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USGS2010

Carbon dioxide (CO 2 ) sequestration in deep saline aquifers and formations: Chapter 3

Carbon dioxide (CO 2 ) capture and sequestration in geologic media is one among many emerging strategies to reduce atmospheric emissions of anthropogenic CO 2 . This chapter looks at the potential of deep saline aquifers – based on their capacity and close proximity to large point sources of CO 2 – as repositories for the geologic sequestration of CO 2 . The petrochemical characteristics which impact on the suitability of saline aquifers for CO 2 sequestration and the role of coupled geochemical transport models and numerical tools in evaluating site feasibility are also examined. The full-scale commercial CO 2 sequestration project at Sleipner is described together with ongoing pilot and demonstration projects.

Book chapter↗

USGS2014

Suppressing bullfrog larvae with carbon dioxide

Current management strategies for the control and suppression of the American Bullfrog ( Lithobates catesbeianus = Rana catesbeiana Shaw) and other invasive amphibians have had minimal effect on their abundance and distribution. This study evaluates the effects of carbon dioxide (CO 2 ) on pre- and prometamorphic Bullfrog larvae. Bullfrogs are a model organism for evaluating potential suppression agents because they are a successful invader worldwide. From experimental trials we estimated that the 24-h 50% and 99% lethal concentration (LC 50 and LC 99 ) values for Bullfrog larvae were 371 and 549 mg CO 2 /L, respectively. Overall, larvae that succumbed to experimental conditions had a lower body condition index than those that survived. We also documented sublethal changes in blood chemistry during prolonged exposure to elevated CO 2 . Specifically, blood pH decreased by more than 0.5 pH units after 9 h of exposure and both blood partial pressure of CO 2 (pCO 2 ) and blood glucose increased. These findings suggest that CO 2 treatments can be lethal to Bullfrog larvae under controlled laboratory conditions. We believe this work represents the necessary foundation for further consideration of CO 2 as a potential suppression agent for one of the most harmful invaders to freshwater ecosystems.

Journal of Herpetology↗

USGS2005

Carbon, nitrogen, and phosphorus accumulation in floodplains of Atlantic Coastal Plain rivers, USA

Net nutrient accumulation rates were measured in riverine floodplains of the Atlantic Coastal Plain in Virginia, Maryland, and Delaware, USA. The floodplains were located in watersheds with different land use and included two sites on the Chickahominy River (urban), one site on the Mattaponi River (forested), and five sites on the Pocomoke River (agricultural). The Pocomoke River floodplains lie along reaches with natural hydrogeomorphology and on reaches with restricted flooding due to channelization and levees. A network of feldspar clay marker horizons was placed on the sediment surface of each floodplain site 3–6 years prior to sampling. Sediment cores were collected from the material deposited over the feldspar clay pads. This overlying sediment was separated from the clay layer and then dried, weighed, and analyzed for its total carbon (C), nitrogen (N), and phosphorus (P) content. Mean C accumulation rates ranged from 61 to 212 g·m −2 ·yr −1 , N accumulation rates ranged from 3.5 to 13.4 g·m −2 ·yr −1 , and P accumulation rates ranged from 0.2 to 4.1 g·m −2 ·yr −1 among the eight floodplains. Patterns of intersite variation in mineral sediment and P accumulation rates were similar to each other, as was variation in organic sediment and C and N accumulation rates. The greatest sediment and C, N, and P accumulation rates were observed on Chickahominy River floodplains downstream from the growing metropolitan area of Richmond, Virginia. Nutrient accumulation rates were lowest on Pocomoke River floodplains that have been hydraulically disconnected from the main channel by channelization and levees. Sediment P concentrations and P accumulation rates were much greater on the hydraulically connected floodplain immediately downstream of the limit of channelization and dense chicken agriculture of the upper Pocomoke River watershed. These findings indicate that (1) watershed land use has a large effect on sediment and nutrient retention in floodplains, and (2) limiting the hydraulic connectivity between river channels and floodplains minimizes material retention by floodplains in fluvial hydroscapes.

Delaware, Maryland, Virginia↗

USGS2010

Experimental drought in a tropical rain forest increases soil carbon dioxide losses to the atmosphere

Climate models predict precipitation changes for much of the humid tropics, yet few studies have investigated the potential consequences of drought on soil carbon (C) cycling in this important biome. In wet tropical forests, drought could stimulate soil respiration via overall reductions in soil anoxia, but previous research suggests that litter decomposition is positively correlated with high rainfall fluxes that move large quantities of dissolved organic matter (DOM) from the litter layer to the soil surface. Thus, reduced rainfall could also limit C delivery to the soil surface, reducing respiration rates. We conducted a throughfall manipulation experiment to investigate how 25% and 50% reductions in rainfall altered both C movement into soils and the effects of those DOM fluxes on soil respiration rates. In response to the experimental drought, soil respiration rates increased in both the −25% and −50% treatments. Throughfall fluxes were reduced by 26% and 55% in the −25% and −50% treatments, respectively. However, total DOM fluxes leached from the litter did not vary between treatments, because the concentrations of leached DOM reaching the soil surface increased in response to the simulated drought. Annual DOM concentrations averaged 7.7 ± 0.8, 11.2 ± 0.9, and 15.8 ± 1.2 mg C/L in the control, −25%, and −50% plots, respectively, and DOM concentrations were positively correlated with soil respiration rates. A laboratory incubation experiment confirmed the potential importance of DOM concentration on soil respiration rates, suggesting that this mechanism could contribute to the increase in CO 2 fluxes observed in the reduced rainfall plots. Across all plots, the data suggested that soil CO 2 fluxes were partially regulated by the magnitude and concentration of soluble C delivered to the soil, but also by soil moisture and soil oxygen availability. Together, our data suggest that declines in precipitation in tropical rain forests could drive higher CO 2 fluxes to the atmosphere both via increased soil O 2 availability and through responses to elevated DOM concentrations.

Golfo Dulce Forest Reserve↗

USGS2010

Pleistocene carbonate stratigraphy of South Florida: Evidence for high-frequency sea-level cyclicity

Pleistocene carbonates of south Florida and islands of the Florida Keys are currently divided into five marine sequences designated, from oldest to youngest, the Q1–Q5 units. The units include a mosaic of freshwater and shallow marine deposits that accumulated on the Florida platform during high sea-level stands. The units are separated by regional-scale subaerial-exposure surfaces that formed during glacioeustatic lowstands. Analyses of cores recovered at Grossman Ridge Rock Reef and Joe Ree Rock Reef in the Florida Everglades reveal additional subaerial-exposure surfaces that are used to delineate subdivisions within units Q1 (Q1a–Q1b), Q2 (Q2a–Q2d), and Q4 (Q4a–Q4b). Units Q1–Q5 preserve evidence of at least 10 separate sea-level highstands, rather than 5 as indicated by previous studies. Compilation of available uranium-series dates on corals recovered from the Florida Keys indicates that the Q4 unit accreted during sea-level maxima associated with marine oxygen-isotope Stage 9 (Q4a) and isotope Stage 7 (Q4b). The Q5 unit formed during isotope Stage 5. No reliable dates are available for units Q1–Q3. We infer that unit Q3 was formed during the extended sea-level highstand of isotope Stage 11 and that units Q2 and Q1 predate isotope Stage 11.

Florida↗

USGS2016

Oxygen, hydrogen, sulfur, and carbon isotopes in the Pea Ridge magnetite-apatite deposit, southeast Missouri, and sulfur isotope comparisons to other iron deposits in the region

Oxygen, hydrogen, sulfur, and carbon isotopes have been analyzed in the Pea Ridge magnetite-apatite deposit, the largest historic producer among the known iron deposits in the southeast Missouri portion of the 1.5 to 1.3 Ga eastern granite-rhyolite province. The data were collected to investigate the sources of ore fluids, conditions of ore formation, and provenance of sulfur, and to improve the general understanding of the copper, gold, and rare earth element potential of iron deposits regionally. The δ 18 O values of Pea Ridge magnetite are 1.9 to 4.0‰, consistent with a model in which some magnetite crystallized from a melt and other magnetite—perhaps the majority—precipitated from an aqueous fluid of magmatic origin. The δ 18 O values of quartz, apatite, actinolite, K-feldspar, sulfates, and calcite are significantly higher, enough so as to indicate growth or equilibration under cooler conditions than magnetite and/or in the presence of a fluid that was not entirely magmatic. A variety of observations, including stable isotope observations, implicate a second fluid that may ultimately have been meteoric in origin and may have been modified by isotopic exchange with rocks or by evaporation during storage in lakes. Sulfur isotope analyses of sulfides from Pea Ridge and seven other mineral deposits in the region reveal two distinct populations that average 3 and 13‰. Two sulfur sources are implied. One was probably igneous melts or rocks belonging to the mafic- to intermediate-composition volcanic suite that is present at or near most of the iron deposits; the other was either melts or volcanic rocks that had degassed very extensively, or else volcanic lakes that had trapped rising magmatic gases. The higher δ 34 S values correspond to deposits or prospects where copper is noteworthy—the Central Dome portion of the Boss deposit, the Bourbon deposit, and the Vilander prospective area. The correspondence suggests that (1) sulfur either limited the deposition of copper or was cotransported with copper, and (2) sulfur isotope analysis may be useful in evaluating southeast Missouri iron deposits for copper and possibly for gold.

Missouri↗

USGS1955

Is Carbon dioxide an ore-forming fluid under shallow-earth conditions?

A review of some of the physical-chemical properties of CO 2 and of the system CO 2 --H 2 O indicates that under some shallow-earth conditions CO 2 can exist as a separate phase with a density approximately that of water. The effect of dissolved neutral or acid salts on the solubility of CO 2 in H 2 O is not large. Carbonates, oxides, and silicates, through reactions with a CO 2 -saturated water phase, will eventually cause the disappearance of a CO 2 phase. The prevalence of CO 2 in the earth's crust is attested by its abundance in natural gases and fluid inclusions in minerals. Some of the characteristics of uranium ores of the Colorado Plateau are not incompatible with the assumption that deposition was from a fluid CO 2 phase.

Economic Geology↗

USGS1970

Uraninite-bearing contact metamorphic deposits, Heaths Peak, Carbon County, Wyoming

Deposits that contain uraninite and sulfide minerals at Heaths Peak, Carbon County, Wyo., display a zoned distribution of metals from the edge of granite into adjacent metamorphic rocks. The metallic minerals -- uraninite, molybdenite, pyrite, chalcopyrite, galena, pyrrhotite, and marcasite -- are concentrated on the undersides of metamorphosed roof pendants. At the Little Man mine, deposition was related to a small cupola projecting into the central part of an elongate pendant. The host rocks and the deposits are of Precambrian age.

Wyoming↗

USGS1974

Carbon, hydrogen, oxygen, and sulfur isotope study of the Darwin lead-silver-zinc deposit, Southern California

The ores at Darwin occur as massive replacement bodies in silicated limestones of Pennsylvanian and Permian age adjacent to a Jurassic quartz monzonite stock. Three types of ore have a definite spatial relationship to the quartz monzonite: (1) pyrite-sphalerite-galena ores, (2) pyrite-pyrrhotite-magnetite-sphalerite-galena ores, and (3) galena-Ag-Bi-Se ores.The delta 34 S values of all sulfide minerals range from +4.4 to --5.7 permil. The delta 34 S values for individual minerals tend to decrease with respect to both space and paragenetic time. The delta (sub sl-gn) values range from 1.5 to 2.5 permil and correspond to a temperature range of 325 degrees + or - 55 degrees C. The sphalerite-galena sulfur isotope temperatures at a given locality are reproducible to + or -30 degrees C and are consistent with temperatures determined by other means.Analyses of water in three samples of fluid inclusions in sphalerite indicate that the ore fluids had delta D values of --66 + or - permil, a total salinity that reached at least 20 percent, and K/Na atomic ratios of 0.23 + or - 0.03. Isotopic and thermochemical data indicate that the ore fluids had average values of delta 34 S (sub Sigma S) = 3 permil, delta 13 C (sub Sigma O) = -- 3.5 permil, Sigma S = 0.01 mole/Kg H 2 O, f (sub CO 2 ) = 12 + or - 8 bars, and Sigma C = 0.15 + or - 0.06 mole/Kg H 2 O.The delta 18 O values of postsulfide calcites have a range of 12.8 + or - 1.5 permil in the pyrite ores and 17 + or - 2 permil in the pyrrhotite ores. Similar values for relict limestone host rock in these areas indicate that oxygen isotopic equilibrium was established between the calcite precipitating fluids and the wall rock. The delta 13 C values of the calcites, however, range from --5.8 to --3.6 permil and are considerably more negative than the limestone in the host rock, indicating that carbon isotopic equilibrium was not established between the fluids and the wall rock.Thermochemical data indicate that the pH of the ore fluids was about 4.8 as they traveled through the quartz monzonite at T nearly equal 350 degrees C. When the fluids completely equilibrated with the relict limestone and calc-silicate host rock, the pH increased to 6.7. This increase in pH as the fluids traveled upward and away from the quartz monzonite was responsible for the spatial distribution of iron sulfide assemblages, for variations in delta 34 S values of sulfides, and probably caused precipitation of the ore.

California↗

USGS1991

Reduction of nitrate in aquifer microcosms by carbon additions

Aquifer microcosms were used to examine the effects of NO − 3 and C amendments on groundwater from the Claiborne aquifer. Nitrate concentrations of 12.17 mg L −1 in aquifer microcosms were reduced 0.92%/d to 5.84 mg L −1 by the addition of 10 mg C L −1 for 35 d. Nitrate disappearance correlated with increases in number of denitrifiers and dissolved N 2 O concentration and decreases in dissolved oxygen, suggesting biological denitrification. Nitrate/chloride ratios decreased in microcosms with 10 mg C L −1 added and then increased when the C addition was removed. Carbon additions of 0.4 mg C L −1 had no effect on the microbial or chemical properties of the microcosms. Nitrous oxide levels in wells sampling the Claiborne aquifer showed an increase with depth, indicating N 2 O production within the aquifer. Microcosms are useful tools to examine biological transformations of chemical contaminants in unconsolidated aquifer material. The remediation of NO − 3 contaminated aquifers by organic infusion is possible and appears to be a function of microbial denitrification.

Journal of Environmental Quality↗

USGS2010

Determining sources of dissolved organic carbon and disinfection byproduct precursors to the McKenzie River, Oregon

This study was conducted to determine the main sources of dissolved organic carbon (DOC) and disinfection byproduct (DBP) precursors to the McKenzie River, Oregon (USA). Water samples collected from the mainstem, tributaries, and reservoir outflows were analyzed for DOC concentration and DBP formation potentials (trihalomethanes [THMFPs] and haloacetic acids [HAAFPs]). In addition, optical properties (absorbance and fluorescence) of dissolved organic matter (DOM) were measured to provide insight into DOM composition and assess whether optical properties are useful proxies for DOC and DBP precursor concentrations. Optical properties indicative of composition suggest that DOM in the McKenzie River mainstem was primarily allochthonous - derived from soils and plant material in the upstream watershed. Downstream tributaries had higher DOC concentrations than mainstem sites (1.6 ?? 0.4 vs. 0.7 ?? 0.3 mg L-1) but comprised <5% of mainstem flows and had minimal effect on overall DBP precursor loads. Water exiting two large upstream reservoirs also had higher DOC concentrations than the mainstem site upstream of the reservoirs, but optical data did not support in situ algal production as a source of the added DOC during the study. Results suggest that the first major rain event in the fall contributes DOM with high DBP precursor content. Although there was interference in the absorbance spectra in downstream tributary samples, fluorescence data were strongly correlated to DOC concentration (R 2 = 0.98), THMFP (R2 = 0.98), and HAAFP (R2 = 0.96). These results highlight the value of using optical measurements for identifying the concentration and sources of DBP precursors in watersheds, which will help drinking water utilities improve source water monitoring and management programs. Copyright ?? 2010 by the American Society of Agronomy.

Journal of Environmental Quality↗

USGS2015

Importance of the colmation layer in the transport and removal of cyanobacteria, viruses, and dissolved organic carbon during natural lake-bank filtration

This study focused on the importance of the colmation layer in the removal of cyanobacteria, viruses, and dissolved organic carbon (DOC) during natural bank filtration. Injection-and-recovery studies were performed at two shallow (0.5 m deep), sandy, near-shore sites at the southern end of Ashumet Pond, a waste-impacted, kettle pond on Cape Cod, MA, that is subject to periodic blooms of cyanobacteria and continuously recharges a sole-source drinking-water aquifer. The experiment involved assessing the transport behaviors of bromide (conservative tracer), Synechococcus sp. IU625 (cyanobacterium, 2.6 ± 0.2 µm), AS-1 (tailed cyanophage, 110 nm long), MS2 (coliphage, 26 nm diameter), and carboxylate-modified microspheres (1.7 µm diameter) introduced to the colmation layer using a bag-and-barrel (Lee-type) seepage meter. The injectate constituents were tracked as they were advected across the pond water–groundwater interface and through the underlying aquifer sediments under natural-gradient conditions past push-point samplers placed at &sim;30-cm intervals along a 1.2-m-long, diagonally downward flow path. More than 99% of the microspheres, IU625, MS2, AS-1, and &sim;44% of the pond DOC were removed in the colmation layer (upper 25 cm of poorly sorted bottom sediments) at two test locations characterized by dissimilar seepage rates (1.7 vs. 0.26 m d −1 ). Retention profiles in recovered core material indicated that >82% of the attached IU625 were in the top 3 cm of bottom sediments. The colmation layer was also responsible for rapid changes in the character of the DOC and was more effective (by three orders of magnitude) at removing microspheres than was the underlying 20-cm-thick segment of sediment.

Massachusetts↗

USGS1995

Carbon sequestration in an aggrading forest ecosystem in the Southeastern USA

An analysis of C pools at the Panola Mountain Research Watershed (PMRW) near Atlanta, GA, indicates that aggrading forests in the U.S. Southeast are an important regional C sink. The forests in this area were cut in the early 1800s and the land was cultivated until the early 1900s, when farming was abandoned and forest regeneration began. Cultivation resulted in extensive erosion, which depleted soil C pools. The rate of soil C sequestration during the 70-yr period of forest regeneration was estimated to be between 0.34 (standard error [SE] = 0.12) and 0.79 (SE = 0.19) Mg C ha −1 yr −1 . There is a large potential for continued C accumulation in the soil at PMRW based on the difference between current measured soil C pools of 82 Mg C ha −1 at PMRW and 122 Mg C ha −1 at the nearby “undisturbed” Fernbank Forest in Atlanta, GA. The rate of C sequestration in biomass at PMRW was 1.47 Mg C ha −1 yr −1 for the regeneration period, bringing the ecosystem total to between 1.81 and 2.26 Mg C ha −1 yr −1 . Carbon sequestration in temperate forest ecosystems partially mitigates the effects of increased atmospheric loading of CO 2 .

Georgia↗

USGS2000

Carbon distribution in subalpine forests and meadows of the Olympic Mountains, Washington

stimates of C storage in mountainous regions are rare. Forest–meadow ecotones in subalpine ecosystems, which contain a mosaic of forests and meadows, may be particularly sensitive to future changes in climate and are therefore important to include in estimates of terrestrial C storage. In this study, we quantified soil C and ecosystem C pools in subalpine forest and meadow soils of the northeastern (NE, dry climate) and southwestern (SW, wet climate) Olympic Mountains. Carbon concentrations of mineral soil are relatively high in upper horizons, ranging from 43 to 142 g kg −1 in NE soils and 27 to 162 g kg −1 in SW soils. Northeastern meadow soils store more C than NE forests ( P = 0.009) , while SW forest soils store more C than SW meadows ( P = 0.038) Ecosystem C storage is greater in forests than in meadows. Under a warmer climatic scenario with drier summers and wetter winters, subalpine C storage may decrease in the NE and increase in the SW, and changes in C storage will be closely related to vegetation distribution, ecosystem productivity, decomposition rates, and local disturbance regimes. Because ecosystem processes and associated C storage differ between high- and low-elevation ecosystems, it is important that data from both high- and low-elevation sites are included in estimates of C storage in terrestrial ecosystems.

Soil Science Society of America Journal↗

USGS2010

Erosion and vegetation restoration impacts on ecosystem carbon dynamics in South China

To quantify the consequences of erosion and vegetation restoration on ecosystem C dynamics (a key element in understanding the terrestrial C cycle), field measurements were collected since 1959 at two experimental sites set up on highly disturbed barren land in South China. One site had received vegetation restoration (the restored site) while the other received no planting and remained barren (the barren site). The Erosion-Deposition Carbon Model (EDCM) was used to simulate the ecosystem C dynamics at both sites. The on-site observations in 2007 showed that soil organic C (SOC) storage in the top 80-cm soil layer at the barren site was 50.3 ± 3.5 Mg C ha −1 , half that of the restored site. The SOC and surface soil loss by erosion at the restored site from 1959 to 2007 was 3.7 Mg C ha −1 and 2.2 cm, respectively—one-third and one-eighth that of the barren site. The on-site C sequestration in SOC and vegetation at the restored site was 0.67 and 2.5 Mg C ha −1 yr −1 , respectively, from 1959 to 2007, driven largely by tree growth and high atmospheric N deposition in the study area. Simulated findings suggested that higher N deposition resulted in higher on-site SOC storage in the soil profile (with SOC in the top 20-cm layer increasing more significantly), and higher on-site ecosystem C sequestration as long as N saturation was not reached. Lacking human-induced vegetation recovery, the barren site remained as barren land from 1959 to 2007 and the on-site C decrease was 0.28 Mg C ha −1 yr −1 Our study clearly indicated that vegetation restoration and burial by soil erosion provide a large potential C sink in terrestrial ecosystems.

Soil Science Society of America Journal↗

USGS2024

Managing basin-scale carbon sequestration: A tragedy of the commons approach

The Tragedy of the Commons is a well studied problem in the literature of ecology, economics, and environmental policy which illustrates the deleterious consequences of managing common pool resources when individual and social incentives are misaligned. In this work, we apply a simple model of carbon sequestration in a deep saline aquifer by two neighboring geologic CO 2 storage (GCS) operators to begin investigating if a Tragedy of the Commons framework applies to GCS. Specifically, we consider the pressure space as a “commons” because the injection by each firm at its own well increases the downhole injection pressure at both wells. We assume that a firm will decrease its injection rate if the downhole pressure at its well exceeds a predefined maximum (i.e., exceeds the “pressure limit”). With this assumption in place, we find that the same injection flowrates are optimal for both wells, regardless of whether they are owned by the same firm or competing firms. This suggests that GCS may not be best represented by a pure Tragedy of the Commons framework under our initial assumptions. However, there could be economic incentives or contractual obligations that may result in either or both GCS operators being unwilling to reduce their injection rates. Thus, we conclude the conference paper with a discussion of future extensions of our approach that may demonstrate closer alignment with the Tragedy of the Commons, including explicit definitions of pore-space rights, firm uncertainty regarding the parameters of the Theis equation, and the potential role of unitization.

Conference Paper↗

USGS1997

Evaluation of estimation methods for organic carbon normalized sorption coefficients

A critically evaluated set of 94 soil water partition coefficients normalized to soil organic carbon content ( K oc ) is presented for 11 classes of organic chemicals. This data set is used to develop and evaluate K oc estimation methods using three different descriptors. The three types of descriptors used in predicting K oc were octanol/water partition coefficient ( K ow ), molecular connectivity ( m X t ) and linear solvation energy relationships (LSERs). The best results were obtained estimating K oc from K ow , though a slight improvement in the correlation coefficient was obtained by using a two-parameter regression with K ow and the third order difference term from m X t . Molecular connectivity correlations seemed to be best suited for use with specific chemical classes. The LSER provided a better fit than m X t but not as good as the correlation with K oc . The correlation to predict K oc from K ow was developed for 72 chemicals; log K oc = 0.903* log K ow + 0.094. This correlation accounts for 91% of the variability in the data for chemicals with log K ow ranging from 1.7 to 7.0. The expression to determine the 95% confidence interval on the estimated K oc is provided along with an example for two chemicals of different hydrophobicity showing the confidence interval of the retardation factor determined from the estimated K oc . The data showed that K oc is not likely to be applicable for chemicals with log K ow < 1.7. Finally, the K oc correlation developed using K ow as a descriptor was compared with three nonclass-specific correlations and two 'commonly used' class-specific correlations to determine which method(s) are most suitable.

Water Environment Research↗

USGS1998

Nitrogen and carbon soil dynamics in response to climate change in a high-elevation ecosystem in the Rocky Mountains, U.S.A.

We have implemented a long-term snow-fence experiment at the Niwot Ridge Long-Term Ecological Research (NWT) site in the Colorado Front Range of the Rocky Mountains, U.S.A., to assess the effects of climate change on alpine ecology and biogeochemical cycles. The responses of carbon (C) and nitrogen (N) dynamics in high-elevation mountains to changes in climate are investigated by manipulating the length and duration of snow cover with the 2.6 × 60 m snow fence, providing a proxy for climate change. Results from the first year of operation in 1994 showed that the period of continuous snow cover was increased by 90 d. The deeper and earlier snowpack behind the fence insulated soils from winter air temperatures, resulting in a 9°C increase in annual minimum temperature at the soil surface. The extended period of snow cover resulted in subnivial microbial activity playing a major role in annual C and N cycling. The amount of C mineralized under the snow as measured by CO 2 production was 22 g m -2 in 1993 and 35 g m -2 in 1994, accounting for 20% of annual net primary above-ground production before construction of the snow fence in 1993 and 31% after to snow fence was constructed in 1994. In a similar fashion, maximum subnivial N 2 O flux increased 3-fold behind the snow fence, from 75 μg N m -2 d -1 in 1993 to 250 μg N m -2 d -1 in 1994. The amount of N lost from denitrification was greater than the annual atmospheric input of N in snowfall. Surface litter decomposition studies show that there was a significant increase in the litter mass loss under deep and early snow, with no significant change under medium and little snow conditions. Changes in climate that result in differences in snow duration, depth, and extent may therefore produce large changes in the C and N soil dynamics of alpine ecosystems.

Colorado↗