Impact of water on microbial nitrogen transformation in soil causing atmospheric nitrous acid (HONO) and nitric oxide (NO) emissions

<p>Biological soil crusts (referred to as biocrusts hereafter) represent communities comprising a fraction of photoautotrophs (photoautotrophic bacteria, algae, lichens, and bryophytes) growing together with heterotrophic organisms like bacteria, archaea, and fungi. The organisms are all poikilohydric, which means they are only active if water is present. They occur frequently in dryland ecosystems, where vascular vegetation is sparse or even absent, or wherever dry microclimatic conditions occur. Biocrusts fulfill a wide range of important ecosystem services, as they are relevant in regional water cycling, soil stabilization, plant germination and growth, and also global carbon (C) and nitrogen (N) cycling. According to initial estimates, they are supposed to globally emit ~1.7 Tg of reactive nitrogen (N<sub>r</sub>) per year, corresponding to ~20% of the global nitrogen oxide emissions from soils under natural vegetation. The underlying mechanisms of N<sub>r</sub> emissions in biocrusts, however, are not well understood and are still a focus of ongoing research.</p><p>This study aimed to explore the functional roles of microbial organisms in N<sub>r</sub> emissions along a full wetting and drying cycle. Therefore, N<sub>r</sub> fluxes were analyzed at three key hydration stages, i.e., immediately after wetting (T1), prior to (T2), and after maximum N<sub>r</sub> fluxes (T3). At all three stages, the transcriptome (microarray analysis) and proteome (metaproteomics) were profiled to highlight changes in biological processes linked to nitrogen transformation. Additionally, at T1 and T2, the bacterial, archaeal, and nitrite-oxidizing bacterial communities were quantified utilizing catalyzed reporter deposition fluorescence in situ hybridization (CARD-FISH). Soil nitrite and nitrate contents of both intact and sterilized biocrust samples were analyzed before and after a measurement cycle.</p><p>Our results showed a fast recovery of microbial activity minutes after wetting of the biocrusts (T1) by means of mRNA expression of nitrogen transformative genes. Transcripts of genes encoding all major N-cycling processes that are already known from soil were detected. The number of N-transforming species and processes detected by the microarray analysis significantly increased from T1 to T2 to T3. The most prominent nitrogen transforming microorganisms belonged to Alpha- and Gammaproteobacteria. The CARD-FISH data showed a significant increase in archaeal numbers from T1 to T2, which is in line with an observed increase in N<sub>r</sub> emissions. The majority of identified proteins were related to ATP synthesis, photosynthesis, protein biosynthesis and stress response, whereas proteins assigned to N transformation could not be observed. Soil N-content analysis showed a significant increase of nitrite in living biocrusts after a wetting and drying cycle, which was likely promoted by nitrifying Archaea and Proteobacteria, but also by various denitrifying bacteria, as suggested by microarray analysis and CARD-FISH. This indicates that N<sub>r</sub> fluxes largely originated from nitrite formed by various aerobic and anaerobic biotic processes, likely occurring simultaneously in different microhabitats within the biocrust.</p>

Enhanced Removal of Contaminants of Emerging Concern through Hydraulic Adjustments in Soil Aquifer Treatment

Water reclamation through the use of soil aquifer treatment (SAT) is a sustainable water management technique with high potential for application in many regions worldwide. However, the fate of contaminants of emerging concern (CECs) during the infiltration of treated wastewater during SAT is still a matter of research. This study investigates the removal capacity of 27 CECs during SAT by means of infiltration experiments into a 6 m soil column. Additionally, the influence of the hydraulic operation of SAT systems on the removal of CECs is investigated by changing the wetting and drying cycle lengths. Sixteen out of 27 CECs are efficiently removed during SAT under various operational modes, e.g., bezafibrate, diclofenac and valsartan. For six substances (4-methylbenzotriazole, amidotrizoic acid, benzotriazole, candesartan, hydrochlorothiazide and sulfamethoxazole), removal increased with longer drying times. Removal of amidotrizoic acid and benzotriazole increased by 85% when the drying cycle was changed from 100 to 444 min. For candesartan and hydrochlorothiazide, removal improved by 35%, and for 4-methylbenzotriazole and sulfamethoxazole, by 57% and 39%, respectively. Thus, enhanced aeration of the vadose soil zone through prolonged drying times can be a suitable technique to increase the removal of CECs during SAT.

Coupled Effect of Wet-Dry Cycles and Rainfall on Highway Slope Made of Yazoo Clay

Expansive Yazoo clay soil is susceptible to volumetric deformation and is dominant in central Mississippi and other neighboring southern states of the United States. Recurring shrink-swell behavior causes a significant problem to infrastructures in the area. Although Yazoo clay causes a significant problem in the deep southern states, limited study has been conducted on the behavior of Yazoo clay, especially in the presence of rainfall. The objective of this current study is to investigate the coupled effect of changes in void ratio due to wet-dry cycles and rainfall on the stability of highway slopes made of Yazoo clay. The finite element method in Plaxis 2D by Bentley System (https://www.plaxis.com/) has been utilized to investigate the coupled effect of changes in mechanical properties and rainfall using flow-deformation and stability analysis. Reconstituted expansive clay soil samples were used for the laboratory experiment. The reconstituted Yazoo clay samples were subjected to 3, 5, and 7 wetting and drying cycles in an enclosed chamber for a 24-h period. The axial deformation of the samples and the change in void ratios at each number of the cycle was closely monitored. The strength change at each wet and dry cycle was also investigated and used for slope stability analysis in the presence of rainfall. The test results indicate that the void ratio increases with the increasing number of wet-dry cycles. A continuous increment in void ratios from 0.99 in an undisturbed state with no wet-dry cycle to 1.49 at the 7th wet-dry cycle, indicating a 48.9% increase, as the wetting and drying cycle increases was recorded; in turn, decreasing the cohesion of the soil by 77%. The factor of safety considering the effect of two total rainfall periods of Rv = 126.2 mm (2 h) and Rv = 271.7 mm (3 days) reduced from 1.7 to 1.2 and 1.68 to 1.02, considering the effect of the 7th wet-dry cycle at the topsoil. The changes in the void ratio due to the wetting and drying cycle of Yazoo clay soil reduces the shear strength to a fully softened condition, increasing the possibility of slope failure. This condition further worsens in the presence of a perched water condition due to the infiltration of rain water.

Study of Wet-Drying Cycles on Sisal, Jute and White Curaua Fibers on the Resistance Parameters of Cement-Based Composites

This study presents the results of the mechanical characterization of cement composites reinforced with short fibers of jute, sisal and curauá. Tests of direct tension in flexion and traction, after wetting and drying cycle (5 cycles) to determine the first crack were performed to determine the first crack, the tension and post-peak toughness and strengh of the composites. To ensure the the composite durability, the ordinary Portland cement matrix was modified by adding metakaolin, to consume the calcium hydroxide generated during Portland cement hydration. The composites were produced using short fibers of jute, sisal and curauá (50 mm) at levels of 2%, 4% and 6% of sisal and white curauá, and 3%, 6% and 9% to jute. The fibers of jute and white curauá employed in this study came from the Brazilian Amazon, while the sisal came from the Brazilian Northeast.This fibers have great economic importance in the producing region. Composites with high toughness, strength and multiple cracking processes under bending load were obtained when volume fractions equal to 3% of jute were used as reinforcement and when 6% of sisal and 4% of white curauá were used as reinforcement.

Experimental Test of Chloride Penetration in Reinforced Concrete Subjected to Wetting and Drying Cycle

Chloride ingress is one of the major causes of durability problems in reinforced concrete structures. This research focused to investigate the chloride penetration process through the concrete subjected to wetting and drying cycle. This research used 150 x 150 mm normal concrete prism sample with a 40 mm concrete cover. Three wetting and drying configurations used in this study to investigate the effect of wetting and drying period to the chloride penetration. The result indicated that the chloride concentration and penetration depth were highly influenced by the duration of wetting and drying. Based on the experimental result, concrete exposed to 5 hours drying and 3 hours wetting has the highest chloride concentration compared with the sample exposed to other wetting and drying configuration.

Different Salt Solution on the Deterioration of Marine Engineering Concrete under the Action of Chemical-Mechanical Coupling

The loaded specimens were put in fresh water, 3.5%NaCl solution, 5.0%Na2SO4 solution, and simulated sea water with different concentrations respectively, and then the damage process under wetting and drying cycle was investigated. The ultrasonic non-metal testing technology, X-CT scanned image, free chloride and sulfate ions chemical titration were used to investigate the degradation of the marine concrete under the coupling effect of Chemistry and Mechanics. The effect of solutions, wetting and drying cycle and bending stress to the durability of marine concrete were further studied. The results indicate that different salt solution affects marine concrete at different degrees: sulfate salt is more corrosive than chloride salt, simulated seawater is similar to 5.0%Na2SO4 solution, while five-time simulated seawater is the most corrosive; wetting and drying cycle remarkably accelerates the penetration of corrosive ions, which results in the concrete damage, compared to the corrosive environment, concrete is damaged violently under the coupling effect of Chemistry-Mechanics and tensile stress has greater influence on the damage.

Removal of Pharmaceuticals and Personal Care Products during Water Recycling: Microbial Community Structure and Effects of Substrate Concentration

ABSTRACTMany pharmaceuticals and personal care products (PPCPs) have been shown to be biotransformed in water treatment systems. However, little research exists on the effect of initial PPCP concentration on PPCP biotransformation or on the microbial communities treating impacted water. In this study, biological PPCP removal at various concentrations was assessed using laboratory columns inoculated with wastewater treatment plant effluent. Pyrosequencing was used to examine microbial communities in the columns and in soil from a soil aquifer treatment (SAT; a method of water treatment prior to reuse) site. Laboratory columns were supplied with different concentrations (0.25, 10, 100, or 1,000 μg liter−1) of each of 15 PPCPs. Five PPCPs (4-isopropyl-3-methylphenol [biosol],p-chloro-m-xylenol, gemfibrozil, ketoprofen, and phenytoin) were not removed at any tested concentrations. Two PPCPs (naproxen and triclosan) exhibited removals independent of PPCP concentration. PPCP removal efficiencies were dependent on initial concentrations for biphenylol,p-chloro-m-cresol, chlorophene, diclofenac, 5-fluorouracil, ibuprofen, and valproic acid, showing that PPCP concentration can affect biotransformation. Biofilms from sand samples collected from the 0.25- and 10-μg liter−1PPCP columns were pyrosequenced along with SAT soil samples collected on three consecutive days of a wetting and drying cycle to enable comparison of these two communities exposed to PPCPs. SAT communities were similar to column communities in taxonomy and phylotype composition, and both were found to contain close relatives of known PPCP degraders. The efficiency of biological removal of PPCPs was found to be dependent on the concentration at which the contamination occurs for some, but not all, PPCPs.