Spatial distribution of soil hydraulic parameters estimated by pedotransfer functions for the Jialing River Catchment,Southwestern China

Soil hydraulic parameters θs,α,n,Ks,L and θr of the van Genuchten-Mualem model were estimated using three pedotransfer functions(PTFs) based on soil properties for surface soils of the largest main tributary catchment(the Jialing River) of the upper Yangtze River in China.The soil database was from the second national soil survey of China with a spatial 30 × 30 arc-second resolution.According to the statistical analysis of the differences between the continuous-PTFs-estimated values of soil hydraulic parameters for the study catchment and the reference values for a specific texture class provided in the development database of a specific PTF,best estimations were obtained using the W?sten PTF.The Rawls & Brakenssiek PTF was good estimation for parameter θr that was assumed as zero by W?sten PTF.The established higher θr(0.08%) and lower Ks(20 cm/d) and θs(0.43%) in the mid-downstream area relative to the other areas of the catchment could lead to larger amounts of surface runoff andconsequently provide higher energy to erode soil.Thus,these factors provide a supporting explanation for previously reported severe soil erosion occurring in this area.Spatial heterogeneity analysis for estimated hydraulic parameters in terms of semivariogram showed that the spatial correlation distance was in the range of 50-80 km and that the spatial variability(sill) was not large except for parameters Ks and L.The semi-variance with the exponential model at the zero distance(nugget) was 30%-50% of the sill.This study provided a practical PTF approach for estimating soil hydraulic properties from soil survey data at a large watershed scale.The estimation results could provide better insight into the mechanism of surface runoff and soil erosion,which is important to better understand and manage erosion in the catchment.

Potential for natural and enhanced attenuation of sulphanilamide in a contaminated chalk aquifer

Understanding antibiotic biodegradation is important to the appreciation of their fate and removal from the environment. In this research an Isotope Ratio Mass Spectrometry（IRMS）method was developed to evaluate the extent of biodegradation of the antibiotic,sulphanilamide, in contaminated groundwater. Results indicted an enrichment in δ^（13）C of8.44‰ from-26.56（at the contaminant source） to-18.12‰（300 m downfield of the source）.These results confirm reductions in sulphanilamide concentrations（from 650 to 10 mg/L）across the contaminant plume to be attributable to biodegradation（56%） vs. other natural attenuation processes, such as dilution or dispersion（42%）. To understand the controls on sulphanilamide degradation ex-situ microcosms assessed the influence of sulphanilamide concentration, redox conditions and an alternative carbon source. Results indicated, high levels of anaerobic capacity（~50% mineralisation） to degrade sulphanilamide under high（263 mg/L）, moderate（10 mg/L） and low（0.02 mg/L） substrate concentrations. The addition of electron acceptors; nitrate and sulphate, did not significantly enhance the capacity of the groundwater to anaerobically biodegrade sulphanilamide. Interestingly, where alternative carbon sources were present, the addition of nitrate and sulphate inhibited sulphanilamide biodegradation. These results suggest, under in-situ conditions, when a preferential carbon source was available for biodegradation, sulphanilamide could be acting as a nitrogen and/or sulphur source. These findings are important as they highlight sulphanilamide being used as a carbon and a putative nitrogen and sulphur source, under prevailing iron reducing conditions.