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A survey of nitric oxide (NO) emission from Chihuahuan desert soils found mean NO fluxes <0.1 ng NO-N cm-2 h-1 during the dry season. These fluxes were at the lower end of the range reported for temperate grassland and woodland ecosystems. NO fluxes from wet or watered soils were higher (0.1-35 ng NO-N cm-2 h-1 ). Watering of black grama grassland soils produced an initial pulse of 12 ng cm-2 h-1 (12-h after 1-cm watering) with high fluxes sustained over 4 days with repeated watering. Initial pulses from shrubland soils were lower (maximum 5 ng cm-2 h-1 ), and fluxes declined with repeated watering. Repeated watering of creosotebush soils depleted the soil NH4 + pool, and NO emissions were directly related to soil...
Whole air drawn from four heights within the high elevation (3,340 m asl), deep, winter snowpack at Niwot Ridge, Colorado, were sampled into stainless steel canisters, and subsequently analyzed by gas chromatography for 51 volatile inorganic and organic gases. Two adjacent plots with similar snow cover were sampled, one over bare soil and a second one from within a snow-filled chamber where Tedlar/Teflon-film covered the ground and isolated it from the soil. This comparison allowed for studying effects from processes in the snowpack itself versus soil influences on the gas concentrations and fluxes within and through the snowpack. Samples were also collected from ambient air above the snow surface for comparison...
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We examined the 10-day response of soil microbial biomass-N to additions of carbon (dextrose) and nitrogen (NH4NO3) to water-amended soils in a factorial experiment in four plant communities of the Chihuahuan desert of New Mexico (U.S.A.). In each site, microbial biomass-N and soil carbohydrates increased and extractable soil N decreased in response to watering alone. Fertilization with N increased microbial biomass-N in grassland soils; whereas, fertilization with C increased microbial biomass-N and decreased extractable N and P in all communities dominated by shrubs, which have invaded large areas of grassland in the Chihuahuan desert during the last 100 years. Our results support the hypothesis that the control...
Strontium isotope sourcing has become a common and useful method for assigning sources to archaeological artifacts. In Chaco Canyon, an Ancestral Pueblo regional center in New Mexico, previous studies using these methods have suggested that significant portion of maize and wood originate in the Chuska Mountains region, 75 km to the East. In the present manuscript, these results were tested using both frequentist methods (to determine if geochemical sources can truly be differentiated) and Bayesian methods (to address uncertainty in geochemical source attribution). It was found that Chaco Canyon and the Chuska Mountain region are not easily distinguishable based on radiogenic strontium isotope values. The strontium...
Categories: Publication; Types: Citation; Tags: Agriculture, Anthropology, Archaeology, Archaeometry, Atoms, All tags...
Fluxes of CO2 during the snow-covered season contribute to annual carbon budgets, but our understanding of the mechanisms controlling the seasonal pattern and magnitude of carbon emissions in seasonally snow-covered areas is still developing. In a subalpine meadow on Niwot Ridge, Colorado, soil CO2 fluxes were quantified with the gradient method through the snowpack in winter 2006 and 2007 and with chamber measurements during summer 2007. The CO2 fluxes of 0.71 ?mol m?2 s?1 in 2006 and 0.86 ?mol m?2 s?1 in 2007 are among the highest reported for snow-covered ecosystems in the literature. These fluxes resulted in 156 and 189 g C m?2 emitted over the winter, ~30% of the annual soil CO2 efflux at this site. In general,...
Physical ecosystem engineers are organisms that physically modify the abiotic environment. They can affect biogeochemical processing by changing the availability of resources for microbes (e.g., carbon, nutrients) or by changing abiotic conditions affecting microbial process rates (e.g., soil moisture or temperature). Physical ecosystem engineers can therefore create biogeochemical heterogeneity in soils and sediments. They do so via general mechanisms influencing the flows of materials (i.e., modification of fluid dynamic properties, fluid pumping, and material transport) or the transfer of heat (i.e., modification of heat transfer properties, direct heat transfer, and convective forcing). The consequences of physical...
Research in river-floodplain systems has emphasized the importance of nutrient delivery by floodwaters, but the mechanisms by which floods make nutrients available are rarely evaluated. Using a laboratory re-wetting experiment, we evaluated the alternative hypotheses that increased nutrient concentrations in riparian groundwater during flash floods are due to (HI) elevated nutrient concentrations in surface floodwaters entering the riparian zone or (H2) re-mobilization of nutrients from riparian soils. We sampled soils from the riparian zone of a 400 m reach of Sycamore Creek, AZ. Two sub-samples from each soil were re-wetted with a solution that mimicked the chemistry of floodwaters, with one subsample simultaneously...
Nitrates minerals from the Dry Valleys of Antarctica have been analyzed for their oxygen and nitrogen isotopic compositions. The 15N was depleted with δ15N values ranging from −9.5 to −26.2‰, whereas the 17O and 18O isotopes were highly enriched (with excess 17O) with δ18O values spanning 62–76‰ and Δ17O values from 28.9 to 32.7‰. These are the largest 17O enrichments observed in any known mineral. The oxygen isotopes indicate that nitrate is from a combination of tropospheric transport of photochemically produced HNO3 and HNO3 formed in the stratosphere.
A lower limit for nitrogen loss from desert ecosystems in the southwestern United States was estimated by comparing nitrogen inputs to the amount of nitrogen stored in desert soils and vegetation. Atmospheric input of nitrogen for the last 10 000 years was conservatively estimated to be 2.99 kg N/m2. The amount of nitrogen stored in desert soils was calculated to be 0.604 kg N/m3 using extant data from 212 profiles located in Arizona, California, Nevada, and Utah. The average amount of nitrogen stored in desert vegetation is approximately 0.036 kg N/m2. Desert conditions have existed in the southwestern United States throughout the last 10 000 years. Under such conditions, vertical leaching of nitrogen below a depth...
Over the past 50 years, conceptual developments in stream ecology and ecosystem ecology have converged, thanks to biogeochemistry and the recognition that in situ processing on one hand and spatial translation of materials, processes, and influence along flowpaths on the other, unite to generate a holistic picture of ecosystem functioning at the landscape level. Early emphases in stream biogeochemistry involved organic carbon dynamics and whole-ecosystem budgets. These approaches were holistic but cumbersome and laborious and ignored several crucial issues, such as variation in organic matter quality. Nutrient-spiraling approaches rectified this shortcoming and provided a flowpath-specific technique for resolving...
The effect of snow cover on surface-atmosphere exchanges of nitrogen oxides (nitrogen oxide (NO) + nitrogen dioxide (NO2); note, here ?NO2? is used as surrogate for a series of oxidized nitrogen gases that were detected by the used monitor in this analysis mode) was investigated at the high elevation, subalpine (3,340 m asl) Soddie site, at Niwot Ridge, Colorado. Vertical (NO + NO2) concentration gradient measurements in interstitial air in the deep (up to ~2.5 m) snowpack were conducted with an automated sampling and analysis system that allowed for continuous observations throughout the snow-covered season. These measurements revealed sustained, highly elevated (NO + NO2) mixing ratios inside the snow. Nitrogen...
Much of the research on the chemistry of snow and surface waters of the western US, Europe, and Asia has been conducted in high-elevation catchments above treeline. Here we provide information on the solute content of the seasonal snowpack at the Soddie site on Niwot Ridge, Colorado, a subalpine site near treeline. We focus on the storage and release of both inorganic and organic solutes to the soils underneath the snowpack, and subsequent effects on the chemical and nutrient content of the underlying soil solution and the adjacent headwater stream. The concentration of inorganic nitrogen (N) stored in the seasonal snowpack at the Soddie site of about 11 Î&frac14;eq L−1 was on the upper end of values reported...
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Microbial biomass nitrogen was measured in unamended (dry) and wetted soils in ten shrubland and grassland communities of the Chihuahuan desert, southern New Mexico, by the fumigation-extraction method. Microbial biomass-N in dry soils was undetectable. Average microbial biomass-N in wetted soils among all plant communities was 15.3 ?g g-1 soil. Highest values were found in the communities with the lowest topographic positions, and the minimum values were detected in the spaces between shrubs. Microbial biomass was positively and significantly correlated to soil organic carbon and extractable nitrogen (NH4 + + NO3 -). In a stepwise multiple regression, organic carbon and extractable nitrogen accounted for 40.9 and...
Hurricanes cause severe impacts on forest ecosystems in the United States. These events can substantially alter the carbon biogeochemical cycle at local to regional scales. We selected all tropical storms and more severe events that made U.S. landfall between 1900 and 2011 and used hurricane best track database, a meteorological model (HURRECON), National Land Cover Database (NLCD), U. S. Department of Agirculture Forest Service biomass dataset, and pre- and post-MODIS data to quantify individual event and annual biomass mortality. Our estimates show an average of 18.2 TgC/yr of live biomass mortality for 1900–2011 in the US with strong spatial and inter-annual variability. Results show Hurricane Camille in 1969...
Denitrification, the anaerobic reduction of nitrogen oxides to nitrogenous gases, is an extremely challenging process to measure and model. Much of this challenge arises from the fact that small areas (hotspots) and brief periods (hot moments) frequently account for a high percentage of the denitrification activity that occurs in both terrestrial and aquatic ecosystems. In this paper, we describe the prospects for incorporating hotspot and hot moment phenomena into denitrification models in terrestrial soils, the interface between terrestrial and aquatic ecosystems, and in aquatic ecosystems. Our analysis suggests that while our data needs are strongest for hot moments, the greatest modeling challenges are for hotspots....
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Recent research has dramatically advanced our understanding of soil organic matter chemistry and the role of N in some organic matter transformations, but the effects of N deposition on soil C dynamics remain difficult to anticipate. We examined soil organic matter chemistry and enzyme kinetics in three size fractions (>250 Î&frac14;m, 63–250 Î&frac14;m, and <63 Î&frac14;m) following 6 years of simulated atmospheric N deposition in two ecosystems with contrasting litter biochemistry (sugar maple, Acer saccharum—basswood, Tilia americana and black oak, Quercus velutina—white oak, Q. alba). Ambient and simulated (80-kg NO3 −–N ha−1 year−1) atmospheric N deposition were studied in three replicate stands...
map background search result map search result map Environmental Controls on Nitric Oxide Emission from Northern Chihuahuan Desert Soils Carbon and nitrogen limitations of soil microbial biomass in desert ecosystems Factors Determining Soil Microbial Biomass and Nutrient Immobilization in Desert Soils Nitrogen deposition effects on soil organic matter chemistry are linked to variation in enzymes, ecosystems and size fractions Carbon and nitrogen limitations of soil microbial biomass in desert ecosystems Environmental Controls on Nitric Oxide Emission from Northern Chihuahuan Desert Soils Factors Determining Soil Microbial Biomass and Nutrient Immobilization in Desert Soils Nitrogen deposition effects on soil organic matter chemistry are linked to variation in enzymes, ecosystems and size fractions