Modelling a discrete spatial response using generalized linear mixed models: application to Lyme disease vectors     

Abhik Das  Subhash R. Lele  Gregory E. Glass  Timothy Shields  Jonathan Patz 《International journal of geographical information science》2013,27(2):151-166

Predicting disease risk by identifying environmental factors responsible for the geographical distribution of disease vectors can help target control strategies and optimize preventive measures. In this study we present a hierarchical approach to model the distribution of Lyme disease ticks as a function of environmental factors. We use the Poisson framework natural for count data while allowing for spatial correlations. To help identify environmental factors that best explain tick abundance, we develop an intuitive procedure for covariate selection in the spatial context. These methods could be useful in analysing effects of environmental and climatological changes on the distribution of disease vectors, and the spatial extrapolation of vector abundance under such scenarios.  相似文献   

Electrokinetic Restoration of Sulfate‐Accumulated Saline Greenhouse Soil     

Jung‐Min Cho  Do‐Hyung Kim  Jung‐Seok Yang  Kitae Baek 《洁净——土壤、空气、水》2011,39(12):1036-1040

Electrokinetic (EK) process was performed to restore sulfate‐originated saline soil and to evaluate the effect of treatment duration. Sulfate and potassium were the major ionic salts in the saline soil used in this study. A constant voltage gradient of 1 V/cm was applied for 8, 12, and 16 days. After EK treatment, anions and cations were transported toward anode and cathode, respectively, by electromigration. Chloride was completely removed, and 85.6% of nitrate was removed after 8 days of treatment. The increase of treatment period from 8 to 12 days had a negligible effect on the enhancement in the rate of sulfate removal; however, over 70% was removed after16 days. At the end of experiment, the electrical conductivity (EC) of the soil, an indicator of soil salinity, decreased to 1.93 dS/m from an initial value of 5.3 dS/m, and the distribution of sulfate was similar to that of EC. The operation time of 16 days was sufficient to restore the sulfate‐originated saline soil using the EK process.  相似文献   

桂林寨底地下河硝酸根含量特征研究   总被引：1，自引：0，他引：1  

王松  裴建国 《地下水》2011,33(3):21-22,25

工农业生产迅速发展使地下水硝酸盐污染成为世界性的环境问题.因此,研究地下水中硝酸根含量特征具有重要意义,在水文地质条件特殊的西南岩溶地区尤为重要.本文以岩溶地区典型地下河--广西桂林寨底地下河为例,分析了地下河系统不同季节硝酸根含量特征,发现地下河中硝酸根含量受降雨和人类活动影响较大.  相似文献   

Close coupling between ammonium uptake by phytoplankton and excretion by Antarctic krill, Euphausia superba     

M.J. WhitehouseA. Atkinson  A.P. Rees 《Deep Sea Research Part I: Oceanographic Research Papers》2011,58(7):725-732

In this study we examined the hypothesis that, under conditions of replete macronutrients and iron in the Southern Ocean, phytoplankton abundance and specific N uptake rates are influenced strongly by the processes of grazing and NH₄ regeneration. NH₄ and NO₃ uptake rates by marine phytoplankton were measured to the northeast and northwest of the island of South Georgia during January-February 1998. Mean specific uptake rate for NO₃ (vNO₃) was 0.0026 h⁻¹ (range 0.0013-0.0065 h⁻¹) and for NH₄ (vNH₄) was 0.0097 h⁻¹ (0.0014-0.0376 h⁻¹). vNH₄ was related positively with NH₄ availability, which ranged from 0.1 to 1.5 mmol m⁻³ within the upper mixed layer. Ambient NH₄ concentrations and vNH₄ were both positively related to local krill biomass values, computed from mean values along acoustic transect segments within 2 km of the uptake measurement stations. These biomass values ranged from ∼1 g krill fresh mass m⁻² in the northwest to >4 kg krill wet mass m⁻² in the northeast. In contrast to the variability found with NH₄ concentrations and uptake rates, vNO₃ was more uniform across the sampling sites. Under these conditions, increasing NH₄ concentration appeared to represent an additional N resource. However, high vNH₄ tended to be found for stations with lower phytoplankton standing stocks, across a total range of 0.24-20 mg chlorophyll a m⁻³. These patterns suggest a coupling between phytoplankton biomass, vNH₄ and krill in this region of variable but high krill biomass. Locally high concentrations of krill in parts of the study area appeared to have two opposing effects. On the one hand they could graze down phytoplankton stocks, but on the other hand, their NH₄ excretion supported enhanced uptake rates by the remaining, ungrazed cells.  相似文献   

Trends and occurrences of nitrate in the groundwater of the West Bank, Palestine   总被引：2，自引：0，他引：2  

Fathi M. Anayah  Mohammad N. Almasri   《Applied geography (Sevenoaks, England)》2009,29(4):588-601

Groundwater is the major source of water to the Palestinians. Efficient management of this resource requires a good understanding of its status. This understanding necessitates a characterization of the quality of the utilizable volumes. This paper focuses on the assessment of nitrate concentrations in the aquifers of the West Bank, Palestine. A preliminary statistical analysis is carried out for the spatial and temporal distributions of the nitrate concentrations. GIS is utilized to facilitate the analysis and to efficiently account for the spatiality of nitrate concentrations. The analysis was carried out at different spatial levels and key parameters including soil type, watersheds, depth, population, and rainfall. It is observed that elevated nitrate concentrations in the groundwater greatly coincide with increasing rainfall, particularly in the last few years. Results confirm that the annual mean nitrate concentration in the Western groundwater basin has an increasing trend over the period from 1982 to 2004 indicating its vulnerability to contamination. This result can be attributed to the agricultural activities along with the high groundwater recharge. However, leaking septic and sewer systems are considerably causing nitrate contamination of groundwater in populated areas. Overall, the recommendations call for an immediate intervention to manage the quality problems in the West Bank aquifers.  相似文献   

昆明盆地北部浅层地下水硝酸盐污染分析     

戴启  莫美仙  陈海宁 《云南地质》2009,28(4):437-444

研究认为东部浅层地下水的污染比较严重,硝酸盐超标率达到了88％;在靠近湖滨平原区地下水硝酸盐为中等污染,其超标率在（30．77～66．67）％之间。时间上,研究区随着土地利用的变化,地下水硝酸盐污染在最近几年在逐渐趋向减轻。  相似文献   

Groundwater quality in the lower Varuna River basin,Varanasi district,Uttar Pradesh   总被引：2，自引：0，他引：2  

N. Janardhana Raju  Prahlad Ram  Sangita Dey 《Journal of the Geological Society of India》2009,73(2):178-192

The lower Varuna River basin in Varanasi district situated in the central Ganga plain is a highly productive agricultural area, and is also one of the fast growing urban areas in India. The agricultural and urbanization activities have a lot of impact on the groundwater quality of the study area. The river basin is underlain by Quaternary alluvial sediments consisting of clay, silt, sand and gravel of various grades. The hydrogeochemical study was undertaken by randomly collecting 75 groundwater samples from dug wells and hand pumps covering the entire basin in order to understand the sources of dissolved ions, and to assess the chemical quality of the groundwater through analysis of major ions. Based on the total dissolved solids, two groundwater samples are considered unsuitable for drinking purpose, but all samples are useful for irrigation. Graphical treatment of major ion chemistry by Piper diagram helps in identifying hydro-geochemical facies of groundwaters and the dominant hydrochemical facies is Ca-Mg-HCO₃ with appreciable percentage of the water having mixed facies. As per Wilcox’s diagram and US Salinity laboratory classification, most of the groundwater samples are suitable for irrigation except two samples (No’s 30 and 68) which are unsuitable due to the presence of high salinity and medium sodium hazard. Irrigation waters classified based on residual sodium carbonate, have revealed that all groundwaters are in general safe for irrigation except one sample (No. 27), which needs treatment before use. Permeability index indicates that the groundwater samples are suitable for irrigation purpose. Although the general quality of groundwater of the lower Varuna River basin is suitable for irrigation purpose, fifty seven percent of the samples are found having nitrate content more than permissible limit (>45 mg/l) which is not good for human consumption. Application of N-Fertilizers on agricultural land as crop nutrients along the Varuna River course may be responsible for nitrate pollution in the groundwater due to leaching by applied irrigation water. The other potential sources of high nitrate concentration in extreme northern, southern and southwestern parts of study area are poor sewerage and drainage facilities, leakage of human excreta from very old septic tanks, and sanitary landfills. The high fluoride contamination (>1.5 mg/l) in some of the samples may be due to the dissolution of micaceous content in the alluvium. Nitrate and fluoride contamination of groundwater is a serious problem for its domestic use. Hence an immediate protective measure must be put into action in the study area.  相似文献   

Impact of fertilizer application and urban wastes on the quality of groundwater in the Cambrai Chalk aquifer,Northern France     

Hani Serhal  Daniel Bernard  Jamal El Khattabi  Bastin-Lacherez Sabine  Isam Shahrour 《Environmental Geology》2009,57(7):1579-1592

Since 1975, Europe sets up its policy to limit the degradation and the pollution of the aquatic environments through 30 directives and regulations. In the north of France, the nitrate concentrations measured in the groundwater exceed the water drinking limit fixed at 50 mg/L by the European framework directive in the field of water (2000/60/EC). This high concentration is due to intensive agriculture, industrialization and demographic growth. Several programs were launched in order to resolve this situation: “Ferti-better” or the use of fertilizer in moderation and installation and amelioration of wastewater collect and treatment systems. In order to estimate the influence of the anthropic activities on the quality of groundwater in the “Artois-Picardy” basin, a preliminary validation on parcel and district scale were necessary. The impact of these programs in the “Cambrai district” was evaluated using an integrated approach, which is based on the use of four numerical models: AgriFlux, VS2DT, Modflow and MT3D. The results illustrate an improvement due to the “Ferti-Better” program initiated in 1990 and punctual degradation under urbanized areas. Predictions (2015) show a spatial evolution of nitrates concentration varying with the thickness of unsaturated layer. The integrated model constitutes an efficient tool for predicting the evolution of the groundwater quality. This approach is important to control the application of the new European laws in the water field.  相似文献   

Assessment of nitrate contamination in unsaturated zone of urban areas: The case study of Tehran,Iran   总被引：1，自引：0，他引：1  

Vahid Joekar-Niasar  Behzad Ataie-Ashtiani 《Environmental Geology》2009,57(8):1785-1798

Modeling fate of nitrogen in unsaturated and saturated zone is a complex process, which requires detailed geochemical data. Complexities of the process as well as data insufficiencies are two major issues, which make quantitative assessment of the problem more complicated. In this work, a lumped-parameter model (LPM) is proposed that has been evaluated for a data-limited case to study temporal and steady-state behavior of Nitrate and Ammonium in unsaturated zone. The concentration of components in the model are assumed as the depth-averaged concentrations, and dispersive fluxes have been neglected. The case study area is Tehran City aquifer, which is highly contaminated by domestic wastewater discharge into the groundwater. Three sources for Nitrogen contamination have been studied, namely domestic wastewater, park/recreational applications, and wet deposition. Results show that Nitrate production in the first few meters (<5 m) is quite large. To compare the model results with the measurements, error estimation analysis based on Vornoi map has been fulfilled. Finally, it is shown that there is a fairly good correlation coefficient between simulation and measurements, which approves the validity of the LPM.  相似文献   

Advance in Studies on Intracellular Nitrate Storage and Denitrification of Benthic Foraminifera     

Xu Zhaomeng  Liu Sumei 《地球科学进展》2017,32(9):949-958

Benthic foraminifera is the first kind of eukaryotes reported to carry on denitrification, which breaks the understanding of the eukaryotic metabolic way. Numerous studies have demonstrated that the contribution of benthic foraminifera to sedimentary denitrification exceeds the prokaryotes. Furthermore, benthic foraminifera stores large amount of nitrate intracellularly, which far exceeds the amount of nitrate in pore water. These findings challenge our understanding of the nitrogen cycle in sediments. The study of foraminiferal intracellular nitrate storage and denitrification is significant to figure out the metabolic way of eukaryote in anoxic environment and to quantify the balance of nitrogen in marine environment. The history of foraminiferal intracellular nitrate storage and denitrification study was discussed. In addition, the distribution of foraminiferal intracellular nitrate and denitrification rates in marine environment was also discussed. The latest research progresses about the related mechanism were also summarized. Finally, the problems and challenges in present and future studies were discussed.  相似文献