Effect of contaminant concentration on in situ bacterial sulfate reduction and methanogenesis in phenol-contaminated groundwater

The availability of dissolved O₂ can limit biodegradation of organic compounds in aquifers. Where O₂ is depleted, biodegradation proceeds via anaerobic processes, including NO₃-, Mn(IV)-, Fe(III)- and SO₄-reduction and fermentation/methanogenesis. The environmental controls on these anaerobic processes must be understood to support implementation of management strategies such as monitored natural attenuation (MNA). In this study stable isotope analysis is used to show that the relative significance of two key anaerobic biodegradation processes (bacterial SO₄ reduction (BSR) and methanogenesis) in a phenol-contaminated sandstone aquifer is sensitive to spatial and temporal changes in total dissolved phenols concentration (TPC) (= phenol + cresols + dimethylphenols) over a 5-a period. In general, ³⁴SO₄-enrichment (characteristic of bacterial SO₄ reduction) is restricted spatially to locations where TPC < 2000 mg L⁻¹. In contrast, ¹³C-depleted CH₄ and ¹³C-enriched CO₂ isotope compositions (characteristic of methanogenesis) were measured at TPC up to 8000 mg L⁻¹. This is consistent with previous studies that demonstrate suppression of BSR at TPC of >500 mg L⁻¹, and suggests that methanogenic microorganisms may have a higher tolerance for TPC in this contaminant plume. It is concluded that isotopic enrichment trends can be used to identify conditions under which in situ biodegradation may be limited by the properties of the biodegradation substrate (in this case TPC). Such data may be used to deduce the performance of MNA for contaminated groundwater in similar settings.     

Radio source calibration for the Very Small Array and other cosmic microwave background instruments at around 30 GHz

Accurate calibration of data is essential for the current generation of cosmic microwave background (CMB) experiments. Using data from the Very Small Array (VSA), we describe procedures which will lead to an accuracy of 1 per cent or better for experiments such as the VSA and CBI. Particular attention is paid to the stability of the receiver systems, the quality of the site and frequent observations of reference sources. At 30 GHz the careful correction for atmospheric emission and absorption is shown to be essential for achieving 1 per cent precision.
The sources for which a 1 per cent relative flux density calibration was achieved included Cas A, Cyg A, Tau A and NGC 7027 and the planets Venus, Jupiter and Saturn. A flux density, or brightness temperature in the case of the planets, was derived at 33 GHz relative to Jupiter which was adopted as the fundamental calibrator. A spectral index at ∼30 GHz is given for each.
Cas A, Tau A, NGC 7027 and Venus were examined for variability. Cas A was found to be decreasing at 0.394 ± 0.019 per cent yr⁻¹ over the period 2001 March to 2004 August. In the same period Tau A was decreasing at 0.22 ± 0.07 per cent yr⁻¹. A survey of the published data showed that the planetary nebula NGC 7027 decreased at 0.16 ± 0.04 per cent yr⁻¹ over the period 1967–2003. Venus showed an insignificant (1.5 ± 1.3 per cent) variation with Venusian illumination. The integrated polarization of Tau A at 33 GHz was found to be 7.8 ± 0.6 per cent at position angle =148°± 3°.     

用相关函数优化法计算离散线性水文模型参数

借助于日降雨和出流资料系列,采用相关函数优化方法确定离散线性水文模型参数是一种新的方法.文中选用4个流域8年日降雨和径流资料系列来检验相关函数优化法(6年作为率定期,2年作为验证期),所得结果与常规最小二乘法计算的结果进行比较表明:新方法计算精度比常规最小二乘法计算的精度有所提高,常规最小二乘法仅是相关函数优化法的一种特例.     

Estimation of PKP times from ISC data

The International Seismological Centre (ISC) treats reports of the earliest observed core phase arrivals from earthquakes as PKIKP observations and provides residuals based on Jeffreys-Bullen PKIKP times. An analysis of some 30 000 such data from ISC bulletins for the year 1967 has shown that the data include, in addition to PKIKP, many observations of PKP₁ and precursors to PKP. By the use of simple truncation and trimming techniques, travel-time curves (expressed as differences from JB), with standard errors, have been obtained for PKIKP in the ranges 110 to 139° and 152 to 173°, and for PKP₁ in the range 144 to 154°. The PKIKP curve in these ranges agrees quite closely with the curve obtained by Cleary and Hales, and with one derived from model 1066B of Gilbert and Dziewonski, except that the Cleary-Hales curve is up to 0.7 s earlier at distances below 120°, and the 1066B curve is up to 1 s later beyond 152°. The PKP₁ curve is in good agreement with that derived from 1066B.A plot of the number of observations in each 1° distance interval has been used to estimate the positions of the cusps B, C and D on the PKP curve as 144, 152.5 and 115°, again in reasonable agreement with 1066B.     

Effects of time under rain,sampling technique and transport of samples on size distributions of water-stable aggregates

Two methods for sampling aggregates in the soil surface under simulated rain were compared using two soil types. Results showed that aggregate size distributions obtained by spatula sampling were not significantly different from those obtained using rings buried in the soil surface, provided both were sampled to the same depth. The effect of transporting samples over a distance of 60 km was non-significant when samples were placed in bottles half-filled with rainwater and transported in an upright position. The per cent aggregates > 0.125 mm was found to be the most suitable index of aggregate stability for both soils.