Nitrogen Fluxes Research Articles

Evaluating MONICA's capability to simulate water, carbon and nitrogen fluxes in a wet grassland at contrasting water tables

Wet grasslands, which are vital for water and nutrient regulation, are characterised by distinct water, carbon (C) and nitrogen (N) dynamics, and their interactions. Due to their shallow groundwater table, wet grasslands promote a strong interconnection between diverse vegetation and soil water. Researchers have investigated how wet grasslands respond to environmental changes, using various simulation models to understand how these sites contribute to water, C and N dynamics. However, a comprehensive, simultaneous study of all three of these dynamics is still lacking. This study makes use of a grassland lysimeter study with differently managed groundwater levels and employs the process-based MOdel for NItrogen and Carbon dynamics in Agroecosystems (MONICA) to simulate these dynamics. By using SPOTPY (Statistical Parameter Optimization Tool) to optimise the relevant parameters, we find that MONICA performs well in simulating vegetation growth (aboveground biomass), and elements of the water (evapotranspiration), C (gross primary productivity, ecosystem respiration) and N (N in aboveground biomass, nitrate in soil solution, Nitrous oxide emissions) balance, with Willmott's Refined Index of Agreement always larger than 0.35. This level of accuracy demonstrates that MONICA is ready to be applied for scenario simulations of groundwater management and climate change to evaluate their impact on greenhouse gas emissions and long-term carbon storage, as well as water and nitrogen losses in wet grasslands.

Effect of N2 reactive gas flow rate on the structural, optical and wettability properties of silicon carbon oxynitride thin films

In the current research, the silicon carbon oxynitride (SiCON) thin film was deposited on the silicon (Si) substrate by radio frequency (RF) reactive magnetron sputtering method. To comprehensively assess the impact of nitrogen flux rate on thin film characteristics, a suite of advanced analytical methods was utilized. The GIXRD analysis confirmed that the SiCON thin film is amorphous in structure. Additionally, Raman spectroscopy detected no graphite nanocrystals within the film. Ellipsometry measurements further showed that the refractive index of the thin films rises with increased nitrogen flux in the reactive gas, indicating a direct correlation between nitrogen concentration during deposition and optical properties. Based on the designs made with McLeod's software, the amount of reflection can be reduced up to 5.7 % at the wavelength of 4 μm and up to 8.5 % in the wavelength range of 3–5 μm for an optimal thickness thin film. The atomic force microscopy (AFM) examination revealed that the surface roughness of the thin films decreases as the nitrogen flux in the reactive gas mixture increases. Additionally, measurements of the water contact angle (WCA) indicated that the SiCON thin films exhibit a hydrophilic state.

Screening Cover Crops for Utilization in Irrigated Vineyards: A Greenhouse Study on Species' Nitrogen Uptake and Carbon Sequestration Potential.

This study examines the potential of 23 plant species, comprising 10 legumes, 9 grasses, and 4 forbs, as cover crops to enhance carbon (C) sequestration and soil nitrogen (N) in vineyards. After a 120-day evaluation period, cover crop biomass was incorporated into the soil, and grapevine seedlings were planted in its place. Among the established cover crops, the C input potential ranged from 0.267 to 1.69 Mg ha-1, and the N input potential ranged from 12.3 to 114 kg ha-1. Legume species exhibited up to threefold greater shoot dry weight (SDW) compared to grass species. Ladino white clover, Dutch white clover, and Clover blend were superior in SDW, total dry weight (TDW), total C content, and total N content. Legumes exhibited slightly higher root dry weight (RDW) than grasses, with the exception of Fall rye leading at 15 g pot-1, followed by Ladino white clover and Dutch white clover at an average of 12 g pot-1. Legumes, particularly clover blend and Alsike clover, displayed high shoot N concentration at an average of 2.95%. Root N concentration in Legumes (Fabaceae) were significantly higher at 1.82% compared to other plant families at 0.89%, while their root C/N ratio was lower at 18.3, contrasting with others at 27.7, resulting in a faster turnover. Biomass production exhibited a negative relationship (R2 = 0.51) with soil residual NO3-. Fall rye, Winfred brassica, and buckwheat had the highest N utilization efficiency (NUtE) values (ava. 121 g g-1). Alsike clover, Ladino white clover, and clover blend showed the highest N uptake efficiency (NUpE) values (ava. 75%). The Readily Available N (RAN) Reliance Index (RANRI) is introduced as a novel indicator for quantifying the extent to which a plant relies on RAN for its total N requirement. The RANRI value represents the percentage of the plant's total N sourced from RAN, ranging from 11% for legumes to 86% for grasses. This implies a substantial influx of nitrogen through a pathway independent of RAN in legumes. Grape shoot N concentration positively correlated with soil NO3- (R2 = 0.31) and cover crop C/N ratio (R2 = 0.17) but negatively correlated with cover crop TDW (R2 = 0.31). This study highlights legume plants as more effective in C and N assimilation during establishment but cautions about potential soil mineral N depletion before reaching their full biological N fixation capacity.

Different effects of seasonal impoundment and land use change on microbiome in a tributary sediment of the three gorgers reservoir

Anthropogenic activities significantly impact river ecosystem nutrient fluxes and microbial metabolism. Here, we examined the seasonal and spatial variation of sediments physicochemical parameters and the associated microbiome in the Pengxi river, a representative tributary of Three Gorges Reservoir, in response to seasonal impoundment and land use change by human activities. Results revealed that seasonal impoundment and land use change enhanced total organic carbon (TOC), total nitrogen (TN) and ammonium nitrogen (NH4+-N) concentration in the sediment, but have different effects on sediment microbiome. Sediment microbiota showed higher similarity during the seasonal high-water level (HWL) in consecutive two years. The abundant phyla Acidobacteria, Gemmatimonadetes, Cyanobacteria, Actinobacteria and Planctomycetes significantly increased as water level increased. Along the changes in bacterial taxa, we also observed changes in predicted carbon fixation functions and nitrogen-related functions, including the significantly higher levels of Calvin cycle, 4HB/3HP cycle, 3HP cycle and assimilatory nitrate reduction, while significantly lower level of denitrification. Though land use change significantly increased TOC, TN and NH4+-N concentration, its effects on spatial variation of bacterial community composition and predicted functions was not significant. The finding indicates that TGR hydrologic changes and land use change have different influences on the carbon and nitrogen fluxes and their associated microbiome in TGR sediments. A focus of future research will be on assessing on carbon and nitrogen flux balance and the associated carbon and nitrogen microbial cycling in TGR sediment.

Assessment of soil-groundwater nitrogen cycling processes in the agricultural region through flux model, stable isotope

The nitrogen cycle in the soil-groundwater system of agricultural land is a crucial process within the global nitrogen cycle. Human activities have significantly intensified this cycling process in agricultural fields, consequently leading to substantial accumulation of nitrogen in the soil-groundwater system and giving rise to numerous ecological health issues. Quantitative assessment of soil-groundwater nitrogen cycling processes can facilitate the optimization of nitrogen management strategies in agricultural fields and the prevention and management of groundwater nitrogen pollution. However, accurately quantifying the intricate soil-groundwater nitrogen cycling dynamics in agro-irrigation areas characterized by diverse nitrogen sources and complex hydrogeological conditions poses a significant challenge. The Songhua River Basin in the Sanjiang Plain was selected as the study area for this investigation. We utilized the INCA-N model to simulate annual nitrogen fluxes in the soil-groundwater system of an agricultural watershed, and employed stable isotope and water chemistry methods to identify sources of groundwater nitrogen contamination and transformation processes. Ultimately, we conducted a comprehensive assessment of nitrogen cycling within the soil-groundwater system of the agricultural watershed. The findings revealed that atmospheric deposition, nitrogen fixation, and fertilization constituted the primary mechanisms of soil nitrogen input. Plant uptake, riverine nitrogen transport, and denitrification were identified as the three principal processes responsible for soil-groundwater nitrogen export. The results obtained from the MIXSIAR model demonstrate a substantial contribution of nitrogen fertiliser and soil nitrogen to groundwater nitrate, followed by faeces and sewage. Additionally, the annual input fluxes of nitrogen simulated by INCA-N reveal that fertiliser application is the primary contributor, which aligns to some extent with the findings of the MIXSIAR model. Soil nitrogen can serve as a relatively stable source of groundwater nitrate, while anthropogenic activities such as fertilizer application, manure deposition, and sewage discharge are likely to be the primary drivers of groundwater nitrate pollution. By quantifying the N input and output fluxes, it was determined that approximately 58% of the total annual nitrogen input has the potential to accumulate within the soil-groundwater system. The effective utilization of legacy nitrogen can contribute to the reduction of soil-groundwater nitrogen fluxes, while maintaining crop yields and mitigating greenhouse gas emissions. This study aims to optimize nitrogen management practices in agricultural areas and provide valuable insights for water conservation strategies.

Lateral redox variability in ca. 1.9 Ga marine environments indicated by organic carbon and nitrogen isotope compositions.

The stepwise oxygenation of Earth's surficial environment is thought to have shaped the evolutionary history of life. Microfossil records and molecular clocks suggest eukaryotes appeared during the Paleoproterozoic, perhaps shortly after the Great Oxidation Episode at ca. 2.43 Ga. The mildly oxygenated atmosphere and surface oceans likely contributed to the early evolution of eukaryotes. However, the principal trigger for the eukaryote appearance and a potential factor for their delayed expansion (i.e., intermediate ocean redox conditions until the Neoproterozoic) remain poorly understood, largely owing to a lack of constraints on marine and terrestrial nutrient cycling. Here, we analyzed redox-sensitive element contents and organic carbon and nitrogen isotope compositions of relatively low metamorphic-grade (greenschist facies) black shales preserved in the Flin Flon Belt of central Canada to examine open-marine redox conditions and biological activity around the ca. 1.9 Ga Flin Flon oceanic island arc. The black shale samples were collected from the Reed Lake area in the eastern part of the Flin Flon Belt, and the depositional site was likely distal from the Archean cratons. The black shales have low Al/Ti ratios and are slightly depleted in light rare-earth elements relative to the post-Archean average shale, which is consistent with a limited contribution from felsic igneous rocks in Archean upper continental crust. Redox conditions have likely varied between suboxic and euxinic at the depositional site of the studied section, as suggested by variable U/Al and Mo/Al ratios. Organic carbon and nitrogen isotope compositions of the black shales are approximately -23‰ and +13.7‰, respectively, and these values are systematically higher than those of broadly coeval continental margin deposits (approximately -30‰ for δ13Corg and +5‰ for δ15Nbulk). These elevated values are indicative of high productivity that led to enhanced denitrification (i.e., a high denitrification rate relative to nitrogen influx at the depositional site). Similar geochemical patterns have also been observed in the modern Peruvian oxygen minimum zone where dissolved nitrogen compounds are actively lost from the reservoir via denitrification and anammox, but the large nitrate reservoir of the deep ocean prevents exhaustion of the surface nitrate pool. Nitrogen must have been widely bioavailable in the ca. 1.9 Ga oceans, and its supply to upwelling zones must have supported habitable environments for eukaryotes, even in the middle of oceans around island arcs.

Carbon, Nitrogen, and Phosphorus Fluxes in Sixty Tropical Brazilian Rivers: Current Status, Stoichiometry and Trends

Carbon, Nitrogen, and Phosphorus Fluxes in Sixty Tropical Brazilian Rivers: Current Status, Stoichiometry and Trends

Contribution of vibrational excited molecular nitrogen to ammonia synthesis using an atmospheric-pressure plasma jet

The contribution of atomic nitrogen is fairly possible in plasma-assisted catalytic synthesis of ammonia since it has high adsorption probabilities on solid surfaces. On the other hand, recently, the contribution of vibrational excited molecular nitrogen to ammonia synthesis has been discussed. In this work, we compared the fluxes of atomic nitrogen and vibrational excited molecular nitrogen with the rate of plasma-assisted ammonia synthesis. We employed an atmospheric-pressure nitrogen plasma jet, and the spatial afterglow of the plasma jet and a hydrogen flow irradiated the surface of a ruthenium catalyst. The fluxes of atomic nitrogen and vibrational excited molecular nitrogen were measured by two-photon absorption laser-induced fluorescence spectroscopy and laser Raman scattering, respectively. The synthesis rate of ammonia had a positive correlation with the flux of vibrational excited molecular nitrogen, while the variation of the synthesis rate with the gas flow rate was opposite to the flux of atomic nitrogen. The experimental results indicate the contribution of vibrational excited molecular nitrogen to the synthesis of ammonia using the atmospheric-pressure plasma, where the flux of vibrational excited molecular nitrogen is more than four orders of magnitude higher than that of atomic nitrogen.

Toxin production and transcriptomic response to nitrate concentrations in the toxic dinoflagellate Alexandrium tamarense

The bloom-forming dinoflagellate Alexandrium tamarense is one of the most important producers of paralytic shellfish poisoning toxins. Annually recurrent blooms of this dinoflagellate species is associated with the incremental nitrogen influx, especially excessive nitrate input. However, limited studies have been conducted on the toxin production and underlying molecular regulation mechanisms of A. tamarense under various nitrate (N) conditions. Therefore, toxin production and transcriptomic responses of this species were investigated. The toxin profile of A. tamarense was consistently dominated by the C2-toxins, and the cellular toxicity increased with N concentrations peaking at 9.23 ± 0.03 fmol/cell in the 883 μM N-added group. Under lower N conditions, expressions of two STX-core genes, sxtA and sxtG, were significantly down-regulated, suggesting that N regulated sxt expression and triggered responses related to toxin biosynthesis. Results of this study provided valuable insights into the ecophysiology of A. tamarense, enhancing our understanding of the occurrence of toxification events in natural environments.

Experimental Study of Influence of the Gas Flux on Urotropine Gasification in the Low-Temperature Gas Generator

The experimental study was carried out to investigate the gasification of urotropine (hexamethylenetetramine) in a low-temperature solid fuel gas generator under varying inlet gas flows. Nitrogen was applied as the filter gas. The filter gas flow was varied from 0.6 to 1.4 L/s with a step of 0.2 L/s. The inlet gas's initial temperature was equal to 910 K. It was shown that with an increase in the nitrogen flow, the fuel gasification time decreased. Increasing the flux of inlet nitrogen from 0.6 to 1.4 L/s results in an increase in the average urotropine gasification mass rate from 0.63 to 1.61 g/s. When the initial nitrogen flow is raised, the rate of fuel gasification increases almost linearly. Studies have demonstrated that the proportion of mass flows between urotropine gasification products and nitrogen remains constant regardless of the incoming gas flow. The mass flow ratio remains steady at approximately 0.9 g/g when the incoming gas flow is altered. It has been shown that the gaseous products of urotropine gasification consist of nitrogen with a small amount of hydrogen and hydrocarbons. The content of simple gaseous products does not exceed 4% vol.

Contaminant distribution and migration in roofing rainwater: Implications for sustainable utilization and pollution control

Understanding contaminant distribution and migration characteristics is crucial for the sustainable utilization of roofing rainwater resources, given the impacts of rapid urbanization and climate change. This study undertook the monitoring of 15 typical rainfall events in Xi'an, China, to analyze the distribution and migration of organic matter, nitrogen, and typical emerging contaminants (ECs) during wet deposition (WD), roofing erosion, and roof runoff (RR). The results indicate the concentration levels of organic matter, and nitrogen as follows: COD, 22.69 ± 1.52–132.83 ± 3.43 mg/L; TOC, 3.45 ± 0.22–27.64 ± 1.12 mg/L; TON, 4.99 ± 0.28–12.38 ± 1.55 mg/L; DTN, 4.54 ± 0.10–11.87 ± 0.83 mg/L; PTN, 1.32 ± 0.14–6.57 ± 0.40 mg/L. Additionally, specific emerging contaminants were found at the following concentrations: endocrine disruptors, 19.65–178.85 ng/L; pharmaceuticals, 17.78–67.45 ng/L; bactericides, 4.42–119.45 ng/L; personal care products, 7.79–44.10 ng/L; pesticides, 5.50–34.85 ng/L; flame retardants, 1.80–20.90 ng/L. The nitrogen pollution level surpasses that of road runoff and is predominantly attributed to WD. The detection rate of ECs is notably high, with Bisphenol A (BPA) being detected in up to 100 % of samples. Significant differences in pollutant distribution were identified between the initial and late stages of rainfall (P < 0.05). Weak first flush effects (1 < MFF20 < 2) were observed for pollutants present in the runoff of over 50 % of the rainfall events monitored. Furthermore, by controlling the initial 20 % of WD, an effective decrease in nitrogen flux below the threshold level was observed. Consequently, four modes of contaminant migration pathways and a novel strategy have been developed to guide the pollution control and sustainable utilization of roofing rainwater.

The global nitrogen regulator GlnR is a direct transcriptional repressor of the key gluconeogenic gene pckA in actinomycetes.

The GlnR regulator of actinomycetes controls nitrogen metabolism genes and many other genes involved in carbon, phosphate, and secondary metabolisms. Currently, the known GlnR-regulated genes in carbon metabolism are involved in the transport of carbon sources, the assimilation of short-chain fatty acid, and the 2-methylcitrate cycle, although little is known about the relationship between GlnR and the TCA cycle and gluconeogenesis. Here, based on the biochemical and genetic results, we identified GlnR as a direct transcriptional repressor of pckA, the gene that encodes phosphoenolpyruvate carboxykinase, a key enzyme for gluconeogenesis, thus highlighting that GlnR plays a central and complex role for dynamic orchestration of cellular carbon, nitrogen, and phosphate fluxes and bioactive secondary metabolites in actinomycetes to adapt to changing surroundings.

Dynamics of nitrogen genes in intertidal sediments of Darwin Harbour and their connection to N-biogeochemistry

Microbial mediated nitrogen (N) transformation is subject to multiple controlling factors such as prevailing physical and chemical conditions, and little is known about these processes in sediments of wet-dry tropical macrotidal systems such as Darwin Harbour in North Australia. To understand key transformations, we assessed the association between the relative abundance of nitrogen cycling genes with trophic status, sediment partition and benthic nitrogen fluxes in Darwin Harbour. We analysed nitrogen cycling gene abundance using a functional gene microarray and quantitative PCRs targeting the denitrification gene (nosZ) and archaeal ammonia oxidation (AOA.1). We found a significant negative correlation between archaeal ammonia oxidation and silicate flux (P = 0.004), an indicator for diatom and benthic microalgal activity. It is suggested that the degradation of the diatomaceous organic matter generates localised anoxic conditions and inhibition of nitrification. Abundance of the nosZ gene was negatively correlated with nutrient load. The lowest nosZ gene levels were in hyper-eutrophic tidal creeks with anoxic conditions and increased levels of sulphide limiting the coupling of nitrification-denitrification (P = 0.016). Significantly higher levels of nosZ genes were measured in the surface (top 2 cm) compared to bulk sediment (top 10 cm) and there was a positive association with di-nitrogen flux (N2) in surface (P = 0.024) but not bulk sediment. This suggests that denitrifiers are most active in surficial sediment at the sediment-water interface. Elevated levels of nosZ genes also occurred in the sediments of tidal creek mouths and mudflats with these depositional zones combining the diffuse and seaward supply of nitrogen and carbon supporting denitrifiers. N-cycle molecular assays using surface sediments show promise as a rapid monitoring technique for impact assessment and measuring ecosystem function. This is particularly pertinent for tropical macrotidal systems where systematic monitoring is sparse and in many cases challenged by climatic extremes and remoteness.

Enhancing watershed management through adaptive source apportionment under a changing environment

Effective watershed management hinges on understanding water sources and pollution origins. In the Hangbu Watershed of Chaohu Lake, China, we analyze pollution source patterns and propose an adaptive strategy. This adaptive strategy is defined as a flexible and dynamic approach that adjusts management practices and policies in response to evolving environmental conditions and emerging data on pollution sources. The analysis includes examining the trends, periodicity, and mutagenicity of pollution sources. The results demonstrated substantial variations in sources, with nitrogen and phosphorus. The adaptive approach enables prioritizing crucial pollution sources, with farmland identified as a significant contributor under varying conditions. Specific pollution sources with growth trends and control robustness have been recognized as vital contributors, even though their contributions to the nitrogen and phosphorus flux at the watershed outlets may not be the most prominent. The results of this study could guide the sustainable management of watersheds.

Grazing strategies for reducing contaminant losses in surface runoff from winter forage crop fields located in hill country and grazed by sheep

ABSTRACT A paired catchment study approach was used to quantify fluxes of Nitrogen (N), Phosphorus (P), sediment and Escherichia coli (E. coli) in surface runoff from fields where sheep were wintered on swede (Brassica napus) and kale (Brassica oleracea) crops. The effectiveness of a strategic grazing approach that protected critical source areas (CSAs) was examined to determine if these fluxes could be reduced. Averaged over two years, estimated fluxes of N, P and sediment in surface runoff recorded in winter and early spring (June-September) were up to 0.64, 0.22 and 51 kg ha−1, respectively, and up to 2 × 1011 MPN ha−1 for E. coli. With the exception of E. coli, these fluxes were low compared to those reported in other studies and largely attributed to the low amounts of surface runoff recorded. This, in turn, can be explained by relatively benign weather conditions recorded during the study period and the relatively light grazing pressures imposed by sheep. Compared to standard grazing practice, protection of CSAs reduced N, P, sediment, and E. coli fluxes by 38%, 48%, 55% and 63%, respectively. These reductions can largely be attributed to lower concentrations of contaminants in surface runoff when the CSA was protected.

Fluxes of nitrogen and phosphorus in fouling communities on artificial offshore structures

The number of offshore artificial structures in the North Sea is continuously increasing. Apart from the structures that have been added to the marine environment accidentally (e.g., shipwrecks), structures are also deliberately developed to meet the increasing needs for renewable energy. These structures provide habitat for fouling organisms. The fouling communities vary in abundance and composition based on location, depth, and structure age. Most fouling species filter particles from the water column, changing phytoplankton production and affecting larval settlement success, while releasing ammonium that can fuel phytoplankton growth as well as (pseudo)faeces that enriches the seabed, changing local biogeochemical cycles.Our study used in-situ incubation chambers to investigate oxygen, nitrogen, and phosphate fluxes associated with fouling organisms to improve understanding of these changes in biogeochemical cycles. Divers used incubation chambers (domes) on shipwrecks in the southern North Sea where over 55 years mature fouling communities have established. A series of water samples was collected from each dome during deployment to measure the change in concentration of ammonium, nitrite, nitrate, and phosphate. All fauna enclosed in the domes was collected after each measurement for further analysis.The full macrofauna dataset contained 65 unique species on 4 shipwrecks (25 to 50 species per sample). Abundance ranged from 2187 to 59,427 individuals per sample (683 cm2). On average, a decrease in oxygen concentration of 126 μmol/g ash free dry weight/h was found. The sequential water samples also showed clear changes in nutrient concentration with time in all incubations. The largest changes were observed with high fouling community abundances and biomass. Ammonium, nitrite, and phosphate always increased, with 1.5-to-5-fold increases from start to end of the incubation, while for nitrate both an efflux and influx were measured. Oxygen decreased in all incubations. Mean fluxes (all in μmol per m2 per hour with standard error) were significant for ammonium (945 ± 300), nitrite (80 ± 30), phosphate (61 ± 8), and oxygen (−11,794 ± 3289), but not for nitrate (−206 ± 122). Per gram AFDW, only ammonium (12.7 ± 3.5) and oxygen (−126 ± 48) had fluxes that differed significantly from zero.Compared to average seabed (sandy bottom) oxygen demand and community fluxes from previous studies, the observed fluxes were high. Our findings resembled those from temperate biogenic reef studies. Further data collection across a larger spatial and temporal scale is needed to fully understand offshore structure effects on marine environments.

Restructuring of soil food webs reduces carbon storage potential in boreal peatlands

Microbial and faunal decomposers regulate the flux of carbon and nitrogen belowground, thus controlling the storage/release of carbon and nitrogen in soil systems. Warming is anticipated to alter decomposer biomass, and accelerate organismal metabolism and soil carbon release. We parameterized six soil food webs using empirical data for 18 trophic nodes at two boreal peatland sites under three climate scenarios (control, +2 °C, +4 °C), and model carbon and nitrogen flux, loss and retention using an energetic ecostoichiometric food web model. Differences in microbial biomass between sites dictated flux under warming. The community biomass of the fungal-dominated site was more impacted by warming, but fluxes were more responsive to warming at the bacterial-dominated site. Decreased metabolic efficiency of the soil food web at both sites in response to warming led to greater per capita carbon losses, indicating the long-term carbon storage potential of both systems is diminished.

The effect of solid nitrogen on nucleate boiling heat transfer in a slush nitrogen pool

The nucleate boiling heat transfer in a slush nitrogen pool has been studied across a heat-flux range from 5 to 400 kW/m2 and a system pressure range from 12.5 kPa (triple point pressure) to 101 kPa (atmospheric pressure). The effect of solid nitrogen on the heat transfer process was found to vary with the heat flux and the pressure. Experimental results reveal that the nucleate boiling heat transfer coefficient (HTC) of slush nitrogen is higher than that of subcooled liquid nitrogen at the low heat flux, which can be attributed to the fact that the solid nitrogen particles (with their latent heat of melting) absorb heat in the thermal boundary layer and form a sharper temperature gradient near the boiling surface. However, at the high heat flux, the HTC of slush nitrogen is lower than that of subcooled liquid nitrogen, which can be attributed to the invasion and inhibition occurring between the solid nitrogen particles and the bubbles during boiling, leading to the accumulation of vapor phase with low thermal conductivity on the boiling surface, thereby the heat transfer will be suppressed. As a result, a dual effect for the nucleate boiling heat transfer in slush nitrogen can be observed. Furthermore, the critical heat flux (CHF) of slush nitrogen is obtained and compared with the CHF of subcooled liquid nitrogen. According to the CHF model, the bubble period is the dominant parameter in determining the CHF. A calibrated CHF correlation for slush nitrogen is developed based on the hypothesis that the bubble period is prolonged as the effective viscosity of slush nitrogen increases with the solid volume fraction. The CHF values of slush nitrogen with the solid volume fraction of 10%, 20% and 30% are 0.96, 0.91 and 0.84 times those of subcooled liquid nitrogen, respectively, at the pressures higher than 50 kPa. Consequently, the solid volume fraction of slush nitrogen and the degree of subcooling of subcooled liquid nitrogen are found to have opposite effects on CHF.

Low temperature sputtering deposition of Al1−xScxN thin films: Physical, chemical, and piezoelectric properties evolution by tuning the nitrogen flux in (Ar + N2) reactive atmosphere

This work investigates the physical properties of Al1−xScxN thin films sputtered at low temperatures by varying the process conditions. Specifically, the films were deposited at room temperature by applying a radio frequency power equal to 150 W to an AlSc alloy (60:40) target, varying the nitrogen flux percentage in the (Ar + N2) sputtering atmosphere (30%, 40%, 50%, and 60%) and keeping constant the working pressure at 5 × 10−3 mbar. The structural and chemical properties of the Al1−xScxN films were studied by x-ray diffraction and Rutherford backscattering spectrometry techniques, respectively. The piezoelectric response was investigated by piezoresponse force microscopy. In addition, the surface potential was evaluated for the first time for Sc-doped AlN thin films by Kelvin probe force microscopy, providing piezoelectric coefficients free from the no-piezoelectric additional effect to the mechanical deformation, i.e., the electrostatic force. By alloying AlN with scandium, the piezoelectric response was strongly enhanced (up to 200% compared to undoped AlN), despite the low deposition temperature and the absence of any other additional energy source supplied to the adatoms during thin film growth, which generally promotes a better structural arrangement of polycrystalline film. This is a strategic result in the field of microelectromechanical systems completely fabricated at low temperatures.

Typhoon-induced stormwater drives nutrient dynamics and triggers phytoplankton blooms in Laizhou Bay, China

In this study, we investigated the hydrological and ecological impacts of heavy rainfall caused by the storm Rumbia and Typhoon Lekima on Laizhou Bay (LZB) through land‒sea synchronous field surveys, online remote sensors, and simulated enclosure experiments. Within two weeks of Rumbia, approximately 9% and 16% of the annual riverine total nitrogen (TN) and total phosphorus (TP) fluxes, respectively, were transported to the LZB and the proportions were 17% and 35%, respectively, for Lekima. The land use on the watersheds increased the rates of land-derived nutrient loading and altered their biogeochemical forms. Consequently, the average concentrations of dissolved inorganic nitrogen (DIN) and phosphorus (DIP) in the LZB increased by 2.6 and 1.0 times post-Rumbia and by 3.5 and 1.3 times post-Lekima, respectively. Relatively lower salinity and temperature, sudden increases in DIN, and strengthened coastal currents stimulated the growth of highly adaptable and small diatoms, resulting in the first diatom blooms. Subsequently, a bloom of Noctiluca scintillans formed.