ALBERT

Description: Salinization and secondary salinization often appear after irrigation with saline water. The Taklimakan Desert Highway Shelterbelt has been irrigated with saline ground water for more than ten years; however, soil salinity in the shelterbelt has not been evaluated. The objective of this study was to analyze the spatial and temporal distribution of soil moisture and salinity in the shelterbelt system. Using a non-uniform grid method, soil samples were collected every two days during one ten-day irrigation cycle in July 2014 and one day in spring, summer, and autumn. The results indicated that soil moisture declined linearly with time during the irrigation cycle. Soil moisture was greatest in the southern and eastern sections of the study area. In contrast to soil moisture, soil electrical conductivity increased from 2 to 6 days after irrigation, and then gradually decreased from 6 to 8 days after irrigation. Soil moisture was the greatest in spring and the least in summer. In contrast, soil salinity increased from spring to autumn. Long time drip-irrigation with saline groundwater increased soil salinity slightly. The soil salt content was closely associated with soil texture. The current soil salt content did not affect plant growth, however, the soil in the shelterbelt should be continuously monitored to prevent salinization in the future.

Description: Understanding the formation and spatial-temporal distribution of soil salt crusts (SSCs) is important for the sustainable management of the artificial shelterbelt and high-salinity groundwater utility in the Taklimakan Desert in Northwest China. The SSCs in this area were sampled, and their thickness and electrical conductivity (EC) were analyzed to examine the formation mechanism and the spatial-temporal patterns of the SSCs in the shelterbelt, which is drip irrigated with high-salinity groundwater in the Taklimakan Desert. Results demonstrated the following: (1) Soil-moisture depletion and salt accumulation at the soil surface occurred simultaneously. The soil water and salt in the different areas around the drip irrigation emitter showed different temporal dynamics in an irrigation cycle; (2) SSCs EC increased at a logarithmic rate, and SSCs thickness increased linearly with irrigation water salinity; (3) SSCs showed evident spatial distribution around the drip irrigation emitter. The EC initially increased with increasing distance from the emitter but subsequently decreased in different directions around the emitter. The highest EC was recorded at 40 cm from the emitter; (4) Topography had a significant effect on the spatial distribution of SSCs. The EC at the upslope of the emitter was higher than that at the downslope; (5) SSCs thickness showed an initial rapid increase with shelterbelt age, which was followed by a gradual increase. However, EC decreased with shelterbelt age. Our findings can contribute to the shelterbelt design, construction, utility, and sustainable management and the soil and water conservation in shifting desert regions.

Description: Hydrological extremes are closely related to extreme hydrological events, which have been and continue to be one of the most important natural hazards causing great damage to lives and properties. As two of the main factors affecting the hydrological cycle, land-use change and climate change have attracted the attention of many researchers in recent years. However, there are few studies that comprehensively consider the impacts of land-use change and climate change on hydrological extremes, and few researchers have made a quantitative distinction between them. Regarding this problem, this study aims to quantitatively distinguish the effects of land-use change and climate change on hydrological extremes during the past half century using the method of scenarios simulation with the soil and water assessment tool (SWAT). Furthermore, the variations of hydrological extremes are forecast under future scenarios by incorporating the downscaled climate simulations from several representative general circulation models (GCMs). Results show that: (1) respectively rising and declining risks of floods and droughts are detected during 1960–2017. The land use changed little during 1980–2015, except for the water body and building land. (2) The SWAT model possesses better simulation effects on high flows compared with low flows. Besides, the downscaled GCM data can simulate the mean values of runoff well, and acceptable simulation effects are achieved for the extreme runoff indicators, with the exception of frequency and durations of floods and extreme low flows. (3) During the period 1970–2017, the land-use change exerts little impact on runoff extremes, while climate change is one of the main factors leading to changes in extreme hydrological situation. (4) In the context of global climate change, the indicators of 3-day max and 3-day min runoff will probably increase in the near future (2021–2050) compared with the historical period (1970–2005). This research helps us to better meet the challenge of probably increased flood risks by providing references to the decision making of prevention and mitigation measures, and thus possesses significant social and economic value.

Description: Water, Vol. 10, Pages 1073: Laboratory Studies on Nearshore Density-Driven Exchange Flow over a Partly Vegetated Slope Water doi: 10.3390/w10081073 Authors: Zhenghua Gu Hao-Che Ho Zijing Wang Ying-Tien Lin Density-driven exchange flows, which are important to the transport of nutrients, pollutants and chemical substances without external forcing, were studied through laboratory lock-exchange experiments. Rigid and emergent cylinders were placed in one of two reservoirs in a partitioned wedge-shaped tank to simulate a partly vegetated slope. The experimental results found that cylinders placed on only one side of the tank lead to different current speeds in the current head and tail that subsequently create various flow patterns and significantly affect the downslope current motions. By fitting with the experimental data, some unknown coefficients can be obtained in the theoretical formulae that are able to predict the intrusion length and exchange flowrate in real field systems. Compared to the flat bed cases, the total exchange discharge over a steep slope decreases by up to 4% for vegetation distributed in shallow water and increases by 14% for vegetation distributed in deeper regions. These results suggest that bed slope and vegetation distribution are crucial to the density-driven exchange flows in the flushing of nearshore regions.

Description: Water, Vol. 10, Pages 532: Adsorption of Isothiazolone Biocides in Textile Reverse Osmosis Concentrate by Powdered Activated Carbon Water doi: 10.3390/w10040532 Authors: Bing-Tian Li Zhuo Chen Wen-Long Wang Ying-Xue Sun Tian-Hui Zhou Ang Li Qian-Yuan Wu Hong-Ying Hu Isothiazolones have been widely applied as non-oxidizing biocides to prevent biofouling of reverse osmosis (RO) membranes. However, few studies have investigated suitable RO concentrate treatments to remove these biocides. This study evaluated the adsorption behavior of four isothiazolone biocides, 2-methyl-4-isothiazolin-3-one (MIT), 5-chloro-2-methyl-4-isothiazolin-3-one (CMIT), 1,2-benzisothiazol-3(2H)-one (BIT), and 2-n-octyl-4-isothiazolin-3-one (OIT), by powdered activated carbon (PAC). Isothiazolones adsorption was found to obey pseudo second-order kinetics. Langmuir adsorption isotherms were more suitable to simulation of the adsorption effects than Freundlich isotherms. The adsorption amount followed the order OIT > BIT > CMIT > MIT, in accordance with the isothiazolones octanol/water partition coefficients (Kow), indicating that hydrophobicity is the main factor for influencing adsorption amounts. Following normalization with Kow, the amounts of isothiazolones adsorbed at equilibrium and normalized aqueous concentrations showed a linear relationship in a log-linear form. 1,2-benzisothiazol-3(2H)-one is anionic at high pH, and difficult to adsorb, while neutral BIT is more likely to be adsorbed. Textile reverse osmosis concentrate had an adverse effect on MIT, CMIT and BIT adsorption, but little effect on adsorption of OIT, which has a high log Kow value. There was competition between organics and isothiazolones for PAC adsorption sites, which influenced the adsorption efficiency.

Description: Channel reservoirs have the characteristics of both rivers and lakes, in which hydrodynamic conditions and the factors affecting the eutrophication process are complex and highly affected by weather conditions. Water age at any location in the reservoir is used as an indicator for describing the spatial and temporal variations of water exchange and nutrient transport. The hyper-eutrophic Changtan Reservoir (CTR) in Southern China was investigated. Three weather conditions including wet, normal, and dry years were considered for assessing the response of water age by using the coupled watershed model Soil Water Assessment Tool (SWAT) and the three-dimensional hydrodynamic model Environmental Fluid Hydrodynamic Code (EFDC). The results showed that the water age in CTR varied tremendously under different weather conditions. The averaged water ages at the downstream of CTR were 3 d, 60 d, and 110 d, respectively in the three typical wet, normal, and dry years. The highest water ages at the main tributary were >70 d, >100 d, and >200 d, respectively. The spatial distribution of water ages in the tributaries and the reservoir were mainly affected by precipitation. This paper provides useful information on water exchange and transport pathways in channel reservoir, which will be helpful in understanding nutrient dynamics for controlling algal blooms.

Description: This study aimed to investigate the Hg removal efficiency of iron sulfide (FeS), sulfurized activated carbon (SAC), and raw activated carbon (AC) sorbents influenced by salinity and dissolved organic matter (DOM), and the effectiveness of these sorbents as thin layer caps on Hg-contaminated sediment remediation via microcosm experiments to decrease the risk of release. In the batch adsorption experiments, FeS showed the greatest Hg2+ removal efficiencies, followed by SAC and AC. The effect of salinity levels on FeS was insignificant. In contrast, the Hg2+ removal efficiency of AC and SAC increased as increasing the salinity levels. The presence of DOM tended to decrease Hg removal efficiency of sorbents. Microcosm studies also showed that FeS had the greatest Hg sorption in both freshwater and estuary water; furthermore, the methylmercury (MeHg) removal ability of sorbents was greater in the freshwater than that in the estuary water. Notably, for the microcosms without capping, the overlying water MeHg in the estuary microcosm (0.14−1.01 ng/L) was far lesser than that in the freshwater microcosms (2.26−11.35 ng/L). Therefore, Hg compounds in the freshwater may be more bioavailable to microorganisms in methylated phase as compared to those in the estuary water. Overall, FeS showed the best Hg removal efficiency, resistance to salinity, and only slightly affected by DOM in aqueous adsorption experiments. Additionally, in the microcosms, AC showed as the best MeHg adsorber that help inhibiting the release of MeHg into overlying and decreasing the risk to the aqueous system.