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The removal of nitrogen from water is a consequence of the synergistic action of plant uptake, sediment sorption, and microbial decomposition. However, there is a lack of long-term experimental studies on the effects of each component in the process of nitrogen removal. In this study, we investigated the effect of sediment, plants, and microorganisms on nitrogen removal by setting up three systems: water–sterilized sediment, water–sediment, and water–sediment–plant. The nitrogen removal effect followed the following rank order of effectiveness: the "water–sediment–plant" system > the "water–sediment" system > the "water–sterilized sediment" system. The ditch sediment had a strong enrichment effect for nitrogen. In addition, the migration rate of nitrogen in the sediment with different depths was different. The ammonia-nitrogen migration rate in the sediment showed an increasing trend with time and depth. The nitrate-nitrogen migration process in the sediment showed a trend of enrichment toward the middle layer (15.0–25.0 cm). Aquatic plants and microorganisms can promote the removal of nitrogen in water, with the average purification rates of 13.92% and 19.92%, respectively. [ABSTRACT FROM AUTHOR]

This study develops a coupled model of chemical clogging and permeability coefficient of geotextile envelope. Based on the distribution characteristics of crystal precipitates on geotextile envelope and their influence on the permeability coefficient, a permeability coefficient model of an actual geotextile envelope that considers the overlapping effect is developed. Then, the densification effects of geosynthetic fiber hypothesis and the filter cake effect hypothesis are proposed to simulate the processes of increasing fiber diameter after crystal precipitation and the accumulation of crystal precipitates on the surface of geotextile envelope. The crystal precipitation module and permeability coefficient module are coupled, and their experimental values are used to confirm the availability of the model. Results indicate the satisfactory performance of the model. In addition, the parameter sensitivity analysis and trend prediction show that the saturation index SI and solution flow rate V are the main factors that affect the chemical clogging and permeability of geotextile envelope. When the solution conditions are not considered, the sensitivity of geotextile envelope parameter d f increased with the amount of precipitation in crystal precipitation. When the pores of the geotextile envelope are completely clogged, the permeability coefficient of the geotextile envelope will drop sharply, then decline slowly. • A coupled model for chemical clogging and permeability coefficient of geotextile envelope is developed. • The densification effect of geosynthetic fiber and the filter cake effect are proposed to generalize chemical clogging. • The sensitivity of geotextile envelope parameter d f increased with the amount of precipitation. [ABSTRACT FROM AUTHOR]

A reasonable layout of subsurface drainage systems is considered essential for maximizing its drainage and salt control effectiveness. In the saline-alkali farmland of arid regions in Northwest China, low-permeability interlayers (clay, clay-loam or silty-loam) within the soils are common. However, the influence of the low-permeability interlayers on the layout of the subsurface drainage has not been extensively considered in the literature. This study investigated the process of subsurface drainage and salt discharge in salt-affected fields with silty-loam interlayers using field experiments and numerical simulations. Four field experiments were conducted, considering three different relative positions between the drainage pipes and silty-loam interlayers. The results showed that the silty-loam interlayers hindered water infiltration, and the distribution of soil salinity in the soil profile varied with the buried depth of drainage pipes at different positions relative to the silty-loam interlayer. When the buried depth of drainage pipes increased, the amount of water and salt discharged from drainage pipes increased, and the increase rate in salt discharge was greater than water drainage. A numerical model was calibrated and validated using the field experiment data, and 25 orthogonal numerical experiments were conducted to investigate the soil desalination effects of buried depth of drainage pipes, spacing between the pipes, saturated hydraulic conductivity of the interlayer, and position of the low-permeability interlayer. The results showed that the drainage pipe buried depth, spacing, and saturated hydraulic conductivity of the low-permeability interlayer had significant effects on the desalination rate (P < 0.01), while the position of the low-permeability interlayer had no significant effect (P > 0.05). Subsurface drainage pipes should be placed below the low-permeability interlayer. The desalination rate linearly increased with the buried depth of drainage pipe and saturated hydraulic conductivity of the interlayer, and it increased exponentially with decreased spacing. An empirical formula for soil desalination rate considering interlayer and subsurface drainage pipe layout parameters was fabricated and used to determine the appropriate layout parameters. • Field experiment with a silty-loam interlayer and different drain depth pipes was conducted. • The soil desalination rate was significantly influenced by the K s of the interlayer. • The effects of subsurface pipe layout parameters and interlayer on N were analyzed. • A formula considering the interlayer and subsurface pipe layout parameters was built. [ABSTRACT FROM AUTHOR]

Accurately assessing the clogging risk of the drainage pipe envelopes is a prerequisite for the reasonable design and proper management of subsurface drainage. However, the current assessment of clogging risk for subsurface drainage envelopes in arid areas mainly focuses on the impacts of single factors such as physical or chemical factors, with less attention given to combined physical–chemical clogging, which is more likely to occur and causes significant harm. Based on the evaluation indicators for physical and chemical clogging risks, this study utilized the entropy weight method to determine the weights of physical and chemical clogging risks, then proposed evaluation indicators for combined clogging risks and generated risk maps of physical, chemical, and combined clogging within the Xinjiang watershed. Furthermore, field excavation and sampling of subsurface drainage pipes were conducted to apply the proposed evaluation indicators for combined clogging risks and analyze the influencing factors. The results show that the combined clogging risk map based on the proposed combined clogging evaluation indicators is consistent with the actual clogging situation in the subsurface drainage system. Both physical and chemical clogging coexisted in the subsurface drainage system in Xinjiang, with a higher mass content of SiO 2 than CaCO 3 in the clogging substances. The combined clogging risk increased with rises in the drainage temperature and salinity. Under current conditions, the proportions of high, moderate, and low-risk areas of combined clogging risk are 22.10%, 30.37%, and 47.53%, respectively. The high-risk areas are mainly concentrated in Southern Xinjiang, which accounts for 91.7% of the high-risk area. This study can provide technical support for the prevention and control of clogging in subsurface drainage systems for saline-alkali farmland in arid areas. • Risk evaluation indicators for combined clogging of subsurface drainage were proposed. • Risk maps of physical, chemical, and combined clogging in Xinjiang were generated. • The combined clogging risk increased with rises of drainage temperature and salinity.. [ABSTRACT FROM AUTHOR]

• Quantitatively describes the groundwater recharge process for lakes. • Constructed a model for the groundwater table-lake area relationship in groundwater-dependent lakes in arid regions. • Suggested a groundwater depth of 1.73 m to maintain stable lake area within the Hetao Irrigation District. • Constructed model can serve as an effective reference tool for groundwater management and the protection of lake ecosystems. The groundwater table constitutes a significant factor in sustaining the ecosystems of lakes in arid regions. To elucidate the mechanism by which variations in groundwater tables affect lake areas, this paper presents a case study of a typical groundwater-fed lake in China's Hetao Irrigation District. An analytical model correlating groundwater tables with lake areas was developed to simulate and predict the impact of changes in groundwater tables on lake areas. The findings indicate that the analytical model adeptly simulates the lake area dynamics of the groundwater-fed lake cluster (Taerhu lake cluster) from 1998 to 2018, achieving a Nash-Sutcliffe efficiency (NSE) value exceeding 0.6 and a root mean square error (RMSE) value below 0.1 square kilometers. Maintaining a groundwater depth at 1.73 m ensures the stability of the lake area; a decrease in groundwater depth to 1.93 m would result in a 79.5 % reduction in lake area. The model constructed in this study offers a crucial tool for the ecological protection of lakes and groundwater management in arid regions. [ABSTRACT FROM AUTHOR]

• A model to predict permeability in calcite precipitation porous media is developed. • Effects of solution velocity and concentration on precipitation are analyzed. • The main factors of calcite precipitation influencing permeability are quantified. The effects of the concentration and flow velocity of the solution on calcite precipitation process in porous media and its permeability were investigated with a combined experimental and modeling approach. In the column precipitation experiments, calcite precipitation was mainly distributed at the inlet of experimental column and quickly decreases along the flow direction, and precipitates completely wrapped the quartz sands at the inlet, and the gaps between the quartz sands were filled. The permeability coefficient of experimental column decreases quickly in the early stage and then decreases slowly. The calcite precipitates in the experimental column increased with the saturation index and gradually stretched along the flow direction with the flow velocity increase. The precipitates were distributed within 1.0 cm of the experimental column inlet. In the model, based on the classical Kozeny-Carman equation and the principle of series superposition, a coupled model of mineral precipitation and permeability coefficient in porous media was developed, the model was verified, and the parameter sensitivity was analyzed. It revealed that the mineral precipitation at the inlet interface of experimental column was the dominant factor determining the permeability coefficient of porous media. When considering solution conditions, the saturation indices SI and flow velocity V were the main factors affecting calcite precipitation and permeability coefficient in porous media. When the solution conditions were not considered, the quartz sand diameter d s , the length of quartz sand column L and porosity φ aiming at mineral precipitation had higher sensitivity, and the porosity ϕ aiming at permeability coefficient had higher sensitivity. [ABSTRACT FROM AUTHOR]

This paper focuses on the effects of chemical precipitation on the permeability of geotextile envelopes for a subsurface drainage system in arid areas by conducting precipitation experiments of the geotextile in static or flowing solution. The results show that the precipitation process is not significantly promoted or inhibited by the network structure of geotextile. The precipitates in the form of rhombus wrap around the fiber surface. The number of geotextile pores with the smaller diameters decreases significantly after precipitation experiments. As the increase of the area density of precipitates (Δ R), the variation of the pore area (Δ S) and the variation of permeability coefficient (Δ K) of the geotextile decrease rapidly at first and then slowly. The Δ K and Δ S VS Δ R data were best fitted with logarithmic trend line. This study provides a preliminary reference for quantifying the chemical clogging process of geotextile envelopes in arid areas. • The precipitation process is not significantly promoted or inhibited by the network structure of geotextile. • The precipitates wrap around the fiber surface. • The number of geotextile pores with the smaller diameters decreases significantly after precipitation experiments. [ABSTRACT FROM AUTHOR]

This study investigates the influence of clogging substances on pore characteristics and permeability of geotextile envelopes that were used for 3, 7 and 15 years in irrigated farmlands in Xinjiang region, which is arid and suffers from the soil salinity problem. Results show that the macropores (above 125 μm) of envelopes are evidently clogged, whereas the smaller pores less than 100 μm are still unblocked after operation. The permeability coefficients of geotextile envelopes after serving for 3 and 15 years are smaller than the minimum required permeability coefficients after clogging. The main chemical components of clogging substances in the geotextile envelope are silicon dioxide and calcium carbonate. Calcium carbonate content of the geotextile envelope is consistent with calcium carbonate content of soil. Chemical clogging susceptibility increases with the operation time of the subsurface drainage pipes. The ratio of O 90 size of envelope material over d 90 of soils (O 90 / d 90) and saturation index (SI) can be used to assess the susceptibility of physical and chemical clogging respectively. This study provides a preliminary reference for estimating the clogging susceptibility of geotextile envelopes in arid areas. [ABSTRACT FROM AUTHOR]

Understanding the patterns of greenhouse gas emissions and the changes in pollution load in terrestrial freshwater systems is crucial for accurately assessing the global carbon cycle and overall greenhouse gas emissions. However, current research often focuses on wetlands and rivers, with few studies on agricultural drainage ditches, which are an important part of the agricultural ecosystem. Investigating the greenhouse gas emission patterns and pollution load changes in agricultural drainage ditches can help accurately assess the greenhouse effect of agricultural systems and improve fertilization measures in farmlands. This study explored the effects of nitrogen input and aeration on the pollution load and greenhouse gas emission processes in paddy field drainage ditches. The results showed that aeration significantly reduced the concentration of ammonium nitrogen (NH4+) in the water, decreased the emissions of nitrous oxide (N2O) and methane (CH4), and slightly increased the emission of carbon dioxide (CO2), resulting in an overall reduction of the global warming potential (GWP) by 34.02%. Nitrogen input significantly increased the concentration of ammonium nitrogen in the water, slightly reduced the emissions of N2O and CH4, and increased the CO2 emissions by 46.60%, thereby increasing the GWP by 15.24%. The drainage ditches reduced the pollution load in both the water and sediment, with the overall GWP downstream being 9.34% lower than upstream. [ABSTRACT FROM AUTHOR]

Nitrogen is an indispensable and limiting element for plant and microbial growth. To investigate the combined effects of salinity and freezing–thawing (FT) processes on soil inorganic nitrogen (SIN) transformation in seasonally freezing salinized farmland, laboratory incubation experiments were conducted under five soil salt content (SSC) treatments (0.08%, 0.25%, 0.35%, 0.50%, and 0.70%), four FT temperature treatments (C (5 °C), FT (−5 + 5 °C), FT (−10 + 5 °C), and FT (−15 + 5 °C)), and two soil water content (SWC) treatments (40% and 80% of maximum water holding capacity (WHC)). Ammonium (NH4+-N) and nitrate (NO3−-N) nitrogen were monitored at the first, second, fifth, and eighth incubation days. The FT processes increased relative NH4+-N content by 13%, 39%, and 77% with the decreasing of freezing temperature from −5 °C to −15 °C compared with C (5 °C) treatments, respectively. FT (−5 + 5 °C) and FT (−15 + 5 °C) treatments decreased the relative NO3--N contents by 4% and 6% compared with C (5 °C) treatments, respectively. Under FT treatments, the increment of relative NH4+-N content was higher in low-SSC treatments and lower in high-SSC treatments. The relationship between relative NO3–-N content and SSC gradually changed from a decrease in C (5 °C) to an increase in FT (−15+5 °C) treatments. SWC decreased NH4+-N content in high-SSC and low-freezing temperature treatments (SSC × freezing temperature < −2.5%· °C), while NH4+-N increased in low-SSC and unfrozen treatments. The variations of SIN/Rmin (nitrogen mineralization rate) were mostly affected by NO3–-N/Rnit (net nitrification rate) and NH4+-N/Ra (net ammonification rate) in C (5 °C) and FT treatments, respectively. Overall, the results suggested that enhanced salinity inhibited the effects of freezing temperature on NH4+-N and NO3−-N formation, respectively. The increase in SWC weakened the NH4+-N formation induced by the decrease in freezing temperature, and this function increased with the increase in salinity. [ABSTRACT FROM AUTHOR]

Rice is distributed worldwide; thus, quantitative analyses of water and heat fluxes between the land and air in paddy fields are vital for understanding basin-scale water cycles. In this study, eddy covariance and meteorological gradient systems on a 20-meter flux tower in the Jianghan Plain, Yangtze River Basin, China, were used to measure turbulent and meteorological parameters in paddy fields in 2021. Three micrometeorological methods, namely the eddy covariance (EC), Bowen Ratio-Energy Balance (BREB), and aerodynamic (AERO) methods, were used to calculate the latent heat flux (LE) and sensible heat flux (H); BREB and AERO are collectively referred to as gradient methods. The effects of measurement heights, growth stage, and weather conditions on the consistency among them were analyzed. The difference in meteorological measurement heights affected the results of gradient methods. Among the five height combinations, the error in the 2 and 4 m combination was the smallest, and the coefficients of determination of LE EC –LE BREB/AERO and H EC –H BREB/AERO reached 0.96 and 0.84, respectively. The stratification of the near-surface layer was formed due to the heterogeneous underlying surface of the experimental area, and the instrument needed to be installed within the range between roughness layer and new equilibrium layer. The height difference of gradient methods can be amplified within this range to avoid the influence of instrument resolution. The difference among methods was affected by growth stage, and weather conditions (sunny, cloudy, rainy days and different wind speed class). Both factors influenced atmospheric stability, and the error was the maximum in neutral stratification. This study provides a reference for the selection of flux calculation methods and error analyses for paddy fields in humid areas. • We compared eddy covariance, Bowen Ratio-Energy Balance, and aerodynamic methods. • Increase of measurement height difference did not reduce the error of gradient methods in heterogeneous source area. • Rice growth stage and weather affected the applicability of the methods. [ABSTRACT FROM AUTHOR]

Water and nitrogen losses from farmland during the snowmelt process play a vital role in water and nitrogen management in cold regions. To explore the mechanisms and factors contributing to water and nitrogen loss from different sloping farmlands during the snowmelt period, field experiments were conducted under two slope treatments (8° and 15°), two soil water content (SWC) treatments, and two snow water equivalent (SWE) (5 mm and 10 mm) treatments in a seasonal freezing agricultural watershed of Northeast China. The results showed that during the snowmelt process, SWE was the most important factor affecting water and nitrogen production through the surface and total runoff of the sloping farmland, followed by the slope. The water and nitrogen yield in the high snow (HS) treatments ranged from 1.76 to 8.15 and 1.65 to 12.62 times higher than those in the low snow (LS) treatments. The generation of nitrogen was advanced compared with that of water induced by the preferential production of nitrogen. A higher slope promoted this preferential production function of nitrogen. Enhanced infiltration combined with the preferential yield of nitrogen resulted in a greatly decreased yield of water and nitrogen in the gentle slope and LS (GS_LS) treatments. These findings are valuable for accurately describing the water and nitrogen cycling in seasonally freezing sloping farmland. [ABSTRACT FROM AUTHOR]

Streptococcus suis (S.suis)is an important zoonotic pathogen in pigs and human. Bacterial ghosts (BGs) which are empty envelopes were used recently as efficient delivery system in vaccine development. In this study, S.suis ghosts were prepared and protective efficacy was evaluated in mice. Sodium hydroxide was used to prepare S.suis ghosts which were visualized under scanning electron microscopy. The optimum concentration of is Sodium hydroxide 6 mg/mL for ghosts formed. To investigate the S.suis ghosts as a candidate vaccine, the 50 BALB/c mice were randomly divided into three groups: Group A (control group), group B (subcutaneous injection of inactivated S.suis 2), group C (subcutaneous injection of inactivated S.suis 9), group D (subcutaneous injection of S.suis 2 ghosts), group E (subcutaneous injection of S.suis 9 ghosts). Serum were collected from five groups on the day of 7, 14, 21 and 28 after the first immunization for potency assay. Indirect ELISA results showed that antibody titer of blood serum of mice from group S.suis2 ghosts and group S.suis 9 ghosts were significantly higher than blank group(P < 0.01), but were approximate to the conventional inactivated vaccine group SS2. In comparison with the conventional inactivated vaccine, S.suis ghosts as candidate vaccine strategy showed the excellent immunogenicity and provided protection against S.suis challenge in mice model. • A novel method to prepare Streptococcus suis ghost vaccine by treating bacteria with 6 mg/mL NaOH. • The antibody titer of blood serum shows that, for SS9, ghost vaccine group has higher antibody titer than the inactivated vaccine group in mice modle. • S.suis ghosts vaccine showed the excellent immunogenicity and provided protection against S.suis challenge in mice model. [ABSTRACT FROM AUTHOR]