Assessment of excess nitrate development in the subtropical North Atlantic     

D.A. Hansell  D.B. Olson  F. Dentener  L.M. Zamora   《Marine Chemistry》2007,106(3-4):562-579

Geochemical estimates of N₂ fixation in the North Atlantic often serve as a foundation for estimating global marine diazotrophy. Yet despite being well-studied, estimations of nitrogen fixation rates in this basin vary widely. Here we investigate the variability in published estimates of excess nitrogen accumulation rates in the main thermocline of the subtropical North Atlantic, testing the assumptions and choices made in the analyses. Employing one of these previously described methods, modified here with improved estimates of excess N spatial gradients and ventilation rates of the main thermocline, we determine a total excess N accumulation rate of 7.8 ± 1.7 × 10¹¹ mol N yr^− 1. Contributions to excess N development include atmospheric deposition of high N:P nutrients (adding excess N at a rate of 3.0 ± 0.9 × 10¹¹ mol N yr^− 1 for  38% of the total), high N:P dissolved organic matter advected into and mineralized in the main thermocline (adding excess N at 2.2 ± 1.1 × 10¹¹ mol N yr^− 1 for  28% of the total), and, calculated by mass balance of the excess N field, N₂ fixation (adding excess N at 2.6 ± 2.2 × 10¹¹ mol N yr^− 1 for  33% of the total). Assuming an N:P of 40 and this rate of excess N accumulation due to the process, N₂ fixation in the North Atlantic subtropical gyre is estimated at  4 × 10¹¹ mol N yr^− 1. This relatively low rate of N₂ fixation suggests that i) the rate of N₂ fixation in the North Atlantic is greatly overestimated in some previous analyses, ii) the main thermocline is not the primary repository of N fixed by diazotrophs, and/or iii) the N:P ratio of exported diazotrophic organic matter is much lower than generally assumed. It is this last possibility, and our uncertainty in the N:P ratios of exported material supporting excess N development, that greatly lessens our confidence in geochemical measures of N₂ fixation.  相似文献   

Effect on marine sediment nitrogen fluxes caused by organic matter enrichment with varying organic carbon structure and nitrogen content     

Ingela Dahllf  Ida-Maja Karle 《Marine Chemistry》2005,94(1-4):17

Enrichments with five types of organic carbon, differing in nitrogen content and type of organic carbon, were made to a marine sediment in order to study effects on nitrogen fluxes. The enrichments used were Ulva lactuca, Ascophyllum nodosum, Zostera marina, Ceratium spp., lignin, and mixtures of U. lactuca and A. nodosum. Fluxes of ammonium, nitrate, and phosphate were measured in short-term (48 h) microcosm experiments, using a carbon enrichment loading similar to that at the sampling site. Changes in microbial community growth and structure due to three types enrichments were also detected using molecular methods in a microcosm experiment run for 4 days to allow for detection at DNA-level.Ammonium fluxes changed from an efflux in the control to an influx for all enrichments apart from U. lactuca. The change was significantly related to the added material's C:N ratio when Ceratium spp. was excluded. All enrichments induced an influx of nitrate suggesting the formation of anoxic micro zones, but there was no relationship with C:N ratio. Instead, the magnitude of the nitrate influx is suggested to be related to the structure of the organic carbon, where enrichments containing a large pool of cellulose and lignin (Z. marina and lignin) gave rise to a lower influx, compared to algal material with more easily degraded organic matter like lipids and starch, which induced the highest influx of nitrate (Ceratium spp., U. lactuca, and A. nodosum). The occurrence of an ammonium influx together with increased nitrate influx and a lower efflux of phosphate in the enrichments suggests a growth of heterotrophic bacteria. This was also confirmed using molecular methods (PCR-DGGE) where the relative abundance of bacterial species in the enrichments increased.The sum of ammonium and nitrate fluxes showed that total nitrogen removal was enhanced in all enrichments compared to the nonenriched control sediment, but in different ways. Ceratium spp. induced the highest removal followed by A. nodosum, U. lactuca, Z. marina, and lastly, by lignin. The same pattern was observed also in a second experiment. These results indicate that easily degradable organic carbon, together with a lower C:N ratio of the added material, will remove nitrogen from the water phase, making the recycling of nitrogen to the overlying water mass smaller.  相似文献   

海洋中氮营养盐循环及其模型研究   总被引：17，自引：1，他引：17  

任玲  杨军 《地球科学进展》2000,15(1):58-64

对某一海区营养盐的去向、不同形态间的相互转化及其与生物相关的过程的研究是研究整个海洋生态系统的基础和关键。氮是海洋环境中主要的营养元素之一,并被认为是大部分海区的限制营养元素。人们对于氮在海洋环境中的循环过程的研究随着分析方法及对化学和生物知识的掌握和理解而不断加深。模型研究是研究海洋生态系统的一个有效方法,营养盐循环模型是其中重要的环节,随着理论和观测数据的补充而不断发展。综述了海洋环境中氮营养盐循环主要过程的实验研究,主要包括:浮游植物的吸收、氮的再生、微生物在其循环中的作用、不同形态氮的化学转化、水体-沉积物界面等,及其相关过程近十年来模型化研究的进展。  相似文献   

地下水NO3-氮与氧同位素研究进展   总被引：1，自引：0，他引：1  

邓林  曹玉清  王文科 《地球科学进展》2007,22(7):716-724

人为活动通常是地下水硝酸盐污染的主要原因.不同来源的NO3-具有不同的氮、氧同位素组成,利用地下水NO3-中的δ15N和δ18O值可有效识别地下水硝酸盐污染的来源.引起地下水中NO3-含量显著减少的不同物理、化学和生物过程,所产生的氮、氧同位素分馏效应有明显差别.地下水系统中反硝化作用发生时,NO3-中氮和氧同位素分馏系数呈一定比例.因此NO3-中δ15N和δ18O值也是示踪地下水硝酸盐循环,尤其是反硝化作用的有效手段.利用NO3-中氮和氧双同位素,并与其他环境同位素及化学分析技术相结合,示踪NO3-来源及其循环是地下水硝酸盐污染研究的重要方向之一.综述了利用地下水硝酸盐中氮和氧同位素识别NO3-污染源与循环的研究进展,简述了近年迅速发展的阴离子交换树脂取样法,概述了此方面研究存在的主要问题,并展望了今后的研究方向.  相似文献   

Assessment of groundwater pollution around Torbali,Izmir, Turkey     

A. O. Aksoy  T. Scheytt 《Environmental Geology》2007,53(1):19-25

The Kuihe River is in Xuzhou, Jiangsu, China. It contains high concentrations of nitrogen. The water in the Kuihe River recharges the groundwater via riverbank filtration (RBF) along the Xucun and Huangqiao reaches, which are characterized by unsaturated and saturated percolations, respectively. The two sections were selected to study the effectiveness of RBF to the nitrogen removal from the infiltrating river water. The results showed that the RBF in the saturated percolation had the potential to remove the nitrogen through biochemical processes. The nitrogen-removal rates were more than 95% over the monitoring period. However, the RBF in the unsaturated percolation resulted mainly from the physical process and thus had no efficacy for nitrogen removal.  相似文献   

区域化学输送模式中NO x和O3源示踪法的引入   总被引：4，自引：0，他引：4  

江文华  马建中 《气象学报》2006,64(3):281-292

发展了化学输送模式中氮氧化合物(NOx)和臭氧(O3)的一种源示踪方法,对这种示踪法及其应用模式作了详细介绍,并结合臭氧光化学反应机理的分析描述了NOx和O3示踪物浓度方程的推导过程。将这种示踪法引用到区域化学输送模式中,并以太原和石家庄地表NOx人为排放产生的活性氮化物和臭氧为例,演示了污染物向北京的输送过程,模拟的O3,NOx和NOz示踪物浓度时空分布与O3,NOx和NOz在大气中的衰减尺度分析一致,表明该示踪法是一种有效的研究区域氮氧化物以及臭氧来源和输送转化过程的方法。个例模拟分析结果显示:太原和石家庄的地表人为排放产生的NOx本身并不能输送到北京,但通过它们产生的O3和HNO3可以输送到北京,对北京地表附近大气污染造成影响。  相似文献   

Before and after riparian management: sediment and nutrient exports from a small agricultural catchment, Western Australia   总被引：6，自引：0，他引：6  

Lucy A. McKergow  David M. Weaver  Ian P. Prosser  Rodger B. Grayson  Adrian E. G. Reed 《Journal of Hydrology》2003,270(3-4):253-272

Riparian vegetation can trap sediment and nutrients sourced from hillslopes and reduce stream bank erosion. This study presents results from a 10-year stream monitoring program (1991–2000), in a 6 km² agricultural catchment near Albany, Western Australia. After 6 years, a 1.7 km stream reach was fenced, planted with eucalyptus species and managed independently from the adjacent paddocks. Streamflow, nutrient and sediment concentration data were collected at the downstream end of the fenced riparian area, so there are data for before and after improved riparian management. Suspended sediment (SS) concentrations fell dramatically following improved riparian management; the median event mean concentration (EMC) dropped from 147 to 9.9 mg l⁻¹. Maximum SS concentrations dropped by an order of magnitude. As a result, sediment exports from the catchment decreased following improved riparian management, from over 100 to less than 10 kg ha⁻¹ yr⁻¹. Observations suggest that this was the result of reduced bank erosion and increased channel stability. Riparian management had limited impact on total phosphorus (TP) concentrations or loads, but contributed to a change in phosphorus (P) form. Before improved riparian management, around half of the P was transported attached to sediment, but after, the median filterable reactive P (FRP) to TP ratio increased to 0.75. In addition, the median FRP EMC increased by 60% and the raw median FRP concentration increased from 0.18 to 0.35 mg l⁻¹. These results suggest that there was a change in the dominant P form, from TP to FRP. Changes in total nitrogen (TN) following improved riparian management were less clear. There were reductions in TN concentrations at high flows, but little change in the loads or EMC. This study demonstrates the benefits of riparian management in reducing stream bank erosion, but suggests that in catchments with sandy, low P sorption soils, there may be limitations on the effectiveness of riparian buffers for reducing P and N exports.  相似文献   

Nutrient Budgets,Dynamics and Storm Effects in a Eutrophic,Stratified Baltic Lake     

Gerald Schernewski 《洁净——土壤、空气、水》2003,31(2):152-161

Between 1989 and 1998 the small eutrophic stratified Lake Belau was investigated intensively and multidisciplinarily. This article is a short, comprehensive summary and re‐evaluation of the hydrochemistry of the lake, with focus on nitrogen and phosphorus. In several aspects the lake can be regarded as a typical example of the glacial north German lakes. The 1960's and 1970's are characterised by heavy nutrient inputs and fast eutrophication. During the last two decades the external nutrient load, especially the phosphorus load into Lake Belau was significantly reduced. But phosphorus‐rich sediments and large areas with summerly anoxic sediment surface conditions cause intensive release of phosphorus from older deeper sediment layers. Annual budgets reveal that despite an average sediment accumulation of 3 mm a^?1 the lake has lost its function as net phosphorus sink and it is very likely that internal eutrophication by the sediments will keep the lake in its eutrophic state during the next decades. Despite that, monthly budgets of five vertical layers show that the main phosphorus supplier for the phosphorus depleted epilimnion during summer is the creek Alte Schwentine. The annual nitrogen budget indicates groundwater and interflow water as well as atmospheric input as additional important nitrogen sources. 36% (98 μmol m ^?2 h^?1 N) of all nitrogen input is lost to atmosphere mainly due to denitrification. The example of a heavy storm shows that about 10% of the annual nitrogen loss to the atmosphere can take place during a single day and in form of ammonia. The storm further made obvious that these unpredictable events can have strong impact on nutrient cycling and ecology in Lake Belau and the lake can become an unexpected nutrient source for downstream systems.  相似文献   

三江平原大豆田氮循环模拟研究   总被引：12，自引：0，他引：12  

王毅勇  杨青  王瑞山 《地理科学》1999,19(6):555-558

三江平原是我国面积最大的湿地分布区,经多年开垦现已发展成为我国重要的商品粮基地,由于开垦后下垫面条件发生了很大变化,加之农业生产活动的影响,使本区土壤氮循环发生了根本性的改变。以三江平原地区典型低湿地大豆田为研究对象,采用美国新罕布什尔大学李长生教授所提出的一种生物地球化学模型ＤＮＤＣ来模拟农田生态系统中土壤－植被－大气之间氮素的循环,以及温室气体Ｎ２Ｏ的排放规律。  相似文献   

Der Ozean als Quelle reaktiver Stickstoffverbindungen     

U. Lenhard  H. -W. Georgii 《Pure and Applied Geophysics》1980,118(2):1145-1154

The paper deals with the atmospheric gaseous nitrogen-compounds under special consideration of the ocean being a source for NH₃. The distribution of NH₃ and NH₄ ⁺ in the ocean is discussed. Additionally a survey of measured marine pH-values is given. While in temperate latitudes the source-strength of the ocean seems to be low, no such statement can be made at present for tropical latitudes owing to lack of measurements.

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