Spatial Distribution Of Nitrogen Research Articles

Identification of livestock farms with potential risk of environmental pollution by using a model for returning livestock manure to cultivated land.

Livestock farms produce a large amount of livestock manure, which, if not disposed of properly, will become an environmental pollution source. However, limited research has been conducted on identifying livestock farms with a potential risk of environmental pollution. In this study, a model for returning livestock manure to cultivated land was constructed. Livestock manure was returned to cultivated land, and the amount of surplus livestock manure nutrients, including nitrogen and phosphorus, in livestock farms was calculated with pig manure as an example. Then, livestock farms with a potential risk of environmental pollution in Shanggan Town and part of Xiangqian Town in Fuzhou City were identified using phosphorus as an index. Results showed that the spatial distributions of nitrogen and phosphorus from pig manure in the cultivated land varied. All cultivated lands exhibited the maximum carrying capacity for phosphorus, and 1811 cultivated lands exhibited potential nitrogen carrying capacity. A total of 13,958.997kg of phosphorus from pig manure in 144 livestock farms could not be disposed to cultivated lands. In all, 144 livestock farms with surplus phosphorus from pig manure were identified as potential environmental pollution sources. These findings can serve as a scientific basis for the utilization of livestock manure, prevention of environmental pollution caused by livestock farms, and layout planning of livestock farms.

Spatial Distribution of Nitrogen and Phosphorus Nutrients in the Main Stream and Typical Tributaries of Tuojiang River and Fujiang River

The Tuojiang River and Fujiang River, two important tributaries of the upper reaches of the Yangtze River, have serious water pollution problems, among which nitrogen (N) and phosphorus (P) are the most important pollutants. Therefore, the aim of this study was to identify the influencing factors of water quality in different spaces and provide a scientific basis for the prevention and control of surface water pollution in the upper reaches of the Yangtze River and its tributaries. Water samples of trunk and tributaries in the Tuojiang River and Fujiang River were collected, and the spatial distribution characteristics of water N and P were analyzed. The results showed that the Tuojiang River and Fujiang River showed serious pollution of total nitrogen (TN), with a water quality worse Ⅴ-section proportion as high as 94% and 50%, respectively. Both rivers showed that TN and TP concentrations in the tributaries were higher than those in the main stream. For both rivers, total phosphorus (TP), with moderate pollution, was mainly concentrated in Ⅱ, Ⅲ, and Ⅳ class water quality, whereas the P pollution was more serious for the Fujiang River compared to that of the Fujiang River. For the Tuojiang River, nitrate nitrogen (NN) concentration from upstream to downstream showed a trend of decreasing after the first increase, with the maximum concentration of ammonium nitrogen (AN) exhibiting at the upstream site. In particular, TP concentration increased significantly after rivers flowed through a city. For the Fujiang River trunk stream, TN and NN concentration exhibited a gradually increasing trend from the middle to lower reaches. Generally, our study revealed that TN, TP, and NN in the rivers were affected by water pH and water temperature (T). Therefore, the control of N and P pollution in rivers should pay attention to the influence of water environmental factors.

Spatial characteristics of nitrogen forms in a large degenerating lake: Its relationship with dissolved organic matter and microbial community

It is crucial to clarifying the interactions among nitrogen, dissolved organic matter, and microorganisms to understand the ecological response mechanisms of degenerating large shallow lakes. This study focused on the spatial patterns of several nitrogen forms in Honghu Lake (Hubei province, China) in combination with the sediment physical and chemical properties. The dissolved organic matter (DOM) composition, the humification degree and the bacterial and eukaryotic communities responses were analyzed. The results showed that the spatial distribution of nitrogen was related to the particle size composition. The maximum mean value of total nitrogen appeared in the southwest region (4813.77 mg kg−1). DOM was mainly composed of humic-like substances, with a high degree of humification at the entrance of the inflowing lake (projection value peaked at 2.22). Structural equation model analysis also showed that the direct and indirect effects of the microenvironment physical and chemical properties and nitrogen and DOM jointly explained the changes in bacterial community diversity. However, there were no similar spatial distribution characteristics between eukaryotes and environmental parameters, suggesting a single, irregular dominant species and a low level of diversity. This suggests an internal ecological response of nitrogen, DOM, and microorganisms in the degenerating lake environment.

Spatial Distributions of Nitrogen and Phosphorus in Surface Sediments in Intertidal Flats of the Yellow River Delta, China

The spatial distributions of nitrogen (N) and phosphorus (P) in surface sediments are of great significance in studying the ecological process of nutrient cycling in intertidal flats. However, little is known about N and P’s spatial distribution in intertidal flats of the Yellow River Delta (YRD). We analyzed the N and P contents in surface sediments and Suaeda glauca density at the low-tidal level to identify the spatial distributions of nutrients and their influencing factors in coastal tidal flat sediments. The results showed that the total nitrogen (TN) and total phosphorus (TP) concentrations in this study were both lower than the background values of China’s shallow sea sediments. The spatial distributions of N and P had significantly spatial heterogeneity, while those of the nutrients at different distances from the low-tidal level to the coastline showed no significant distance effects. The spatial distribution of S. glauca in coastal tidal flats had significant location characteristics and was closely related to the distribution of TN and pH. The TN in non-estuarine intertidal flats was less than that in estuaries; in contrast, the TP was higher in non-estuaries. There are some differences of N and P between estuary and non-estuary areas.

Spatial distributions of nitrogen and phosphorus losses in a basin and responses to best management practices — Jialing River Basin case study

Tracing the main sources and spatial distributions of pollutants and quantifying the effects of various factors on soil erosion and pollution loads are important to allow appropriate management systems to be developed for large complex watersheds and allow water pollution to be controlled efficiently and economically. A distributed water, sediment, and pollutant model was used to qualitatively and quantitatively assess temporal and spatial variations in water and sediment characteristics and nitrogen (N) and phosphorus (P) loss distributions in a basin from a macroscopic point of view and to trace the sources of pollutants, using the Jialing River Basin as an example. Changes in N and P losses in the basin caused by various management practices were assessed. The results indicated that the average annual water and sediment yield in the study area were 103–857 mm and 2.4–1274.1 t/ha, respectively. The loss of total N and P were 1.1–21.6 kg/ha and 0.01–11.2 kg/ha. The spatial distribution varied greatly, but the annual variation trend was relatively stable. The contribution of N from industrial point sources reached 1973 tons, which was dominant. And the total N distribution in the watershed was closely related to woodland. Total P pollution was most severe for cultivated land. The P load caused by fertilization reached 805 tons, which was significantly more than the point source discharge. Assessments of the effects of implementing various management practices in the watershed indicated that N losses would be decreased more effectively by filter belt in woodland than by other practices. The total N loss would be reduced by 4.4% for every 0.5 m filter belt added to woodland. The losses would be decreased more effectively by a cultivated land filter belt and controlling fertilizer application than by other practices. The 0.5 m filter belt of cultivated land can reduce total P by 5%, and reducing fertilization by 5% can reduce total P by 7.3%. Understanding the temporal and spatial distributions of pollutant sources in a river basin and tracing pollutant sources will allow appropriate management practices to be implemented in key areas to effectively control pollutants.

Optimal control of nonpoint source pollution in the Bahe River Basin, Northwest China, based on the SWAT model.

This study conducts in the Bahe River Basin, an agricultural basin in Northwest China. We use the Soil and Water Assessment Tool (SWAT) model to identify the spatial distribution characteristics of non-point source (NPS) pollution and determine the critical source areas (CSA). Then the relationship between landscape pattern and NPS pollution is analyzed by spearman correlation analysis and redundancy analysis (RDA). On this basis, we set up eight landscape management practices in the CSA and evaluate their reduction effects on NPS pollution loads. The results show that the spatial distribution of nitrogen and phosphorus loss intensity has a certain correlation with rainfall and runoff, and the correlation between phosphorus loss intensity and sediment loss intensity is more significant. The NPS pollution load is closely related to the landscape pattern of the river basin, and is affected by the fragmentation, aggregation and complexity of the landscape. Farmland, forest land, and grassland are the main landscape components of the river basin. Farmland is the main source of NPS pollution, whereas forest land and grassland can effectively inhibit the output of NPS pollution, and the reduction effect of forest land is significantly better than that of grassland. The largest patch index (LPI), landscape shape index (LSI), patch density (PD) are the main landscape factors that affect the output of NPS pollution load. Among all the scenarios, the reduction effect of returning farmland to forest land in slopes above 15° is the best, and the reduction rates of total nitrogen (TN) and total phosphorus (TP) loads have reached about 25%. This study provides some reference for the management of NPS pollution in the Bahe River Basin and other similar basins.

Distribution characteristics of nitrogen and the related microbial community in the surface sediments of the Songhua River.

Nitrogen in surface sediments is becoming an ecological risk to the river environment and it is essential to clarify the relationship between the different forms of nitrogen and related microorganisms. A survey was conducted to analyze the distribution characteristics of the nitrogen and related microbial community in the sediments of the Songhua River during normal season and dry season. In the surface sediments of the Songhua River, no total nitrogen (TN) pollution risk was observed according to the U.S. EPA assessment criteria (1000 mg kg−1) for sediment contamination, but TN in several sampling sites (554.9–759.7 mg kg−1) exceeded the alert values (550 mg kg−1) should be concerned according to the guidelines issued by the Ministry of Environment and Energy of Ontario, Canada. The average TN, NH4+–N, NO3−–N and total organic nitrogen (TON) in the surface sediments of the Songhua River during normal season were higher than those in the dry period. TON was the main form of nitrogen in the sediment of Songhua River, NO2−–N content was lowest and no obvious difference was observed between normal and dry seasons. The highest average NH4+–N of both seasons occurred in the Nenjiang River, and the highest average NO3−–N of both seasons were found in the main stream of the Songhua River. The community abundance of AOB genes (1.1 × 107 to 2.5 × 108 copies per g soil in normal season, 7.2 × 105 to 3.3 × 108 copies per g soil in dry season) was higher than that (1.2 × 106 to 9.7 × 107 copies per g soil in normal season, 6.6 × 104 to 3.2 × 107 copies per g soil in dry season) of AOA genes in both normal and dry seasons. The denitrifying nirS genes were predominant in both seasons, and their abundance (1.8 × 106 to 8.0 × 108 copies per g soil) in dry season was higher than that (9.7 × 105 to 4.6 × 108 copies per g soil) in normal season. Moreover, the moisture concentration, pH, dissolved oxygen and different formation of nitrogen were key factors affecting the variation of nitrogen-transformation microorganisms during normal and dry seasons. This research could help to explain the relationship between nitrogen transformation and the related microbial community in the surface sediment, which could provide a scientific basis for water ecological restoration and water environment improvement of Songhua River.

Application of GIS and Remote Sensing in Spatial Distribution of Nitrogen and Phosphorus Pollutant in Urban Rivers: A Case Study of Linyi Economic Development Zone, China

Liu, C.; Qian, B.; Wang, L., and Miao, Q., 2019. Application of GIS and remote sensing in spatial distribution of nitrogen and phosphorus pollutant in urban rivers: A case study of Linyi Economic Development Zone, China. In: Guido-Aldana, P.A. and Mulahasan, S. (eds.), Advances in Water Resources and Exploration. Journal of Coastal Research, Special Issue No. 93, pp. 250–256. Coconut Creek (Florida), ISSN 0749-0208.The objectives of this paper were to develop, evaluate and apply the remote sensing based on models of ammonia nitrogen (NH3-N) and total phosphorus (TP) for the Yi and Shu River in Linyi Economic Development Zone, Shandong Province, China. The scenes of Landsat-8 OLI satellite data were used to establish the relationship between the planetary reflectance and the measured data for five years (i.e., 2014-2017). The five spectral bands (i.e., Coastal, Blue, Green, Red, NIR) were used to obtain the most suitable modeling factor from the different band combinations. The liner regression analysis showed that red band both had highest correlation with NH3-N and TP in Yi and Shu River. For the Yi River, the co-efficient of determination (R2) of red band was 0.541 for the NH3-N model and 0.498 for the TP model. For the Shu River, the co-efficient of determination (R2) of red band was 0.643 for the NH3-N model and 0.565 for the TP model. The best-fit Models were validated with measured data and found that the errors of the NH3-N and TP models of the Yi River were 34.93% and 29.33%, respectively, and while 33.66% and 32.48% for the Shu River. With the models, the distribution diagrams of NH3-N and TP were generated, which can be assisted analysis of spatial and temporal for Yi and Shu River. The results showed that the established models could indicate the trend of NH3-N and TP in rivers that was validated by field visit. The proposed approach in this paper has satisfactory validity and practicability, thus could be reference for study on NH3-N and TP in water based on remote sensing.

Speciation and spatial distribution of nitrogen in surface sediments of in Ming Lake

To reveal the diverse occurrence forms and spatial distribution characteristics of nitrogen in the surface sediments of Ming Lake, a sequential leaching method was employed to determine the nitrogen in the surface sediments of Ming Lake. The results show that the total Nitrogen (TN) of the surface sediments of Ming Lake are between 383.23 and 3270.38 ug/g, and the spatial distribution is generally shown as southwest>middle>southeast>west of the lake. The results indicate the nutrient level of the whole lake is not very high. However, for some local areas a risk of high eutrophication pollution may exist due to excessive content; the average TTN is 638.77 ug/g which occupying 36 % of the lake; the spatial distribution is the same with TN; the average (NTN) is 928.61 ug/g that occupied 61 % of TN. With the exception of SAEF-N, every occurrence form of nitrogen was positive with TOM, indicating that the content and spatial distribution of organic matter in the surface sediments of Minghu Lake are the main controlling factors for the content and spatial distribution characteristics of various forms of nitrogen in the sediments.

Using a nitrogen and oxygen isotopic approach to identify nitrate sources and cycling in the Wei River of northwestern China

ABSTRACTThe Wei River is the largest tributary of the Yellow River in China. To understand the sources and cycling of nitrate in the Wei River, we determined the concentrations and nitrogen and oxygen isotopic values of nitrate from water samples. Our results revealed that NO3−-N dominated the inorganic N and ranged from 0.1 to 8.8 mg/L (averaging 3.3 mg/L). Although this NO3−-N concentration does not exceed the World Health Organization's drinking water standard of 10 mg/L, the NO3−-N content of most water samples exceeded 3 mg/L, indicating poor water quality. The NO3−-N concentrations and δ15N-NO3− values demonstrate that there are significant differences in the spatial distribution of nitrogen between the tributaries and the main stream of the Wei River. In addition, a negative linear relationship (r2 = 0.63) between NO3−-N concentrations and δ18O-NO3− values suggests mixing between two distinct sources (fertilizer and manure or sewage). Furthermore, we infer that the main source of nitrate is not manure or sewage itself, but rather the nitrification of NH4+ in manure and sewage. Finally, no obvious denitrification processes were observed. These results expand our understanding of sewage as a major source of nitrate to the Wei River, emphasizing the role of nitrification.

Risk Assessment of Nitrogen and Phosphorus Loss in a Hilly-Plain Watershed Based on the Different Hydrological Period: A Case Study in Tiaoxi Watershed

Non-point source pollution is widely considered a serious threat to drinking water. Eutrophication in Chinese watershed is mainly due to nitrogen and phosphorus output from agricultural source. Taihu Lake is a typical eutrophic lake in China, a basin representative for the study of the temporal-spatial characteristics of pollution loading of nitrogen and phosphorus to provide scientific basis for reasonable estimation and targeted control measures of nitrogen and phosphorus loss. Based on data from nitrogen and phosphorus loss in agricultural land, livestock breeding, domestic discharge and aquaculture, this study calculated the levels of nitrogen and phosphorus comprehensive loss risk for each pollution source. Using the superposition of ArcGIS raster data, we also described the spatial distribution of nitrogen and phosphorus comprehensive loss risk by the formula of comprehensive loss risk. The results showed that critical risk areas of nitrogen and phosphorus loss mainly originated from livestock breeding and agricultural land during flood period in Tiaoxi watershed. Agricultural land and livestock breeding sources formed major parts of nitrogen loss, accounting for 30.85% and 36.18%, respectively, while phosphorus loss mainly originated from livestock breeding (56.28%). During non-flood period, integrated management of livestock breeding and domestic discharge requires much attention to control nitrogen and phosphorus loss in the critical risk area. Finally, it is of great practical significance to propose spatial-temporal targeted measurements to control nitrogen and phosphorus pollution in watershed for various periods and different areas.

Structural analysis and oxygen reduction reaction activity in bamboo-like nitrogen-doped carbon nanotubes containing localized nitrogen in nodal regions

Nitrogen-doped carbon nanotubes (N-CNTs) act as a metal-free catalyst for oxygen reduction reaction (ORR), but improving the ORR activity of N-CNTs remains challenging due to a lack of structural information. The N-CNTs with higher nitrogen concentration (an average surface nitrogen concentrations, 14.3 at.%) than the N-CNTs fabricated by conventional chemical vapor deposition method were synthesized using a dielectric barrier discharge in high pressure nitrogen and the spatial distribution of nitrogen in the N-CNTs was demonstrated by transmission electron microscopy in conjunction with electron energy loss spectroscopy. Nitrogen atoms were found to be concentrated at nodal regions in the bamboo-like structure, at concentrations above 23 at.%. At the point of the ORR, the highest onset potential was observed in the N-CNTs due to relatively highly incorporated pyridine-like nitrogen.

Enhanced visible light adsorption of heavily nitrogen doped TiO2 thin film via ion beam assisted deposition

Nitrogen doping is widely used to enhance the visible light absorption of TiO2 by narrowing the bandgap. It is recognized that this modification is sensitively affected by the spatial distribution of anion doping. In order to explore the effects of nitrogen distributions in TiO2, we synthesized nitrogen-doped TiO2 thin films via the ion-beam assisted deposition (IBAD) technique and calcinations in NH3 atmosphere. The morphology and crystal structure of these thin films were characterized by scanning electron microscope and X-ray diffraction respectively. The chemical states and spatial distributions of nitrogen in the TiO2 were investigated by X-ray photoelectron spectroscopy. The nitrogen can be heavily and uniformly doped in anatase thin film by the IBAD technique with the N/Ti atomic ratio ranging from 61.3 to 51.9 %, much higher than that calcinated at 500 °C under NH3 atmosphere, which fluctuated from 23.2 to 4.5 %. The time-dependent depth profile of the N 1s spectrum shows that the doped nitrogen in the TiON thin film synthesized via IBAD distributes from the surface to the inner layer. Compared to the traditional calcinations synthesized methods, the as-synthesized TiON thin film, shows a much higher absorption in the visible-light range. Its light absorbance spectrum extends to over 700 nm, covering most of the visible-light region.

Temporal and Spatial Distribution Characteristics of Nitrogen and Phosphorus in Soil with Typical Crops Planted on in Headwater Region of Liao He

This paper discusses the temporal and spatial distribution of nitrogen, phosphorus in the soil with typical crops planted on in Headwater Region of Liao He. The purpose is to provide theoretical basis for the prediction of the non-point source pollution and protection of the environment in Headwater Region of Liao He. The results show that the content of the substance which can be absorbed by plants was higher in the surface soil than that in the bottom soil. The nitrate nitrogen content in soil was lower in autumn than that in spring except normal planting surface soil. And the ammonia nitrogen content was also a little lower in autumn than that in spring except normal planting surface soil and blank control land 1. In autumn, the hydrolyzable nitrogen content in the surface soil was decreased slightly and it was nearly unchanged in the bottom soil. The total nitrogen content was higher in autumn. The content of available phosphorus was a little higher or nearly unchanged in autumn than that in spring, the content of total phosphorus changed irregularly.

Spatial-uniform application method of methane fermentation digested slurry with irrigation water in the rice paddy field

Promoting biomass utilization, the objectives of this study were to clarify the spatial distribution of nitrogen, one of the most important fertilizer components in the methane fermentation digested slurry (i.e., the digested slurry), and to establish an effective method to apply spatial-uniformly digested slurry with irrigation water in the rice paddy field. A numerical model describing the unsteady two-dimensional flow and solution transport of paddy irrigation water was introduced. The accuracy of this model was verified with a field observation. The tendencies of the TN simulated in inlet and outlet portions had good agreement with the measured data and the accuracy of the numerical model could be verified. Using the numerical model, scenario analyses were conducted to determine the method for spatial-uniform application of the digested slurry with irrigation water. The simulated results indicated that drainage of the surface water and trenches at the soil surface were effective for spatial-uniform application of the digested slurry with irrigation water in the rice paddy fields. The effect of the trenches was maximized when the surface water of the rice paddy field was drained adequately.

3D Analysis of the Morphology and Spatial Distribution of Nitrogen in Nitrogen-Doped Carbon Nanotubes by Energy-Filtered Transmission Electron Microscopy Tomography

We present here the application of the energy-filtered transmission electron microscopy (EFTEM) in the tomographic mode to determine the precise 3D distribution of nitrogen within nitrogen-doped carbon nanotubes (N-CNTs). Several tilt series of energy-filtered images were acquired on the K ionization edges of carbon and nitrogen on a multiwalled N-CNT containing a high amount of nitrogen. Two tilt series of carbon and nitrogen 2D maps were then calculated from the corresponding energy-filtered images by using a proper extraction procedure of the chemical signals. Applying iterative reconstruction algorithms provided two spatially correlated C and N elemental-selective volumes, which were then simultaneously analyzed with the shape-sensitive reconstruction deduced from Zero-Loss recordings. With respect to the previous findings, crucial information obtained by analyzing the 3D chemical maps was that, among the two different kind of arches formed in these nanotubes (transversal or rounded ones depending on their morphology), the transversal arches contain more nitrogen than do the round ones. In addition, a detailed analysis of the shape-sensitive volume allowed the observation of an unexpected change in morphology along the tube axis: close to the round arches (with less N), the tube is roughly cylindrical, whereas near the transversal ones (with more N), its shape changes to a prism. This relatively new technique is very powerful in the material science because it combines the ability of the classical electron tomography to solve 3D structures and the chemical selectivity of the EFTEM imaging.

Light–nitrogen relationships within reproductive wheat canopy are modulated by plant modular organization

Within dense canopies, the spatial distribution of nitrogen between leaves in relation to the local light environment is an important and widely investigated adaptive response of plant carbon and nitrogen economy. However a general picture of how nitrogen distribution in photosynthetic tissues, not only in leaf laminae, is structured at plant scale and is affected by the topology and light environment of plant modules (i.e. lamina, sheath, internode) is missing. We investigated the spatial patterns of nitrogen distribution in relation with plant botanical structure for wheat (Triticum aestivum L.) culms. Nitrogen distribution between and within laminae, sheaths and internodes was quantified at anthesis and during grain filling, for two cultivars with contrasted leaf posture grown in the field under low and high N fertilization. We found that independently of leaf posture, specific nitrogen mass (i.e. nitrogen mass per unit surface area) was homogeneous within individual laminae and sheaths, although they spanned a significant depth in the canopy. Sharp changes in nitrogen specific mass at module boundaries were observed. At the canopy level, vertical nitrogen gradients resulted from a decrease of mean specific nitrogen mass of individual plant modules with their position along the culm, and laminae and sheaths specific nitrogen mass decreased linearly with the distance from the top of the canopy. There was no significant gradient of N concentration on a dry mass basis within and between the enclosed internodes, only the distal part of the ear peduncle, which was exposed to the light, showed a strong N gradient. This study gives important information to better understand the phenotypic plasticity of nitrogen distribution in wheat and to build a process-based model of N distribution within wheat culms during the post-anthesis period. It strongly supports the idea that processes should be formalized at the module scale and that a similar formalization can be used for individual laminae and sheaths.

Optimization of Monitoring Network Point about Total N in Soil in Hangjiahu Plain

In this paper, Monitoring network point about total content of Nitrogen in surface soil was studied on optimization in Hangjiahu plain, based on the geostatistics, variance and linear correlation. And Background of Total N in soil were compared before and after network point optimization. The result showed that sampling density may improve from 1 point/4km2 to 1 point/64km2. this monitoring result of Total N only can reflect spatial distribution of Nitrogen, but can not reveal its actual circumstance. Detailed investigation of the lowest scale must be done if the distribution of Nitrogen in surface Soil wanted to be understood comprehensively. Zhejiang Province had firstly completed multi-purpose geochemical survey for 1:250000 from 2002 to 2005 [1]. Total N content in surface soil was the central task of the survey because high nitrogen content in soil fertility was not only the characteristics of the land but also one of the reasons of non-point source pollution. In order to grasp the overall trend of geochemical in Hangjiahu plain and timely discover the changes about environment quality of soil total N elements, a multi-level environmental geochemistry monitoring network must be promptly established[2]. But it’s a problem needed to be solved immediately by the geological, environmental and agricultural scientists that how to meet the needs of the accuracy of the premise, with a minimum of sampling points to design the best program of distribution, thereby saving time and cost of sampling. At present, most people used properties of soil spatial variability and spatial analysis methods to solve this problem [3].

Nitrogen and phosphorus in Estonian rivers discharging into Lake Peipsi: estimation of loads and seasonal and spatial distribution of concentrations

Our study aims to estimate the riverine loads of nutrients to Lake Peipsi sensu stricto and to assess their effect on the lake's water quality. The data of national monitoring of 1992-2007 were used for the determination of seasonal and spatial distribution of nitrogen and phosphorus in the rivers discharging into Lake Peipsi s.s. Statistical conclusions and tests were based on a multi- parametric model. Our calculations revealed that the major Estonian rivers discharged approximately 5600 tonnes of nitrogen and 179 tonnes of phosphorus annually to Lake Peipsi s.s. Nitrogen export coefficients varied from 4 to 8 kg N ha -1 yr -1 , while the range of P losses was from 0.12 to 0.21 kg P ha -1 yr -1 . Seasonal variation in nitrogen concentrations had a sinusoidal pattern, with high concentrations during winter and spring and low values in summer, whereas phosphorus dynamics created a slightly different picture, with a much more irregular variation and a smaller amplitude over the year. Only a few rivers showed a pattern of notably higher phosphorus concentrations during summer low flows and more diluted concentrations during winter and spring. The differences in the concentration of phosphorus were mainly explained by variation in water discharge, while the availability of nitrogen in rivers was determined rather by seasonality. Nutrient concentrations in rivers discharging into Lake Peipsi are probably still influenced by nutrient stores from the period of intensive fertilization. Although a local effect of nitrogen loads on the lake's water quality was detected, the concentration of phosphorus in lake water remained insensitive to year-to-year changes in the riverine load of phosphorus.

Nitrogen and Luminescent Nitrogen‐Vacancy Defects in Detonation Nanodiamond

An efficient method to investigate the microstructure and spatial distribution of nitrogen and nitrogen-vacancy (N-V) defects in detonation nanodiamond (DND) with primary particle sizes ranging from approximately 3 to 50 nm is presented. Detailed analysis reveals atomic nitrogen concentrations as high as 3 at% in 50% of diamond primary particles with sizes smaller than 6 nm. A non-uniform distribution of nitrogen within larger primary DND particles is also presented, indicating a preference for location within the defective central part or at twin boundaries. A photoluminescence (PL) spectrum with well-pronounced zero-phonon lines related to the N-V centers is demonstrated for the first time for electron-irradiated and annealed DND particles at continuous laser excitation. Combined Raman and PL analysis of DND crystallites dispersed on a Si substrate leads to the conclusion that the observed N-V luminescence originates from primary particles with sizes exceeding 30 nm. These findings demonstrate that by manipulation of the size/nitrogen content in DND there are prospects for mass production of nanodiamond photoemitters based on bright and stable luminescence from nitrogen-related defects.