Influences of temperature and nutrients on Synechococcus abundance and biomass in the southern Mid-Atlantic Bight   总被引：1，自引：0，他引：1  

Tiffany A. Moisan  Kristen L. Blattner  Carla P. Makinen 《Continental Shelf Research》2010

Synechococci are small (<1 μm) coccoid prokaryotes that play a significant ecological role in microbial food webs and are important contributors to carbon and nitrogen biogeochemical cycles. Under funding from NOAA and NASA, we developed a time series observatory to understand the seasonal variability of Synechococcus and other phytoplankton. Our goal is to understand the distribution and relative contribution of Synechococcus to the carbon cycle and how they relate to nutrients and temperature. Synechococcus in the southern Mid-Atlantic Bight exhibited a clear seasonal abundance pattern in both inshore and offshore waters—peaking in abundance (11×10⁴ cells ml⁻¹) during warm periods of summer. Synechococci were numerically important during periods of stratification when waters were warm and macronutrients were low. Using a simple algorithm to convert cellular volume to cellular carbon using image analysis, we estimated that Synechococcus cellular carbon ranged from 0.1 to 1.5 pg C per cell and was most significant compared to total particulate carbon in the summer peaking at ∼25% of the total carbon available. No direct correlations were found between Synechococcus abundance and nitrate, nitrite, ammonium, phosphate, and silicate. However, inshore Synechococcus abundance peaked at 10⁴ cells ml⁻¹ when nitrogen concentrations were lowest. Our results suggest that Synechococcus is adapted to warm temperatures and are capable of demonstrating rapid growth during summer when macronutrients are limiting. The ability of Synechococcus to take advantage of high summer temperatures, low nutrient concentrations and low light levels allows them to maintain a picoplankton community during periods of low detritus and nanophytoplankton is nutrient limited. Temperature-dependence is important in altering the size spectrum of the phytoplankton community and affects the carbon cycle on the Mid Atlantic Bight.  相似文献   

Fluoride,nitrate and water hardness in groundwater supplied to the rural communities of Ensenada County,Baja California,Mexico   总被引：1，自引：0，他引：1  

L. W. Daesslé  L. Ruiz-Montoya  H. J. Tobschall  R. Chandrajith  V. F. Camacho-Ibar  L. G. Mendoza-Espinosa  A. L. Quintanilla-Montoya  K. C. Lugo-Ibarra 《Environmental Geology》2009,58(2):419-429

The hydrogeochemistry of 26 wells belonging to ten different aquifers in the county of Ensenada, Baja California, is studied. These wells are all used to supply the rural communities in the region, which comprise ~37,000 inhabitants, excluding the city of Ensenada. High total dissolved solids (TDS) concentrations (maximum 7.35 g l⁻¹) indicate that salt is a ubiquitous contaminant in the aquifers due to seawater intrusion. The aquifers that support extensive agriculture activities (Maneadero, San Quintín, San Simón and El Rosario) are characterized by higher N–NO₃ concentrations (maximum 20 mg l⁻¹) derived from fertilizers. Fluoride concentrations exceed the 1.5 mg l⁻¹ Mexican official limit in only four wells. The enrichments of F⁻ in the southern aquifers are thought to be associated to water–rock interactions controlled mainly by Na–Ca equilibrium reactions with fluorite, as suggested from high dissolved Na concentrations in these waters. In the northern aquifer of Maneadero, no enrichment of Na is found and a geothermal source for F⁻ is likely. Water is hard to moderately hard, with Ca/Mg ratios >1. Although drinking water directly from the tap is not a common practice in these localities, most sources have concentrations of major ions and TDS that exceed the Mexican official limits.  相似文献   

Impact of the Use of Reclaimed Water on the Quality of Groundwater Resources in the Jordan Valley,Jordan     

Mustafa Al Kuisi  Taiseer Aljazzar  Thomas Rüde  Armin Margane 《洁净——土壤、空气、水》2008,36(12):1001-1014

The use of reclaimed water and its impact on groundwater quality in the middle and southern parts of the Jordan Valley are investigated. The chemical analyses indicate that nitrate and bacteriological pollution is widespread, and thus, seriously affects groundwater use. During the study, 365 water samples were collected from wells and springs to determine the water chemistry and the extent of nitrate pollution. Three hydrochemical facies are identifed, i. e., (Ca–(Mg)–Na–HCO₃), (Ca–Na–SO₄–Cl) and (Ca–Na–Cl). The change of facies is accompanied by a gradual increase in the groundwater total dissolved solids (TDS), which is mainly controlled by evaporates and carbonates dissolution in the aquifer matrix. Water analyses indicate that the shallow aquifer in the study area is affected by non‐point pollution sources, primarily from natural (manure) and chemical nitrogen (N)‐fertilizers and treated wastewater used for agriculture. The concentration of nitrate in the groundwater ranges from 10 to 355 mg/L. Considerable seasonal fluctuations in groundwater quality are observed as a consequence of agricultural practices and other factors such as annual rainfall distribution and the Zarqa River flow. The noticeable levels of total coliform and Escherichia coli in the northern part of the study area may be attributed to contamination from the urban areas, intensive livestock production, and illegal dumping of sewage. Heavy metal concentrations in all samples were found to be significantly lower than the permissible limits for drinking water standards.  相似文献   

东海北部海水中硝酸盐(NO_3-N)的分布及其成因     

臧家业 《海洋科学进展》1999,(3)

本文根据“中日黑潮合作调查”在东海的调查资料,探讨了硝酸盐的分布特征,以及水文条件对其分布的影响,并比较了不同年份夏季硝酸盐的分布差异及其原因。分析表明,表层海水中硝酸盐分布明显受长江冲淡水影响,陆架区测值高于外海,冬季测值高于夏季; ５０ｍ ,１００ｍ 层上陆架、黑潮锋区存在着硝酸盐锋面,黑潮主干的摆动可能是影响锋面位置的主要因素  相似文献   

硝酸盐中氮和氧同位素比值的测定及其地质意义   总被引：3，自引：0，他引：3       下载免费PDF全文

尹德忠  肖应凯 《盐湖研究》1999,7(1):61-66

本文系统总结了硝酸盐中氮和氧同位素组成的测定方法及其地质意义研究现状。基于此,作者指出硝酸盐中氮和氧同位素在地质上的应有前景依赖于两方面：精确灵敏快捷的同位素测定方法及其地质意义的深入开发研究。  相似文献   

Progress in the Study of Marine Stable Nitrogen Isotopic Changes and Its Geological Records     

Yanchen Zhu  Li Li  Peng Wang  Juan He  Guodong Jia 《地球科学进展》2020,35(2):167-179

Marine stable nitrogen isotope containing much key biogeochemical information, is an important way in identifying marine nitrogen sources and understanding the marine nitrogen cycles. These isotopic signals can be preserved in marine sediments and used to trace the marine biogeochemical cycles and environment changes during geological history. Studies in recent decades have illustrated the key role of nitrogen fixation and denitrification. Because of the spatiotemporal variability and the complexity of ocean processes and nitrogen sources in the marine environment, we need to combine the modern observations with geological records, integrate oceanography, biology, and geology, and consider the hydrological environment, geological processes and climate changes, to understand the coupling between the ocean nitrogen cycle, climate and environmental changes.  相似文献   

Potential rates and environmental controls of denitrification and nitrous oxide production in a temperate urbanized estuary   总被引：4，自引：0，他引：4  

Catarina Teixeira  Catarina Magalhes  Rui A.R. Boaventura  Adriano A. Bordalo 《Marine environmental research》2010,70(5):336-342

  相似文献   

沈阳市城乡梯度湿地水体碳氮磷含量变化研究     

王娇月  郗凤明  侯伟  邴龙飞  尹岩  徐婷婷  王佳凤  马铭婧 《气候变化研究进展》2020,16(4):453-465

湿地是人类生存和发展的重要环境之一,然而城镇化在带动经济发展的同时也严重影响了湿地生态系统。本文利用城乡梯度研究方法结合湿地分布特征,设置从沈阳城市中心到城市边缘的研究样带,沿着城镇密集区（浑河）—郊区（蒲河）—乡村（卧龙湖,仙子湖）梯度带选取典型湖泊和河流湿地样地为研究对象,系统分析城镇化对湿地水体碳氮磷含量的影响。研究发现湿地水体碳氮磷含量与城乡梯度具有相关性,总碳（TC）和可溶性有机碳（DOC）含量及SUVA₂₈₀值沿城镇密集区—郊区—乡村梯度带逐渐增加,即远离市中心的乡村卧龙湖湿地最高,分别为（120.68±2.34）mg/L,（41.56±6.27）mg/L和（0.35±0.10）L/(mg·m),显著高于位于四环以外乡村仙子湖湿地、流经沈阳市四环蒲河和穿越三环浑河湿地水体。湿地水体氮磷含量总体上沿着城乡梯度带呈降低趋势,但蒲河湿地水体总氮（TN）和总磷（TP）含量最高,分别为（5.35±0.19）mg/L和（1.45±0.07）mg/L,显著高于位于城镇密集区的浑河湿地水体。城镇化作用总体上增加了湿地水体铵态氮（NH₄⁺-N）和硝态氮（NO₃^--N）含量,其中,横穿城镇密集区的浑河湿地水体NH₄⁺-N含量最高,为（1.28±0.14）mg/L;NO₃^--N含量则是位于郊区的蒲河湿地水体最高,为(1.42±0.15) mg/L。研究结果表明城镇化改变了湿地生态系统水体碳氮磷含量,使水体DOC含量降低,小分子化合物增多,不利于DOC在水体中的累积;同时由于人类活动的加剧也使氮磷排放增加,使水体氮磷超标,导致流经城镇密集区部分的浑河和蒲河湿地NH₄⁺-N和NO₃^--N含量高于乡村。未来随着城镇化的不断发展,应严加控制和合理规划,防止城镇化导致的湿地水体污染和生态系统的破坏。  相似文献   

吉南元古代片岩建造中构造蚀变带型金矿床控矿因素——以通化南岔金矿为例     

华铭  张梅生 《国土资源》1997,(1)

吉林南部沿老岭断块南缘分布的金矿床（点）以南岔金矿床为代表，应属产于元古代片岩建造中的构造蚀变带型金矿床。其区域控矿因素是老岭群花山组片岩建造、断裂构造和燕山期岩浆岩。  相似文献   

Sensitivity of DaisyGIS to LAI: Implications for land use based modelling of nitrate leaching     

Anita Veihe  Niels H. Jensen  Eva Boegh  Peter Frederiksen  Michael W. Pedersen 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(2):75-85

Geografisk Tidsskrift, Danish Journal of Geography 106(2): 75–85, 2006

Scaling is an important issue when measuring, modelling and understanding coupled socio-environmental terrestrial systems. Scaling may be enhanced through the incorporation of remotely sensed data. This paper assesses the sensitivity of DaisyGIS to changes in the Leaf Area Index (LAI) and discusses the implications for land use based modelling of nitrate leaching using remote sensing based LAI estimates. It is shown how DaisyGIS simulates nitrate leaching quite well over the period 2001 to 2004 except for one plot during a season with winter rape. It was found that the model is sensitive to changes in LAI with increases of up to 262% on nitrate leaching rates when reducing LAI by 15%. At the same time, the nitrate leaching rates at the field level vary considerably due to local changes in the water balance determined by soil profile characteristics. DaisyGIS is already an important tool for aiding decision makers and this study has shown how remote sensing based LAI estimates may be a valuable tool for model parameterisation and potentially for model validation.  相似文献