon (SOC) changes in response to climate change remain unclear and depend on the spatial distribution of SOC across landscapes. Uncertainties regarding the fate of SOC are greater in high-latitude systems where data are sparse and the soils are affected by sub-zero temperatures. To address these issues in Alaska, a first-order assessment of data gaps and spatial distributions of SOC was conducted from a recently compiled soil carbon database. Temperature and landform type were the dominant controls on SOC distribution for selected ecoregions. Mean SOC pools (to a depth of 1-m) varied by three, seven and ten-fold across ecoregion, landform, and ecosystem types, respectively. Climate interactions with landform type and SOC were greatest in the uplands. For upland SOC there was a six-fold non-linear increase in SOC with latitude (i.e., temperature) where SOC was lowest in the Intermontane Boreal compared to the Arctic Tundra and Coastal Rainforest. Additionally, in upland systems mineral SOC pools decreased as climate became more continental, suggesting that the lower productivity, higher decomposition rates and fire activity, common in continental climates, interacted to reduce mineral SOC. For lowland systems, in contrast, these interactions and their impacts on SOC were muted or absent making SOC in these environments more comparable across latitudes. Thus, the magnitudes of SOC change across temperature gradients were non-uniform and depended on landform type. Additional factors that appeared to be related to SOC distribution within ecoregions included stand age, aspect, and permafrost presence or absence in black spruce stands. Overall, these results indicate the influence of major interactions between temperature-controlled decomposition and topography on SOC in high-latitude systems. However, there remains a need for more SOC data from wetlands and boreal-region permafrost soils, especially at depths > 1 m in order to fully understand the effects of climate on soil carbon in Alaska.

Integrating research and education is a fundamental goal of institutions and agencies supporting science because of the benefits to society of a more informed and scientifically literate population. The value of engaging public interest in ecological research is to maintain support for and integrate science in solutions to environmental problems (Hudson, 2001; Avila, 2003). The National Science Foundation lists criteria for assessing broader impacts of research projects which include (1) the integration of research and education—advancing discovery and understanding while promoting teaching, training, and learning; and (2) developing opportunities to broaden the participation of groups underrepresented in science (NSF, 2006). Educational researchers are developing models and assessing outcomes of integrating research and education at diverse grade levels (Trautmann and Krasny, 2006; Bowen and Roth, 2007); the value of integrating traditional ecological knowledge (TEK) in research has been demonstrated in several ecosystems (Huntington, 2000; Kimmerer, 2002; Ford et al., 2007; Garcia-Quijano, 2007) but specific approaches and achievements of efforts integrating research and education are not widely disseminated in environmental research journals. Thus, while there is a call for environmental scientists to broaden their activities to engage in outreach (i.e., have broader impact) there is a lag in the assessment of the effectiveness of these activities and of their value in mainstream scientific culture. Environmental scientists seldom evaluate these impacts, and there are few venues or incentives to report on these activities in ways that would enhance their research careers. For an individual scientist, efforts expended in integrating research and education often occur at the expense of research productivity and this results in a lack of reward for a researcher’s efforts to broaden research impacts (Andrews et al., 2005; Uriarte et al., 2007). One way to address the imbalance between efforts devoted to broader impacts vs. avenues for reporting on these efforts is through the publication of case studies and assessments of integration efforts in journals that reach a research audience as opposed to an education audience. This venue exists in a very few, high-profile, broad-interest research journals (e.g., Science, Bioscience) but could be more widespread in journals addressing a range of environmental research. Examples of successful integration help researchers and institutions evolve better mechanisms to achieve goals beneficial to society, including improved public understanding of science, greater diversity of research and stakeholders, and better application of current scientifically based information to managing environmental issues. In that spirit, we present as an example an effort integrating an interdisciplinary research project investigating the interactions of climate, vegetation, and permafrost in the study Biocomplexity of Arctic Tundra Ecosystems with a university field course, Arctic Field Ecology, and with indigenous Inuit students and elders. The integration allowed university students and native community members to participate with the research team, drawn by the opportunity to gain education and experience. This participation has had synergistic benefits with the research agenda and diversified the pool of stakeholders involved in the research (see Box 1).

The 7–8 August 2008 eruption of Kasatochi Island volcano blanketed the island in newly generated pyroclastic deposits and deposited ash into the ocean and onto nearby islands. Concentrations of water soluble Fe, Cu, and Zn determined from a 1:20 deionized water leachate of the ash were sufficient to provide short-term fertilization of the surface ocean. The 2008 pyroclastic deposits were thicker in concavities at bases of steeper slopes and thinner on steep slopes and ridge crests. By summer 2009, secondary erosion had exposed the pre-eruption soils along gulley walls and in gully bottoms on the southern and eastern slopes, respectively. Topographic and microtopographic position altered the depositional patterns of the pyroclastic flows and resulted in pre-eruption soils being buried by as little as 1 m of ash. The different erosion patterns gave rise to three surfaces on which future ecosystems will likely develop: largely pre-eruptive soils; fresh pyroclastic deposits influenced by shallowly bu...

Little is understood about chemical weathering processes in Alaskan arctic soils, where moisture is generally not limited but acidity varies and the average soil temperature is close to or below freezing. Weathering reactions in soil convert primary minerals into secondary clay minerals. Silty loam textured soils from three sites in moist acidic tundra (MAT) and three sites in moist nonacidic tundra (MNT) in the northern Arctic Foothills, Alaska, were characterized with emphasis on the origin of the clay minerals. The MNT soils had a discontinuous and thinner organic layer, which leads to a deeper summer thaw and greater cryoturbation than the MAT soils. The MNT had higher cation exchange capacity and base saturation than MAT. These buffer against acidification and account for the pH differences of MAT and MNT. Other chemical characteristics including C and N content as well as Fe and Al were similar (by horizon) across the MAT/MNT boundary. X-ray diffraction of coarse (0.0002-0.002 mm) and fine clay (

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.

Decaying wood is an important structural and functional component of forests: it contributes to generate habitat diversity, acts as either sink or source of nutrients, and plays a preponderant role in soil formation. Thus, decaying wood might likely have measurable effects on chemical properties of the underlying soil. We hypothesized that decaying wood would have a stronger effect on soil as decomposition advances and that such effect would vary according to wood quality. Twenty logs from two species with contrasting wood properties (Dacryodes excelsa Vahl. and Swietenia macrophylla King) and at two different decay stages (6 and 15 years after falling) were selected, and soil under and 50 cm away from decaying logs was sampled for soil organic matter (SOM) fractions [NaOH-extractable and water-extractable organic matter -(WEOM)] and properties (WEOM aromaticity). NaOH-extractable C and WEOM were higher in the soil influenced by 15-year-old logs, while the degree of aromaticity of WEOM was higher in the soil influenced by the 6-year-old logs. Decaying logs did influence properties of the underlying soil with differing effects according to the species since there was more NaOH-extractable C in the soil associated to D. excelsa logs and more WEOM in the soil associated to S. macrophylla older logs. It is proposed that such effects occurred through changes in the relative quantity and quality of different SOM fractions, as influenced by species and advancement in decomposition. Through its effect on SOM and nutrient dynamics, decaying wood can contribute to the spatial heterogeneity of soil properties, and can affect process of soil formation and nutrient cycling.

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...

backslopes is shallow to moderately deep due to gelifluction and slope movement but deep toward toeslopes. Charcoal particles, commonly central Canada. The watershed is representative of found within the soil profiles, attest to frequent fire events in the past. non-glaciated upland headwater stream basins found Fire has the greatest impact on soil properties on south aspect slopes throughout interior Alaska. Forest communities in the because the organic horizons are thin and dry, and easily destroyed by watershed are representative of the boreal forest zone fire. The underlying mineral horizons often develop hydrophobicity in Alaska. Forest fire is a dominant ecological factor in resulted from moderately and severe burn. Slope, aspect, and slope this region (Kasischke and Stocks, 2000) and there has gradient are major controlling factors for the contrasting soil types along the catena sequences in the watershed. been wide interest in the effects of wildfires on forest ecosystem but little on soils. Quantitative, site-specific baseline soils data are essential for comparing pre- and J enny’s functional-factoral soil formation model postfire changes within and below the forest floor. Rieger (Jenny, 1941) identifies the major components of et al. (1972) provide descriptions and maps (at a scale pedogenesis to be parent material, organisms, topogra- of 1:31 680) for seven soil series within the watershed; phy, climate, and time. These factors tend to be highly however, little quantitative data are provided. Viereck interdependentanddifficulttoisolateinnaturalsettings. etal. (1983) addressed, in detail, the soils, vegetation, and Landscape topography dictates microclimate, water dy- their relationship along a toposequence at the Bonanza namics, and material redistribution processes that criti- Creek Long-Term-Ecological-Research site 90 km to the callyinfluencethenatureofsoilsandvegetationmosaics southwest. The soils at Bonanza Creek developed on (Hole and Campbell, 1985; Hunckler and Schaetzl, 1997). deep loess deposits associated with the nearby Tanana Slope gradient and aspect strongly affect soil morpho- River and are not representative of the soils formed logicalcharacteristicsandgeochemicalprocessesinmidin the Yukon-Tanana Uplands metamorphic complex.

The physical and chemical properties of Arctic tundra soils were studied along a 250-km latitudinal transect in northern Alaska. The transect includes the nonacidic tundra of the Arctic Coastal Plain, the moist nonacidic tundra of the northern Arctic Foothills, and moist acidic tundra of the southern Arctic Foothills. The parent material of the coastal plain consists of carbonate-rich alluvium. The northern foothills have a mantle of calcareous loess. Further south the parent materials are moraines of late Quaternary. Vegetation changes from sedges on the coastal plain, to grasses on the northern foothills, and tussock and shrub tundra in southern foothills. Following the same order, soil pH and base saturation decrease and soil acidity increases. Most of the soil exchangeable acidity and cation exchange capacity are from soil organic matter.

Aim Describe the spatial and temporal properties of transitions in the Arctic and develop a conceptual understanding of the nature of these spatial transitions in the face of directional environmental change. Location Arctic tundra ecosystems of the North Slope of Alaska and the tundra-forest region of the Seward Peninsula, Alaska Methods We synthesize information from numerous studies on tundra and treeline ecosystems in an effort to document the spatial changes that occur across four arctic transitions. These transitions are: (i) the transition between High-Arctic and Low-Arctic systems, (ii) the transition between moist non-acidic tundra (MNT) and moist acidic tundra (MAT, also referred to as tussock tundra), (iii) the transition between tussock tundra and shrub tundra, (iv) the transition between tundra and forested systems. By documenting the nature of these spatial transitions, in terms of their environmental controls and vegetation patterns, we develop a conceptual model of temporal dynamics of arctic ecotones in response to environmental change. Results Our observations suggest that each transition is sensitive to a unique combination of controlling factors. The transition between High and Low Arctic is sensitive primarily to climate, whereas the MNT/MAT transition is also controlled by soil parent material, permafrost and hydrology. The tussock/shrub tundra transition appears to be responsive to several factors, including climate, topography and hydrology. Finally, the tundra/forest boundary responds primarily to climate and to climatically associated changes in permafrost. There were also important differences in the demography and distribution of the dominant plant species across the four vegetation transitions. The shrubs that characterize the tussock/shrub transition can achieve dominance potentially within a decade, whereas spruce trees often require several decades to centuries to achieve dominance within tundra, and Sphagnum moss colonization of non-acidic sites at the MNT/MAT boundary may require centuries to millennia of soil development. Main conclusions We suggest that vegetation will respond most rapidly to climatic change when (i) the vegetation transition correlates more strongly with climate than with other environmental variables, (ii) dominant species exhibit gradual changes in abundance across spatial transitions, and/or (iii) the dominant species have demographic properties that allow rapid increases in abundance following climatic shifts. All three of these properties characterize the transition between tussock tundra and low shrub tundra. It is therefore not surprising that of the four transitions studied this is the one that appears to be responding most rapidly to climatic warming.

Air temperature, ground surface temperature (GST; 0 cm at depth), precipitation and freezing depth data at 50 meteorological stations in the Qinghai–Tibet Plateau (QTP) were analyzed to examine changes of climate and seasonally frozen ground (SFG) in the past 30 years. The latitude, longitude, elevation, mean annual air temperature (MAAT), annual precipitation (AP) and maximum freezing depth at each station were used as the criterions to group the stations by the Hierarchical Cluster Analysis method. Fifty stations were grouped into four clusters, which are distributed in different regions of QTP. The most significant climate warming occurred in northeastern QTP, and the warming trend was greater in the cold season than in the warm season. Annual precipitation (AP) increased in the northwestern, inland and southeastern regions of QTP, but decreased in the northeastern QTP. The most significant changes of seasonally frozen ground (SFG) occurred in regions with thickest SFG, i.e., inland QTP, then northeastern and northwestern QTP. The duration of SFG shortened differently in different regions. Significant changes also occurred in the inland and northeastern regions of QTP. The cold season air temperature is the main factor controlling SFG change. The warming trends of ground surface temperatures are more significant than air temperature, and the warm season warming is greater than cold season warming. Changes of SFG depth, duration and surface temperature are likely to enhance heat exchanges between ground and atmosphere, in favor of stronger plateau monsoons. D 2004 Elsevier B.V. All rights reserved.

Frost boils in northern Alaska vary from large, 2–3-m diameter, barren non-sorted circles to completely vegetated hummocks. Summer warmth increases southwards from the coast. Average thaw-layer thickness shows the opposite trend. Frost heave shows no trend along the climate gradient but is affected by soil texture. Heave is greatest on frost boils with fine-grained sediments. Biomass increases from 183 g m � 2 at the coast to 813 g m � 2 in the Arctic Foothills. An aggrading permafrost table is evident in most of the frost-boil soil profiles, indicating that, over time, accumulation of plant biomass leads to reduced thaw-layer thickness. A conceptual model suggests how vegetation affects the morphology of patterned ground forms. In the coldest parts of the High Arctic well-developed frost boils do not form and there is little vegetation on frost boils or the inter-boil areas. In the warmest parts of the Low Arctic, vegetation is usually sufficient to stabilize the frost boil soils. Frost boils play an important role in Arctic ecosystems functions, including the flux of trace gases to the atmosphere, flux of water and nutrients to streams, and the recycling of important nutrients to wildlife populations. Copyright # 2004 John Wiley & Sons, Ltd.