河口季节性缺氧在沉积物中记录的研究进展   总被引：3，自引：0，他引：3  

冯旭文  于晓果  陈建芳  金翔龙 《海洋学研究》2006,24(1):50-61

综述了用分子地层学方法反演河口缺氧及富营养化发生与发展的研究进展,对可追溯缺氧发生的时间及变化趋势、表征人类活动对缺氧的影响的表征的参数的研究进展进行了分析。研究表明:美国河口缺氧事件的发生可追溯到上世纪中期,自70年代起也呈愈演愈烈的发展趋势。沿海人口的增加及人类活动的加剧导致了营养物质输入的增加,再加上全球变暖的趋势,河口区域缺氧将朝更加严重的方向发展,为此需要采取必要措施,通过减少营养物质尤其是硝酸盐的输入来减缓缺氧。  相似文献   

钱塘江河口段长周期泥沙冲淤和河床变形   总被引：2，自引：0，他引：2  

余炯  曹颖 《海洋学研究》2006,24(2):28-38

通过对钱塘江河口段50多年连续水下地形资料的整理和分析,给出了该河口段在遭遇连续丰、枯水文年时的长周期泥沙冲淤特点,以及相应塑造的顺直、弯曲两种河势在河床形态与演变上的差异。研究结果认为,长周期泥沙冲淤和河床变形是钱塘江河口段保持冲淤平衡的一种自动调整手段;与冲积河流不同的是,钱塘江河口段通过河型、比降、断面等因素的调整来改变进入该河口段潮流量的大小。  相似文献   

Variation in canopy conductance of Cunninghamia lanceolata forest and its response to environmental factors after an extreme rainfall event     

Wanqiu Xing  You Cheng  Lilin Yang  Weiguang Wang 《水文研究》2024,38(3):e15121

Canopy conductance (g_c) is a crucial parameter in simulating evapotranspiration and modulating water exchange, but its variation mechanism has regional uncertainties and complex environmental co-controls. In addition, the effect of extreme rainfall on g_c cannot be ignored under the changing climate. Here, we investigated the variation and environmental controls on g_c and the effect of extreme rainfall events in a Cunninghamia lanceolata forest across the subtropical area of Southern China. In July 2020, an extreme rainstorm hit the source area of the Xin'an River, with the cumulative rainfall on July 7 and 8 reaching 216.6 mm. The thermal diffusion probe method was used to measure the density of sap flow, and the environmental factors such as air temperature (T_a), net solar radiation (R_n) and soil water content (SWC) were monitored during the growing seasons of 2020 and 2021. Ultimately, g_c obtained by the Penman-Monteith equation was adopted since the result from the Köstner equation was overestimated. g_c showed a unimodal curve on the diurnal scale, and this characteristic was more obvious after the extreme rainfall. Daily g_c appeared a fluctuating pattern with a maximum in summer. g_c was simultaneously affected by T_a, R_n, water vapour pressure difference (VPD), SWC, among which T_a was the most significant driving factor at both the diurnal and daily timescales. The regulation of T_a, VPD and SWC on g_c had obvious thresholds, and the most definite response mode was VPD (2020: 1.25 kPa; 2021: 0.95 kPa). SWC and T_a were the dominant factors after the rainfall period, and the promotion effect of VPD on post-rainy days turned to inhibition effect on typical sunny days. These findings will further reveal the water exchange mechanism between atmosphere and vegetation and impacts of environmental factors in subtropical coniferous forests, especially after the extreme rainfall events.  相似文献   

Chlorophyll distributions in the Delaware estuary: Regulation by light-limitation     

Jonathan R. Pennock 《Estuarine, Coastal and Shelf Science》1985,21(5):711-725

Phytoplankton chlorophyll concentrations in the Delaware estuary range over two orders of magnitude and display several maxima over the seasonal cycle. These maxima were found to be regulated both spatially and temporally by light availability. Both the spring chlorophyll maximum, which reaches 50–60 μg chlorophyll l^?1 during a Skeletonema costatum dominated bloom, and transient fall blooms (15–20 μg l^?1) are focused in mid-estuary. These blooms are regulated spatially by settling out of suspended sediment below the turbidity maximum and both spatially and temporally by physical factors (e.g. river flow) that cause vertical stratification in mid-estuary. In freshwater regions, chlorophyll concentrations display seasonal periodicity correlated with solar irradiance; summer chlorophyll concentrations average 30 μg l^?1. These freshwater and mid-estuarine biomass maxima may be correctly predicted using a steady-state light-limitation model. In contrast, summer chlorophyll concentrations in the lower estuary remain below 10 μg l^?1 and are not correctly modeled, despite minimum turbidity, and non-nutrient limiting conditions. These chlorophyll concentrations appear to be regulated by a combination of light availability and grazing.Although extremely high anthropogenic nutrient inputs in the freshwater region of the Delaware River provide non-limiting nutrient concentrations throughout the estuary, regulation of phytoplankton growth by light-limitation restricts chlorophyll concentrations below the nuisance levels found in many eutrophic systems.  相似文献   

Effects of Sediment-induced Stratification on Floc Breakup in an Idealized Tidal Estuary： A Numerical Modelling Study     

X.H.Wang 《中国海洋大学学报(英文版)》2004,3(2):115-122

Floc breakup dynamics are studied by a sediment transport numerical model in an idealized tidal estuary that has a constant water depth and rapid flocculation of cohesive sediments. The focus is placed on the effects of boundary layer stratification induced by a bottom nepheloid layer on floc breakup and size distribution in the water column. In a neutrally stratified estuary, the floc size distribution follows a parabolic function with maximum values at the surface and bottom. The sediment-induced stratification in the bottom boundary layer increases the median floc sizes. Furthermore, sediment-voided convection caused by the settling lutocline generates significant turbulent kinetic energy dissipation and reduces floc size at the depth where the convective mixing happens. Below that depth, a weak local maxima in the floc size is predicted due to presence of the lutocline. The effect of sediment-stratified bottom boundary layer on the floc breakup can be consistently approximated by a linear regression between the maximal floc size and flux Richardson number.  相似文献   

广东南部地理景观中土壤重金属垂直分异及其地球化学分层性     

洪继华  章申 《地理研究》1988,7(4):21-31

本文研究热带亚热带土壤中重金属分布的垂直分异及其分层性特征.土壤剖面中,水溶态、可交换态和有机结合态的重金属浓度自上层向底层降低.水溶态和有机结合态重金属的分布与有机质一致,而与pH值相反.Fe-Mn氧化物结合态的重金属分布与粘粒一致.残渣态分布的差异极小.  相似文献   

Redox cycling of iron and manganese in sediments of the Kalix River estuary, Northern Sweden     

Anders Widerlund  Johan Ingri 《Aquatic Geochemistry》1996,2(2):185-201

Iron and manganese redox cycling in the sediment — water interface region in the Kalix River estuary was investigated by using sediment trap data, pore-water and solid-phase sediment data. Nondetrital phases (presumably reactive Fe and Mn oxides) form substantial fractions of the total settling flux of Fe and Mn (51% of Fe_total and 84% of Mn_total). A steady-state box model reveals that nondetrital Fe and Mn differ considerably in reactivity during post-depositional redox cycling in the sediment. The production rate of dissolved Mn (1.6 mmol m^–2 d^–1) exceeded the depositional flux of nondetrital Mn (0.27 mmol m^–2 d^–1) by a factor of about 6. In contrast, the production rate of upwardly diffusing pore-water Fe (0.77 mmol m^–2 d^–1) amounted to only 22% of the depositional flux of nondetrital Fe (3.5 mmol m^–2 d^–1). Upwardly diffusing pore-water Fe and Mn are effectively oxidized and trapped in the oxic surface layer of the sediment, resulting in negligible benthic effluxes of Fe and Mn. Consequently, the concentrations of nondetrital Fe and Mn in permanently deposited, anoxic sediment are similar to those in the settling material. Reactive Fe oxides appear to form a substantial fraction of this buried, non-detrital Fe. The in-situ oxidation rates of Fe and Mn are tentatively estimated to be 0.51 and 0.16–1.7 mol cm^–3 d^–1, respectively.  相似文献   

SOUTHERN BOUNDARY FORCING RELATIVE TO GENESIS,MAINTENANCE AND OSCILLATION OF A SUBTROPICAL HIGH          下载免费PDF全文

陆维松  陶丽 《Acta Meteorologica Sinica》1998,(1)

A nonlinear critical layer and a Kelvin cat's eye excited thereupon are simulated through fourschemes in the context of a nonlinear quasi-geostrophic barotropic vorticity equation model withforced stationary wave acting along the southern boundary to investigate effects of tropical steadyforcing on the genesis,maintenance and oscillation of a subtropical high(STH).Evidence suggeststhat the southern forcing is responsible for the planetary quasi-steady anticyclonic Kelvin cat's eye-form flow field inside the nonlinear critical layer,with the eye shifting,vigor and shape changingquite similar to the behaviors of a summer STH,in striking contrast to the northern stationaryforcing.As such,the southern boundary-caused cat's eye is likely to be an even more importantmechanism for STH genesis and evolution.In addition,a physical mechanism is introduced forquasi-steady planetary wave moving through the critical layer at subtropical latitudes.  相似文献   

徐六泾潮流量测验及整编技术研究     

宋志宏  胡国栋 《水文》1998,(2):31-36

徐六泾水文站是长江干流最后一个控制站,该站水文测验断面位于长江口感潮河段。为探求该站的潮流变化规律,按规范要求整编出该处的逐潮潮量,徐六泾水文站十几年来进行了大量的测验技术及整编方案的研究,本文将这些研究成果和发展方向作一个简要的介绍。  相似文献   

Different Configurations of Interannual Variability of the Western North Pacific Subtropical High and East Asian Westerly Jet in Summer     

Xinyu LI  Riyu LU  Gen LI 《大气科学进展》2021,38(6):931-942

This study investigates the circulation and precipitation anomalies associated with different configurations of the western North Pacific subtropical high(WNPSH) and the East Asian westerly jet(EAJ) in summer on interannual timescales. The in-phase configuration of the WNPSH and EAJ is characterized by the westward(eastward) extension of the WNPSH and the southward(northward) shift of the EAJ, which is consistent with the general correspondence between their variations. The out-of-phase configuration includes the residual cases. We find that the in-phase configuration manifests itself as a typical meridional teleconnection. For instance, there is an anticyclonic(cyclonic) anomaly over the tropical western North Pacific and a cyclonic(anticyclonic) anomaly over the mid-latitudes of East Asia in the lower troposphere. These circulation anomalies are more conducive to rainfall anomalies over the Yangtze River basin and south Japan than are the individual WNPSH or EAJ. By contrast, for the out-of-phase configuration, the mid-latitude cyclonic(anticyclonic) anomaly is absent, and the lower-tropospheric circulation anomalies feature an anticyclonic(cyclonic)anomaly with a large meridional extension. Correspondingly, significant rainfall anomalies move northward to North China and the northern Korean Peninsula. Further results indicate that the out-of-phase configuration is associated with the developing phase of ENSO, with strong and significant sea surface temperature(SST) anomalies in the tropical central and eastern Pacific which occur simultaneously during summer and persist into the following winter. This is sharply different from the in-phase configuration, for which the tropical SSTs are not a necessity.  相似文献