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At least 37 records · Page 2Linked to original sources
USGS2007

State factor relationships of dissolved organic carbon and nitrogen losses from unpolluted temperate forest watersheds

We sampled 100 unpolluted, old-growth forested watersheds, divided among 13 separate study areas over 5 years in temperate southern Chile and Argentina, to evaluate relationships among dominant soil-forming state factors and dissolved carbon and nitrogen concentrations in watershed streams. These watersheds provide a unique opportunity to examine broad-scale controls over carbon (C) and nitrogen (N) biogeochemistry in the absence of significant human disturbance from chronic N deposition and land use change. Variations in the ratio dissolved organic carbon (DOC) to nitrogen (DON) in watershed streams differed by underlying soil parent material, with average C:N = 29 for watersheds underlain by volcanic ash and basalt versus C:N = 73 for sedimentary and metamorphic parent materials, consistent with stronger adsorption of low C:N hydrophobic materials by amorphous clays commonly associated with volcanic ash and basalt weathering. Mean annual precipitation was related positively to variations in both DOC (range: 0.2-9.7 mg C/L) and DON (range: 0.008-0.135 mg N/L) across study areas, suggesting that variations in water volume and concentration may act synergistically to influence C and N losses across dry to wet gradients in these forest ecosystems. Dominance of vegetation by broadleaf versus coniferous trees had negligible effects on organic C and N concentrations in comparison to abiotic factors. We conclude that precipitation volume and soil parent material are important controls over chemical losses of dissolved organic C and N from unpolluted temperate forest watersheds. Our results raise the possibility that biotic imprints on watershed C and N losses may be less pronounced in naturally N-poor forests than in areas impacted by land use change and chronic N deposition. Copyright 2007 by the American Geophysical Union.

Journal of Geophysical Research G: Biogeosciences↗
USGS2007

Nutrient (N, P) loads and yields at multiple scales and subbasin types in the Yukon River basin, Alaska

Loads and yields of dissolved and particulate nitrogen (N) and phosphorus (P) were measured and modeled at three locations on the Yukon River (YR) and on the Tanana and Porcupine Rivers in Alaska during 2001-2005. Total export of N and P upstream of Yukon Delta averaged 120 Gg N a-1 and 56 Gg P a-1, respectively, with 43.5% of total N (TN) as dissolved organic N, and 98% of total P (TP) as particulate phosphorus. Approximately half of the annual export of TN and TP occurred during spring. Hydrologic yields ofTN (5.6-13.3 mmol N m-2 a-1) and TP (0.8-9.0 mmol P m-2 a-1) were least in the Porcupine basin and greatest in the Tanana basin and were proportional to water yield. Comparison of current and historical dissolved organic matter (DOM) export from the basin indicates decreased DON export with respect to total water discharge during summer and autumn in recent decades. Any possible climate-related change in annual water discharge will result in proportional changes in N and P export.

Journal of Geophysical Research G: Biogeosciences↗
USGS2007

The role of historical fire disturbance in the carbon dynamics of the pan-boreal region: A process-based analysis

[1] Wildfire is a common occurrence in ecosystems of northern high latitudes, and changes in the fire regime of this region have consequences for carbon feedbacks to the climate system. To improve our understanding of how wildfire influences carbon dynamics of this region, we used the process-based Terrestrial Ecosystem Model to simulate fire emissions and changes in carbon storage north of 45°N from the start of spatially explicit historically recorded fire records in the twentieth century through 2002, and evaluated the role of fire in the carbon dynamics of the region within the context of ecosystem responses to changes in atmospheric CO 2 concentration and climate. Our analysis indicates that fire plays an important role in interannual and decadal scale variation of source/sink relationships of northern terrestrial ecosystems and also suggests that atmospheric CO 2 may be important to consider in addition to changes in climate and fire disturbance. There are substantial uncertainties in the effects of fire on carbon storage in our simulations. These uncertainties are associated with sparse fire data for northern Eurasia, uncertainty in estimating carbon consumption, and difficulty in verifying assumptions about the representation of fires that occurred prior to the start of the historical fire record. To improve the ability to better predict how fire will influence carbon storage of this region in the future, new analyses of the retrospective role of fire in the carbon dynamics of northern high latitudes should address these uncertainties.

Journal of Geophysical Research G: Biogeosciences↗
USGS2008

Biogeochemical legacy of prescribed fire in a giant sequoia - Mixed conifer forest: A 16-year record of watershed balances

The effects of prescription burning on watershed balances of major ions in mixed conifer forest were examined in a 16-year paired catchment study in Sequoia National Park, California. The objective was to determine whether fire-related changes in watershed balances persist as long as estimated low-end natural fire-return intervals (???10 years), and whether cumulative net export caused by fire could deplete nutrient stocks between successive fires. Inputs (wet + dry deposition) and outputs (stream export) of N, S, Cl-, HCO3-, Ca2+, Mg2+, Na+, K+, H+, and SiO2 were measured for 7 years preceding, and 9 years following, a prescribed burn of one of the catchments. After fire, runoff coefficients increased by 7% (in dry years) to 35% (in wet years). Inorganic N was elevated in stream water for 3 years after fire. Increased export of water, SO42-, Cl-,SiO2, and base cations continued through the end of the study. Pools and processes attributed to fire led to the cumulative loss, per hectare, of 1.2 kg N, 16 kg S, 25 kg Cl-, 130 kg Ca2+, 19 kg Mg2+, 71 kg Na+, 29 kg K+ and 192 kg Si, above that predicted by prefire regression equations relating export in the paired catchments. This additional export equaled <1% of the N, up to one-third of the Ca and Mg, and up to three-fourths of the K, contained in the forest floor prior to combustion. Changes in watershed balances indicated that low-end natural fire-return intervals may prevent complete reaccumulation of several elements between fires. Copyright 2008 by the American Geophysical Union.

Journal of Geophysical Research G: Biogeosciences↗
USGS2007

Hydrogeologic controls on nitrate transport in a small agricultural catchment, Iowa

Effects of subsurface deposits on nitrate loss in stream riparian zones are recognized, but little attention has been focused on similar processes occurring in upland agricultural settings. In this paper, we evaluated hydrogeologic controls on nitrate transport processes occurring in a small 7.6 ha Iowa catchment. Subsurface deposits in the catchment consisted of upland areas of loess overlying weathered pre-Illinoian till, drained by two ephemeral drainageways that consisted of Holocene-age silty and organic rich alluvium. Water tables in upland areas fluctuated more than 4 m per year compared to less than 0.3 m in the drainageway. Water quality patterns showed a distinct spatial pattern, with groundwater in the drainageways having lower nitrate concentrations (<0.5 mg L-1 compared to upland areas (>10 mg L-1) as wells as lower pH, dissolved oxygen and redox, and higher ammonium and dissolved organic carbon levels. Several lines of evidence suggested that conditions are conducive for denitrification of groundwater flowing from uplands through the drainageways. Field-measured nitrate decay rates in the drainageways (???0.02 day-1) were consistent with other laboratory studies and regional patterns. Results from MODFLOW and MT3DMS simulations indicated that soils in the ephemeral drainageways could process all upland groundwater nitrate flowing through them. However, model-simulated tile drainage increased both water flux and nitrate loss from the upland catchment. Study results suggest that ephemeral drainageways can provide a natural nitrate treatment system in our upland glaciated catchments, offering management opportunities to reduce nitrate delivery to streams. Copyright 2007 by the American Geophysical Union.

Journal of Geophysical Research G: Biogeosciences↗
USGS2007

Influence of disturbance on carbon exchange in a permafrost collapse and adjacent burned forest

We measured CO 2 and CH 4 exchange from the center of a Sphagnum ‐dominated permafrost collapse, through an aquatic moat, and into a recently burned black spruce forest on the Tanana River floodplain in interior Alaska. In the anomalously dry growing season of 2004, both the collapse and the surrounding burned area were net sinks for CO 2 , with a mean daytime net ecosystem exchange of −1.4 μ mol CO 2 m −2 s −1 , while the moat was a CH 4 source with a mean flux of 0.013 μ mol CH 4 m −2 s −1 . Regression analyses identified temperature as the dominant factor affecting intragrowing season variation in CO 2 exchange and soil moisture as the primary control influencing CH 4 emissions. CH 4 emissions during the wettest portion of the growing season were four times higher than during the driest periods. If temperatures continue to warm, peatland vegetation will likely expand with permafrost degradation, resulting in greater carbon accumulation and methane emissions for the landscape as a whole.

Alaska↗
USGS2008

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

Permafrost is a defining characteristic of the Arctic environment. However, climate warming is thawing permafrost in many areas leading to failures in soil structure called thermokarst. An extensive survey of a 600 km2 area in and around the Toolik Lake Natural Research Area (TLNRA) revealed at least 34 thermokarst features, two thirds of which were new since ???1980 when a high resolution aerial survey of the area was done. Most of these thermokarst features were associated with headwater streams or lakes. We have measured significantly increased sediment and nutrient loading from thermokarst features to streams in two well-studied locations near the TLNRA. One small thermokarst gully that formed in 2003 on the Toolik River in a 0.9 km2 subcatchment delivered more sediment to the river than is normally delivered in 18 years from 132 km2 in the adjacent upper Kuparuk River basin (a long-term monitoring reference site). Ammonium, nitrate, and phosphate concentrations downstream from a thermokarst feature on Imnavait Creek increased significantly compared to upstream reference concentrations and the increased concentrations persisted over the period of sampling (1999-2005). The downstream concentrations were similar to those we have used in a long-term experimental manipulation of the Kuparuk River and that have significantly altered the structure and function of that river. A subsampling of other thermokarst features from the extensive regional survey showed that concentrations of ammonium, nitrate, and phosphate were always higher downstream of the thermokarst features. Our previous research has shown that even minor increases in nutrient loading stimulate primary and secondary production. However, increased sediment loading could interfere with benthic communities and change the responses to increased nutrient delivery. Although the terrestrial area impacted by thermokarsts is limited, the aquatic habitat altered by these failures can be extensive. If warming in the Arctic foothills accelerates thermokarst formation, there may be substantial and wide-spread impacts on arctic stream ecosystems that are currently poorly understood. Copyright 2008 by the American Geophysical Union.

Journal of Geophysical Research G: Biogeosciences↗
USGS2008

Oceanic loading of wildfire-derived organic compounds from a small mountainous river

Small mountainous rivers (SMRs) export substantial amounts of sediment into the world's oceans. The concomitant yield of organic carbon (OC) associated with this class of rivers has also been shown to be significant and compositionally unique. We report here excessively high loadings of polycyclic aromatic hydrocarbons (PAHs), lignin, and levoglucosan, discharged from the Santa Clara River into the Santa Barbara Channel. The abundance of PAHs, levoglucosan, and lignin in Santa Barbara Channel sediments ranged from 201.7 to 1232.3 ng gdw-1, 1.3 to 6.9 ??g gdw-1, and 0.3 to 2.2 mg per 100 mg of the sedimentary OC, respectively. Assuming a constant rate of sediment accumulation, the annual fluxes of PAHs, levoglucosan, and lignin, to the Santa Barbara Channel were respectively, 885.5 ?? 170.2 ng cm-2 a-1, 3.5 ?? 1.9 ??g cm-2 a-1 and 1.4 ?? 0.3 mg per 100 mg OC cm-2 a-1, over ???30 years. The close agreement between PAHs, levoglucosan, and lignin abundance suggests that the depositional flux of these compounds is largely biomass combustion-derived. To that end, use of the Santa Clara River as a model for SMRs suggests this class of rivers may be one of the largest contributors of pyrolyzed carbon to coastal systems and the open ocean. Wildfire associated carbon discharged from other high yield fluvial systems, when considered collectively, may be a significant source of lignin, pyrolytic PAHs, and other pyrogenic compounds to the ocean. Extrapolating these methods over geologic time may offer useful historical information about carbon sequestration and burial in coastal sediments and affect coastal carbon budgets. Copyright 2008 by the American Geophysical Union.

Journal of Geophysical Research G: Biogeosciences↗
USGS2007

Sulfur species behavior in soil organic matter during decomposition

Soil organic matter (SOM) is a primary re??servoir of terrestrial sulfur (S), but its role in the global S cycle remains poorly understood. We examine S speciation by X-ray absorption near-edge structure (XANES) spectroscopy to describe S species behavior during SOM decomposition. Sulfur species in SOM were best represented by organic sulfide, sulfoxide, sulfonate, and sulfate. The highest fraction of S in litter was organic sulfide, but as decomposition progressed, relative fractions of sulfonate and sulfate generally increased. Over 6-month laboratory incubations, organic sulfide was most reactive, suggesting that a fraction of this species was associated with a highly labile pool of SOM. During humification, relative concentrations of sulfoxide consistently decreased, demonstrating the importance of sulfoxide as a reactive S phase in soil. Sulfonate fractional abundance increased during humification irrespective of litter type, illustrating its relative stability in soils. The proportion of S species did not differ systematically by litter type, but organic sulfide became less abundant in conifer SOM during decomposition, while sulfate fractional abundance increased. Conversely, deciduous SOM exhibited lesser or nonexistent shifts in organic sulfide and sulfate fractions during decomposition, possibly suggesting that S reactivity in deciduous litter is coupled to rapid C mineralization and independent of S speciation. All trends were consistent in soils across study sites. We conclude that S reactivity is related to spqciation in SOM, particularly in conifer forests, and S species fractions in SOM change, during decomposition. Our data highlight the importance of intermediate valence species (sulfoxide and sulfonate) in the pedochemical cycling of organic bound S. Copyright 2007 by the American Geophysical Union.

Journal of Geophysical Research G: Biogeosciences↗
USGS2009

Hydrologic support of carbon dioxide flux revealed by whole-lake carbon budgets

Freshwater lakes are an important component of the global carbon cycle through both organic carbon (OC) sequestration and carbon dioxide (CO 2 ) emission. Most lakes have a net annual loss of CO 2 to the atmosphere and substantial current evidence suggests that biologic mineralization of allochthonous OC maintains this flux. Because net CO 2 flux to the atmosphere implies net mineralization of OC within the lake ecosystem, it is also commonly assumed that net annual CO 2 emission indicates negative net ecosystem production (NEP). We explored the relationship between atmospheric CO 2 emission and NEP in two lakes known to have contrasting hydrologie characteristics and net CO 2 emission. We calculated NEP for calendar year 2004 using whole-lake OC and inorganic carbon (IC) budgets, NEP oc and NEP IC , respectively, and compared the resulting values to measured annual CO 2 flux from the lakes. In both lakes, NEP Ic and NEP Ic were positive, indicating net autotrophy. Therefore CO 2 emission from these lakes was apparently not supported by mineralization of allochthonous organic material. In both lakes, hydrologie CO 2 inputs, as well as CO 2 evolved from netcalcite precipitation, could account for the net CO 2 emission. NEP calculated from diel CO 2 measurements was also affected by hydrologie inputs of CO 2 . These results indicate that CO 2 emission and positive NEP may coincide in lakes, especially in carbonate terrain, and that all potential geologic, biogeochemical, and hydrologie sources of CO 2 need to be accounted for when using CO 2 concentrations to infer lake NEP. Copyright 2009 by the American Geophysical Union.

Journal of Geophysical Research G: Biogeosciences↗
USGS2009

Measurement of soil carbon oxidation state and oxidative ratio by 13 C nuclear magnetic resonance

The oxidative ratio (OR) of the net ecosystem carbon balance is the ratio of net O 2 and CO 2 fluxes resulting from photosynthesis, respiration, decomposition, and other lateral and vertical carbon flows. The OR of the terrestrial biosphere must be well characterized to accurately estimate the terrestrial CO 2 sink using atmospheric measurements of changing O 2 and CO 2 levels. To estimate the OR of the terrestrial biosphere, measurements are needed of changes in the OR of aboveground and belowground carbon pools associated with decadal timescale disturbances (e.g., land use change and fire). The OR of aboveground pools can be measured using conventional approaches including elemental analysis. However, measuring the OR of soil carbon pools is technically challenging, and few soil OR data are available. In this paper we test three solid-state nuclear magnetic resonance (NMR) techniques for measuring soil OR, all based on measurements of the closely related parameter, organic carbon oxidation state (C ox ). Two of the three techniques make use of a molecular mixing model which converts NMR spectra into concentrations of a standard suite of biological molecules of known C ox . The third technique assigns C ox values to each peak in the NMR spectrum. We assess error associated with each technique using pure chemical compounds and plant biomass standards whose C ox and OR values can be directly measured by elemental analyses. The most accurate technique, direct polarization solid-state 13 C NMR with the molecular mixing model, agrees with elemental analyses to ??0.036 C ox units (??0.009 OR units). Using this technique, we show a large natural variability in soil C ox and OR values. Soil C ox values have a mean of -0.26 and a range from -0.45 to 0.30, corresponding to OR values of 1.08 ?? 0.06 and a range from 0.96 to 1.22. We also estimate the OR of the carbon flux from a boreal forest fire. Analysis of soils from nearby intact soil profiles imply that soil carbon losses associated with the fire had an OR of 1.09 1 (??0.00 3 ). Fire appears to be a major factor driving the soil C pool to higher oxidation states and lower OR values. Episodic fluxes caused by disturbances like fire may have substantially different ORs from ecosystem respiration fluxes and therefore should be better quantified to reduce uncertainties associated with our understanding of the global atmospheric carbon budget. Copyright 2009 by the American Geophysical Union.

Journal of Geophysical Research G: Biogeosciences↗
USGS2009

Fluorescence-based proxies for lignin in freshwater dissolved organic matter

Lignin phenols have proven to be powerful biomarkers in environmental studies; however, the complexity of lignin analysis limits the number of samples and thus spatial and temporal resolution in any given study. In contrast, spectrophotometric characterization of dissolved organic matter (DOM) is rapid, noninvasive, relatively inexpensive, requires small sample volumes, and can even be measured in situ to capture fine-scale temporal and spatial detail of DOM cycling. Here we present a series of cross-validated Partial Least Squares models that use fluorescence properties of DOM to explain up to 91% of lignin compositional and concentration variability in samples collected seasonally over 2 years in the Sacramento River/San Joaquin River Delta in California, United States. These models were subsequently used to predict lignin composition and concentration from fluorescence measurements collected during a diurnal study in the San Joaquin River. While modeled lignin composition remained largely unchanged over the diurnal cycle, changes in modeled lignin concentrations were much greater than expected and indicate that the sensitivity of fluorescence-based proxies for lignin may prove invaluable as a tool for selecting the most informative samples for detailed lignin characterization. With adequate calibration, similar models could be used to significantly expand our ability to study sources and processing of DOM in complex surface water systems.

Journal of Geophysical Research G: Biogeosciences↗
USGS2010

Source water controls on the character and origin of dissolved organic matter in streams of the Yukon River basin, Alaska

Climate warming and permafrost degradation at high latitudes will likely impact watershed hydrology, and consequently, alter the concentration and character of dissolved organic carbon (DOC) in northern rivers. We examined seasonal variation of DOC chemistry in 16 streams of the Yukon River basin, Alaska. Our primary objective was to evaluate the relationship between source water (shallow versus deep groundwater flow paths) and DOC chemical composition. Using base cation chemistry and principal component analysis, we observed high contributions of deep groundwater to glacial and clearwater streams, whereas blackwater streams received larger contributions from shallow groundwater sources. DOC concentration and specific ultraviolet absorbance peaked during spring snowmelt in all streams, and were consistently higher in blackwater streams than in glacial and clearwater streams. The hydrophobic acid fraction of DOC dominated across all streams and seasons, comprising between 35% and 56% of total DOC. The hydrophilic acid fraction of DOC was more prominent in glacial (23% ± 3%) and clearwater streams (19% ± 1%) than in blackwater streams (16% ± 1%), and was enriched during winter base flow (29% ± 1%) relative to snowmelt and summer base flow. We observed that an increase in the contribution of deep groundwater to streamflow resulted in decreased DOC concentration, aromaticity, and DOC-to-dissolved organic nitrogen ratio, and an increase in the proportion of hydrophilic acids relative to hydrophobic acids. Our findings suggest that future permafrost degradation and higher contributions of groundwater to streamflow may result in a higher fraction of labile DOM in streams of the Yukon basin.

Journal of Geophysical Research G: Biogeosciences↗
USGS2010

Carbon, water, and energy fluxes in a semiarid cold desert grassland during and following multiyear drought

The net exchanges of carbon dioxide, water vapor, and energy were examined in a perennial Colorado Plateau grassland for 5 years. The study began within a multiyear drought and continued as the drought ended. The grassland is located near the northern boundary of the influence of the North American monsoon, a major climatic feature bringing summer rain. Following rain, evapotranspiration peaked above 8 mm d -1 but was usually much smaller (2-4 mm d -1 ). Net productivity of the grassland was low compared to other ecosystems, with peak hourly net CO 2 uptake in the spring of 4 (mu or u)mol m -2 s -1 and springtime carbon gain in the range of 42 + or - 11 g C m -2 (based on fluxes) to 72 + or - 55 g C m -2 (based on carbon stocks; annual carbon gain was not quantified). Drought decreased gross ecosystem productivity (GEP) and total ecosystem respiration, with a much larger GEP decrease. Monsoon rains led to respiratory pulses, lasting a few days at most, and only rarely resulted in net CO 2 gain, despite the fact that C 4 grasses dominated plant cover. Minor CO 2 uptake was observed in fall following rain. Spring CO 2 uptake was regulated by deep soil moisture, which depended on precipitation in the prior fall and winter. The lack of CO 2 uptake during the monsoon and the dependence of GEP on deep soil moisture are in contrast with arid grasslands of the warm deserts. Cold desert grasslands are most likely to be impacted by future changes in winter and not summer precipitation.

Colorado Plateau↗
USGS2011

Hydrological mobilization of mercury and dissolved organic carbon in a snow-dominated, forested watershed: Conceptualization and modeling

The mobilization of mercury and dissolved organic carbon (DOC) during snowmelt often accounts for a major fraction of the annual loads. We studied the role of hydrological connectivity of riparian wetlands and upland/wetland transition zones to surface waters on the mobilization of Hg and DOC in Fishing Brook, a headwater of the Adirondack Mountains, New York. Stream water total mercury (THg) concentrations varied strongly (mean = 2.25 ± 0.5 ng L −1 ), and the two snowmelt seasons contributed 40% (2007) and 48% (2008) of the annual load. Methyl mercury (MeHg) concentrations ranged up to 0.26 ng L −1 , and showed an inverse log relationship with discharge. TOPMODEL‐simulated saturated area corresponded well with wetland areas, and the application of a flow algorithm based elevation‐above‐creek approach suggests that most wetlands become well connected during high flow. The dynamics of simulated saturated area and soil storage deficit were able to explain a large part of the variation of THg concentrations (r 2 = 0.53 to 0.72). In contrast, the simulations were not able to explain DOC variations and DOC and THg concentrations were not correlated. These results indicate that all three constituents, THg, MeHg, and DOC, follow different patterns at the outlet: (1) the mobilization of THg is primarily controlled by the saturation state of the catchment, (2) the dilution of MeHg suggests flushing from a supply limited pool, and (3) DOC dynamics follow a pattern different from THg dynamics, which likely results from differing gain and/or loss processes for THg and/or DOC within the Fishing Brook catchment.

New York↗
USGS2010

Seasonal ice and hydrologic controls on dissolved organic carbon and nitrogen concentrations in a boreal-rich fen

[1] Boreal wetland carbon cycling is vulnerable to climate change in part because hydrology and the extent of frozen ground have strong influences on plant and microbial functions. We examined the response of dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) across an experimental manipulation of water table position (both raised and lowered water table treatments) in a boreal-rich fen in interior Alaska. DOC and TDN responses to water table manipulation exhibited an interaction with seasonal ice dynamics. We observed consistently higher DOC and TDN concentrations in the lowered water table treatment (71.7 ± 6.5 and 3.0 ± 0.3 mg−L) than in both the control (55.6 ± 5.1 and 2.3 ± 0.2 mg−L) and raised (49.1 ± 4.3 and 1.9 ± 0.1 mg L−1, respectively) water table treatments. Across all plots, pore water DOC concentrations at 20 cm increased as the depth to water table increased (R2 = 0.43, p < 0.001). DOC concentrations also increased as the seasonal thaw depth increased, with solutes increasing most rapidly in the drained plot (R2 = 0.62, p < 0.001). About half of the TDN pool was composed of dissolved organic N (DON). Inorganic N and DON were both highly correlated with changes in DOC, and their respective constraints to mineralization are discussed. These results demonstrate that a declining water table position and dryer conditions affect thaw depth and peat temperatures, and interactions among these ecosystem properties will likely increase DOC and TDN loading and potential for export in these systems.

Alaska↗
USGS2011

Vulnerability of high-latitude soil organic carbon in North America to disturbance

This synthesis addresses the vulnerability of the North American high-latitude soil organic carbon (SOC) pool to climate change. Disturbances caused by climate warming in arctic, subarctic, and boreal environments can result in significant redistribution of C among major reservoirs with potential global impacts. We divide the current northern high-latitude SOC pools into (1) near-surface soils where SOC is affected by seasonal freeze-thaw processes and changes in moisture status, and (2) deeper permafrost and peatland strata down to several tens of meters depth where SOC is usually not affected by short-term changes. We address key factors (permafrost, vegetation, hydrology, paleoenvironmental history) and processes (C input, storage, decomposition, and output) responsible for the formation of the large high-latitude SOC pool in North America and highlight how climate-related disturbances could alter this pool's character and size. Press disturbances of relatively slow but persistent nature such as top-down thawing of permafrost, and changes in hydrology, microbiological communities, pedological processes, and vegetation types, as well as pulse disturbances of relatively rapid and local nature such as wildfires and thermokarst, could substantially impact SOC stocks. Ongoing climate warming in the North American high-latitude region could result in crossing environmental thresholds, thereby accelerating press disturbances and increasingly triggering pulse disturbances and eventually affecting the C source/sink net character of northern high-latitude soils. Finally, we assess postdisturbance feedbacks, models, and predictions for the northern high-latitude SOC pool, and discuss data and research gaps to be addressed by future research.

Journal of Geophysical Research G: Biogeosciences↗