Effect of emersion and immersion on the porewater nutrient dynamics of an intertidal sandflat in Tokyo Bay   总被引：2，自引：0，他引：2  

Tomohiro Kuwae  Eiji Kibe  Yoshiyuki Nakamura 《Estuarine, Coastal and Shelf Science》2003,57(5-6):929-940

Porewater nutrient dynamics during emersion and immersion were investigated during different seasons in a eutrophic intertidal sandflat of Tokyo Bay, Japan, to elucidate the role of emersion and immersion in solute transport and microbial processes. The water content in the surface sediment did not change significantly following emersion, suggesting that advective solute transport caused by water table fluctuation was negligible. The rate of change in nitrate concentration in the top 10 mm of sediments ranged from −6.6 to 4.8 μmol N l⁻¹ bulk sed. h⁻¹ during the whole period of emersion. Steep nutrient concentration gradients in the surface sediment generated diffusive flux of nutrients directed downwards into deeper sediments, which greatly contributed to the observed rates of change in porewater nutrient concentration for several cases. Microbial nitrate reduction within the subsurface sediment appeared to be strongly supported by the downward diffusive flux of nitrate from the surface sediment. The stimulation of estimated nitrate production rate in the subsurface layer in proportion to the emersion time indicates that oxygenation due to emersion caused changes in the sediment redox environment and affected the nitrification and/or nitrate reduction rates. The nitrate and soluble reactive phosphorus pools in the top 10 mm of sediment decreased markedly during immersion (up to 68% for nitrate and up to 44% for soluble reactive phosphorus), however, this result could not be solely explained by molecular diffusion.  相似文献   

The influence of salinity on the solubility of Zn and Cd sulphides in the Scheldt estuary   总被引：2，自引：0，他引：2  

L. J. A. Gerringa  H. J. W. de Baar  R. F. Nolting  H. Paucot 《Journal of Sea Research》2001,46(3-4)

In the estuary of the river Scheldt, where an oxygen gradient exists in addition to the salinity gradient, redox processes will be of major importance for trace metal mobilisation. In this study, the influence of salinity and pH on the redox processes of dissolved Zn and Cd sulphides is investigated together with the effects on the ratio of the dissolved Zn and Cd concentrations. The speciation of these metals is calculated with the chemical equilibrium programme +. Zn sulphides are oxidised at lower oxygen concentrations than Cd sulphides, due to lower stability constants, causing a sudden increase or peak in the dissolved Zn/Cd ratio. The formation of dissolved Cd chloride complexes when oxidation occurs at high salinities (S=15) increases the mobility of Cd, causing a decrease in the Zn/Cd peak of the total dissolved concentrations. The peak is three to four times smaller at S=15 than when oxidation occurs at S=2. The simple model calculations compare very well with field data. The Scheldt estuary is suitable to illustrate these calculations. In the 1970s, the anoxic part of the estuary reached S=15–20, but since the early 1980s it has dropped to S=2–10. Historic data on metals in the estuary from 1978, 1987 and the 1990s were used to compare with the equilibrium calculations. The increase of the dissolved Zn/Cd peak at low salinity as a consequence, of the decreasing anoxic region is confirmed well by the data. The good agreement between model calculations and field data is a proof of the extreme importance of redox processes for the solubility of Zn and Cd sulphides in the estuary.  相似文献   

Shallow-Water Gasohydrothermal Vents of Ushishir Volcano and the Ecosystem of Kraternaya Bight (The Kurile Islands)   总被引：2，自引：0，他引：2  

V. G. Tarasov    M. V. Propp    L. N. Propp    A. V. Zhirmunsky    B. B. Namsakakv    V. M. Gorlenko  D. A. Starynin 《Marine Ecology》1990,11(1):1-23

Abstract. A marine ecosystem in the crater of the Ushishir Volcano (Kraternaya Bight, Yankich Island, the Kuriles) showing gasothcrmal activity was studied for hydrographical, hydrochemical, and biological characteristics. Maximal changes in chemical and biological characteristics were observed in the surface water layer of 0–5 m. This layer had higher water temperature, was saturated with volcanogcnic carbon dioxide (up to 2000 10^-6 torr), ovcrsaturatcd with oxygen (up to 200 %), and contained high concentrations of chlorophyll a. Hydrogen sulfide was found in the surface water layer and at a depth of 15 m in the area of maximal effect of volcanic effluents.
The planktonic community is characterized by high rates of production and destruction of organic matter only in the 0–5 m layer. Daily vertical migrations of the ciliatc Mesodinium rubrum were observed, which caused "red tides".
Bacterial, algobacterial, and diatom mats developed on the bottom of the bight in the zone of gasohydrothermal vents and in areas of volcanic water seeping. The rate of organic matter production in algobacterial mats reached 33.4g C-rrr²-d^-l, chcmolithotrophy predominating. Bottom settlements had high population density and great animal biomass, which reached 10 kg m^-2 in gasohydrothermal fields. They obtain sufficient energy from primary production of microphy-tobenthos, algobacterial, and bacterial mats. Bcnthic species dominant in the bight were not found off the Ushishir Islands.
Some species of macrobenthos inhabiting the Kraternaya Bight differ markedly in size and biomass from the same species found beyond the bight.  相似文献   

Elucidating the dynamics and mixing agents of a shallow fjord through age tracer modelling     

Karin E. Gustafsson  Jrgen Bendtsen 《Estuarine, Coastal and Shelf Science》2007,74(4):641

The mixing agents and their role in the dynamics of a shallow fjord are elucidated through an Eulerian implementation of artificial tracers in a three-dimensional hydrodynamic model. The time scales of vertical mixing in this shallow estuary are short, and the artificial tracers are utilized in order to reveal information not detectable in the temperature or salinity fields. The fjord's response to external forcing is investigated through a series of model experiments in which we quantify vertical mixing, transport time scales of fresh water runoff and estuarine circulation in relation to external forcing.Using age tracers released at surface and bottom, we quantify the time scales of downward mixing of surface water and upward mixing of bottom water. Wind is shown to be the major agent for vertical mixing at nearly all depth levels in the fjord, whereas the tide or external sea level forcing is a minor agent and only occasionally more important just close to the bottom. The time scale of vertical mixing of surface water to the bottom or ventilation time scale of bottom water is estimated to be in the range 0.7 h to 9.0 days, with an average age of 2.7 days for the year 2004.The fjord receives fresh water from two streams entering the innermost part of the fjord, and the distribution and age of this water are studied using both ageing and conservative tracers. The salinity variations outside this fjord are large, and in contrast to the salinity, the artificial tracers provide a straight forward analysis of river water content. The ageing tracer is used to estimate transport time scales of river water (i.e. the time elapsed since the water left the river mouth). In May 2004, the typical age of river water leaving the fjord mouth is 5 days. As the major vertical mixing agent is wind, it controls the estuarine circulation and export of river water. When the wind stress is set to zero, the vertical mixing is reduced and the vertical salinity stratification is increased, and the river water can be effectively exported out of the fjord.We also analyse the river tracer fields and salinity field in relation to along estuary winds in order to detect signs of wind-induced straining of the along estuary density gradient. We find that events of down estuary winds are primarily associated with a reduced along estuary salinity gradient due to increased surface salinity in the innermost part of the fjord, and with an overall decrease in vertical stratification and river water content at the surface. Thus, our results show no apparent signs of wind-induced straining in this shallow fjord but instead they indicate increased levels of vertical mixing or upwelling during down estuary wind events.  相似文献   

Temporal variations in benthic communities and their response to physicochemical forcing: a numerical approach   总被引：1，自引：0，他引：1  

Triantafyllou  G.; Petihakis  G.; Dounas  C.; Koutsoubas  D.; Arvanitidis  C.; Eleftheriou  A. 《ICES Journal of Marine Science》2000,57(5):1507-1516

  相似文献   

Meiobenthic Organisms as Indicators of Mixing Processes in the Baltic Surface Sediments*     

Janusz Pempkowiak  Joanna Kozuch  Maria Szymelfenig 《Marine Ecology》1996,17(1-3):175-179

Abstract. Two sediment cores were collected in the southern Baltic Sea and sliced into 1.0cm-thick layers. Sediments of each layer were analysed for activities of ²¹⁰Pb, ¹³⁷Cs, ¹³⁴Cs and for the density of meiobenthic organisms (meiofauna). Zones with the rapid mixing occur in the uppermost layers (0–3 cm) of the cores based on ^I34Cs profiles. The extent and density of meiofauna confirmed the rapid mixing and revealed layers with slow mixing (4–8 cm). Sedimentation rates were derived from ²¹⁰Pb profiles below the mixing zones (1.21 and 1.72 mm a-^I) and were confumed by ¹³⁷Cs distribution. Of twenty-one major meiofauna taxa commonly found in the Baltic sediments, three were present in the cores.  相似文献   

中太平洋CP25岩心的矿物、稀土元素及Sr、Nd同位素组成--晚新生代海底火山活动的证据   总被引：3，自引：0，他引：3  

刘季花  崔汝勇  卢效珍  陈丽蓉 《海洋地质与第四纪地质》1999,19(2):5

中太平洋ＣＰ２５岩心沉积物中钙十字沸石、蒙脱石／伊利石比值（Ｍ／Ｉ）、稀土元素含量、铈异常（δＣｅ）、铕异常（δＥｕ）及Ｓｒ、Ｎｄ同位素特征作为海底火山活动的证据,揭示了中太平洋海盆晚新生代以来火山活动和沉积的历史。其结果是,早中新世约２０～１７ＭａＢ．Ｐ．间,火山活动逐渐强烈,在１７ＭａＢ．Ｐ．最强烈,使得沉积物具有高Ｍ／Ｉ和∈Ｎｄ、低δＣｅ和８７Ｓｒ／８６Ｓｒ。１７～１ＭａＢ．Ｐ．发生沉积间断。１ＭａＢ．Ｐ．至现代,火山活动较早中新世减弱  相似文献   

内陆河流域山区水文与生态研究   总被引：5，自引：0，他引：5  

康尔泗  陈仁升  张智慧  吉喜斌  金博文 《地球科学进展》2008,23(7):675-681

以河西走廊黑河干流山区流域为例,从山区水文循环、水文与生态系统以及径流形成和预测等方面讨论山区流域水文和生态相互作用研究的有关问题。山区降水的空间和时间分布规律和固态、液态降水组成变化主要受制于海拔和地形的影响,而不同海拔和地形条件下的下垫面不同土地覆被和复杂的空间异质性则主要影响蒸散发量。对内陆河山区流域的水文小循环的研究,有助于进一步研究和认识内陆河流域上、中、下游水文和生态系统的相互联系问题。至今,对山区水文过程与生态系统的相互作用问题的研究还非常薄弱,需要研究山区森林草地生态系统在山区水文循环中的作用以及在维持和保护山区生态和环境中的作用和意义。内陆河流域山区水文过程复杂而综合性强,须加强对山区径流形成机理的多学科交叉研究,不断改善出山径流对气候变化和人类活动响应过程的模拟和预测水平。  相似文献   

流变学:构造地质学和地球动力学的支柱学科   总被引：12，自引：6，他引：6  

嵇少丞  钟大赉  许志琴  夏斌 《大地构造与成矿学》2008,32(3)

地球是一动态系统,其各层圈的构造运动归根到底就是多矿物复合岩石在各种物理条件(例如,温度、围压、差应力、应变速率、应变方式等)下和化学环境(例如,氧逸度和水含量)中的形变。流变学作为研究岩石力学性质和变形行为的科学,现已成为地球动力学和构造地质学的支柱学科。本文对国际上近年来岩石流变学的最新进展做些扼要的介绍,呼吁中国固体地学界加强流变学的研究,做出经得起时间淘洗、实践检验的原创性成果来,使中国的构造地质学研究迈进国际先进的行列。  相似文献   

土壤吸湿-湿过程中水力传导度的拟合研究     

郝鹏  郑西来  田守波  马玉杰  李伟 《地下水》2008,30(3):4-7

非饱和含水介质在吸湿和脱湿的不同过程中,水力传导度随介质含水率的变化规律是不同的。本文选取大沽河流域两种代表性砂土,对其吸湿-脱湿两个过程分别进行试验观测,并使用VanGenuchten—Mualem模型对其吸湿-脱湿过程进行水力传导度的拟合。研究结果表明：砂土在吸湿过程的非饱和水力传导度与脱湿过程的非饱和水力传导度大小并不相同,在含水率相同的情况下,吸湿过程的水力传导度要比脱湿过程大,在含水率较低时（小于15％）相差可达1个数量级。  相似文献