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1.
Laboratory incubation experiments were conducted to study the effects of soil chemical and physical properties on CH4 emission and entrapment in 16 selected soils with a pH range of 4.7–8.1, organic matter content of 0.72–2.38%, and soil texture from silt to clay. There was no significant correlation with CH4 emission for most of the important soil properties, including soil aerobic pH (measured before anaerobic incubation), total Kjeldahl N, cation exchange capacity, especially soil organic matter, and soil water-soluble C, which were considered to be critical controlling factors of CH4 emission. A lower CH4 emission was observed in some soils with a higher organic matter content. Differences in soil Fe and Mn contents and their chemical forms contributed to the this observation. A significant correlation between the CH4 emission and the soil organic C content was observed only after stratifying soils into subgroups according to the level of CH4 emission in soils not amended with organic matter. The results also showed that the soil redox potential (Eh), anaerobic pH, anerobic pH, and biologically reducible Fe and Mn affected CH4 emission significantly. Urea fertilization promoted CH4 emission in some soils and inhibited it in others. This result appeared to be related to the original soil pH. CH4 entrapment was positively correlated with soil clay content, indicating the importance of soil physical characteristics in reducing CH4 emissions to the atmosphere.  相似文献   
2.
Methane and C02 production in flooded acid sulfate soils of Thailand were governed primarily by soil oxidation-reduction potential (Eh) and pH. The critical Eh and pH levels at which CH4 emission began was Eh-150 mV, and pH 6.1. Low soil pH limited soil reduction and subsequently CH4 production. Soil respiration (C02 production) was influenced by Eh-pH levels and organic matter content. Soils with higher C02 production rates produced greater amounts of CH4. Soil pH, however, was the dominant variable which influenced organic matter decomposition, low soil Eh conditions and subsequent CH4 and CO2 production. Curvilinear or log transformations of pH, Eh and organic matter content (OM) were used in explaining variables controlling CH4 and CO2 production; CH4 = ?2.359 ? 0.0001 Eh + 2.047 pH ? 3.019 (In pH)2 CO2 = ?5210 ? 1.6 Eh + 3144 (In pH) + 1011 (In OM).  相似文献   
3.
The transformations of applied (100 kg N ha-1)15 N labelled NO3 and NH4 in Mississippi River deltaic plain swamp forest soil which receives agriculture run-off from adjacent sugarcane fields were determined. Using an isotopic dilution technique, the rates of NO3 production (nitrification) and reduction in the 15NO3 treated soil-water-columns were approximately 240 and 2,320 g N ha-1 d-1, whereas NH4 production (mineralization) and removal rates in the 15NH4 treated soil-water-columns were 270 and 2160 g N ha-1 d-1, respectively. It was shown that if nitrification and NH4 assimilation were the primary processes responsible for NH4 removal, average NH4 assimilation would be 145 g N ha-1 d-1. Based on labelled N2-emission, denitrification was 3 fold greater in the NO3 treatment compared to the NH4 treated soil water-columns with rates of 818 and 266 g N ha-1 d-1 respectively. Even though the rate was lower in the NH4 treatment, results show that nitrification-denitrification of NH4 is a significant process. Nitrogen losses determined by15 N2 emissions were 20.4 and 6.4% and N2O emissions were 0.10 and 0.03% of the applied NO3-N and NH4-N, respectively, over 32 days of incubation. Fertilizer loss through N2O emission was only of minor significance compared to the fertilizer loss through N2 evolution. Nitrous oxide fluxes from the control soil-water-columns averaged 9.4 g N ha-1 d-1. Addition of NO3-N to the columns increased N2O production 56% as compared to a 15% increase from the NH4-N addition. Results show that this wetland soil has a large capacity to process inorganic nitrogen entering the system as a result of agriculture run-off.  相似文献   
4.
Field studies were conducted to evaluate Sagittarialancifolia sensitivity to in-situ burning of appliedcrude oil. Twenty-four plots were constructed (2.4 × 2.4× 0.6 m) in a fresh marsh and experimental treatmentswere: 1) control (no oiling and/or burning); 2) oiling (naturalremediation); and 3) oiling plus burning. South Louisiana Crudewas applied at 2 L m-2, with a garden sprayer, on Sagittaria lancifolia stems and leaves of the oiling andoiling/burning treatment plots. Two marsh burns were conducted,one in August (Site A) and a second on separate plotsthe following April (Site B) to compare seasonal effects ofoiling and burning. Burning was initiated three days after oilapplication when the marsh was flooded to a 15–25 cm depth andwinds were calm. Live stem count, plant height growth and carbonfixation were measured up to 9 times over 52 weeks after thefirst burn (August) and 6 times over 19 weeks after the secondin-situ burn (April). Aboveground biomass was measured atthe conclusion of each study. Oil application and oil burninghad short term effects on Sagittaria lancifoliavegetation. Five to six weeks after each burn, measured Sagittaria lancifolia vegetative parameters in control, oiledand oiled/burned plots were not significantly different. Onlybiomass clipped 20 weeks after the April burn showed significanttreatment differences. Under our experimental conditions, datasuggests leaving oil to degrade and the marsh to recovernaturally may be an option to consider. Plant recovery inoiled/burned plots was as rapid as oiled plant recovery. Thissuggests burning may be a viable remediation method if a rapidresponse is needed to remove oil and control oil migration tosensitive areas.  相似文献   
5.
Plough and subsoil layers of two majoragricultural soil series, Rangsit and Thonburi, foundin Bangkok area of Thailand were studied fordetermining the bioavailability and solubilitybehavior of heavy metals (Cd, Cu, Zn, Mn, and Fe)following application of sewage sludge from awastewater treatment plant and a series of laboratoryexperiments. The soils contained low indigenous heavymetals while the sludge contained higher amounts ofheavy metals but in an acceptable range forapplication as plant nutrient source in agriculturalsoil. Applications of sewage sludge increased pH ofthe acid soil and available plant nutrients to thesoils. The heavy metal concentration levels in thesoils also increased. Most partitioned into easilymobile pools and later into sparingly mobile poolsfollowing 12 weeks of incubation time. Bioavailabilityforms of Cd in soil solution were low but that of Cu,Zn, and Mn remained elevated even at 12 weeks of thereaction time. Applied inorganic Zn depressed Cdsorption capacity of two soils studied but it had noeffect on Cd desorption.  相似文献   
6.
In many coastal areas of Louisiana, surface water quality is deteriorating rapidly due to elevated nutrient input from agricultural, domestic and industrial sources. This study investigates the potential use of natural abundance variations in 15N/14N ratios for identification and tracing surface water inorganic N sources. Surface water samples were collected from streams and point sources in Louisiana and analyzed for NH4 +-N, NO3 ?-N and associated 15N/14N (δ15N ‰) concentrations. Ammonium-N from domestic sewage and industrial discharge point sources was found to have distinct δ15N ranges. Domestic sewage discharge into a slow flowing stream was traced for about 30 km downstream using 15N/14N ratios. At the sewage point source NH4 +-δ15N values averaged +43%o and increased linearly to +162‰ with distance from the discharge. In a larger stream with a greater flow velocity the NH4 +-δ15N surface water signature of an industrial discharge source was identifiable for approximately 1 km from the point source. Surface water NO3 ?-°15N values generally ranged from +1 to +99‰ and no significant association was observed between δ15N values with distance from the domestic sewage and industrial point sources. The discrete NH4 +-δ15N signatures of domestic sewage and industrial point sources compared to downstream surface water NH4 +-δ15N values suggest that N isotopic ratios have the potential to be used as tracers in surface waters contaminated with inorganic N.  相似文献   
7.
To determine effective means to reduce methane (CH4) production from flooded rice soil, laboratory measurements were made on methane (CH4) formation in a Crowley silt loam as affected by the addition of potassium nitrate (KNO3), manganese dioxide (MnO2), and air (O2) under flooded conditions. In the experiment, oxidants were added to the soil prior to flooding at the rate of 300 and 1000 ppm O2 equivalent. Methane production was measured over a 32 d incubation period. Potassium nitrate added at rates of 300 and 1000 ppm O2 equivalent reduced CH4 production by 100% and MnO_2, at 300 and 1000 ppm O2 equivalent, significantly decreased CH4 formation approximately 20% and 98-99% over the 32 d period, respectively compared to controls. Air addition did not significantly affect CH4 formation.  相似文献   
8.
In many forested wetlands of Louisiana, surface water quality is being deteriorated by nutrient input from adjacent agricultural production areas. This field study assesses the input of fertilizer N, applied to sugarcane fields, to forested wetlands. The potential use of natural abundance variations in 15N14N ratios for identification and tracing surface water N sources (NH 4 + - and NO3 --N) was evaluated. Runoff and surface water samples were collected from sugarcane fields and bordering forested wetlands (6 stations) over a 16 month period and analyzed for NH 4 + -N, NO 3 - -N, and associated NH 4 + -δ15N and NO 3 - -δ15N ratios. Fertilizer N draining into adjacent forested wetland was estimated to be only a small fraction of the amount applied. Concentrations of NH 4 + - and NO 3 - -N in the collected water samples were low and ranged from 0.02 to 1.79 mg L-1. Isotopic analysis revealed NH 4 + -δ15N and NO 3 - -δ15N means were distinctive and may have the potential to be used as tracers of N contamination. The mean NH 4 + -δ15N value was +18.6 ± 7.1‰ and the NO 3 - -δ15N mean was +8.3 ± 3.1‰. Anomalously high NO 3 - -δ15N values (>30‰) were attributed to denitrification.  相似文献   
9.
Adsorption and desorption of arsenic (As) in the soil are dominant parameters that affect the mobility and bioavailability of arsenic. Batch arsenate adsorption and desorption experiments were conducted using soils collected from three Louisiana, USA, aquaculture ponds representing different crayfish farming and rice cultural practices. Arsenate adsorption behavior in the soils was investigated using Freundlich and Langmuir sorption equations. Results demonstrated that the Langmuir isotherm model was the best fit based on statistical correlation with soil properties governing adsorption, for the entire range of arsenate concentrations for all soils. Adsorption of As(V) was governed by soil physicochemical properties especially Fe and Al oxides, clay and organic matter. Desorption of As(V) was initially fast, but with increasing incubation times desorption occurred progressively slower. Chemical fractionation of arsenic in the soils showed that the most mobile fraction represented 4.74–5.18% of the total arsenic. A part of this mobile fraction could potentially be taken up by rice and enter the food chain, but would require additional research to quantify.  相似文献   
10.
Microbial mineralization rates of a 14C-labelled PCB mixture were determined in PCB-contaminated Capitol Lake, LA, sediment under controlled pH and redox conditions. Mineralization rates were inferred from the activity of 14CO2 evolved from the sediment suspensions. Sediment pH and redox potential significantly affected PCB mineralization. Mineralization rates were higher under moderately aerobic conditions (microaerophilic) ( + 250 mV) than under aerobic conditions ( + 500 mV) or anaerobic conditions (0 mV and ?200 mV). PCB mineralization rates in moderately aerobic sediment were 30 to 40 fold higher than those in anaerobic sediment. Sediment conditions in the oxidized surface layer would promote PCB mineralization. Sediment pH and redox potential were shown to be two sediment parameters which can be managed to enhance degradation of PCBs in contaminated sediment.  相似文献   
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