Nitrogen Concentrations In Water Research Articles

Dune soil nitrogen leaching for Chinese-yam cultivation: Impact of microbe-decomposable slow-release fertilizer

Chinese yam production is thriving in Aomori Prefecture, a cold and snowy region in Japan. Recently, there has been an increasing risk of nitrogen leaching in Chinese-yam fields, which consist of sandy soil, due to localized torrential rain. The relationships between the type of fertilizer used for Chinese-yam cultivation, the amount of nitrogen (N) leaching, and the timing of leaching remain unknown. Therefore, this study aimed to fill this knowledge gap by investigating the effects of different fertilizers (fast-acting and/or slow-release fertilizer) and irrigation practices (conventional and/or excessive irrigation) in order to mitigate the detrimental impact of nitrogen leaching on groundwater quality. An enhanced mathematical model and the spatiotemporal dynamics of inorganic nitrogen concentration in soil pore water were evaluated the negative impact of nitrogen leaching on the groundwater environment was evaluated. The results showed that the combined use of slow-release fertilizers could significantly reduce nitrate-nitrogen concentration in soil-water, especially during the harvest season. This study demonstrated that cultivating Chinese yam with a fertilizer application system that includes the use of slow-release fertilizer can diminish the negative impact of nitrogen leaching on the groundwater environment, contributing to our understanding of sustainable agricultural practices in regions facing similar environmental challenges. Therefore, our findings represent an important advancement providing new approaches to maintaining productivity while mitigating the adverse impacts on groundwater environments, as well as offering guidelines for agricultural practices in regions facing similar environmental challenges.

Characterization and function of particulate organic matter: Evidence from lakes undergoing ecological restoration

Particulate organic matter (POM) plays a crucial role in the organic composition of lakes; however, its characteristics remain poorly understood. This study aimed to characterize the structure and composition of POM in Lake Baiyangdian using many kinds of techniques and investigate the effects of different extracted forms of POM on water quality. The suspended particulate matter in the lake had complex compositions, with its components primarily derived from aquatic plants and their detritus. The organic matter content of the suspended particulate matter was relatively high (organic carbon content 27.29–145.94 g/kg) for the sum of three extractable states (water-extracted organic matter [WEOM], humic acid, and fulvic acid) and one stable bound state (humin). Spatial distribution analysis revealed that the POM content in the water increased from west to east, which was consistent with the water flow pattern influenced by the Baiyangdian water diversion project. Fluorescence spectroscopy analysis of the WEOM showed three prominent peaks with excitation/emission wavelengths similar to those of dissolved organic matter peaks. These peaks were potentially initial products of POM conversion into dissolved organic matter. Furthermore, the intensity of the WEOM fluorescence peak (total fluorescence peak intensity) was negatively correlated with the inorganic nitrogen concentration in water (p < 0.01), while the intensity of the HA fluorescence peak showed a positive correlation with the inorganic nitrogen concentration (p < 0.01). This suggested that exogenous organic matter inputs led to the diffusion of alkaline dissolved nitrogen from sediment into water, while degradation processes of aquatic plant debris contributed to the decrease in inorganic nitrogen concentrations in the water column. These findings enhance our understanding of POM characteristics in shallow lakes and the role of POM in shallow lake ecosystems.

Ferric- and calcium-loaded red soil assist colonization of submerged macrophyte for the in-situ remediation of eutrophic shallow lake: From mesocosm experiment to field enclosure application

Eutrophication and its resulting harmful algal blooms greatly reduce the ecosystem services of natural waters. The use of modified clay materials to assist the phytoremediation of eutrophic water is a promising technique. In this study, ferric chloride and calcium hydroxide were respectively loaded on red soil for algal flocculation and phosphorus inactivation. A two-by-two factorial mesocosm experiment with and without the application of ferric- and calcium- loaded red soil (FA), and with and without planting the submerged macrophyte Vallisneria natans was conducted for the in-situ repair of eutrophic water and sediment. Furthermore, field enclosure application was carried out to verify the feasibility of the technology. At the end of the mesocosm experiment, the total phosphorus, total nitrogen, and ammonia nitrogen concentrations in water were reduced by 81.8 %, 63.3 %, and 62.0 %, respectively, and orthophosphate phosphorus concentration in the sediment-water interface decreased by 90.2 % in the FA + V. natans group compared with those in the control group. The concentration and proportion of chlorophyll-a in cyanobacteria decreased by 89.8 % and 71.2 %, respectively, in the FA + V. natans group. The content of active phosphorus in V. natans decreased and that of inert phosphorus increased in the FA + V. natans group, compared with those in the V. natans alone group, thus may reducing the risk of phosphorus release after decomposing of V. natans. The sediment bacterial diversity index did not change significantly among treatments. Field enclosure application have also been successful, with chlorophyll-a concentration in the water of treated enclosure decreased from above 200 μg/L to below 10 μg/L, and phosphorus concentration in the water decreased from >0.6 mg/L to <0.02 mg/L. These results demonstrated that the FA in combination with submerged macrophyte planting had great potential for the in-situ remediation of eutrophic water, especially those with severe algal blooms.

A stacked extreme learning machines model on detection of nitrite–nitrogen concentration in surface water with ultraviolet–visible spectroscopy

A stacked extreme learning machines model on detection of nitrite–nitrogen concentration in surface water with ultraviolet–visible spectroscopy

Effects of land cover patterns on pond water nitrogen and phosphorus concentrations in a small agricultural watershed in Central China

Seasonal variations in agricultural land cover patterns and their spatial scale effects on surface water nitrogen (N) and phosphorus (P) concentrations in watersheds have been major concerns. Understanding the relationships between land cover metrics and pond nutrients are of great significance to enhance water contamination prediction efficiencies and guide land use planning in agricultural watersheds. In this context, the present study aims to investigate the seasonal variations in the N and P concentrations in 28 ponds in a developed agricultural watershed in central China in 2019. Multivariate statistical analyses were applied to assess the relationships of the pond water N and P concentrations with multi-scale land cover patterns. Besides the pond water ammonium nitrogen (NH4+-N) concentrations, the total nitrogen (TN), nitrate nitrogen (NO3−-N), total phosphorus (TP), and dissolved phosphorus (DP) concentrations in the investigated ponds were higher in summer than those observed in other seasons. The hierarchical partitioning model results demonstrated a spatial consistency in scale effects of land cover metrics on the pond hydrochemical parameters in the different seasons. Redundancy analysis (RDA) showed that the land cover patterns better predicted the variations in the pond water N and P concentrations at the 100 m buffer zone scale in spring and summer, as well as at the 50 m buffer zone scale in fall and winter. Among the land cover metrics considered in this study, the orchard area proportion (POR), landscape shape index (LSI), and largest patch index (LPI) showed the highest significant correlations with the pond water N and P concentrations. The results of this study provide valuable information for effective land use management to control pond water pollution and promote sustainable development in agricultural watersheds.

Nitrogen enrichment decreases seagrass contributions to refractory organic matter pools

AbstractCoastal nitrogen enrichment significantly contributes to the decline of seagrass health and habitat, thereby diminishing its capacity to capture and sequester carbon (i.e., Blue Carbon). However, the consequences to blue carbon stocks due to sublethal changes in chemical recalcitrance of seagrass organic matter (OM) caused by nitrogen enrichment is unknown. In this study, we investigated the effects of nitrogen‐loading on the chemical composition of meadow‐forming Thalassia hemprichii. We found that the amino acid content in seagrass leaves and rhizomes increased with nitrogen loading, while the total labile OM and refractory OM (i.e., cellulose and lignin) content in seagrass leaves, sheaths, and roots generally decreased with nitrogen loading. Additionally, cellulose and lignin within sheath tissues showed a threshold response whereby refractory OM dropped when leaf nitrogen content (i.e., indicator of nitrogen loading) exceeded 2.2%. The rhizome labile OM and cellulose content also peaked at 2.2% leaf nitrogen content but subsequently reduced to a minimum at ~2.9% leaf nitrogen. The threshold of 2.2% leaf nitrogen content, equivalent to 43~72 μM dissolved inorganic nitrogen concentration in sediment pore water, may be utilized to forecast the contribution of seagrass refractory OM to sediments. It was estimated that high nitrogen loading could result in a loss of 309–645 kg ha−1 of refractory OM inputs in this study sites. The findings underscore that nitrogen enrichment has sublethal but significant negative impacts on carbon cycling via the reduction of refractory OM in seagrass biomass, consequently weakening the autochthonous contribution of seagrass to long‐term carbon sequestration.

Estimating the impact of cover crop adoption on ambient nitrogen concentration in the upper Mississippi River drainage

AbstractWe examine cover crop (CC) adoption to determine how this soil health practice has influenced agricultural non‐point source pollution. We use remotely sensed data on practice adoption, and control for hydrological flow direction, weather, and land use to estimate the ex post impact of CC on total Nitrogen concentrations in surface water while controlling for pollutant spillovers from upstream. At the mean treatment level in the study area (3.2%), a 1% increase in CC adoption results in a 0.06 mg/L (2%) reduction in concentration in the study area. Results provide novel estimates based on observed data that can be compared to biophysical simulations of CC effectiveness.

Capturing spatiotemporal heterogeneity in fertilizer application for better modelling paddy water nitrogen and phosphorus pollution at regional scale

Accurately simulating paddy water nitrogen and phosphorus (N/P) concentration is crucial for identifying key control areas of agricultural non-point source pollution (ANPSP), especially in the paddy-dominated regions. In China, smallholder farming has resulted in significant spatiotemporal heterogeneity in fertilizer application date/amount among different fields at the regional scale. However, due to the lack of realistic fertilizer application date/amount data at field scale, previous regional scale models have employed uniform fertilization management, neglecting spatiotemporal heterogeneity in fertilizer application date/amount. This has led to significant uncertainties in assessing paddy water N/P pollution at the regional scale. To address this issue, we developed a new model (PWNPRS) for simulating spatiotemporal hotspots of paddy water N/P pollution, based on remote sensing and a first-order kinetic model: (1) we developed a quantitative assessment method for fertilizer application date/amount based on phenological/vegetation information extracted from remote sensing datasets; (2) we modified and improved the first-order kinetic model by incorporating fertilizer application date/amount to predict paddy water N/P concentration at the regional scale. The spatiotemporal fluctuations of fertilizer application date/amount and paddy water N/P pollution were simulated by using the developed model in a paddy-dominated regions in Danyang, China, as a case study for model validation. The models performances and spatiotemporal evaluation indicate that the PWNPRS model is an innovative and promising approach to accurately capture the spatiotemporal pattern of fertilizer application date/amount and paddy water N/P concentration at the regional scale. The PWNPRS model can be extended to other paddy-dominated regions for N/P concentration prediction under data-limited conditions. Our model considers the interactive effects of fertilization date/amount and N/P concentration attenuation rates, allowing it to capture the dynamic spatiotemporal variations in paddy water N/P concentrations at a regional scale. Simultaneously, a robust and accurate model provide a theoretical basis for optimizing agricultural ecological management.

Abundance and composition of invertebrate-feeding leeches in relation to fish status in ponds

Leeches feeding on invertebrates are an important component of freshwater communities, including those dominated by fish, but the effects of fish on their abundance and distribution are not well explored. The relative densities and assemblage structure of two leech families, Erpobdellidae and Glossiphoniidae, were studied from May to August 2014 in ponds stocked with low biomass densities of young common carp Cyprinus carpio, too small to prey on leeches (low-fish ponds), and in ponds containing high biomass densities of large (one- or two-year-old) carp (high-fish ponds), using two types of activity traps (placed either on the bottom or near the water surface). The most common and numerous species were Erpobdella octoculata, Helobdella stagnalis, and Erpobdella nigricollis. The traps near the water surface captured relatively small numbers of leeches, yet the catches showed that in summer some of the leeches moved to the upper layers of the water column, which was free of macrophytes. No differences in leech species richness or diversity were found with respect to fish status of ponds; however, bottom erpobdellids were more abundant in high-fish ponds. Redundancy analysis identified the fish status of the ponds and total nitrogen concentration in water as the only significant variables explaining the distribution of leeches among ponds. Species distribution was nested, but the nestedness pattern was not affected by the fish status of the pond. While fish are generally believed to adversely affect macroinvertebrate diversity and abundance, our study shows that some predatory leech species can persist in the presence of fish and possibly indirectly benefit from it.

Zeolite enhanced iron-modified biocarrier drives Fe(II)/Fe(III) cycle to achieve nitrogen removal from eutrophic water

The problem of nitrogen removal in eutrophic water needs to be solved. Two new autotrophic nitrogen removal technologies, ammonia oxidation coupled with Fe(III) reduction (Feammox) and Nitrate-dependent Fe(II) oxidation (NDFO), have been shown to have the potential to treat eutrophic water. However, the continuous addition of iron sources not only costs more, but also leads to sludge mineralization. In this study, nano-sized iron powder was loaded on the surface of K3 filler as a solid iron source for the extracellular metabolism of iron-trophic bacteria. At the same time, due to the high selective adsorption of zeolite for ammonia can improve the low nitrogen metabolism rate caused by low nitrogen concentrations in eutrophic water, three kinds of modified functional biological carriers were prepared by mixing zeolite powder and iron powder in different proportions (Z1, Zeolite:iron = 1; Z2, Zeolite:iron = 2; Z3, Zeolite:iron = 3). Z3 exhibited the best performance, with removal efficiencies of 54.8% for total nitrogen during 70 days of cultivation. The chemical structure and state of iron compounds changed under microorganism activity. The ex-situ test detected high NDFO and Feammox activities, with values of 1.02 ± 0.23 and 0.16 ± 0.04 mgN/gVSS/h. The enrichment of NDFO bacteria (Gallionellaceae, 0.73%-1.43%–0.74%) and Feammox bacteria (Alicycliphilus, 1.51%-0.88%–2.30%) indicated that collaboration between various functional microorganisms led to autotrophic nitrogen removal. Hence, zeolite/iron-modified biocarrier could drive the Fe(II)/Fe(III) cycle to remove nitrogen autotrophically from eutrophic water without carbon and Fe resource addition.

Feature multi-level attention spatio-temporal graph residual network: A novel approach to ammonia nitrogen concentration prediction in water bodies by integrating external influences and spatio-temporal correlations

Accurate prediction of ammonia nitrogen concentration in water is of great significance for urban water quality management and pollution early warning. In order to improve the prediction accuracy of ammonia nitrogen concentration in water, this study developed a novel model based on graph neural networks called Feature Multi-level Attention Spatio-Temporal Graph Residual Network (FMA-STGRN). The FMA-STGRN model utilizes external influencing factors such as meteorological factors and point of interest data, as well as the spatio-temporal correlation information of ammonia nitrogen concentration between water quality monitoring stations, to accurately predict the concentration of ammonia nitrogen in water. The model consists of four main components: feature multi-level attention module, spatial graph convolution module, temporal-domain residual decomposition module, and feature fusion and output module. Through the organic combination of these four modules, FMA-STGRN can more effectively explore the complex spatio-temporal correlation relationships between water quality monitoring stations and more accurately integrate and utilize external influencing factors, thereby improving the prediction accuracy of ammonia nitrogen concentration in water. Experimental results show that the FMA-STGRN model outperforms other benchmark models such as RF, MART, MLP, LSTM, GRU, ST-GCN, and ST-GAT in various aspects. In addition, a series of feature ablation experiments were conducted to further reveal the key contributions of meteorological factors and point of interest data to the model performance. Overall, our research provides a powerful and practical tool for water quality monitoring and urban water management, with broad application prospects.

Fog and rain water chemistry in a tea plantation of northern Taiwan.

Tea plantations are expanding globally and many are in mountainous areas with frequent fog but few studies have examined fog chemistry in these areas. We examined chemical composition of fog and rain water at a tea plantation in northern Taiwan. Fog water was collected using a Kroneis passive cylindrical fog-water collector and rain water was collected using a 20-cm-diameter funnel. The most abundant ions were Cl- and Na+ in both fog and rain waters due to the proximity of the site to the coast. The order of abundance of other ions was NO3- > Mg2+ > SO42- > Ca2+ > NH4+ > K+ > H+ in fog water and SO42- > K+ > NO3- > NH4+ > Ca2+ > Mg2+ > H+ in rain water. The concentration enrichment ratio (fog to rain) ranged between 2.2 (K+) and 22 (Mg2+) lying between sites near major emission sources and sites in remote areas, possibly because the immediate surrounding landscape is covered with secondary forests although it is near large cities. Factor analysis highlights the influences of sea-salt aerosols on the variation of fog and rain water chemistry. Sea-salt corrections using Na+ as the sea salt tracer led to negative concentrations of Cl- and Mg2+ suggesting that assumptions involved in sea-salt corrections were not satisfied. Agriculture influence is identified as a unique factor for explaining variance of K+, NH4+, and dissolved organic nitrogen (DON) concentrations in fog water but not rain water. Ion concentrations in fog and rain water were generally higher in the weekly samples associated with air trajectories passing through the continental East Asia than those associated with oceanic trajectories pointing to the role of regional pollution sources in affecting local fog and rain water chemistry. Our study highlights greater effects of tea agriculture on fog than rain water chemistry.

The combined effects of lipoic acid and sodium acetate on metabolism, redox balance, and utilization of yolk reserves of Artemia sp. nauplii

Lipoic acid (LA) has been an antioxidant with proven benefits in different species of productive interest. However, there is evidence of the effect of LA as a growth repressor and, consequently, of zootechnical performance. This study evaluated the effect of the co-administration of LA and short-chain fatty acid, sodium acetate (SA), as an additional source of energy on the utilization of yolk nutrients in Artemia sp. nauplii. A factorial experiment was designed with four levels of LA (0.0, 0.05, 0.5, and 5.0 μM) and four levels of SA (0.0, 2.0, 4.0, and 8.0 mM). Over 24 h, with sampling every 6 h, the total ammoniacal nitrogen (TAN) concentration in water, the concentration of protein, triglycerides, glucose, and the antioxidant capacity (ACAP) was evaluated in the artemia. The electron transporter system (ETS) activity and production of reactive oxygen species (ROS) in vivo were also recorded. Both LA and SA decreased TAN production. At 18 h, LA caused significant decreases in glucose content at the concentrations of 0.5 and 5.0 μM. On the other hand, SA preserved protein values in a dose-dependent manner at 12 h. Regarding ACAP, the LA showed ambivalent effects on this parameter, promoting a higher ACAP at 6 h; however, it promoted a more pro-oxidant state in the metanauplii at 24 h. While the ETS activity increased at 6 h, as an effect of the SA and LA administered separately, the co-administration of LA and SA revealed a possible antagonism that caused a decrease in the ETS activity by the action of LA. As for ROS, a decrease in production rates was found with the administration of LA, which was more noticeable at LA concentrations within the 0 and 2 mM levels of SA from 18 h onwards. Finally, the final energy content showed a scenario of the preservation of the energy reserves of artemia nauplii with the addition of SA. As expected, the LA negatively affected the energy content of the animals; however, the treatment with the highest energy content was the one that received 0.05 μM LA and 8.0 mM SA, suggesting the possibility of using these compounds together in order to compensate the side-effects of LA.

Use of legacy nitrogen as a resource: Unfertilized lotus fields contribute to water quality improvement and biodiversity conservation

Managing legacy nitrogen (N) that has accumulated over decades of intensive agriculture is necessary to balance agricultural production and environmental conservation. Using legacy N as a resource can reduce extant legacy N. The uplands of Japan's Lake Inba watershed are dominated by agroecosystems, and spring waters in the lowlands contain high NO3-N concentrations. We focused on an unfertilized, commercial lotus (Nelumbo nucifera) farm where paddy fields are irrigated with spring waters. We hypothesized that the lotus field could reduce the export of legacy N and provide habitat for fish (co-benefit). Dating of spring waters using sulfur hexafluoride revealed that the residence time of water at the study site was 12.5 years and suggested that the spring waters contained legacy N. We found large reductions of NO3-N and total nitrogen (TN) concentrations in water that passed through the lotus fields. A meta-analysis revealed that the reductions of NO3-N concentrations were highest in unfertilized lotus fields, and reductions of TN concentrations were higher in unfertilized paddy and lotus fields than in fertilized fields. The N removal by harvesting lotus roots 38.7 kg N/ha/year was smaller than the literature-based rate of N removal by denitrification. We used environmental DNA metabarcoding to identify the fish fauna in the lotus fields and an adjacent stream. The native fish richness was a little lower in the lotus fields than in the stream, but the presence of two endangered fish species in the lotus field suggested a moderate biodiversity conservation function. Our case study could be a good example of a nature-based solution to harness ecosystem functions to reduce legacy N.

Soil ecological stoichiometry synchronously regulates stream nitrogen and phosphorus concentrations and ratios

Whether and how to synchronously regulate stream water nitrogen (N) and phosphorus (P) concentrations and ratios is a major challenge for sustainable aquatic functions. Soil carbon (C):N:P ratios influence soil N and P stocks and biogeochemical processes that elicit subsequent substantial impacts on stream water N and P concentrations and ratios. Therefore, bridging soil and stream water with ecological stoichiometry is one of the most promising technologies for improving stream water quality. Here, we quantified the ecological stoichiometry of soil and stream water relationships across nine catchments. Soil C:P ratio was the main driver of water quality, showing negative correlations with stream water N and P concentrations, and positive correlations with the N:P ratio in P-limited catchments. We revealed that soil C:P ratios higher than 97.8 mol mol−1 are required to achieve the simultaneous regulation of stream water N and P concentrations below the eutrophication threshold and make algal growth P-limited. Furthermore, we found that the relationships between catchment landscape and soil ecological stoichiometry likely provided practical options for regulating soil ecological stoichiometry. Our work highlights that soil ecological stoichiometry can effectively indicate the amount and proportion of soil N and P losses, and can be intervened through rational landscape planning to achieve sustainable aquatic ecosystems in catchments.

Gene Expression, Enzyme Activity, Nitrogen Use Efficiency, and Yield of Rice Affected by Controlled-Release Nitrogen.

Controlled- or slow-release urea can improve crop nitrogen use efficiencies and yields in many agricultural production systems. The effect of controlled-release urea on the relationships between levels of gene expression and yields has not been adequately researched. We conducted a 2 year field study with direct-seeded rice, which included treatments of controlled-release urea at four rates (120, 180, 240, and 360 kg N ha-1), a standard urea treatment (360 kg N ha-1), and a control treatment without applied nitrogen. Controlled-release urea improved the inorganic nitrogen concentrations of root-zone soil and water, functional enzyme activities, protein contents, grain yields, and nitrogen use efficiencies. Controlled-release urea also improved the gene expressions of nitrate reductase [NAD(P)H] (EC 1.7.1.2), glutamine synthetase (EC 6.3.1.2), and glutamate synthase (EC 1.4.1.14). With the exception of glutamate synthase activity, there were significant correlations among these indices. The results showed that controlled-release urea improved the content of inorganic nitrogen within the rice root zone. Compared with urea, the average enzyme activity of controlled-release urea increased by 50-200%, and the relative gene expression was increased by 3-4 times on average. The added soil nitrogen increased the level of gene expression, allowing enhanced synthesis of enzymes and proteins for nitrogen absorption and use. Hence, controlled-release urea improved the nitrogen use efficiency and the grain yield of rice. Controlled-release urea is an ideal nitrogen fertilizer showing great potential for improving rice production.

Do stable carbon and nitrogen isotope values of Nitella flexilis differ between softwater and hardwater lakes?

The composition of stable carbon and nitrogen isotopes (δ13C and δ15N) is widely used for tracking the origin of organic matter (OM) present in lacustrine sediments. These isotopes also define the evolution of OM in food web loops. Charophyte species Nitella flexilis C. Agardh, 1824 can be found in different aquatic environments where it contributes significantly to sediment formation and influences biota function. Therefore, it is crucial to study more about δ13C and δ15N in different lake types. Here, we present the results of the first comprehensive study of N. flexilis δ13C and δ15N, which add to the knowledge of the C and N isotope records of charophytes. We obtained the δ13C and δ15N records of N. flexilis OM from hardwater and softwater lakes and checked for differences between these records. We also analyzed the differences in physical and chemical parameters. Finally, we compared the δ13C and δ15N records with physical and chemical parameters to identify the variables that have the highest influence on N. flexilis δ13C and δ15N values. Our study showed that both δ13C and δ15N did not differ significantly in the two types of lakes, although the lakes had significant differences in several physical and chemical parameters (pH, Ca2+, dissolved inorganic carbon, total phosphorus, conductivity). However, we observed that δ13C values were influenced by light conditions (photosynthetic active radiation, depth, dissolved OM), while δ15N values were influenced by the total nitrogen concentration in water.

Response of Forest Ecosystems to Decreasing Atmospheric Nitrogen Deposition

Nitrogen deposition has serious consequences to global change. Excessive nitrogen deposition leads to nitrogen saturation in forests, resulting in soil acidification, nitrate leaching, an increase in nitrous oxide emissions, and a decrease in plant species diversity and vegetation productivity. Under the reduction of atmospheric nitrogen deposition in Europe, North America, and China, summarizing the response of forests to decreasing nitrogen deposition can not only improve the knowledge framework of the impact of nitrogen deposition on forests, but also evaluate the effects of emission abatement actions, as well as provide scientific basis for future air pollution control. This study reviewed the response of soil, surface water, nitrogen cycle, and vegetation of temperate forests in Europe and North America and subtropical forests in southwest China to the reduction in atmospheric nitrogen pollution gases and thus nitrogen deposition. The soil water nitrogen concentration responded rapidly to the nitrogen deposition reduction, although the trend was inconsistent. The soil acidification and nitrogen cycles showed a delayed response of recovery from high nitrogen deposition. The nitrogen mineralization and immobilization, soil carbon retention, and net primary production might take decades to respond to the nitrogen deposition reduction. However, the soil inorganic nitrogen pool and nitrogen leaching decreased with the decline in nitrogen deposition, although a one-or two-year lag existed. The surface water nitrogen concentration was closely related to nitrogen status in forests. After the nitrogen deposition decreased, the nitrogen leaching and thus the surface water nitrogen concentration decreased in the areas with historically high nitrogen deposition. However, the low surface water nitrogen concentration in the nitrogen-limited forests was not significantly affected by the nitrogen deposition changes. The recovery of surface water acidification was affected by soil sulfur desorption/mineralization and nitrification/denitrification. The foliar nitrogen concentration decreased with the decline in nitrogen deposition. The nitrogen-saturated forests and regional surface water in southwest China showed a recovery trend from high nitrogen deposition, as a consequence of the implementation of the Total Emissions Control of Air Pollutants and later the Action Plan of Air Pollution Prevention and Control.

Effects of Aeration on Surface Water Nutrient Dynamics and Greenhouse Gas Emission in Different Straw Returning Paddy Fields

Straw returning is of great significance for improving soil structure, soil fertility, crop yield, and quality. However, straw returning causes environmental problems such as increased methane emission and non-point source pollutant emission risk. How to reduce the negative effects of straw returning is an urgent problem to be solved.In this study, the effects of aerobic treatment on carbon and nitrogen concentration in surface water and greenhouse gas emissions in paddy fields with different treatments of straw returning were systematically compared.The results showed that different treatments of straw returning significantly increased chemical oxygen demand (COD) in the surface water of the paddy field and significantly promoted the methane emission of the rice field and the global warming potential (GWP), although it slightly reduced N2O emission. The increasing trends showed that wheat straw returning>rape straw>broad bean straw returning.Straw returning increased rice yield when compared with the control without straw returning, but the difference was not significant. Aerobic treatment reduced the COD in surface water by 15%-32%, the methane emission of the paddy field by 10.4%-24.8%, and the GWP of paddy field by 9.7%-24.4% under different straw returning treatments, without affecting the rice yield. The mitigation effect of aerobic treatment with wheat straw returning was the best. The results indicated the potential of oxygenation measures in greenhouse gas emission mitigation and COD emission risk reduction in straw returning paddy fields, especially in wheat straw returning paddy fields.

Removal of low concentration ammonia nitrogen enhanced by hydraulic cavitation combined with ozonation

The combination of hydraulic cavitation and ozone oxidation improves the removal efficiency of low concentration ammonia nitrogen. Focusing on the treatment of low concentration ammonia nitrogen wastewater (about 25mg/L), the study discusses the treatment effect of cavitation combined with different gases (O2, O3) on low concentration ammonia nitrogen. The treatment effect of ozone 3L/min combined with cavitation on ammonia nitrogen is 33.07%. The treatment effect of oxygen (3mg/L) combined with cavitation on ammonia nitrogen was 16.91%. At the same time, the treatment efficiency of ammonia nitrogen at different PH values was compared. When the initial concentration was adjusted from 7 to 10, the treatment efficiency increased from 33.07% to 84.55%. When PH=10, the ammonia nitrogen concentration in water finally dropped to 3.5mg/L, reaching the Chinese first-level emission standard (15mg/L). In addition, the mechanism of treating ammonia nitrogen in water by hydraulic cavitation combined with ozonation was discussed. The results show that ozone combined cavitation is very effective for the treatment of low concentration ammonia nitrogen wastewater.