Thawing Arctic permafrost can induce hydrologic change and alter redox conditions, shifting the balance of soil organic matter (SOM) decomposition. There remains uncertainty about how soil saturation and redox transitions impact dissolved and gas phase carbon fluxes, and efforts to link hydrobiogeochemical processes to ecosystem-scale models are limited. This study evaluates SOM decomposition of Arctic tundra soils using column experiments, water chemistry measurements, microbial community analysis, and a PFLOTRAN reactive transport model. Soil columns from a thermokarst channel (TC) and an upland tundra (UC) were exposed to cycles of saturation and drainage, which controlled carbon emissions. During saturation, an outflow of dissolved organic carbon from the UC soil correlated with elevated reduced iron and decreased pH; during drainage, UC carbon dioxide fluxes were 70% higher than TC fluxes. Intermittent methane release was observed for TC, consistent with higher methanogen abundance. Slower drainage in the TC soil correlated with more subtle biogeochemical changes. PFLOTRAN simulations captured experimental trends in soil carbon fluxes, oxygen concentrations, and water contents. The model was then used to evaluate additional soil water drainage rates. This study emphasizes the importance of considering hydrologic change when evaluating and simulating SOM decomposition in dynamic Arctic tundra environments.

Arctic permafrost soils are increasingly subject to thermokarst that is, abrupt ground subsidence caused by thaw. Wetlands can form within these depressions, leading to changes in organic matter decomposition and gas fluxes (CO2, CH4, N2O, NH3). Thermokarst wetlands tend to be dominated by graminoids, while surrounding upland tussock tundra tends to be dominated by mixed communities of shrubs and graminoids. To investigate how thermokarst alters the land-atmosphere exchange of C and N gases in Arctic tundra, we analyzed soil, porewater, above- and belowground biomass, and measured gas fluxes across dominant plant functional types (PFTs) within a lowland thermokarst wetland and adjacent upland tussock tundra. Both locations were overall sinks of CO2, sources of CH4, and sources of both N2O and NH3. We found that thermokarst wetlands emitted enough CH4 to generate a positive radiative forcing in CO2 equivalents (+1.2 μmol m-2 s-1 CO2-eq), counteracting the high CO2 uptake. In contrast, the upland tussock tundra had a net negative radiative forcing (-1.2 μmol m-2 s-1 CO2-eq). Differences in gas flux and soil chemistry between upland and lowland are primarily driven by flooded conditions present in thermokarst wetland. Additionally, root biomass from graminoids across both lowlands and uplands significantly correlated with CH4 fluxes, supporting previous observations of plant-mediated transport of CH4. Graminoid cover was correlated with increases in low molecular weight dissolved organic carbon, possibly associated with root exudates that fuel methanogenesis. Forb cover in the upland tussock tundra was significantly correlated with nine soil chemical variables, indicating that forbs may influence local soil chemistry or conversely, that soil chemistry controls where forbs grow. Overall, our findings indicate the variability in gas fluxes in the upland tussock tundra is partially controlled by PFT cover, while thermokarst wetlands emit enough CH4 to counteract CO2 uptake, with implications for carbon budget changes in Arctic systems.

ABSTRACT Climate change is rapidly transforming Arctic landscapes where increasing soil temperatures speed up permafrost thaw. This exposes large carbon stocks to microbial decomposition, possibly worsening climate change by releasing more greenhouse gases. Understanding how microbes break down soil carbon, especially under the anaerobic conditions of thawing permafrost, is important to determine future changes. Here, we studied the microbial community dynamics and soil carbon decomposition potential in permafrost and active layer soils under anaerobic laboratory conditions that simulated an Arctic summer thaw. The microbial and viral compositions in the samples were analyzed based on metagenomes, metagenome-assembled genomes, and metagenomic viral contigs (mVCs). Following the thawing of permafrost, there was a notable shift in microbial community structure, with fermentative Firmicutes and Bacteroidota taking over from Actinobacteria and Proteobacteria over the 60-day incubation period. The increase in iron and sulfate-reducing microbes had a significant role in limiting methane production from thawed permafrost, underscoring the competition within microbial communities. We explored the growth strategies of microbial communities and found that slow growth was the major strategy in both the active layer and permafrost. Our findings challenge the assumption that fast-growing microbes mainly respond to environmental changes like permafrost thaw. Instead, they indicate a common strategy of slow growth among microbial communities, likely due to the thermodynamic constraints of soil substrates and electron acceptors, and the need for microbes to adjust to post-thaw conditions. The mVCs harbored a wide range of auxiliary metabolic genes that may support cell protection from ice formation in virus-infected cells. IMPORTANCE As the Arctic warms, thawing permafrost unlocks carbon, potentially accelerating climate change by releasing greenhouse gases. Our research delves into the underlying biogeochemical processes likely mediated by the soil microbial community in response to the wet and anaerobic conditions, akin to an Arctic summer thaw. We observed a significant shift in the microbial community post-thaw, with fermentative bacteria like Firmicutes and Bacteroidota taking over and switching to different fermentation pathways. The dominance of iron and sulfate-reducing bacteria likely constrained methane production in the thawing permafrost. Slow-growing microbes outweighed fast-growing ones, even after thaw, upending the expectation that rapid microbial responses to dominate after permafrost thaws. This research highlights the nuanced and complex interactions within Arctic soil microbial communities and underscores the challenges in predicting microbial response to environmental change.

Linear nitramines (R–N(R′)NO2; R′ = H or alkyl) are toxic compounds, some with environmental relevance, while others are rare natural product nitramines. One of these natural product nitramines is N-nitroglycine (NNG), which is produced by some Streptomyces strains and exhibits antibiotic activity towards Gram-negative bacteria. An NNG degrading heme enzyme, called NnlA, has recently been discovered in the genome of Variovorax sp. strain JS1663 (Vs NnlA). Evidence is presented that NnlA and therefore, NNG degradation activity is widespread. To achieve this objective, we characterized and tested the NNG degradation activity of five Vs NnlA homologs originating from bacteria spanning several classes and isolated from geographically distinct locations. E. coli transformants containing all five homologs converted NNG to nitrite. Four of these five homologs were isolated and characterized. Each isolated homolog exhibited similar oligomerization and heme occupancy as Vs NnlA. Reduction of this heme was shown to be required for NnlA activity in each homolog, and each homolog degraded NNG to glyoxylate, NO2− and NH4+ in accordance with observations of Vs NnlA. It was also shown that NnlA cannot degrade the NNG analog 2-nitroaminoethanol. The combined data strongly suggest that NnlA enzymes specifically degrade NNG and are found in diverse bacteria and environments. These results imply that NNG is also produced in diverse environments and NnlA may act as a detoxification enzyme to protect bacteria from exposure to NNG.

A microsampler for collecting aerosol particles on an unmanned aerial system (UAS) was designed and evaluated in the laboratory for dry (no condensed water) and wet (foggy, misty, or rainy) air conditions.

The fate of organic carbon (C) in permafrost soils is important to the climate system due to the large global stocks of permafrost C. Thawing permafrost can be subject to dynamic hydrology, making redox processes an important factor controlling soil organic matter (SOM) decomposition rates and greenhouse gas production. In iron (Fe)‐rich permafrost soils, Fe(III) can serve as a terminal electron acceptor, promoting anaerobic respiration of SOM and increasing pH. Current large‐scale models of Arctic C cycling do not include Fe cycling or pH interactions. Here, a geochemical reaction model was developed by coupling Fe redox reactions and C cycling to simulate SOM decomposition, Fe(III) reduction, pH dynamics, and greenhouse gas production in permafrost soils subject to dynamic hydrology. We parameterized the model using measured CO 2 and CH 4 fluxes as well as changes in pH, Fe(II), and dissolved organic C concentrations from oxic and anoxic incubations of permafrost soils from polygonal permafrost sites in northern Alaska, United States. In simulations of repeated oxic‐anoxic cycles, Fe(III) reduction during anoxic periods enhanced CO 2 production, while the net effect of Fe(III) reduction on cumulative CH 4 fluxes depended on substrate C availability. With lower substrate availability, Fe(III) reduction decreased total CH 4 production by further limiting available substrate. With higher substrate availability, Fe(III) reduction enhanced CH 4 production by increasing pH. Our results suggest that interactions among Fe‐redox reactions, pH and methanogenesis are important factors in predicting CH 4 and CO 2 production as well as SOM decomposition rates in Fe‐rich, frequently waterlogged Arctic soils.

Linear nitramines are potential carcinogens. These compounds result from environmental degradation of high-energy cyclic nitramines and as by-products of carbon capture technologies.

Fe3O4 at 1-2 μm) were measured to assess the performance of the magnetic collector. The high gradient magnetic collector did not remove nanosized magnetic Fe3O4 particles any more effectively than non-magnetic NaCl particles. However, in the larger size range, the collector more efficiently removed Fe3O4 particles compared to SiO2 with a collection efficiency of 99% compared to 84% for SiO2. The removal mechanism could be attributed to both filtration and the high gradient magnetic field.

Dynamic pH change promoted by biogeochemical reactions in Arctic tundra soils can be a major control on the production and release of CO2 and CH4, which contribute to rising global temperatures. Large quantities of soil organic matter (SOM) in these soils are susceptible to microbial decomposition, leading to pH changes during permafrost thaw. Soil pH buffering capacity (beta) modulates the extent of pH change but has not been thoroughly studied and represented in predictive ecosystem scale biogeochemical models in Arctic tundra soils. In this study, we generated titration curves for 21 acidic tundra soils from three Arctic sites across northern Alaska, United States of America. Geochemical and hydrological soil properties were evaluated, and correlations with beta were developed. Strong correlations between beta and both gravimetric water content (theta(g)) (R-2 = 0.847, p < 0.001) and soil water retention (SWR) (R-2 = 0.849, p = 0.001) indicate that the ability of soil to retain water could be associated with its buffering properties. Correlations between beta and soil organic carbon (SOC) and cation exchange capacity (CEC) were also explored, and relationships to SWR are discussed. These correlations were then used with existing soil databases reporting SOC, CEC, and SWR to estimate beta across Alaska soils. We further demonstrated the quantitative relationships between beta and the simulated rates of biogeochemical reactions and show that lower beta leads to higher soil pH and more CH4 production. Our study provides simple proxies for beta in Arctic soils and highlights the importance and implications of representing soil buffering in predictive models, thereby enabling quantitative coupling between pH dynamics associated with biogeochemical reactions. Integrating beta into predictive models of Arctic biogeochemical cycling may reduce model uncertainty and further our understanding of permafrost SOM degradation accelerated by warming.

Arctic tundra soils store a globally significant amount of mercury (Hg), which could be transformed to the neurotoxic methylmercury (MeHg) upon warming and thus poses serious threats to the Arctic ecosystem. However, our knowledge of the biogeochemical drivers of MeHg production is limited in these soils. Using substrate addition (acetate and sulfate) and selective microbial inhibition approaches, we investigated the geochemical drivers and dominant microbial methylators in 60-day microcosm incubations with two tundra soils: a circumneutral fen soil and an acidic bog soil, collected near Nome, Alaska, United States. Results showed that increasing acetate concentration had negligible influences on MeHg production in both soils. However, inhibition of sulfate-reducing bacteria (SRB) completely stalled MeHg production in the fen soil in the first 15 days, whereas addition of sulfate in the low-sulfate bog soil increased MeHg production by 5-fold, suggesting prominent roles of SRB in Hg(II) methylation. Without the addition of sulfate in the bog soil or when sulfate was depleted in the fen soil (after 15 days), both SRB and methanogens contributed to MeHg production. Analysis of microbial community composition confirmed the presence of several phyla known to harbor microorganisms associated with Hg(II) methylation in the soils. The observations suggest that SRB and methanogens were mainly responsible for Hg(II) methylation in these tundra soils, although their relative contributions depended on the availability of sulfate and possibly syntrophic metabolisms between SRB and methanogens.

Objective: The COVID-19 pandemic jeopardizes continuity of operations of workplaces and the health and safety of workers. Exemplar workplace-related SARS-CoV-2 benchmarks are described and illustrated with empirical data. Methods: Benchmarks were collected over a 9-month period on a large workplace (N = 5500+). These ranged from quantitative indices associated with RT-qPCR targeted testing and random surveillance screening, surveillance for new variants of SARS-CoV-2, intensive contact tracing, case management, return to work procedures, to monitoring of antibody seropositive status. Results: Data and analyses substantiated effectiveness of interventions. This was evidenced in suppressed infection rates, rapid case identification and isolation, acceptance of the program by employees, documentation of presumptive immunity, and working relationships with senior management. Conclusions: These SARS-CoV-2 exemplar benchmarks provided an evidence-base for practice and contributed strategically to organizational decisions.

Earth and Space Science Open Archive This preprint has been submitted to and is under consideration at Journal of Geophysical Research - Biogeosciences. ESSOAr is a venue for early communication or feedback before peer review. Data may be preliminary.Learn more about preprints preprintOpen AccessYou are viewing an older version [v1]Go to new versionIron cycle interactions with hydrological dynamics reduce methane production in a simulated Arctic soilAuthorsBenjamin NSulmanFengmingYuanTeriO'MearaBaohuaGuElizabeth M.HerndoniDJianqiuZhengPeter E.ThorntoniDDavid EGrahamiDSee all authors Benjamin N SulmanCorresponding Author• Submitting AuthorOak Ridge National Laboratoryview email addressThe email was not providedcopy email addressFengming YuanOak Ridge National Laboratoryview email addressThe email was not providedcopy email addressTeri O'MearaSmithsonian Environmental Research Centerview email addressThe email was not providedcopy email addressBaohua GuOak Ridge National Laboratory (DOE)view email addressThe email was not providedcopy email addressElizabeth M. HerndoniDKent State UniversityiDhttps://orcid.org/0000-0002-9194-5493view email addressThe email was not providedcopy email addressJianqiu ZhengPacific Northwest National Laboratoryview email addressThe email was not providedcopy email addressPeter E. ThorntoniDOak Ridge National Laboratory (DOE)iDhttps://orcid.org/0000-0002-4759-5158view email addressThe email was not providedcopy email addressDavid E GrahamiDOak Ridge National Laboratory (DOE)iDhttps://orcid.org/0000-0001-8968-7344view email addressThe email was not providedcopy email address

Warming temperatures in continuous permafrost zones of the Arctic will alter both hydrological and geochemical soil conditions, which are strongly linked with heterotrophic microbial carbon (C) cycling. Heterogeneous permafrost landscapes are often dominated by polygonal features formed by expanding ice wedges: water accumulates in low centered polygons (LCPs), and water drains outward to surrounding troughs in high centered polygons (HCPs). These geospatial differences in hydrology cause gradients in biogeochemistry, soil C storage potential, and thermal properties. Presently, data quantifying carbon dioxide (CO2) and methane (CH4) release from HCP soils are needed to support modeling and evaluation of warming-induced CO2 and CH4 fluxes from tundra soils. This study quantifies the distribution of microbial CO2 and CH4 release in HCPs over a range of temperatures and draws comparisons to previous LCP studies. Arctic tundra soils were initially characterized for geochemical and hydraulic properties. Laboratory incubations at −2, +4, and +8°C were used to quantify temporal trends in CO2 and CH4 production from homogenized active layer organic and mineral soils in HCP centers and troughs, and methanogen abundance was estimated from mcrA gene measurements. Results showed that soil water availability, organic C, and redox conditions influence temporal dynamics and magnitude of gas production from HCP active layer soils during warming. At early incubation times (2–9 days), higher CO2 emissions were observed from HCP trough soils than from HCP center soils, but increased CO2 production occurred in center soils at later times (>20 days). HCP center soils did not support methanogenesis, but CH4-producing trough soils did indicate methanogen presence. Consistent with previous LCP studies, HCP organic soils showed increased CO2 and CH4 production with elevated water content, but HCP trough mineral soils produced more CH4 than LCP mineral soils. HCP mineral soils also released substantial CO2 but did not show a strong trend in CO2 and CH4 release with water content. Knowledge of temporal and spatial variability in microbial C mineralization rates of Arctic soils in response to warming are key to constraining uncertainties in predictive climate models.

Readers are invited to submit letters for publication in this department. Submit letters online at http://joem.edmgr.com. Choose “Submit New Manuscript.” A signed copyright assignment and financial disclosure form must be submitted with the letter. Form available at www.joem.org under Author and Reviewer information. To the Editor: Global efforts are being marshalled against the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) pandemic. A key component of public health response is sanitizing or disinfecting the workplace, including the healthcare environment. Recently we launched what appears to be the first study of anti-microbial properties of silver hardware touch surfaces or fomites in an occupational health clinic setting. We preview our major finding in order to emphasize the vital role of active sanitation measures, as opposed to reliance on passive controls, in public health response. Antimicrobial properties of silver (Ag) and copper (Cu) have been known for centuries.1,2 In view of their bactericidal and viricidal effects, Ag and/or Cu hardware or surface coatings have been studied in both laboratory conditions and settings such as hospitals, intensive care units, long term care and athletic centers, and schools.2–7 Although antimicrobial touch surfaces are not designed to replace active cleaning and disinfecting, self-disinfecting surfaces offer promise of sustained benefits.8 Approximately weekly, over a 127-day period, we assessed microbial burden on doorknobs, doorway push bars and pull and push plates, and bathroom sink faucets (32 sites) in a busy occupational health clinic. We sampled for initial burden, established a baseline from five samples over 71 days, and measured post-intervention microbial burden over seven samples (56 days) from October 2019 to March 2020. After baseline, 20 hardware sites were changed to commercially available antimicrobial silver fixtures, and 12 sites remained as controls. Prior to initiating the study, all surfaces were cleaned routinely (about weekly) with commercial cleaning agents. During the study, each site was cleaned after each sampling using a commercial benzethonium chloride wipe (a quaternary amine). Swabs were placed in collectors of 1 mL room-temperature Letheen broth and a research microbiology laboratory measured total aerobic heterotrophic bacteria in samples by plating on modified tryptic soy agar with 5% sheep blood and incubated for 48 hours at 37 °C. Direct colony counts were made and those with substantial clearing were counted as hemolytic colony forming units (CFUs). CFU counts, indicating total microbial contamination,9 were converted to their natural logarithms for data analysis because the raw counts had a non-normal distribution. We found nuance with respect to parameters of type of touch surface, weather (temperature, relative humidity), and local and regional health department reported rates of influenza-like-illness (ILI), but our key comparison was microbial burden before and after installation of Ag hardware. A paired t test for the Ag group showed significantly higher mean microbial burden with a medium effect size at post-test (t = –2.58, 19 df, P < 0.02; Cohen d = 0.69), and a similar result for hemolytic counts (t = –3.10, 19 df, P < 0.01; Cohen d = 0.92). The control group mean pre- and post-comparisons were not significantly different (t = –0.238 and –0.132, P < 0.82 and 0.89, respectively). Analysis of raw counts across all sites using the Wilcoxon matched-pairs sign test found a significant difference with a medium effect size for the Ag group (P < 0.04, d = 0.57), and no meaningful difference for the control sites. In short, unexpectedly we found Ag touch surfaces associated with higher microbial burdens compared with the existing pre-intervention hardware. Of note, the control sites showed generally high CFU levels and variances with median CFU levels two to five times higher than the Ag sites, rendering them less comparable to the Ag sites. The influence of local influenza rate may be relevant. We found that our local and regional ILI rates reported to the Centers for Disease Control (CDC) differed significantly from our baseline to post-change out period (t = 2.573, df 11, P < 0.03; d = 1.44). Thus, we examined point-biserial correlations between CFU and hemolytic counts with pre- versus post-Ag change status over 13 time samplings and found correlations of r = 0.515 and 0.455, respectively. The suggestively higher values for the post-change out period were not significant at P < 0.05 (N = 13). Removing variance associated with both regional and local ILI rates by partial correlation for the log CFU values yielded an r = 0.682 (not significantly different from r = 0.515). However, the partial correlation for log hemolytic counts was significantly different (r = 0.075 vs r = 0.455; z = P < 0.02). Thus, ILI rates did not materially affect the observed rise in CFU for the Ag sites, but the hemolytic count increase could be related to a covariate of elevated local rates of influenza. We speculate that the apparent lack of a robust Ag-effect may be attributable in part to subtle behavioral factors like increased use of the new hardware and perhaps less stringent cleaning may have been inadvertently applied to the novel fixtures. Regardless, our results suggest this brand of commercial Ag hardware does not substantially reduce total microbial burden. Importantly, we observed the first time sampling (reflecting prior cleaning practices) yielded elevated counts for both total CFU and hemolytic bacteria relative to subsequent baseline time samplings (both t = 3.58, df 31, P < 0.001; Cohen d = 0.49 and 0.57). There is a lesson here. Our results suggest two conclusions. First, there is no substitute for rigorous and standardized active cleaning protocols (ie, old fashioned “elbow grease”). Second, although using passive controls such as antimicrobial Ag hardware may be seductive, by itself this is inadequate in a naturalistic medical environment such as a busy occupational medicine clinic—even though Ag is known to have antimicrobial and viricidal properties, including on coronaviruses.10 In view of the current pandemic and our results, we now have instituted intensive twice-a-day disinfecting with certified broad spectrum bactericidal/viricidal cleaning agents and installed touchless hardware where practical.

CRISPR/Cas9 has been widely applied to various plant species accelerating the pace of plant genome editing and precision breeding in crops. Unintended effects beyond off-target nucleotide mutations are still somewhat unexplored. We investigated the degree and patterns of epigenetic changes after gene editing. We examined changes in DNA methylation in genome-edited promoters of naturally hypermethylated genes (AT1G72350 and AT1G09970) and hypomethylated genes (AT3G17320 and AT5G28770) from Arabidopsis. Transgenic plants were developed via Agrobacterium-mediated floral dip transformation. Homozygous edited lines were selected from segregated T2 plants by an in vitro digestion assay using ribonucleoprotein complex. Bisulfite sequencing comparisons were made between paired groups of edited and non-edited plants to identify changes in DNA methylation of the targeted loci. We found that directed mutagenesis via CRISPR/Cas9 resulted in no unintended morphological or epigenetic alterations. Phenotypes of wild-type, transgenic empty vector, and transgenic edited plants were similar. Epigenetic profiles revealed that methylation patterns of promoter regions flanking target sequences were identical among wild-type, transgenic empty vector, and transgenic edited plants. There was no effect of mutation type on epigenetic status. We also evaluated off-target mutagenesis effects in the edited plants. Potential off-target sites containing up to 4-bp mismatch of each target were sequenced. No off-target mutations were detected in candidate sites. Our results showed that CRISPR/Cas9 did not leave an epigenetic footprint on either the immediate gene-edited DNA and flanking DNA or introduce off-target mutations.

CRISPR/Cas9 has been widely applied to various plant species accelerating the pace of plant genome editing and precision breeding in crops. Unintended effects beyond off-target nucleotide mutations are still somewhat unexplored. We investigated the degree and patterns of epigenetic changes after gene editing. We examined changes in DNA methylation in genome-edited promoters of naturally hypermethylated genes (AT1G72350 and AT1G09970) and hypomethylated genes (AT3G17320 and AT5G28770) from Arabidopsis. Transgenic plants were developed via Agrobacterium-mediated floral dip transformation. Homozygous edited lines were selected from segregated T2 plants by an in vitro digestion assay using ribonucleoprotein complex. Bisulfite sequencing comparisons were made between paired groups of edited and non-edited plants to identify changes in DNA methylation of the targeted loci. We found that directed mutagenesis via CRISPR/Cas9 resulted in no unintended morphological or epigenetic alterations. Phenotypes of wild-type, transgenic empty vector, and transgenic edited plants were similar. Epigenetic profiles revealed that methylation patterns of promoter regions flanking target sequences were identical among wild-type, transgenic empty vector, and transgenic edited plants. There was no effect of mutation type on epigenetic status. We also evaluated off-target mutagenesis effects in the edited plants. Potential off-target sites containing up to 4-bp mismatch of each target were sequenced. No off-target mutations were detected in candidate sites. Our results showed that CRISPR/Cas9 did not leave an epigenetic footprint on either the immediate gene-edited DNA and flanking DNA or introduce off-target mutations.

We investigated rates and controls on greenhouse gas (CO(2)and CH4) production in two contrasting water-saturated tundra soils within a permafrost-affected watershed near Nome, Alaska, United States. Three years of field sample analysis have shown that soil from a fen-like area in the toeslope of the watershed had higher pH and higher porewater ion concentrations than soil collected from a bog-like peat plateau at the top of the hillslope. The influence of these contrasting geochemical and topographic environments on CO(2)and CH(4)production was tested in soil microcosms by incubating both the organic- and mineral-layer soils anaerobically for 55 days. Nitrogen (as NH4Cl) was added to half of the microcosms to test potential effects of N limitation on microbial greenhouse gas production. We found that the organic toeslope soils produced more CO(2)and CH4, fueled by higher pH and higher concentrations of water-extractable organic C (WEOC). Our results also indicate N limitation on CO(2)production in the peat plateau soils but not the toeslope soils. Together these results suggest that the weathering and leaching of ions and nutrients from tundra hillslopes can increase the rate of anaerobic soil organic matter decomposition in downslope soils by (1) increasing the pH of soil porewater; (2) providing bioavailable WEOC and fermentation products such as acetate; and (3) relieving microbial N limitation through nutrient runoff. We conclude that the soil geochemistry as mediated by landscape position is an important factor influencing the rate and magnitude of greenhouse gas production in tundra soils.