An airborne microwave temperature profiler (MTP) was deployed during the Texas 2000 Air Quality Study (TexAQS-2000) to make measurements of boundary layer thermal structure. An objective technique was developed and tested for estimating the mixed layer (ML) height from the MTP vertical temperature profiles. The technique identifies the ML height as a threshold increase of potential temperature from its minimum value within the boundary layer. To calibrate the technique and evaluate the usefulness of this approach, coincident estimates from radiosondes, radar wind profilers, an aerosol backscatter lidar, and in situ aircraft measurements were compared with each other and with the MTP. Relative biases among all instruments were generally less than 50 m, and the agreement between MTP ML height estimates and other estimates was at least as good as the agreement among the other estimates. The ML height estimates from the MTP and other instruments are utilized to determine the spatial and temporal evolution of ML height in the Houston, Texas, area on 1 September 2000. An elevated temperature inversion was present, so ML growth was inhibited until early afternoon. In the afternoon, large spatial variations in ML height developed across the Houston area. The highest ML heights, well over 2 km, were observed to the north of Houston, while downwind of Galveston Bay and within the late afternoon sea breeze ML heights were much lower. The spatial variations that were found away from the immediate influence of coastal circulations were unexpected, and multiple independent ML height estimates were essential for documenting this feature.

The degradation potential of trichloroethene by the aerobic methane- and ammonia-oxidizing microorganisms naturally associated with wetland plant (Carex comosa) roots was examined in this study. In bench-scale microcosm experiments with washed (soil free) Carex comosa roots, the activity of root-associated methane- and ammonia-oxidizing microorganisms, which were naturally present on the root surface and/or embedded within the roots, was investigated. Significant methane and ammonia oxidation were observed reproducibly in batch reactors with washed roots incubated in growth media, where methane oxidation developed faster (2 weeks) compared to ammonia oxidation (4 weeks) in live microcosms. After enrichment, the methane oxidizers demonstrated their ability to degrade 150 μg l(-1) TCE effectively at 1.9 mg l(-1) of aqueous CH(4). In contrast, ammonia oxidizers showed a rapid and complete inhibition of ammonia oxidation with 150 μg l(-1) TCE at 20 mg l(-1) of NH(4)(+)-N, which may be attributed to greater sensitivity of ammonia oxidizers to TCE or its degradation product. No such inhibitory effect of TCE degradation was detected on methane oxidation at the above experimental conditions. The results presented here suggest that microorganisms associated with wetland plant roots can assist in the natural attenuation of TCE in contaminated aquatic environments.

Trichloroethene (TCE) can undergo natural attenuation within wetland environments, particularly by oxidative processes that occur in the vegetated subsurface. The goal of this study was to evaluate TCE degradation potential through aerobic cometabolism by methane-oxidizing microorganisms associated with the roots of wetland plant species, Carex comosa and Scirpus atrovirens. The degradation experiments were conducted in 2.4 L Teflon microcosms with 15 g of washed, soil-free roots and amended with methane (2.1 mg/L), oxygen (8 mg/L), and TCE (three enrichment cycles without TCE and four cycles at 150 μg/L, one cycle at 600 μg/L, and one cycle at 900 μg/L of TCE). Our results indicated that methane-oxidizing activity and TCE degradation potential were comparable for the plant species investigated. The initial rates of methane degradation with TCE amendments varied between 0.21 and 0.30 mg L -1 d -1 for Carex comosa, and between 0.14 and 0.25 mg L -1 d -1 for Scirpus atrovirens. The average TCE mass removal per cycle varied between 24 and 32%, and the overall transformation yield was 0.0004 mmol TCE/mmol CH 4 for both plant species. This study suggests that wetland plants can play an important role in the natural attenuation of TCE in contaminated aquatic environments.

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