Separate and interactive effects of eutrophication and climate variables on the ecosystem elements of the Gulf of Riga   总被引：1，自引：0，他引：1  

Jonne Kotta  Ilmar Kotta  Mart Simm  Maria Pllupüü 《Estuarine, Coastal and Shelf Science》2009,84(4):509-518

There is currently a critical knowledge gap in how eutrophication and climate variables separately and interactively impact the dynamics of marine ecosystems. Based on long-term monitoring data we quantified the separate and combined impacts of nutrient loading, temperature, salinity, and wind conditions on zooplankton, zoobenthos and fish inhabiting a brackish water ecosystem in the Gulf of Riga. Changes in zoobenthos communities and herring stock were largely explained by climate variables. Zooplankton species were related to both eutrophication and climate variables, and models combining all environmental variables explained additional variation in zooplankton data compared to the separate models of climate and eutrophication. This suggests that zoobenthos communities and herring stock are largely driven by weather conditions, whereas the combined effect of weather and nutrient loads are likely the cause for dynamic zooplankton communities in the Gulf of Riga.  相似文献   

Determining the age of water and long-term transport timescale of the Chesapeake Bay   总被引：5，自引：0，他引：5  

Jian Shen  Harry V. Wang 《Estuarine, Coastal and Shelf Science》2007,74(4):585-598

The concept of age of water (AW) is applied to the Chesapeake Bay to investigate the long-term transport properties for dissolved substances. A real-time calibrated hydrodynamic Chesapeake Bay model in 3 Dimensions (CH3D), employing a boundary-fitted curvilinear grid, is used for the study. The long-term transport properties, represented by AW, are investigated under the conditions of low river inflow of 1995 and high river inflow of 1996, as well as for constant mean inflows. The influences of freshwater, density-induced circulation, and wind-induced transport on age distribution have been investigated. Model results show that river inflows, wind stress, and density-induced circulation play important roles in controlling the long-term transport in the Bay. The model results shows that it requires 120–300 days for a marked change in the characteristics of the pollutant source discharged into the Bay from the Susquehanna River to affect significantly the conditions near the mouth under different hydrodynamic conditions. An increase of river discharge results in increases of downstream residual current and gravitational circulation, and thus reduces AW. The density-induced circulation contributes to the transport substantially. The dissolved substances discharged into the Bay are transported out of the Bay more rapidly when the estuary becomes more stratified. Southeasterly and southwesterly winds have strong impacts on the transport compared to the northeasterly and northwesterly winds. The former increases lateral and vertical mixing significantly. Consequently, the gravitational circulation is reduced and the transport time is increased by 50%. The model results provide useful information for understanding the long-term transport processes in the Bay.  相似文献   

Long-term changes in summer phytoplankton communities of the open northern Baltic Sea   总被引：16，自引：0，他引：16  

Sanna Suikkanen  Maria Laamanen  Maija Huttunen 《Estuarine, Coastal and Shelf Science》2007,71(3-4):580-592

Changes in the biomass and species composition of phytoplankton may reflect major shifts in environmental conditions. We investigated relationships between the late summer biomass of different phytoplankton taxa and environmental factors, and their long-term (1979–2003) trends in two areas of the Baltic Sea, the northern Baltic proper (NBP) and the Gulf of Finland (GF), with statistical analyses. An increasing trend was found in late summer temperature and chlorophyll a of the surface water layer (0–10 m) in both areas. There was also a significant decrease in summer salinity and an increase in winter dissolved inorganic nitrogen to phosphorus (DIN:DIP) ratio in the NBP, as well as increases in winter DIN concentrations and DIN:SiO₄ ratio in the GF. Simultaneously, the biomass of chrysophytes and chlorophytes increased in both areas. In the NBP, also the biomass of dinophytes increased and that of euglenophytes decreased, whereas in the GF, cyanobacteria increased and cryptophytes decreased. Redundancy analysis (RDA) indicated that summer temperature and winter DIN concentration were the most important factors with respect to changes in the phytoplankton community structure. Thus, the phytoplankton communities seem to reflect both hydrographic changes and the ongoing eutrophication process in the northern Baltic Sea.  相似文献   

河口物质和水体长期输运分离的理论分析和观测验证 Ⅰ.物质和水体长期输运分离的理论分析     

朱首贤  丁平兴  沙文钰  张文静 《海洋学报》2008,30(6):24-29

基于单宽断面潮周期平均水体和物质对流输运通量,定义了二维水体和物质长期输运速度,它们分别描述单宽断面水体和物质长期输运的方向及快慢。通过二维水体和物质长期输运速度的对比分析,提出了物质和水体长期输运分离概念:受物质浓度影响,在物质和水体瞬时运动速度相同的情况下,物质和水体潮周期平均对流输运的方向和快慢可能存在差异。本文将二维物质长期输运速度分解为二维水体长期输运速度、二维潮泵输运速度和垂向切变输运速度,它们分别描述余流输运、潮泵输运和垂向切变输运,后两种输运造成单宽断面物质和水体长期输运分离。本文的分析表明,河口受地形、径流、潮流、密度梯度影响,存在有利于物质和水体长期输运分离的自然条件。  相似文献   

珠江口近30a的SST变化特征分析   总被引：5，自引：0，他引：5  

汤超莲  郑兆勇  游大伟  邓松  黄亚如 《台湾海峡》2006,25(1):96-101

根据珠江口多个定点站近30a表层海水温度（SST）实测资料和气象站观测的气温资料，使用功率谱和小波分析方法，计算分析珠江口SST变化特点、上升趋势及其与El Nino／La Nino的响应关系．结果表明各月SST存在着1-2℃的海域差异，SST的年较差达10～11℃，SST的季节变化与全球气候变暖呈显著相关．1971-2003年SST呈显著上升趋势，其线性上升率为0．019～0．034℃／a，且珠江口外高于口内．El Nino／La Nino事件对珠江口SST变化的影响并非单一的对应关系．  相似文献   

The Long-term Variation of Extreme Heavy Precipitation and Its Link to Urbanization Effects in Shanghai during 1916–2014     

Ping LIANG  Yihui DING 《大气科学进展》2017,34(3):321-334

Using the hourly precipitation records of meteorological stations in Shanghai, covering a period of almost a century(1916–2014), the long-term variation of extreme heavy precipitation in Shanghai on multiple spatial and temporal scales is analyzed, and the effects of urbanization on hourly rainstorms studied. Results show that:(1) Over the last century, extreme hourly precipitation events enhanced significantly. During the recent urbanization period from 1981 to 2014, the frequency of heavy precipitation increased significantly, with a distinct localized and abrupt characteristic.(2) The spatial distribution of long-term trends for the occurrence frequency and total precipitation intensity of hourly heavy precipitation in Shanghai shows a distinct urban rain-island feature; namely, heavy precipitation was increasingly focused in urban and suburban areas.Attribution analysis shows that urbanization in Shanghai contributed greatly to the increase in both frequency and intensity of heavy rainfall events in the city, thus leading to an increasing total precipitation amount of heavy rainfall events. In addition,the diurnal variation of rainfall intensity also shows distinctive urban–rural differences, especially during late afternoon and early nighttime in the city area.(3) Regional warming, with subsequent enhancement of water vapor content, convergence of moisture flux and atmospheric instability, provided favorable physical backgrounds for the formation of extreme precipitation.This accounts for the consistent increase in hourly heavy precipitation over the whole Shanghai area during recent times.  相似文献   

Absence of interactions between perennial bunchgrasses in a semi-arid temperate savanna: a 5-year field experiment     

Guy R McPherson 《Journal of Arid Environments》1997,36(4):565-570

There is widespread recognition of the importance of long-term experimental studies of plant interactions, but such experiments are rarely conducted. Pairwise interactions between three species of perennial grasses were assessed and described over a 5-year period. Experimental treatments in which some or all neighbors were removed were maintained and plant basal area was monitored throughout the experiment. In addition, above-ground biomass was collected over a 3-year period. Repeated-measures analysis of variance revealed no evidence of interactions between plants.  相似文献   

县域中长期科技发展规划的几个基本问题   总被引：2，自引：0，他引：2  

张占仓 《地域研究与开发》1997,16(3):1-7

适应科教兴国战略实施的需要，县域科技发展引起广泛重视，制定县域科技发展中长期规划是指导县域科技发展的重要措施之一。本文系统地论述了什么叫县域中长期科技发展规划？为什么制定这样的规划？怎样组织和制定这种规划？并就一般意义上，提出了县域中长期科技发展规划的内容体系。  相似文献   

Monitoring the recovery of a previously exploited surf-zone fish community in the St Lucia Marine Reserve,South Africa,using a no-take sanctuary area as a benchmark     

BQ Mann  H Winker  JQ Maggs  SN Porter 《African Journal of Marine Science》2016,38(3):423-441

Limiting accessibility to a fishing area can reduce fishing effort effectively and may therefore promote local recovery of depleted stocks. In January 2002, beach driving was banned in South Africa, thereby reducing angler access to large areas of the coastline, particularly in less-developed areas. In November 2001 a project had been established in the St Lucia Marine Reserve, on the east coast of South Africa, to compare surf-zone fish populations inside a no-take sanctuary zone with those in an adjacent exploited area. Subsequent to the ban, the aim of the project was adapted such that surf-zone fish populations were monitored for potential recovery in what had been the exploited area, located to the north of Cape Vidal, which anglers could no longer access easily, because of the prohibition on beach driving. Standardised research fishing was conducted at two sites in the previously exploited area and two sites in the no-take sanctuary. Conventional stock-status indicators showed evidence of recovery in the four most common species caught in the previously exploited area, in terms of both abundance and biomass. Generalised additive mixed models were used to account for the influence of targeting specific species; however, subtle differences in habitat between the sampling sites, improved angling skill over time, variability in recruitment, and differential species-specific responses complicated interpretation of results. The implications of the findings are discussed in terms of the future monitoring and management of marine protected areas both within the St Lucia Marine Reserve and farther afield.  相似文献   

Study on the Long-term Settlement of Subway Tunnel in Soft Soil Area     

Jun Tan  Li Yuan 《Marine Georesources & Geotechnology》2016,34(5):486-492

The long-term settlement of a subway tunnel, especially the differential settlement affects the safe operation of the subway. In this article, the settlement of a subway tunnel was studied from the theoretical and numerical analyses based on the monitoring data. According to the monitoring data, the deformation of segments at different locations is different, and the deformation around a channel is larger than other places. The settlements of tunnel calculated by two theoretical methods are consistent with that obtained in the centrifuge model test. The numerical simulation indicates that the vertical displacement is much bigger than the horizontal displacement.  相似文献