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  • 1
    ISSN: 1573-515X
    Keywords: iron monosulfide ; acid volatile sulfide ; pyrite ; stannous chloride ; sediments
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Iron monosulfides are important intermediates in pyrite formation, and are operationally defined as sulfides soluble in concentrated hydrochloric acid. A number of variations are currently employed in their isolation and quantification. In this study, the active distillation of acid volatile sulfide from sediment samples was studied to determine the effects of stannous chloride and heat. The addition of SnCl2 caused recovery of sulfide to increase by 20% during distillations performed at room temperature. If distillations with SnCl2 were then heated and boiled, recovery increased by up to 100%. Tests with 98% pure pyrite and elemental sulfur showed that these compounds were reduced to sulfide in solutions of 15% and 20% SnCI2 in boiling 6N HCI, and that these reactions were grain size dependent. The compounds were not significantly reduced by solutions of SnCI2 at room temperature, or by boiling 6N HCl not containing SnCl2.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Biogeochemistry 38 (1997), S. 189-205 
    ISSN: 1573-515X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Direct groundwater inputs are receiving increasingattention as a potential source of nutrients and otherdissolved constituents to the coastal ocean. Seepageinto St. George Sound, Florida was measuredextensively from 1992 to 1994 using seepage meters. Spatial and temporal variations were documented alonga 7-km stretch of coastline and up to 1 km from shore. Measurements were made at 3 transects perpendicular toshore and 1 transect parallel to shore. The generalresults indicated that seepage decreased with distancefrom shore (2 of 3 transects), and substantialtemporal and spatial variability was observed inseepage flow from nearshore sediments. In addition,trends in mean monthly integrated seepage rates weresimilar to precipitation patterns measured at a nearbycoastal weather station. Based on these measurements, weestimate that the magnitude of groundwater seepage intothe study area is substantial, representing from 0.23 to4.4 m3 ⋅ sec-1of flow through the sediments, approximately equivalentto a first magnitude spring. Although it is unknown howrepresentative this region is with respect to globalgroundwater discharge, it demonstrates thatgroundwater flow can be as important as riverine andspring discharge in some cases. Our subsurfacedischarge rates suggest groundwater is an importanthydrologic source term for this region and may beimportant to the coastal biogeochemistry as well.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1573-515X
    Keywords: methane emissions ; tropical floodplains ; Orinoco River ; floodplain forest ; wetlands
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Methane emissions were measured over a 17-monthinterval at 21 locations on the Orinoco fringingfloodplain and upper delta (total area,14,000 km2). Emissions totaled 0.17 Tgyr−1, or 7.1 mmol d−1 (114 mg d−1;standard deviation, ±18%) per m2 of watersurface. Ebullition accounted for 65% of emissions. Emission rates were about five times as high forfloodplain forest as for open water or macrophytemats. Emission rates were positively correlated withcarbon content of sediment and amount of methane inthe water column, and negatively correlated withdissolved oxygen, but the correlations were weak. Emission from floodplain soils occurred only when thewater content of soil exceeded 25%, which occurredwithin 20 m of standing water during floodplaindrainage (3 months/yr). Bare soils emitted 60mmol/day per m of shoreline length; soils covered bystranded macrophyte beds emitted five times thisamount. Total emissions were accounted for primarilyby flooded forest (94%); macrophyte mats, open water,and exposed soils made only small contributions. Theflux-weighted mean δ13C for the floodplainwas −62 ± 8‰; for δD the mean was −271 ± 27‰. The δ13C and δD were negativelycorrelated. Overall emission rates were notably lowerthan for the Amazon. The depth and duration offlooding are considerably less for the Orinoco thanfor the Amazon floodplain; oxygen over sediments isthe rule for the Orinoco but not for the Amazon. TheOrinoco data illustrate the difficulty of generalizingemission rates. Current information for tropicalAmerica, including revised estimates for inundatedarea along the Amazon, indicate that methane emissionsfrom tropical floodplains have been overestimated.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1573-515X
    Keywords: carex ; methane oxidation ; methyl fluoride ; peatlands ; rhizosphere
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Rhizospheric methane oxidation was evaluated at a Carex (spp.) dominated fen in Alberta, Canada overthree growing seasons. Aerobic incubations of bulkpeat and live roots in the laboratory show a clearassociation between active methane oxidizing bacteriaand the rhizosphere. Aerobic incubations also show anoxidation potential that far exceeds methaneproduction potential measured in the laboratory. Quantitative estimates of how this oxidation potentialis expressed in situ depend strongly on which of twocommon approaches are used. (1) Subtracting in situmethane emission rates from methane production ratesmeasured in the laboratory with anaerobic incubationssuggest that methane oxidation may attenuate emissionsby 58 to 92%. (2) Applying the inhibitor methylfluoride (CH3F) to whole plants in situ suggestmethane oxidation attenuates emissions by less than20% seasonally. The production minus emissiontechnique likely overestimates methane oxidationbecause methane production measured via anaerobicincubations in the laboratory are probablyoverestimates. Oxidation percentages measured byCH3F were greatest early in the growing seasonwhen emission rates were low and fell to almostnondetectable levels as emission rates peaked in latesummer. Estimates provided by the CH3F techniquewere generally in better agreement with estimates ofoxidation based on a stable isotope mass balance(0–34%) determined in a companion study (Popp et al. 1999).
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  • 5
    ISSN: 1573-515X
    Keywords: aquatic marcrophytes ; methane ; methane oxidation ; methyl fluoride ; plant/microbial ; interactions ; rhizosphere
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Methane oxidation rates in the rhizosphere of Pontederia cordata,Sagittaria lancifolia, and Typha latifolia were quantified in fieldstudies using the methyl fluoride inhibition technique. An averageoxidation of 22.9 ± 17.7% (sd,n = 44) was found for all field experiments (oxidation is expressedas a % of total potential emission in the presumedabsence of oxidation). Greenhouse experiments using the same techniquegave an average rhizospheric oxidation of 64.9 ±17.0% (sd, n = 44). Comparison of a subset ofgreenhouse plants with the methyl fluoride (MF) and a light oxic/darkanoxic (LO/DA) technique for suppressing CH4 oxidationyielded similar percentages (57.7 ±15.0% for MF and 58.5 ±13.9% for LO/DA, n = 11). Rhizospheric oxidationdisplayed a seasonal trend in Typha latifolia with decreasingoxidation percentages during warmer months as the importance ofrhizospheric CH4 oxidation declined relative toCH4 emission (46.5 ±13.8% in December and 13.5 ±1.7% in July). However, the absolute rateof methane oxidation was highest during the warmer months (44.2± 3.4 mg m-2 d-1 inDecember and 318.7 ± 151.4 mg m-2d-1 in July). As methane emission rates increased,the sensitivity of the methyl fluoride technique decreased dueto the larger error between replicate flux measurements.
    Type of Medium: Electronic Resource
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