Soil water and salt distribution under furrow irrigation of saline water with plastic mulch on ridge

Furrow irrigation when combined with plastic mulch on ridge is one of the current uppermost wa- ter-saving irrigation technologies for arid regions. The present paper studies the dynamics of soil water-salt trans- portation and its spatial distribution characteristics under irrigation with saline water in a maize field experiment. The mathematical relationships for soil salinity, irrigation amount and water salinity are also established to evaluate the contribution of the irrigation amount and the salinity of saline water to soil salt accumulation. The result showed that irrigation with water of high salinity could effectively increase soil water content, but the increment is limited com- paring with the influence from irrigation amount. The soil water content in furrows was higher than that in ridges at the same soil layers, with increments of 12.87% and 13.70% for MMF9 （the treatment with the highest water salinity and the largest amount of irrigation water） and MMF1 （the treatment with the lowest water salinity and the least amount of irrigation water） on 27 June, respectively. The increment for MMF9 was gradually reduced while that for MMF1 increased along with growth stages, the values for 17 August being 2.40% and 19.92%, respectively. Soil water content in the ridge for MMF9 reduced gradually from the surface layer to deeper layers while the surface soil water content for MMF1 was smaller than the contents below 20 cm at the early growing stage. Soil salinities for the treatments with the same amount of irrigation water but different water salinity increased with the water salinity. When water salinity was 6.04 dS/m, the less water resulted in more salt accumulation in topsoil and less in deep layers. When water salinity was 2.89 dS/m, however, the less water resulted in less salt accumulation in topsoil and salinity remained basically stable in deep layers. The salt accumulation in the ridge surface was much smaller than that in the furrow bottom under this technology, which was quite different from traditional furrow irrigation. The soil salinities for MMF7, MMF8 and MMF9 in the ridge surface were 0.191, 0.355 and 0.427 dS/m, respectively, whereas those in the furrow bottom were 0.316, 0.521 and 0.631 dS/m, respectively. The result of correlation analysis indicated that compared with irrigation amount, the irrigation water salinity was still the main factor influ- encing soil salinity in furrow irrigation with plastic mulch on ridge.

Salt transport in polymeric pervaporation membrane

The salt transport in a PEBA membrane used in pervaporative desalination was studied.The concentration profile of salt in the membrane during pervaporation was investigated experimentally using a multilayer membrane.The salt was found to be sorbed in the membrane but was not removed during the pervaporative desalination process,and the salt concentration in the membrane varied linearly with position.High purity water was obtained as the permeate as long as the permeate side was kept dry under vacuum.The accumulated salt uptake in the membrane follows the order of MgCl2 N NaCl N Na2 SO4.The solubility of salt in the membrane follows the order of MgCl2 N NaCl N Na2 SO4.Both the permeability and diffusivity of salt in the membrane follow the order of NaCl N MgCl2 N Na2 SO4.The permeability of salt in the membrane is not influenced by the feed salt concentration.It is mainly determined by the diffusion coefficients.

Investigation of saltwater intrusion and salinity stratification in winter of 2007/2008 in the Zhujiang River Estuary in China

Saltwater intrusion is a serious environmental problem in the Zhujiang River Estuary (ZRE),which threatens the water supply of fifteen million people. The hydrological observations as well as meteorological and tidal forcing in the winter of 2007/2008 were analyzed to examine the saltwater intrusion in the ZRE.The observational results suggest that the maximum vertical difference of salinity can reach 10 in the Humen Channel during neap tide,but is very small in the Hengmen Channel. The vertically averaged salinity from time series stations during spring tide is higher than that during neap tide.A three-dimensional finite difference model was developed based on the environmental fluid dynamic code (EFDC) to study the mechanism of saltwater intrusion and salinity stratification in the ZRE.By analyzing the salt transport and the temporal variation of saltwater intrusion,the authors found that the net salt transport due to the estuarine circulation during neap tide was more than that during spring tide.This caused salt to advance more into the estuary during neap tide.However,saltwater intrusion was stronger during spring tide than that during neap tide because the spring-neap variation in salt transport was small relative to the total length of the saltwater intrusion.The physical mechanism causing this saltwater intrusion was investigated by a series of sensitivity experiments,in order to examine saltwater intrusion in response to river discharge and winds.The freshwater source was a dominant influencing factor to the saltwater intrusion and controlled salinity structure,vertical stratification and length of the saltwater intrusion.The prevailing northeast monsoon during winter could increase the saltwater intrusion in the ZRE.Though the southwest wind was uufavorable to saltwater intrusion during spring tide,it could increase stratification and saltwater intrusion during neap tide.

Resistance of the diffusive boundary layer to salt release from saline sediments to freshwater

The diffusive boundary layer （DBL） is the zone for matter exchange between surface water and aquatic sediments. To elucidate the influence of DBL on salt release from saline sediments to freshwater, two experiments with or without wind blowing were conducted. According to the experiments, a 3.5 cm DBL is formed above the smoothed sediments at a steady wind field and this thickness is greater than other studies. The observed flux of salt through the DBL is 6% larger than the calculated value from Fick＇ s first law. The results indicate that molecular diffusion is the dominant mechanism for salt transport through the DBL. The presence of DBL suppresses the hydrodynamic enhancement for matter exchange between sediments and overlying water. Therefore, salts in the sediments of a polder reservoir may influence the water quality chronically.

TIBET’S LAST CARAVAN WITH TRANSPORTING SALT(III)——SALT LANGUAGE AND THE CARAVAN

Saltmen believed aboriginal gods were everywhere. If anyone in a caravan did something bad, offending the local gods, then these would punish the caravan and even bring down disaster upon it. If everyone respected and offered sacrifices to the gods, and followed all the caravan rules, then they the gods would protect them.

TIBET'S LAST CARAVAN CHARGED WITH TRANSPORTING SALT(Ⅸ):Kelsang Wangdul Arrives at Lhasa

The road became worse by the south part of Namtso;streams of melting snow had eroded the road until it resembled a giant comb.The vehicle alternated between speeding along and a sudden brake that made everyone lurch about as though they were all intoxicated.

TIBET'S LAST CARAVAN CHARGED WITH TRANSPORTING SALT(Ⅶ):Barter Trade between Food Grains and Salt

By setting out for saline lakes in spring, Tibetan caravans on horseback return to farmlands in autumn to barter salt for agricultural products.

The Luzon Strait transport variations during 1997～2000

Based on the output data from 1997 to 2000 obtained by the MITgcm's(general circulation model)adjoint assimilation method, volume, heat and salt transports through the Luzon Strait are calculated. The results indicate that there are obvious different characteristics between 1997 and 1998~2000 on the transports through the Luzon Strait. During 1997, the Luzon Strait had a mean net westward transport of 3.93 ×106 m3/s with a maximum transport of 7.34×106 m3/s in October. During 1998~2000, the Luzon Strait possessed an annual mean eastward transport of 0.93 ×106 , 1.80 ×106 and 1.00 ×106 m3/s respectively with a maximum eastward transport of 4.10 ×106 /3.31 ×106 m3/s in July 1998/ 1999 and 2.06 ×106 m3/s in April 2000, respectively. Moreover, the transports in 1997 indicated a difference from the other years, i.e., that the ranges of westward inflows expanded more obviously to north of the Luzon Strait and downwards exceeding those of the other years. The westward inflows expanded horizontally to the north part of the Luzon Strait until 21o N.

Concentrations,sources,and influential factors of water-soluble ions of atmospheric particles in Dunhuang Mogao Grottoes,a world heritage site in China

Atmospheric particle pollution is one of the major factors leading to degradation of ancient wall paintings,particularly heritage sites in arid and semi-arid regions.However,current systematic research on the changes,sources,and influential factors of atmospheric particulate matter and its water-soluble ion concentrations is not sufficient.Thus,the major water-soluble ion concentrations,sources,and influential factors of atmospheric particles PM_(2.5) and PM_(10)(particulate matter with an aerodynamic equivalent diameter≤2.5 and 10.0μm,respectively,in ambient air)were collected from Cave 16 and its ambient exterior environment in the Dunhuang Mogao Grottoes,China,between April 2015 and March 2016.Results showed that the concentrations of PM_(2.5) and PM_(10) inside and outside the cave were the highest in March 2016 and the lowest in December 2015.The higher particle concentration from March to May was related to the frequent occurrence of sand and dust events,and the lower particle concentration from June to September was associated with good diffusion conditions,increased precipitation,and an established cave shelterbelt.The concentration of particulate matter inside the cave was affected by the concentration of particles in the air outside the cave.Ca2+,NH+4,Na+,Cl-,and SO2-4were the main components of the total ions of PM_(2.5) and PM_(10) both inside and outside the cave.The total ions inside the cave were frequently affected by the disturbance of tourists'activities during the peak tourist season from May to August.Under the influence of dust,the total concentrations of Cl-,SO2-4,Na+,NH+4,and Ca2+in particles of different sizes inside and outside the cave increased,and the concentrations of Cl-,SO2-4,Na+,and Ca2+decreased during precipitation period.Backward air mass trajectory analysis suggested that the pollutants were mainly from Xinjiang,China.The pollutant sources of air particulates are straw burning,secondary pollution sources,soil dust,dry spring rivers,and tourist activities.

Quantifying water quality and flow in multi-branched urban estuaries for a rainfall event with mass balance method

In this study,field observations were conducted after a heavy rainfall event in the Sumida and Shakujii rivers in Tokyo,Japan.The flow dynamics and fluxes of salt,suspended sediment(SS),and dissolved oxygen(DO)were investigated with the mass balance method.The fractions of fresh water and saltwater in seaward and landward flows were separated.The maximum salt flux in the Shakujii River was 53.8 kg/s during the flood tide,and those in the Sumida River were 680.3 kg/s at the upstream station and 703.7 kg/s at the downstream station.The trends of SS and DO fluxes were similar in both rivers.In the Shakujii River,the highest SS(3.1 kg/s)and DO(0.4 kg/s)fluxes appeared during the flood tide after rainfall.In the Sumida River,the maximum SS fluxes(6.1 and 6.3 kg/s at the upstream and downstream stations,respectively)and DO fluxes(1.15 and 1.21 kg/s at the upstream and downstream stations,respectively)appeared during the ebb tide.The mass balance method was used to estimate discharge,salinity,SS concentration,and DO concentration at a station with missing data.The results show that the estimated salinity and SS concentration had a significant correlation with the on-site observations,with correlation coefficients(R)of 0.950 and 0.835,respectively,but not for DO concentration(R?0.638).The disparity between the computed and measured data may be explained by the differences in velocity,salinity,topography,sedimentation,and the presence of organic matter.The analysis based on the advective salt transport components found a lower salt flux per unit width in the Shakujii River(0.36 kg/(m·s))in comparison with that in the Sumida River(2.88 kg/(m·s)).This indicates a higher probability for salt retention in the Shakujii River.©2020 Hohai University.Production and hosting by Elsevier B.V.This is an open access article under the CC BY-NC-ND license(http://creativecommons.org/licenses/by-nc-nd/4.0/).

Effects of drip irrigation and cropping on soil salinity,ionic composition and waxy corn production in a severely saline and calcareous and gypsiferous soil

Drip technologies have been suggested as practical for irrigation under conditions of high salinity and for reclamation of saline soils.Drip irrigation triggered by soil water potential thresholds was applied to both reclaim a severely saline calcareous gypsiferous soil and irrigate a waxy corn crop(Zea mays L.sinesis Kulesh).However,there is a lack of knowledge on the sustainability of reclamation of saline soils with drip irrigation and the changes in soil salinity and salt ion composition during the amelioration process.Therefore,effects on soil salinity,its ionic composition,and on crop growth and yields were evaluated in an experiment conducted in the Yinchuan Plain,northwest China.Treatments included fields in their first to fourth years of the drip irrigation reclamation-cropping scheme and adjacent native,non-cropped or irrigated salinesodic land as control.Yield of waxy corn increased and days of growth to maturity decreased as a function of time and reclamation management.The improvement in crop performance could be largely credited to the reduction of soil salinity and changes in salt composition under the drip-irrigated reclamation protocols.The drip irrigation regime created a region of low salinity proximal to the emitters conducive to germination and plant growth.Deleterious ions for crop growth such as Na+and Cl^(-)were reduced while Ca2+and Mg2+concentration increased,especially in the upper 40 cm of soil.After only a single season of drip-irrigated waxy corn production,both Cl-SO_(4)^(2-)ratios and sodium adsorption ratio(SAR)decreased dramatically.The results suggested that drip irrigation is an effective technology for reclamation of severely saline-affected soils,such as those widely distributed over the Ningxia Plain in China and that this or similar reclamation strategy could be appropriate for reclamation of other hard to manage calcareous and gypsiferous soils.