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• Long-term changes in the water cycle of an arid irrigation district were analyzed. • The major drivers of surface and subsurface hydrological processes were identified. • Approximately 60% of the variation in ET resulted from climate variability. • Human activities induced over 70% changes in subsurface hydrological processes. Climate variability and human activities are the two major driving forces of changes in the hydrological cycle. However, how these two factors separately influence the water cycle in arid irrigation districts with shallow groundwater tables is still unknown. This study aimed to investigate the long-term changes in the water cycle and then quantify the individual contributions of climate variability and human activities to the changes in the water cycle in a large irrigation district. The Hetao Irrigation District (HID), located in the upper Yellow River Basin in Northwest China, was selected as the case study area, and an agro-hydrological model (SWAT-AG), which has powerful capabilities to model complex agro-hydrological processes, was employed as the simulation tool. The results showed that from 2000 to 2018, evapotranspiration (ET) of growing season in the HID remained relatively stable, but there were significant decreases in evaporation and dramatic increases in transpiration. For the subsurface hydrological processes, deep percolation and capillary rise of growing season both showed a decreasing trend, while groundwater drainage showed an increasing trend. The water exchange between the atmosphere layer and the root zone (i.e., ET, including evaporation and transpiration) was more significantly dominated by climatic conditions. In contrast, the subsurface hydrological processes were mainly affected by human activities, e.g., irrigation management, canal seepage, farmland area and cropping pattern. Climate variability contributed to approximately 60% of the changes in ET, whereas human activities introduced over 70% of the changes in deep percolation, capillary rise, and groundwater drainage, respectively. This study provides valuable insights into the impacts of climate variability and human activities on the changes in the water cycle and enhancements of water management practices in arid irrigation districts with shallow groundwater tables. [ABSTRACT FROM AUTHOR]

Photocatalytic reduction of nitrate ( NO 3 − ) is a green and potentially inexpensive technique for reducing NO 3 − pollution in ground water. TiO 2 -based photocatalysts have been studied extensively for this purpose. In the present study, the semiconducting catalyst CuFe 0.7 Cr 0.3 S 2 was applied to NO 3 − reduction. Loading this catalyst with metal co-catalysts (Ru, Au, Cu, Ag, Pt, and Pd) greatly increased the rate of NO 3 − reduction and the N 2 selectivity. In addition, there was a synergistic enhancement of the photocatalytic performance when the catalyst was loaded two co-catalysts. For example, the catalyst loaded with Pd and Au at mass fractions of 0.75% and 3%, respectively, could photocatalyze the complete reduction of NO 3 − in a 100 ppm N aqueous solution with 100% N 2 selectivity in less than 5 h with UV irradiation. However, with an inner irradiation from a full-arc Xe lamp, the NO 3 − conversion rate reduced to 0.065 mg N/h, probably because of the low density of the photoexcited electrons. The results show the potential of metal sulfides for photocatalytic reduction of NO 3 − , and the possibility of use of visible light. [ABSTRACT FROM AUTHOR]

Correct understanding of groundwater/surface-water (GW-SW) interaction in karst systems is of greatest importance for managing the water resources. A typical karst region, Fangshan in northern China, was selected as a case study. Groundwater levels and hydrochemistry analyses, together with isotope data based on hydrogeological field investigations, were used to assess the GW-SW interaction. Chemistry data reveal that water type and the concentration of cations in the groundwater are consistent with those of the surface water. Stable isotope ratios of all samples are close to the local meteoric water line, and the H concentrations of surface water and groundwater samples are close to that of rainfall, so isotopes also confirm that karst groundwater is recharged by rainfall. Cross-correlation analysis reveals that rainfall leads to a rise in groundwater level with a lag time of 2 months and groundwater exploitation leads to a fall within 1 month. Spectral analysis also reveals that groundwater level, groundwater exploitation and rainfall have significantly similar response periods, indicating their possible inter-relationship. Furthermore, a multiple nonlinear regression model indicates that groundwater level can be negatively correlated with groundwater exploitation, and positively correlated with rainfall. The overall results revealed that groundwater level has a close correlation with groundwater exploitation and rainfall, and they are indicative of a close hydraulic connection and interaction between surface water and groundwater in this karst system. [ABSTRACT FROM AUTHOR]

We systematically investigated the occurrence and distribution of 93 pharmaceuticals and personal care products (PPCPs) and 5 artificial sweeteners (ASs) in surface water and groundwater of Dongjiang River basin in south China. In surface water, 52 compounds were detected with median concentrations ranging from 0.06 ng/L to 504 ng/L, while in groundwater, 33 compounds were detected with concentrations up to 4580 ng/L for acesulfame. PPCPs and ASs were widely detected in the surface water and groundwater samples, which indicated contamination by domestic wastewater in the surface water and groundwater of Dongjiang River basin. Temporal and spatial variations of the detected chemicals were observed in surface water. Acesulfame, sucralose and cyclamate can be used as wastewater indicators to imply contamination in groundwater caused by domestic wastewater due to their hydrophilicity, anthropogenic sources and ubiquity in groundwater. Moreover, the detection of the readily degradable ASs, cyclamate, was a strong indication of untreated wastewater in groundwater. Sucralose was found to be a suitable wastewater indicator to reflect domestic wastewater contamination in surface water and groundwater qualitatively and quantitatively, and it can be used to evaluate wastewater burden in surface water and groundwater of Dongjiang River basin. The wastewater burden data from this survey implied serious contamination in surface water and groundwater by domestic wastewater at Shima River, a tributary of the Dongjiang River. The findings from this study suggest that the selected labile and conservative chemicals can be used as indication of wastewater contamination for aquatic environments qualitatively and quantitatively. [ABSTRACT FROM AUTHOR]

Beijing is an international metropolis, where over-exploration of water resource makes land subsidence becoming more and more serious. The related problems cannot be avoided in the coming years because of the giant increase of population. The aims of this study are to quantify land subsidence over the period 2003 to 2010, grasp the evolution of the process, and investigate the relation with the triggering factors in the northern area of the Beijing plain. Various data, including deep compaction from vertical multiple borehole extensometers, land subsidence from Persistent Scatterer Interferometry and leveling surveys, groundwater levels, hydrogeological setting from wellbores, and Landsat TM image were collected and effectively used to detect the spatial and temporal features of land subsidence and its possible relation with groundwater level changes, compressible layer thickness, and urban development. Results show that land subsidence is unevenly distributed and continuously increased from 2003 to 2010. The average loss of elevation over the monitoring period amounted to 92.5 mm, with rates up to 52 mm/y. The distribution of the subsidence bowl is only partially consistent with that of the groundwater depression cone because of the variable thickness of the most compressible fine deposits. In fact, extensometers reveal that silty-clay layers account for the larger contribution to land subsidence, with the 15 m thick silty-clay layer between 102 and 117 m depth accounting for about 25% of the total subsidence. Finally, no clear correlation has been observed between the subsidence rates and the increase of the load on the land surface connected to the impressive urban development. This study represents a first step toward the development of a physically-based model of the subsidence occurrence to be used for planning remediation strategies in the northern Beijing plain. [ABSTRACT FROM AUTHOR]