摘要:

Methane emissions were measured over a 15‐month interval for five lakes and five associated wetland sites in the Rockies of Colorado at elevations between 2800 and 3600 m. Three of the five lakes accumulated dissolved methane under ice; accumulation was as high as 53‐fold above ice‐free water column concentrations in the shallowest lake. The combination of high dissolved oxygen and low dissolved inorganic nitrogen concentrations within the water column during ice breakup suggests that methane emissions rather than methane oxidation led to the substantial loss of dissolved methane from the shallowest lake at the time of spring thaw. A pulsed release of methane to the atmosphere at the time of ice breakup within lakes may be widespread at high latitudes and may play a role in the observed increase in tropospheric methane concentrations in the northern hemisphere. During the ice‐free season, the mean emission rate was 1.6 mmol m−2d−1over open water for the five lakes, but the mean was much higher (13 mmol m−2d−1) over theNuphar luteabeds located in one of the lakes. Open water emissions occurred primarily through diffusion rather than bubbling. For wetlands near the lakes, average lake emissions ranged from negligible to almost 6 mmol m−2d−1; the average across all sites was 2.1 mmol m−2d−1during the warm season. There was no measurable emission during the winter months. Surface dissolved methane explains 40% of the variation in emissions from the open water sites; the combination of soil organic C content and soil temperature explains 40% of variation in emissions from the wetland sites. The data from the Southern Rockies and information that has accumulated on other lake types over the last 15 years indicate that lakes may be a larger source strength of methane

ISSN:0886-6236    

DOI:10.1029/92GB02016

年代:1992

数据来源: WILEY

摘要:

Dry deposition of atmospheric nitrogen gas and aerosol species was estimated for the alpine tundra of Niwot Ridge, 3525 m elevation in the Colorado Rockies. Comparisons, for the 4 month long growing season and the remaining 8 months of the year, were made with wet deposition and throughfall incident measurements taken during 1987‐1989. Dry deposition of N to the tundra is estimated to be equal to or slightly greater than its wet deposition. During the mid‐May to mid‐September growing season, atmospheric N deposition is>1.0 mg N m−2d−1directly from the atmosphere with a similar amount contributed indirectly as NO3‐N in snowmelt water as a result of dry and wet deposition to the winter snowpack. The total N deposition to Niwot Ridge tundra during the growing season of about 2 mg N m−2d−1may be compared to an earlier measurement of dry plus fog deposition (1 ‐ 2 mg N m−2d−1) to a subalpine coniferous canopy at Niwot Ridge. Nitrate yields from two small drainage basins at Niwot Ridge match these fluxes. Seven years of record from an unvegetated glacial cirque suggest an average yield from the alpine of 0.7 mg N m−2d−1. The equivalent estimate for a basin with 50% tundra vegetation cover is 0.4 mg N m−2d−1. The contrast in these two estimates of daily averaged N yields for the entire year suggests the retention of nearly 1 mg N m−2d−1during the growing season in the more vegetated basin. The sink for this N could be the tundra soil and vegetation where biological activity is often

ISSN:0886-6236    

DOI:10.1029/92GB01513

年代:1992

数据来源: WILEY

ISSN:0886-6236    

DOI:10.1029/92GB02548

年代:1992

数据来源: WILEY

ISSN:0886-6236    

DOI:10.1029/92GB02616

年代:1992

数据来源: WILEY

摘要:

Emission Of NOx(principally NO) and N2O from soils is reviewed with particular emphasis placed on the atmospheric and ecological implications of this source. The photochemistry of these species in the atmosphere is summarized as well as the methods available for the determination of fluxes. Processes which produce and consume both NO and N2O in soils are principally microbiological in nature and are linked directly and indirectly with the chemical and physical factors that control gaseous transport through the soil medium. Linkages among these processes occur over many different temporal and spatial scales which makes interpretation of the available data difficult. A summary of results from laboratory and field studies shows that considerable spatial and temporal variability exists in the emissions. This variability can be related to factors such as temperature, water content, soil composition, nutrient availability, vegetation, disturbances (e.g., burning, agricultural practices), and others. Because NOxand N2O play central roles in many important environmental problems, there is a need for accurate estimates of the magnitude of the soil source, but the large degree of variability in the existing data makes extrapolation highly uncertain. To overcome this uncertainty, models are required which can simulate the processes responsible for production, consumption, and transport of these species at all relevant temporal and spatial scales. Integrated field studies will also be required to validate the model results.

ISSN:0886-6236    

DOI:10.1029/92GB02124

年代:1992

数据来源: WILEY

摘要:

Vegetation provides a major source of reactive carbon entering the atmosphere. These compounds play an important role in (1) shaping global tropospheric chemistry, (2) regional photochemical oxidant formation, (3) balancing the global carbon cycle, and (4) production of organic acids which contribute to acidic deposition in rural areas. Present estimates place the total annual global emission of these compounds between approximately 500 and 825 Tg yr−1. The volatile olefinic compounds, such as isoprene and the monoterpenes, are thought to constitute the bulk of these emissions. However, it is becoming increasingly clear that a variety of partially oxidized hydrocarbons, principally alcohols, are also emitted. The available information concerning the terrestrial vegetation as sources of volatile organic compounds is reviewed. The biochemical processes associated with these emissions of the compounds and the atmospheric chemistry of the emitted compounds are discusse

ISSN:0886-6236    

DOI:10.1029/92GB02125

年代:1992

数据来源: WILEY

摘要:

Seasonal emissions of biogenic sulfur gases from marine and terrestrial sources were assessed for 13 regions of the continental United States. The resulting inventory was compared to volcanic and anthropogenic sulfur emissions from the same regions. Terrestrial biogenic sulfur emissions were less than 1% of the total sulfur emissions in each region. However, during the summer, marine biogenic sulfur emissions may be contributing 20–40% of the total sulfur emissions in western coastal region

ISSN:0886-6236    

DOI:10.1029/92GB01987

年代:1992

数据来源: WILEY

摘要:

Models of dust emissions by wind erosion (including winds associated with regional activity as well as dust devils) and vehicular disturbances of unpaved roads were developed, calibrated,and used to estimate alkaline dust emissions from elemental soil and road composition data. Emissions from tillage of soils were estimated from the work of previous researchers. The area of maximum dust production by all of those sources is the area of the old “Dust Bowl” of the 1930s (the panhandles of Texas and Oklahoma, eastern New Mexico and Colorado, and western Kansas). The areas of maximum alkaline dust production are the arid southwest, the “Dust Bowl,” and the midwestern‐mideastern states from Iowa to Pennsylvania. Our calculations show that calcium is the dominant alkaline element produced by “open sources” (sources too great in extent to be controlled by enclosure or ducting). Although the largest dust mass source is wind erosion (by winds associated with regional activity and convective activity), the largest producer of the alkaline component is road dust because the abundance of alkaline materials in road coverings (which include crushed limestone) is significantly higher than for soils. Comparing the above estimated sources of alkaline material with inventories of SO2and NOxemissions by previous investigators gives the rough approximation that alkaline emission rates are of the order of the SO2+ NOxemissions in the western United States and that they are much smaller than SO2+ NOxin the eastern United States. This approximation is substantiated by data on Ca/(SO4+ NO3) for wet deposition for National Atmospheric Deposition

ISSN:0886-6236    

DOI:10.1029/91GB02965

年代:1992

数据来源: WILEY

摘要:

Ammonia (NH3) is the dominant gaseous base in the atmosphere and the principal neutralizing agent for atmospheric acids, yet remains one of the least well characterized atmospheric trace compounds. In particular, the spatial and temporal distribution of the background concentrations in terrestrial ecosystems and the importance of natural emissions from undisturbed soils and vegetation is poorly understood. This situation persists because of experimental difficulties associated with ammonia measurements, the rapid gas‐to‐particle conversion of ammonia in the atmosphere, and the capacity of native soils and vegetation to act as both source and sink for atmospheric ammonia. In the present paper, we attempt to summarize the current understanding of the natural sources and sinks for gaseous NH3and the importance of natural emissions relative to anthropogenic emissions in the United States. We briefly review the physical and chemical processes that transform NH3in the atmosphere, the major anthropogenic and potential natural sources of atmospheric NH3, and the techniques used to measure low concentrations and fluxes of atmospheric NH3. The available background concentrations and flux measurements of ammonia in natural ecosystems are then described and used to infer upper limits for the emissions of NH3into the atmosphere from these systems. While the magnitude of both anthropogenic and natural emissions of NH3remain uncertain, it appears that unperturbed terrestrial ecosystems are generally more important as sinks rather than sources for atmospheric NH3. However, net emissions are likely from many eastern forests and other ecosystems exposed to large inputs of atmospheric sulf

ISSN:0886-6236    

DOI:10.1029/92GB02123

年代:1992

数据来源: WILEY