Paddy rice fields provide an environment for production of two important greenhouse gases, CH4 and N2O, because of variations in soil characteristics, moisture content, and microbial activity during the cropping season. Emissions of CH4 and N2O from a paddy rice field in northern China were measured in situ by static chamber technique during March to December in 1995 and 1996. Factors affecting gas emission, including soil temperature, pH, and redox potential (Eh), were measured as well. Emissions of CH4 and N2O were strongly correlated with changes in soil redox potential. Significant CH4 emission occurred only at soil redox potential lower than approximately −100 mV, while the emission of N2O was not significant below +200 mV. A significant inverse relationship between CH4 and N2O emissions was observed (r = −0.49, n = 16, 5% confidence level). The results suggest the possibility of using management practices to maintain the redox potential in a range where both N2O and CH4 emissions are low. The activities of six related bacteria groups (zymogenic bacteria, acetic acid and hydrogen‐producers, methanogens, CH4 oxidizers, and nitrifiers and denitrifiers) in the soil were also measured in an effort to explain the relationship between gas emission and soil microbiological processes. Methane emission was significantly related to the logarithm number of zymogenic bacteria (r = 0.76, n = 12, 1% confidence level), as well as to soil redox potential (r = −0.72, n = 12, 1% confidence level). Both zymogenic bacteria number and soil redox potential appear to be predicators of CH4 emission potential.

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Floodwaters in New Orleans from Hurricanes Katrina and Rita were observed to contain high levels of fecal indicator bacteria and microbial pathogens, generating concern about long-term impacts of these floodwaters on the sediment and water quality of the New Orleans area and Lake Pontchartrain. We show here that fecal indicator microbe concentrations in offshore waters from Lake Pontchartrain returned to prehurricane concentrations within 2 months of the flooding induced by these hurricanes. Vibrio and Legionella species within the lake were more abundant in samples collected shortly after the floodwaters had receded compared with samples taken within the subsequent 3 months; no evidence of a long-term hurricane-induced algal bloom was observed. Giardia and Cryptosporidium were detected in canal waters. Elevated levels of fecal indicator bacteria observed in sediment could not be solely attributed to impacts from floodwaters, as both flooded and nonflooded areas exhibited elevated levels of fecal indicator bacteria. Evidence from measurements of Bifidobacterium and bacterial diversity analysis suggest that the fecal indicator bacteria observed in the sediment were from human fecal sources. Epidemiologic studies are highly recommended to evaluate the human health effects of the sediments deposited by the floodwaters. Preliminary investigations in mid-September 2005 documented high levels of microbial and toxicant contamination in the NO floodwaters (1-3). Reports of mean total coliform and total Escherichia coli levels as high as 8 ϫ 10 8 CFU per 100 ml and 3 ϫ 10 7 CFU per 100 ml, respectively (1) indicated the presence of sewage contamination and associated sewage-borne pathogens. Elevated concentrations of fecal coliforms have previously been observed in floodwaters of the NO region, but the 2005 event was characterized by an unusually large volume and long duration of human exposure (4). The most contaminated area tested near the Superdome also contained high levels of nonsewage pathogens, with an estimated Aeromonas spp. concentration of 1.7 ϫ 10 8 per 100 ml (1). Concentrations of Vibrio spp. were not measured, but the temperature and salinity of the floodwaters would have been favorable for their growth, and the number of Vibrio infections reported in the month following Hurricane Katrina was higher than normal (5).As shown in the satellite floodwater image, Ϸ34 billion liters of water covered NO as of August 30, 2005, with floodwater depths in several areas in excess of 3 m (Fig. 1). As these floodwaters were pumped back into LP, sediments were deposited throughout the flooded regions of the city (including the interior of homes). To a large extent, these sediments, now dried, remain even after 1 year

Gulf of Mexico saltmarsh sediments were heavily impacted by Macondo well oil (MWO) released from the 2010 Deepwater Horizon (DWH) oil spill. Detailed molecular-level characterization of sediment extracts collected over 48 months post-spill highlights the chemical complexity of highly polar, oxygen-containing compounds that remain environmentally persistent. Electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS), combined with chromatographic prefractionation, correlates bulk chemical properties to elemental compositions of oil-transformation products as a function of time. Carboxylic acid incorporation into parent MWO hydrocarbons detected in sediment extracts (corrected for mass loss relative to C30 hopane) proceeds with an increase of ∼3-fold in O2 species after 9 months to a maximum of a ∼5.5-fold increase after 36 months, compared to the parent MWO. More importantly, higher-order oxygenated compounds (O4-O6) not detected in the parent MWO increase in relative abundance with time as lower-order oxygenated species are transformed into highly polar, oxygen-containing compounds (Ox, where x > 3). Here, we present the first molecular-level characterization of temporal compositional changes that occur in Deepwater Horizon derived oil contamination deposited in a saltmarsh ecosystem from 9 to 48 months post-spill and identify highly oxidized Macondo well oil compounds that are not detectable by routine gas-chromatography-based techniques.