Influence of a hedge surrounding bottomland on seasonal soil‐water movement

The influence of a hedge surrounding bottomland on soil‐water movement along the hillslope was studied on a plot scale for 28 months. The study was based on the comparison of two transects, one with a hedge, the other without, using mainly a dense grid of tensiometers. The influence of the bottomland hedge was located in the area where tree roots were developed, several metres upslope from the hedge, and could be observed both in the saturated and non‐saturated zone, from May to December. The hedge induced a high rate of soil drying, because of the high evaporative capacity of the trees. We evaluated that water uptake by the hedge during the growing season was at least 100 mm higher than without a hedge. This increased drying rate led to a delayed rewetting of the soils upslope from the hedge in autumn, of about 1 month compared with the situation without a hedge. Several consequences of this delayed rewetting are expected: a delay in the return of subsurface transfer from the hillslope to the riparian zone, a buffering effect of hedges on floods, already observed at the catchment scale, and an increased residence time of pollutants. Copyright © 2003 John Wiley & Sons, Ltd.     

A simple method using climatic variables to estimate canopy temperature,sensible and latent heat fluxes in a winter wheat field on the North China Plain

Estimation of evapotranspiration from a crop field is of great importance for detecting crop water status and proper irrigation scheduling. The Penman–Monteith equation is widely viewed as the best method to estimate evapotranspiration but it requires canopy resistance, which is very difficult to determine in practice. This paper presents a simple method simplified from the Penman–Monteith equation for estimating canopy temperature (T_c). The proposed method is a biophysically‐sound extended version of that proposed by Todorovic. The estimated canopy temperature is used to calculate sensible heat flux, and then latent heat flux is calculated as the residual of the surface energy balance. An eddy covariance (EC) system and an infrared thermometer (IRT) were installed in an irrigated winter wheat field on the North China Plain in 2004 and 2005, to measure T_c, and sensible and latent heat fluxes were used to test the modified Todorovic model (MTD). The results indicate that the original Todorovic model (TD) severely underestimates T_c and sensible heat flux, and hence severely overestimates the latent heat flux. However, the MTD model has good capability for estimating T_c, and gives acceptable results for latent heat flux at both half‐hourly and daily scales. The MTD model results also agreed well with the evapotranspiration calculated from the measured T_c. Copyright © 2008 John Wiley & Sons, Ltd.     

Comparison of radial basis function networks and empirical equations for converting from pan evaporation to reference evapotranspiration

Evapotranspiration (ET) is one of the major processes in the hydrological cycle, and its reliable estimation is essential to water resources management. Numerous equations have been developed for estimating ET, most of which are complex and require numerous items of weather data. In many areas, the necessary data are lacking, and simpler techniques are required. Evaporation pans are used throughout the world because of the simplicity of technique, low cost, and ease of application. In this study, the radial basis function (RBF) network is applied for pan evaporation to evapotranspiration conversions. The adaptive pan‐based RBF network was trained using daily Policoro data from 15 May 1981 to 23 December 1983. The RBF network obtained, Christiansen, FAO‐24 pan, and FAO‐56 Penman–Monteith equations were verified in comparison with lysimeter measurements of grass evapotranspiration using daily Policoro data from 25 February to 18 December 1984. Based on summary statistics, the RBF network ranked first with the lowest RMSE value (0·433 mm day^?1). The RBF network obtained on the basis of the daily data from Policoro, Italy and pan‐based equations were further tested using mean monthly data collected in Novi Sad, Serbia, and Kimberly, Idaho, USA. The overall results favoured use of the RBF network for pan evaporation to evapotranspiration conversions. The use of the RBF network is very simple and does not require any knowledge of ANNs. Users require only code (RBF network), E_pan data and corresponding R_a data. Copyright © 2009 John Wiley & Sons, Ltd.     

扬州江都区邵伯农田土壤环境质量及生态风险评价

选取扬州邵伯地区作为研究区,根据评价标准（GB 15618—2018）对其农田土壤环境质量及生态风险进行评价。研究区农田土壤中8种重金属元素平均含量均低于农用地污染风险筛选值,除Ni外其余7种重金属元素的平均含量均超过江苏土壤平均背景值,其中Hg含量均值为江苏土壤平均背景值的2.16倍;通过对比内梅罗指数法和综合指数法评价结果,认为综合指数法能更客观准确地反映研究区农田土壤环境质量状况,结果显示研究区农田土壤轻度污染以上样本占总样本的2.35%;研究区农田土壤属中度生态风险,综合潜在风险指数平均值为200.56,主要贡献因子是Hg。     

Temporal variations of reference evapotranspiration and controlling factors: Implications for climatic drought in karst areas

Variations in reference evapotranspiration (ET₀) and drought characteristics play a key role in the effect of climate change on water cycle and associated ecohydrological patterns. The accurate estimation of ET₀ is still a challenge due to the lack of meteorological data and the heterogeneity of hydrological system. Although there is an increasing trend in extreme drought events with global climate change, the relationship between ET₀ and aridity index in karst areas has been poorly studied. In this study, we used the Penman–Monteith method based on a long time series of meteorological data from 1951 to 2015 to calculate ET₀ in a typical karst area, Guilin, Southwest China. The temporal variations in climate variables, ET₀ and aridity index (AI) were analyzed with the Mann–Kendall trend test and linear regression to determine the climatic characteristics, associated controlling factors of ET₀ variations, and further to estimate the relationship between ET₀ and AI. We found that the mean, maximum and minimum temperatures had increased significantly during the 65-year study period, while sunshine duration, wind speed and relative humidity exhibited significant decreasing trends. The annual ET₀ showed a significant decreasing trend at the rate of ?8.02 mm/10a. However, significant increase in air temperature should have contributed to the enhancement of ET₀, indicating an “evaporation paradox”. In comparison, AI showed a slightly declining trend of ?0.0005/a during 1951–2015. The change in sunshine duration was the major factor causing the decrease in ET₀, followed by wind speed. AI had a higher correlation with precipitation amount, indicating that the variations of AI was more dependent on precipitation, but not substantially dependent on the ET₀. Although AI was not directly related to ET₀, ET₀ had a major contribution to seasonal AI changes. The seasonal variations of ET₀ played a critical role in dryness/wetness changes to regulate water and energy supply, which can lead to seasonal droughts or water shortages in karst areas. Overall, these findings provide an important reference for the management of agricultural production and water resources, and have an important implication for drought in karst regions of China.     

基于GIS的镇巴县耕地质量分等定级

以2010年镇巴县土地利用数据库为基础数据,在对已有的农用地分等工作确定的相关参数、分等因素及其权重分析论证的基础上,利用GIS空间分析技术,采用多因素综合分析法,对耕地质量等级评价指标信息值进行补充和完善,确定镇巴县耕地质量等级,为镇巴县农用地质量动态监测提供决策依据.     

甲氨基阿维菌素苯甲酸盐对黑土区农田土壤动物群落的影响

甲维盐属高效半合成抗生素杀虫剂。在哈尔滨市典型黑土农田区,研究不同浓度甲维盐处理对土壤动物群落结构的影响。结果表明:甲维盐处理显著降低了土壤动物群落的个体密度和类群数量,且这种趋势随着甲维盐浓度的增加而增强;显著改变了群落的垂直分布格局,表聚性特征被削弱,使动物较多地聚集于5~15 cm土层;改变了群落多样性特征,其中螨类和跳虫对多样性的贡献相对较大;显著改变了表层土壤化学性质,但不同动物类群对土壤环境变化的响应规律不同,螨类和跳虫对甲维盐干扰具有较强的适应能力。甲维盐处理可以显著改变黑土区农田土壤动物群落结构,浓度是影响该过程的重要因素,施用杀虫剂时需慎重评价其生态后果。