Impact of irrigation implementation on hydrology and water quality in a small agricultural basin in Spain

Abstract

Irrigation practice has increased considerably recently and will continue to increase to feed a growing population and provide better life standards worldwide. Numerous studies deal with the hydrological impacts of irrigation, but little is known about the temporal evolution of the affected variables. This work assesses the effects on a gully after irrigation was implemented in its hydrological basin (7.38 km²). Flow, electrical conductivity, nitrate concentration and exported loads of salts and nitrates were recorded in Lerma gully (Zaragoza, Spain) for eight hydrological years (2004–2011), covering the periods before, during and after implementation of irrigation. Non-parametric statistical analysis was applied to understand relationships and trends. The results showed the correlation of irrigation with flow and the load of salts and nitrates exported, although no significant relationship with precipitation was detected. The implementation of irrigation introduced annual trends in flow (3.2 L s^-1, +23%), salinity (–0.38 mS cm^-1, –9%), and nitrate concentration (5.4 mg L^-1, +8%) in the gully. In addition, the annual loads of contaminants exported increased (salts and nitrates, 27.3 Mg km^-2 year^-1, +19%, and 263 kg NO₃^–-N km^-2 year^-1, +27%, respectively). The trends presented a strong seasonal pattern, with higher and more significant trends for the irrigation season. The changes observed were different from those of larger irrigation districts or regional basins, due to the differences in land use and irrigation management. It is important to understand these changes in order to achieve an adequate management of the environment and water resources.

Editor Z.W. Kundzewicz

Citation Merchán, D., Causapé, J., and Abrahão, R., 2013. Impact of irrigation implementation on hydrology and water quality in a small agricultural basin in Spain. Hydrological Sciences Journal, 58 (7), 1400–1413.     

分形法估算分散性污染物的运移时间

污染物运移的分形模型导出一个新的适于任意浓度的污染物运移时间公式.对于一个高度非均质含水层中逐渐形成的污染羽,新公式预算出低浓度更早到达的测点.污染峰或羽的运移时间一般经常从达西定律中采用估算平均孔隙流速法得到,而此估算仅仅提供平均浓度(或污染脉冲的峰值浓度)的运移时间信息.近来,计算出任意浓度的运移时间是一个很直接的过程,并且对一个无反应污染物而言,其突破曲线部分的方程被发展.在文中,我们推导出这些方程去概括污染物运移的分形模型.     

有机污染物在完好复合衬垫中的迁移分析

在复合衬垫中,有机污染物除了在土工膜缺陷处发生迁移外,在完好土工膜中的迁移也是主要方式。考虑有机污染物在土工膜边界处的浓度跳跃现象,建立了有机污染物在完好复合衬垫中迁移的一维模型,得到了解析解。通过与有限差分解的比较,验证了解答的合理性。应用该解答分析了GCL复合衬垫和CCL复合衬垫防止有机污染物渗漏的效果。结果表明,CCL复合衬垫的效果较好,可以通过黏土改性和增加黏土厚度的方法来提高其有效性。有机污染物类型的选择对GCL复合衬垫的分析结果影响较大,而阻滞系数的变化对分析结果影响较小。     

有机插层蛭石对有机污染物苯酚和氯苯的吸附特性研究

分别应用溴化十六烷基三甲基溴化铵(HDTMA)和溴化十六烷基吡啶(HDPY)改性插层级石对苯酚和氮苯两种非离于型环境污染物进行吸附性能研究。结果表明，蛭石原矿对苯酚和氮苯的吸附能力很小，经表面活性剂处理后其吸附能力大大增强。有机插层级石对苯酚的吸附具有表面吸附特征，其吸附等沮线为Freundish型；而对氮苯的吸附实际上是氮苯在水相与有机级石中有机相之间的一种分配过程，其吸附等沮线为直线型。苯酚和氮苯的竞争吸附并末减弱有机蛭石对氯苯的吸附能力，反而由于它们同时存在产生协同效应，使有机插层蛭石对氯苯总的吸附能力有所提高。     

基于不同地质统计方法的渗透系数场对污染物运移的影响

渗透系数场的空间变异性是影响污染物运移结果的决定因素,而地质统计方法是解决渗透系数空间变异性的主要技术手段。本文利用野外场地实测数据,采用普通克里格法和指示克里格法、顺序高斯模拟法和顺序指示模拟法四种地质统计方法,插值估测和模拟再现随机渗透系数场,进而对比研究四种渗透系数场对大尺度污染物运移的影响。研究结果表明,污染羽的质心位置（一阶矩）主要由渗透系数的平均值来决定;污染羽在空间上的展布范围（二阶矩）主要受渗透系数空间变异方差的影响;条件模拟克服了估计法的平滑效果,较好地再现真实曲线的波动性,渗透系数（ lnK）估计方差与污染羽空间二阶矩随着条件模拟次数的增加而减小,并且顺序指示模拟程度更加明显。     

Arrenotokous toxic action and mechanism of atmospheric contamination： Toluene Diisocyanate

Toluene Diisocyanate is an atmospheric contaminant. To evaluate the arrenotokous toxic action and mechanism of Toluene Diisocyanate, diversifications of mice＇s testis tissue in the level of morphology and enzyme were observed and the effect on the content of RNA/DNA in arrenotokous cells was evaluated. Results showed Toluene Diisocyanate induced toxic action on spermatogenic cell, while the chondriosome was its target within the length and concentrations of exposure to TDI. TDI interfered not only with the energy-supply process of aerobic and anaerobic glycolysis, but also the energy-utilization in testis tissue by affecting enzyme activities. In addition, TDI also damnified spermatogenic cell and led to inreversible harm on spermatogenic epithelium. All resulted in toxic action on male mice＇s genital system. TDI had certain restraining effects on nucleic acid metabolism and DNA composition in arrenotokous cell. All the evidence sufficiently proved that TDI had certain arrenotokous toxic action on the level of morphology, enzyme and gene.     

考虑非等温环境下污染物在黏土中的运移解析模型

利用广义积分变换法推导了非等温条件下污染物在压实黏土衬垫中的运移解析解。所提出的解析解考虑了分子扩散、对流、吸附和热扩散的耦合效应,并考虑了压实黏土的渗透系数、分布系数和有效扩散系数3个参数随温度的变化。通过与热扩散试验结果、已有的解析解和基于COMSOL软件的数值模型的对比,验证了所提出的解析解。利用经过验证的解析解,研究了非等温环境以及压实黏土的渗透系数、有效扩散系数和分布系数3个参数随温度的变化对甲苯在压实黏土衬垫系统中迁移的影响。结果表明,非等温环境以及压实黏土的渗透系数、有效扩散系数和分布系数随温度的变化均对甲苯在压实黏土衬垫中迁移有着显著的影响。不考虑非等温环境的影响将极大低估污染物的溢出量和污染物的击穿时间。既有解析解忽略压实黏土的渗透系数和有效扩散系数随温度的变化会极大低估甲苯的流出速率,而忽略压实黏土分布系数随温度的变化会极大高估甲苯击穿衬垫系统的时间和达到稳态的时间。所提出的解析解能够考虑热扩散作用,同时考虑了压实黏土的渗透系数、分布系数和有效扩散系数3个参数随温度的变化,较既有解析解更贴近工程实际,能够为压实黏土衬垫系统的设计和服役性能评价提供指导和借鉴。     

Numerical modelling of competitive components transport with non‐linear adsorption

A characteristic finite element (CFE) algorithm for modelling contaminant transport problems coupled with non‐linear competitive adsorption is presented. An alternative algorithm, termed as the transport‐equilibrium Petrov–Galerkin (TEPG) methods in this paper, is also presented for comparison. Through analyses of a number of examples with Peclet number ranging from zero to infinity, it is shown that the CFE algorithm is very competitive with the middle–point TEPG method in terms of accuracy, stability and efficiency. The fully explicit and fully implicit TEPG methods are found to be less appropriate for transport problems coupled with non‐linear equilibrium equations. Copyright © 2000 John Wiley & Sons, Ltd.     

Groundwater,salt and contaminant transport in a coastal aquifer system with a low-permeability layer in the intertidal zone

Low-permeability layer (LPL), formed by natural deposit or artificial reclamation and commonly found below the intertidal zone of coastal groundwater system, can retard the ingress of seawater and contaminants, and shorten the travel time of the land-sourced contaminant to the marine environment compared with a homogenous sandy coastal aquifer. However, there is limited understanding on how an intertidal LPL, a condition occurred in a coastal aquifer at Moreton Bay, Australia, influences the groundwater and contaminant transport across the shallow beach aquifer system. We characterized the aquifer hydrological parameters, monitored the in situ groundwater heads, and constructed a 2-D numerical model to analyses the cross-shore hydrological processes in this stratified system. The calibrated model suggests that in the lower aquifer, the inland-source fresh groundwater flowed horizontally towards the sea, upwelled along the freshwater–saltwater interface, and exited the aquifer at the shore below the LPL. Whereas in the upper aquifer, the tidally driven seawater circulation formed a barrier that prevented fresh groundwater from horizontal transport and discharge to the beach above the LPL, thereby directing its leakage to the lower aquifer. A contaminant represented by a conservative tracer was ‘released’ the upper aquifer in the model and results showed that the spreading extent of the contaminant plume, the maximum rate of contaminant discharge to the ocean, and its plume length decreased compared with a simulation case in a homogenous sandy aquifer. Sensitivity analysis was also conducted to investigate the characteristics of the LPL, including its continuity and hydraulic conductivity, which were found to vary along the beach at Moreton Bay. The result shows that with a lower hydraulic conductivity and continuous layer of LPL reduced the groundwater exchange and contaminant transport between upper and lower aquifer. The findings from the combined field and modelling investigations on the impact of an intertidal LPL on coastal aquifer systems highlight its significant implications to alter the groundwater and mass transport across the land–ocean interface.     

复合衬层中变系数有机污染物迁移规律分析

土工膜和下伏压实黏土组成的复合衬层已被广泛用作填埋场的防渗屏障系统。有机污染物在复合衬层中迁移时,其主要运移机制是扩散作用。假设有机污染物在土工膜中稳态扩散,并假设在下伏衬层中扩散系数为迁移距离的线性函数,且考虑降解作用的影响,建立了有机污染物在复合衬层中的一维扩散模型,针对零浓度下边界条件,获得了模型解析解。基于该解析解,分析讨论了相关参数的敏感性。结果表明,相关参数对计算结果影响很大,降解半衰期对污染物运移同样存在较大影响。该解析模型仅适用于有机污染物在两层复合衬垫中的迁移问题,可为填埋场的初步设计提供参考