Salinity Accumulation Research Articles

The Impact of Biotic and Abiotic Stress Factors on Development of European Ash Tissue Cultures

Fraxinus excelsior L. is threatened by a variety of environmental factors causing a decline of the species. The most important biotic factors negatively affecting the condition of the F. excelsior population are fungi such as the pathogen Hymenoscyphus fraxineus. Abiotic factors with potentially harmful effect to the F. excelsior population are the accumulation of heavy metals and salinity in soils. Thus, the aim of this study was to investigate the impact of selected biotic and abiotic stress factors to determine which of them pose a threat to European ash. The study was conducted using in vitro techniques based on callus and seedlings regenerated via indirect organogenesis. Tissue cultures exclude the influence of other factors, including the environmental impact on ash extinction. The results confirmed very strong pathogenic potential of H. fraxineus in which after 14 days the callus tissue cells died as the tissue failed to activate its defense mechanisms. Experiments showed the high toxicity of cadmium in concentration of 0.027 mmol/L. Salinity caused the activity of oxidation enzymes to vary among seedlings and calluses in the control suggesting the enzymes play a role in controlling the morphogenetic development of tissue cultures.

Water reclamation and microbial community investigation: Treatment of tetramethylammonium hydroxide wastewater through an anaerobic osmotic membrane bioreactor hybrid system

Tetramethylammonium hydroxide (TMAH) is a toxic photoresist developer used in the photolithography process in thin-film transistor liquid crystal display (TFT-LCD) production, and it can be removed through anaerobic treatment. TMAH cannot be released into the environment because of its higher toxicity. A tight membrane, such as a forward osmosis (FO) membrane, together with an anaerobic biological process can ensure that no TMAH is released into the environment. Thus, for the first time, an anaerobic osmotic membrane bioreactor (AnOMBR) hybrid system was developed in this study to treat a low-strength TMAH wastewater and to simultaneously investigate its microbial community. Microfiltration extraction was used to mitigate the salinity accumulation, and a periodically physical water cleaning was utilized to mitigate the FO membrane fouling. The diluted draw solute (MgSO4) was reconcentrated and reused by a membrane distillation (MD) process in the AnOMBR to achieve 99.99% TMAH removal in this AnOMBR-MD hybrid system, thereby ensuring that no TMAH is released into the natural environment. Moreover, the membrane fouling in the feed and draw sides were analyzed through the fluorescence excitation-emission matrix (FEEM) spectrophotometry to confirm that the humic acid-like materials were the primary membrane fouling components in this AnOMBR. Additionally, 16S rRNA metagenomics analysis indicated that Methanosaeta was the predominant contributor to methanogenesis and proliferated during the long-term operation. The methane yield was increased from 0.2 to 0.26 L CH4/g COD when the methanogen species acclimatized to the saline system.

Deciphering mono/multivalent draw solute-induced microbial ecology and membrane fouling in anaerobic osmotic membrane bioreactor

Anaerobic osmotic membrane bioreactor (AnOMBR) attracted attention due to high quality effluent production with low energy demand, and draw solute has significant effect on the system performance. However, the mutual relationship between draw solute-induced salinity accumulation and microbial community had many unknown questions to be solved. This study purpose was to construct two AnOMBR to compare the impact of draw solutes of NaCl and MgCl2 on the dynamic change of microbial ecology and membrane fouling. The result indicated that the draw solute of MgCl2 caused less salinity and more membrane biofouling than that of the draw solute NaCl. Multiple microbiological analysis methods were applied to discover keystone species related to the conductivity change and membrane fouling, especially for the MgCl2-AnOMBR system. It was found that draw solute NaCl could benefit the growth of Proteobacteria to become the most abundant phylum to affect the membrane fouling, while Mg2+ introduction could stimulate the growth of NS9, Hydrogenphilaceae and Pedosphaeraceae to potentially cause the biofouling. Furthermore, phylogenetic molecular ecological networks (pMENs) deeply analyzed the microbial structure difference under Na+ and Mg2+ introduction, and indicated that the family Lentimicrobiaceae and Candidatus_Kaiserbacteria were the keystone species in NaCl-AnOMBR, while two genus Anaerolinea and SWB02, and two families Saprospiraceae and NS9 were discovered to have key effect in MgCl2-AnOMBR due to their strong extracellular polymeric substances (EPS) production ability for survival of other microorganisms. This study was significant to give microbial targets under the impact of various draw solutes, as the reference for the engineers to further investigate how to improve the microbial structure to enhance AnOMBR performance and inhibit the membrane biofouling.

Effect of salinity on oleic sunflower (Helianthus annuus Linn.) under drip irrigation in arid area of Northwest China

To achieve secure and efficient saline water irrigation in arid areas, a field experiment was conducted to evaluate the salt distribution in the soil profile and response of sunflower (Helianthus annuus L.) to salinity from 2018 to 2020. The experiment included five levels of irrigation water salinity (ECi = 0.5 dS/m, 3.3 dS/m, 4.9 dS/m, 6.6 dS/m and 8.2 dS/m). The results indicated that the soil salinity rose slightly and was maintained in balance in the first two years owing to the moderate freshwater irrigation after planting. In 2020, surface salinity accumulation occurred when the ECi was greater than 3.3 dS/m. The average soil salinity at 0–100 cm soil depth was near that of the irrigation water. The effects of irrigation water salinity on plant growth and yield were also investigated. Salinity hindered the growth of the sunflower, which was indicated by a decrease of plant height, biomass, and plant water content. Salinity also reduced sunflower yield by reducing the disk diameter and 100-grain weight. IWP increased in the first two years and then decreased in the third year with an increase in the irrigation water salinity. The salinity threshold for oleic sunflower was 1.3 dS/m, and the sunflower seed yield decreased by 4.9% for every 1 dS/m increase in soil salinity. To ensure a seed yield of over 75%, the soil salinity should be less than 6.4 dS/m. It was concluded that for oleic sunflower drip irrigation in arid areas, the plant, should be irrigated with 80 mm of freshwater to leach salt after planting. This not only ensures that the seed yield is no less than 85% but also maintains a balanced soil salinity after harvest when the ECi increases to 8.2 dS/m.

Salinity Accumulation in the Root Area of the Curly Lettuce Grown in Deficit Irrigation Conditions

Bu çalışmada, kıvırcık marul bitkisi için sulama sezonu başlangıcına kıyasla sulama sezonu bitiminde meydana gelen kök bölgesi içindeki tuz birikimi durumu araştırılmıştır. 2018 yılı ilkbahar yetişme döneminde yay çatılı plastik örtülü bir serada yürütülen çalışmada, bitki materyali olarak Campania kıvırcık marul (Lactuca sativa var. crispa) çeşidi kullanılmıştır. Araştırmada, bitki kök bölgesinin her iki tarafının ıslatıldığı geleneksel sulama (GS125, GS100, GS75, GS50) ile birlikte ardışık yarı ıslatmalı sulama (AYIS125, AYIS100, AYIS75, AYIS50) uygulamaları ele alınmıştır. Ardışık yarı ıslatmalı sulama (AYIS) uygulamasında, sırasıyla takip eden sulamalarda ıslak ve kuru kısımlar yer değiştirilmiştir. Diğer bir ifadeyle, AYIS uygulamasında, sulamalar sırasında bitki kök bölgesinin bir yarısı görece olarak ıslatılırken geriye kalan diğer yarısı görece olarak kuru bırakılmış ve bir sonraki sulamada ıslak ve kuru bırakılan kısımlar yer değiştirilmiştir. Bitki kök bölgesi tuzluluk birikimini belirlemek için sulama sezonu başlangıcında üç yinelemeli olarak araziyi temsil edecek şekilde 0-10, 10-20 ve 20-30 cm derinliklerden toprak örneği alınmıştır. Benzer bir şekilde, sulama sezonu bitiminde de, yine üç yinelemeli olarak, her sulama uygulaması altında bitki kök bölgesinden toprak örnekleri alınmıştır. Geleneksel yöntem kullanılarak, laboratuvarda toprak örneklerinden çamur süzükleri elde edilmiş ve tuzluluk ölçümleri yapılmıştır. En düşük tuzluluk değeri GS100 uygulamasında 0.49 dS m-1 olarak ölçülürken, en yüksek tuzluluk değeri ise 1.40 0.49 dS m-1 olarak GS125 uygulamasında kaydedilmiştir. Genel olarak, sezon sonunda en yüksek tuzluluk artışı ilk katman (0-10 cm) için %48, ikinci katman (10-20 cm) için %34 ve üçüncü katman (20-30 cm) için %45 olarak GS125 sulama uygulamasında hesaplanmıştır. Bu artış oranları dikkate alınması gereken değerlerdir. Sonuç olarak, sürdürülebilir bir sulu tarım için yetişme sezonunda iyi bir drenaj sistemi vasıtasıyla, topraktaki tuz birikiminin etkin bir yıkama işlemiyle giderilmesi önerilmektedir.

Submerged versus side-stream osmotic membrane bioreactors using an outer-selective hollow fiber osmotic membrane for desalination

This study investigated the comparative performances, fouling mitigation efficiencies, and operational costs of side-stream and submerged osmotic membrane bioreactors (OMBR) systems using an outer-selective hollow fiber thin-film composite forward osmosis (OSHF TFC FO) membrane. Generally, the submerged OMBR system exhibited the higher fouling mitigation efficiency and a much slower flux decline rate when compared with that of the side-stream system. The side-stream OMBR system demonstrated an initial water flux of 15.8 LMH using 35 g/L NaCl as the draw solution, which was 2-fold higher than that of the submerged system when at its optimal performance. However, salinity accumulation in the reactor of the side-stream system was at a higher rate than for the submerged OMBR system. Both OMBR systems showed comparably high pollutant removal efficiencies over the experimental period. Annual operating costs for the side-stream OMBR system has been estimated to be 38% higher (OPEX) than for the submerged system. Membrane replacement cost accounted for the majority of the OPEX, over 89%, while the energy consumption and cleaning costs only accounted for relatively small portions. Therefore, reducing the membrane replacement cost is critical to realizing the commercial viability of the submerged OMBR system.

Changes in soil salinity under treated wastewater irrigation: A meta-analysis

In view of water shortages, the development and utilization of unconventional water resources have been studied extensively. Treated domestic or industrial wastewater used for agricultural irrigation is an unconventional water resource utilization method. Due to the particularities of water sources, previous studies have mainly focused on changes in soil heavy metals, microorganisms, and organic substances and crop responses to toxic elements; thus, attention to soil salinity is of secondary importance. After selecting qualifying research, a meta-analysis was performed to statistically analyze the data of seven variables (potassium (K), sodium (Na), calcium (Ca), magnesium (Mg), electrical conductivity (EC), pH, and yield) to 1) estimate the mean effects of treated wastewater (TWW) irrigation on the soil salinity, soil pH and crop yield; and 2) identify the wastewater treatment grade (primary treated wastewater (PTW), secondary treated wastewater (STW), and tertiary treated wastewater (TTW)) and soil texture (sandy texture, loamy texture and clayey texture) that benefit TWW irrigation. The results showed that TWW irrigation caused a significant accumulation of soil salinity, and the increase in cation content from high to low was K (90.1%), Na (59.9%), Mg (25.2%) and Ca (17.3%). EC also increased significantly by approximately 57.2%, while there was no significant change in pH, and even the crop yield presented an average reduction of nearly 6.5%. PTW contributed to the largest salt accumulation, followed by TTW and STW. STW showed a significant increase in EC but did not show a significant change for the four ions. In terms of yield, STW can increase yield, while TTW has the opposite effect. In general, the sandier the soil texture, the higher is the salt content detected, although the retention of salt in loamy textured soil may differ depending on the ions. The yield of crops grown increased in the clayey textured soil and decreased in the loamy textured soil. Our study elucidated the response of soil salinity accumulation under TWW irrigation and could provide a reference for unconventional water resource utilization.

Mapping soil salinity using a combined spectral and topographical indices with artificial neural network.

Monitoring the status of natural and ecological resources is necessary for conservation and protection. Soil is one of the most important environmental resources in agricultural lands and natural resources. In this research study, we used Landsat 8 and Artificial Neural Network (ANN) to monitor soil salinity in Qom plain. The geographical location of 72 surface soil samples from 7 land types was determined by the Latin hypercube method, and the samples were taken to determine the electrical conductivity (EC). Thirty percent of the data was considered as a validation set and 70% as a test set. In addition to the Landsat 8 bands, we used spectral indices of salinity, vegetation, topography, and drainage (DEM, TWI, and TCI) because of their impacts on soil formation and development. We used ANN with different algorithms to model soil salinity. We found that the GFF algorithm is the best for soil salinity modeling. Also, the TWI topography index and SI5 salinity index and NDVI vegetation index had the most effect on the outputs of the selected model. It was also found that flood plains and lowlands had the highest levels of salinity accumulation.

Assessing impact of saline intrusion on rice cultivating area in Ke Sach district, Soc Trang province, Vietnam

This study was carried out to evaluate the effects of saline intrusion on agricultural activities, thereby proposing adaptation and mitigation measures for local people. Salinity was measured at 15 locations on the main and tributary rivers in Ke Sach district, Soc Trang province, Vietnam from January to September 2020. The method of direct interview with farmers was used to evaluate the knowledge and effects of saline intrusion on agricultural production. Salinity measurement results showed that salinity intrusion oc-curred and lasted from February to the end of May during the dry season (the Winter-Spring rice crop). During the rainy season (June-September), due to the large amount of water, salinity was only be-tween 0.01 and 0.1‰. However, the research has found significant effects in the Summer-Autumn rice crop due to the accumulation of salinity in the soil from the Winter-Spring rice crop, which reduces the rice yield by 10-30%. The interview results revealed that more than 80% of the farmers were aware of the effects of saline water intrusion. Local authorities also regularly organize seminars to disseminate basic knowledge to the community to minimize the risks and impacts of saltwater intrusion. The proposed temporary solutions include rainwater storage, maintenance of saline prevention sluices, construction of more water regulation canals, financial support, and strengthening of salinity monitoring stations. In order to adapt to the long-term salinity conditions, local authorities need to focus on researching changing cropping patterns, crop structure, using new rice varieties that are able to adapt to drought and salty conditions. Besides, there will be technical assistance, capital for people to adapt well to the saline intrusion situation.

Western boundary current in relation to Atlantic Subtropical Gyre dynamics during abrupt glacial climate fluctuations

Ocean-atmosphere simulations corroborate the relationship between tropical Atlantic subsurface heat and salt storage driven by Salinity Maximum Water (SMW) and deglacial perturbations of the Atlantic Meridional Overturning Circulation (AMOC). Whether AMOC variability of the last glacial cycle affected SMW export into the tropical West Atlantic remained yet elusive. In order to assess the sensitivity of the tropical hydrography during abrupt and rapid glacial climatic and oceanic perturbations, we present century-resolving foraminifera-based subsurface (~200 m water depth) temperature and salinity reconstructions from Tobago Basin core M78/1–235-1. The proxy records were interpreted in terms of the closely related development of the North Brazil Current (NBC) and the North Atlantic Subtropical Gyre (STG) from ~37 to 30 ka BP, and in relation to their deglacial developments. Prior to ~32.8 ka BP, the cyclic variations in subsurface conditions were attributed to the NBC, which acted in line with a recurrent intensification and relaxation of the trade winds, subtle migrations of the Intertropical Convergence Zone, and the related moisture transport across Central America. Major and rapid re-organizations of the tropical Atlantic upper ocean-atmosphere system took place at ~32.8 ka BP and ~ 21.8 ka BP, unmirrored by major AMOC changes. Thresholds for sufficient heat and salinity accumulation in the STG to allow for formation and intensified subsurface dispersal of SMW were not achieved before late HS1, when AMOC weakening, according tropical heat backlog and surface warming by maximum Northern Hemisphere insolation acted together.

Minimizing salinity accumulation via regulating draw solute concentration in a bioelectrochemically assisted osmotic membrane bioreactor

A suitable draw solute (DS) concentration in bioelectrochemically assisted osmotic membrane bioreactor (BEA-OMBR) can convert the “negative effect” of salinity accumulation into a “beneficial effect” by using the reverse-fluxed DS as a buffer agent or a carbon source supplement. Herein, the effect of DS concentration from acid buffer solution (i.e., ammonium chloride, NH4Cl), alkaline buffer solution (i.e., sodium bicarbonate, NaHCO3), and organic solution (i.e., sodium acetate, NaOAc) on salinity accumulation was systematically investigated. Salinity accumulation with NaHCO3 DS mainly derived from reversal fluxed sodium ion (Na+, major contributor with DS concentration ≤0.25 M) and bicarbonate ion (main contributor with DS concentration ≥0.50 M): Na+ accumulation could be mitigated by Na+ transport dominant by electrically driven migration (i.e., 21.3–62.1% of reverse-fluxed Na+), and bicarbonate accumulation could be reduced by buffer system. A medium-low concentration of 0.25 M NH4Cl DS had a better performance on current density of 165.0 ± 23.0 A m−3 and COD removal efficiency of 91.5 ± 3.4% by taking advantage that 77.7 ± 1.3% of reverse-fluxed ammonium could be removed by biological treatment and ammonium transport. A high NaOAc DS concentration (i.e., ≥0.05 M) exhibited a higher current density of 145.3–146.0 A m−3 but a lower COD removal efficiency due to the limited carbon source utilization capacity of anaerobic bacteria. Both concentration diffusion (20.9–28.3%) and electrically driven migration (29.5–39.4%) promoted reverse-fluxed Na+ transport to catholyte and thus mitigated Na+ accumulation in the feed/anolyte. These findings have provided an optimal DS concentration for BEA-OMBR operation and thus encourage its further development.

A study on interannual change features of soil salinity of cotton field with drip irrigation under mulch in Southern Xinjiang.

The drip irrigation under mulch has become one of significant supporting technologies for cotton industry development in Xinjiang, and has shown the good economic and ecological benefits. With the rapid development of society and economy in Southern Xinjiang, the conventional mode of large-quota winter and spring irrigation, salt leaching and alkali decreasing is difficult to support sustainable development of land and water resources in Southern Xinjiang. This study tries to adjust soil moisture and salt content regulation mode of massive water salt leaching and drip irrigation under mulch in the non-growing period of cotton field in Southern Xinjiang, explores interannual soil salinity change features of drip irrigation cotton field without winter and spring irrigation, and provides experimental basis for drip irrigation technology under mulch which can reduce and exempt cotton irrigation in winter and spring. According to ET0, the dual-factor complete combination experiment involving 3 irrigating water quotas (I1, I2, I3) and 2 irrigation times (T12, T16) was designed, and 6 treatments were involved in total(I1T12,I2T12,I3T12,I1T16,I2T16 and I3T16). The investigation results of four-year (2012–2015) field positioning experiment showed that, under the condition of “germination under drip irrigation” without winter and spring irrigation, increasing irrigation quota and irrigation times could lower 0-100cm soil salinity accumulation, but the soil salinity accumulation degree was 40-100cm, and less than 0-30cm. In the seedling stage, bud stage, blossom and boll-forming stage, and boll opening stage, the average salinity of 0-100cm soil increased by 39.81%, 31.91%, 26.85% and 29.47%, respectively. Increasing irrigation quota and irrigation times could ease interannual soil salinity accumulation degree of cotton field with drip irrigation under mulch, without winter and spring irrigation. 0-100cm soil salinity before sowing was related to the irrigation quota of cotton in the growing stage of the last year. The larger the irrigation quota was, the smaller the soil salinity before sowing would be. The accumulation amount of soil salinity at the end of growing stage under different treatments was lower than that before sowing. The drip irrigation of cotton under mulch in the growing stage could effectively regulate soil salinity distribution and space-time migration process in the growing stage of cotton. Compared with the beginning of 2012, 0-100cm average soil salinity under 3 irrigation quotas (I1, I2, I3) was 33.66%, 5.60% and 1.24%, respectively. Salt accumulating rates under 12 irrigations and 16 irrigations were 20.66% and 6.33%, respectively. The soil had the risk of salinization when the “germination under drip irrigation” without winter and spring irrigation was used. Such results can provide the reference for prevention and treatment of soil moisture and salt content of cotton field with drip irrigation under mulch in the arid region.

Comprehensive assessments of soil fertility and environmental quality in plastic greenhouse production systems

The increasing demand of fruits and vegetables has resulted in the rapid growth of plastic greenhouse production (PGP) systems worldwide. A comprehensive assessment method considering both soil fertility and environmental safety is necessary for the sustainable development of PGP systems. A total of 92 vegetable greenhouses in Jingyang County and 28 fruit greenhouses in Dali County in Shaanxi Province, China, were selected for comparing the changes of soil quality under two cultivation patterns. The soil comprehensive quality index (SQI) in Jingyang (0.53) was significantly higher than that in Dali (0.46) (p < 0.05). A significant correlation was found between the SQI and the soil fertility index (SFI) (p < 0.01), suggesting that the SQI was mainly dependent on the soil fertility level in greenhouses. The primary limiting factors of the SFI in PGP in Jingyang and Dali were low soil organic matter content (19.57 g kg−1) and high electrical conductivity (1303 μS cm−1), respectively, indicating that soil in greenhouses in Jingyang and Dali might experience nutrient deficiencies and soil salinity accumulation problems, respectively. Cd and Hg were main limiting factors of soil environmental index (SEI), especially Hg. The SEI in Dali (0.74) was significantly lower than that in Jingyang (0.81) due to differences in the geo-accumulation indexes of heavy metals in the topsoil in greenhouses. Considering that no significant difference was found in the SFI between two study areas, the SEI is likely responsible for the regional differences in the SQI in PGP. The negative correlation of the SEI with the cultivation ages of plasticulture indicated that heavy metal accumulation problems would be the primary limiting factor of the SQI in the future if greenhouses cannot be managed appropriately. Our study provides data support for soil quality management in PGP systems.

Effects of early irrigation and compost addition on soil and vegetation of a restored semiarid limestone quarry are undetectable after 13 years

Semi-arid environments are strongly limited by water and nutrients, which hinders their recovery after anthropogenic disturbances. Application of compost and irrigation can improve soil fertility and enhance vegetation growth during the restoration of these environments. However, these restoration techniques may also favor the establishment of opportunistic communities and arrest natural succession. Mid and long-term assessments (>10 years) of the improvements in soil conditions and water availability after ecological restoration are scarce, although this is particularly important given the slow dynamics characterizing these environments. We assessed the effect of two levels of irrigation and compost addition (full-factorial design) in a limestone quarry under semi-arid conditions after a 13 years-period. These treatments were applied in addition to topsoiling, hydroseeding and plantation of woody species in the entire study area. Whereas the latter restoration treatments produced an overall increase in soil carbon content and salinity during this period (78% more soil carbon, over 200 μS/cm [nearly four times] more salinity), watering and compost addition did not affect the accumulation of soil organic carbon (at 0–10 cm and 10–20 cm) or soil salinity. In contrast to the observed short-term effects, water and compost addition did not affect the cover, biomass and diversity of the herbaceous layer, or the survival and growth of planted woody species 13 years after the treatments ended. Fading treatment effects occurred despite substantial changes in vegetation structure and composition between year 1 and year 13 (25% more herbaceous species, 13% less biomass, up to 80% decline in woody seedling survival). Conversely, similar to what we observed 13 years ago, the survival of woody plants was affected by the composition of the herbaceous layer, with species-specific responses to their cover and composition. Our study illustrates temporal shifts in the effects of two commonly applied restoration treatments, and highlights the need for mid- and long-term monitoring programs to properly assess the effectiveness of restoration actions.

Effects of Polyacrylamide-Based Super Absorbent Polymer and Corn Straw Biochar on the Arid and Semi-Arid Salinized Soil

Green approaches are much more appreciable during the present scenario. Soil amendments are frequently applied for improving water use efficiency, reducing soil salinity in arid and semi-arid areas, controlling the secondary salinization of cultivated soils, and increasing the carbon sequestration capacity of soils. Thus, lab soil column simulation experiments and field experiments were carried out to evaluate these functions of two separate amendments, polyacrylamide-based super absorbent polymer (SAP) and corn straw biochar at different application rates. The simulation experiments showed that both SAP and biochar inhibited the accumulation of soil salinity, with a reduced rate of 9.7–26.3% and 13.5–37.2%, respectively, dependent on the amendment application rates. The field experiments found different salt inhibition effects of the two amendments with growth stages of maize. Soil salinization was inhibited in the pre-germination and early jointing stages by SAP, but throughout the whole growth period by biochar. Both soil amendments reduced soil electrical conductivity, and biochar increased the soil contents of Ca2+, Mg2+, and K+. Our observations demonstrated that application of biochar and SAP played important roles in increasing soil fertility and inhibiting soil salt accumulation. It provided an effective method to potentially mitigate the environmental crisis and promote sustainable development in agriculture.

Effects of Alternating Fresh and Saline Water Irrigation on Soil Salinity and Chlorophyll Fluorescence of Summer Maize

Saline groundwater irrigation is an important way to alleviate the shortage of fresh water resources. In order to find a reasonable saline irrigation method for farmland, an irrigation experiment was conducted with fresh water and saline water at the seedling, jointing, heading, and filling stages. The soil salinity, growth, chlorophyll fluorescence, and yield of summer maize were measured. The results showed that alternating fresh and saline water irrigation led to a smaller increase in soil salinity relative to that irrigation with saline water alone. In addition, different sequences of alternating irrigation also significantly affected the accumulation of soil salinity. The maximum quantum yield, effective quantum yield of photochemical energy conversion, photochemical quenching, and non-photochemical quenching varied greatly at the jointing stage and heading stage. Furthermore, the yield of maize that was irrigated with fresh water at the heading stage (8.53 t ha−1) was greater than that at the jointing (7.69 t ha−1) and filling stages (7.45 t ha−1). Therefore, these findings indicate that in areas where fresh water is scarce, priority should be given to the application of fresh water at the heading stages for summer maize irrigation.

Effects of operating parameters on salinity accumulation in a bioelectrochemically-assisted osmotic membrane bioreactor

Salinity accumulation in osmotic membrane bioreactors (OMBRs) is one of the key challenges, which can be mitigated in situ by reverse-fluxed solute transport through integration of bioelectrochemical systems (BES). The effects of several key operating parameters on salinity accumulation were investigated. Salinity accumulation depended on balance between reversal solute flux (RSF) and reverse-fluxed ammonium (RFA) transport, which was driven by electrical migration and concentration diffusion. DS concentration was the primary factor influencing RSF, and the lowest DS concentration exhibited the minimum solute leakage. Aeration played a vital role in RFA transport, and a higher aeration helped to enhance RFA transport. Increased current generation (i.e., influent flow rate of 0.5 mL min−1 and external resistance of 5.0 Ω) contributed to RFA migration. The lack of electrolyte addition in catholyte contributed to RFA diffusion. These optimal parameters encourage the further development of an effective strategy for salinity mitigation in BES-based OMBR technology.

Performance enhancement of a submerged forward osmotic membrane bioreactor by aerobic granules

Forward osmotic membrane bioreactors (FOMBRs) have broad prospects for application in wastewater reuse and resource recovery. Problems such as concentration polarization, salinity accumulation, and membrane fouling have led to a rapid flux decline, which limit their practical application. In this study, we introduced aerobic granules into a FOMBR to clarify the effect of sludge morphology on reactor performance. The results showed that the average removal efficiency of total organic carbon (TOC) and phosphate-phosphorus (PO43−-P) were maintained above 95% during the operation of activated sludge-based FOMBR (R1) and aerobic granule-based FOMBR (R2), respectively. R2 achieved higher removal efficiency of ammonia–nitrogen (NH4+-N) with an average removal efficiency of 77%, which was significantly higher than R1 (57%). Over the entire operation, the content of the soluble microbial products (SMP) in R1 was generally higher than that in R2, which resulted in more polysaccharides and proteins in the fouling layer of the membrane. The membrane flux of R2 was 1.0 L·m−2·h−1 higher than that of R1. The average size of flocs in R1 decreased from 137.24 μm to 76.84 μm, and that of the aerobic granules in R2 decreased from 2.35 mm to 1.20 mm and then remained stable. The results of microbial analysis showed that the membrane surface had lower microbial diversity than that of the mixed liquid, and the microorganisms enriched at the membrane surface were mainly Proteobacteria and Firmicutes with better salt tolerance.

Identifying Seasonal Accumulation of Soil Salinity with Three-Dimensional Mapping—A Case Study in Cold and Semiarid Irrigated Fields

Soil salinity is an active and complex part of soil property in arid and semiarid irrigation areas that restricts the sustainability of agriculture production. Knowledge of seasonal distributions and migration of soil salinity is important for the management of agriculture. In this study, three-dimensional (3-D) geostatistical methods were used to construct seasonal 3-D spatial distribution maps of soil salinity, and then the quantitative analysis methods were used to study the seasonal accumulation patterns of soil salinity for the 0–150 cm soil depth in cold and semiarid irrigated rice fields. The results revealed that there were different spatial distribution and migration patterns of soil salinity in autumn 2015, spring 2016, autumn 2016, and spring 2017. The migration of soil salinity had a dispersion trend from autumn to spring, and the area of non-saline soil increased. Whereas there was an accumulation trend from spring to autumn, and the area of non-saline soil decreased. There were about 10–20% of the study area had experienced transitional changes of different soil salinity levels in different seasons. The correlation coefficient showed that there were significant positive correlations among the five depth increments (30 cm) in different seasons, and the correlations of soil salinity were higher in adjacent layers than in nonadjacent layers. The ECe values were higher in the topsoil (0–30 cm) and deeper subsoil (120–150 cm), indicating that soil soluble salts accumulated in the soil surface due to evaporation and accumulated in the bottom due to leaching and drainage. Microtopography was the major factor influencing spatial distribution of soil salinity in different seasons. The ECe values were generally higher in the swales or in areas with rather poor drainage, whereas the values were lower in relatively higher-lying slopes or that were well-drained. The results provide theoretical basis and reference for studying the variation of seasonal soil salinity in irrigated fields.

Acceleration of soil salinity accumulation and soil degradation due to greenhouse cultivation: a survey of farmers' practices in China.

Soil environment and water quality face large pressure due to the rapid expansion of greenhouse cultivation in China. However, studies rarely provide the linkage between farmers' practices and soil degradation in greenhouse cultivation field. In this study, a field survey and sampling of greenhouse cultivation soil were conducted in five regions of China to investigate the accumulation and variation characteristics of soil ion compositions in the field. First, the pH, ion compositions, and electrical conductivity (EC) of 132 composite soil samples were analyzed. Second, farmers' practices with regard to fertilizer, crop yield, and soil degradation processes were surveyed. Lastly, soil nutrient status was evaluated by different grades, and the principal component analysis method was used to analyze the main sources of soil ion compositions. Results of the study reveal the following: (1) Enrichment of greenhouse soil nutrient was mainly caused by excessive fertilization, which introduced the secondary salinization phenomenon for 3-5 years in plastic greenhouse and 1-3 years in multispan greenhouse. (2) Significant changes between the EC and salt ion composition of open soil and greenhouse cultivated soil were observed. The contents of nitrate nitrogen and ammonium nitrogen in the greenhouse soil were high. (3) After a certain period of cultivation in the greenhouse, salt accumulation, pH decline, and varying degrees of acidification were observed in the soil profile. The relationship between soil pH and EC values indicated that the balance of soil compositions was broken. The recommended methods for sustaining greenhouse cultivation include balanced fertilization, rotation practices, and reasonable water utilization in the field.