Modelling the effect of in-stream and overland dispersal on gene flow in river networks

Modelling gene flow across natural landscapes is a current challenge of population genetics. Models are essential to make clear predictions about conditions that cause genetic differentiation or maintain connectivity between populations. River networks are a special case of landscape matrix. They represent stretches of habitat connected according to a branching pattern where dispersal is usually limited to upstream or downstream movements. Because of their peculiar topology, and the increasing concern about conservation issues in hydrosystems, there has been a recent revival of interest in modelling dispersal in river networks. Network complexity has been shown to influence global population differentiation. However, geometric characteristics are likely to interact with the way individuals move across space. Studies have focused on in-stream movements. None of the work published so far took into consideration the ability of many species to disperse overland between branches of the same network though. We predicted that the relative contribution of these two dispersal modalities (in-stream and overland) would affect the overall genetic structure. We simulated dispersal in synthetic river networks using an individual-based model. We tested the effect of dispersal modalities, i.e. the ratio of overland/in-stream dispersal, and two geometric parameters, bifurcation angle between branches and network complexity. Data revealed that if geometrical parameters affected population differentiation, dispersal parameters had the strongest effect. Interestingly, we observed a quadratic relationship between p the proportion of overland dispersers and population differentiation. We interpret this U-shape pattern as a balance between isolation by distance caused by in-stream movements at low values of p and intense migrant exchanges within the same branching unit at high values of p. Our study is the first attempt to model out-of-network movements. It clearly shows that both geometric and dispersal parameters interact. Both should be taken into consideration in order to refine predictions about dispersal and gene flow in river network.     

水电开发对河流生态系统服务功能影响的价值评估初探

提出了计算“流量”,即计算受水电开发影响的河流生态系统服务功能的价值变化量的评估思路和方法,并以广东省河源市风光水利枢纽工程为案例进行了定量分析。在对河流生态系统服务功能进行分类的基础上,根据河流生态系统服务功能可能受到水电开发影响的现实情况和影响特征,选择适当的生态系统服务功能价值核算的方法和参数,计算受影响的生态系统服务功能的价值变化量。案例研究结果表明,风光水利枢纽工程开发方案引起的河流生态服务功能价值变化的正效益为7 676万元/a,负效益为-3 894万元/a,负效益占到其正效益的一半以上,说明该工程开发对东江河流生态系统的消极负面影响也是不容忽视的,应采取适当的生态补偿措施。     

Impact of logging activities in a tropical mangrove on ecosystem diversity and sediment heavy metal concentrations

Productivity of mangrove ecosystems is compromised by anthropogenic activities including over-exploitation of wood. This study set out to understand how different wood harvesting regimes have affected the biodiversity of a tropical ecosystem and to identify relationships between the heavy metal concentrations in the mangrove sediments and tree felling. Soil samples were collected and plant diversity studies carried out on seven sites in the mangrove. Physico-chemical, chemical and mineralogical analyses were done on soil samples and plant population structure, species richness, evenness and diversity index at these sites were calculated. Results showed that soils across sites were characteristically clayey and acidic, with high organic matter content. Minerals identified included quartz, gibbsite, goethite, hematite and kaolinite. Heavy metal concentrations were higher in Sites 6 and 7 with a longer history of anthropogenic activity. There were strong negative correlations between the duration of logging and NO₃-N (r = ?0.838, p = 0.019), total N (r = ?0.837, p = 0.019), NH₄ ⁺-N (r = ?0.844, p = 0.017), Mg = (?0.789, p = 0.035), K (r = ?0.819, p = 0.024), and Na (r = ?0.988, p = 0.002). Sites which had experienced logging for longer periods (sites 3, 6, and 7) had lower nutrient content and lower values for species richness and diversity index. Logging in mangrove ecosystems could alter soil characteristics, decreasing plant diversity and abundance. Logging dynamics around mangrove ecosystems should be considered in the wider strategy for management and conservation of similar mangrove ecosystems.     

黑河流域土地利用变化对生态系统服务价值的影响

利用1987年和2000年1：100000Landsat TM图像解译数据分析了黑河流域土地利用变化，在此基础上，采用中国陆地生态系统服务价值的测算方法，评估了黑河流域土地利用变化引起的生态环境质量变化。结果表明，在过去的13年间，黑河流域土地利用变化总的趋势是森林、草地、河流冰川面积大幅减少，耕地、盐碱地和建筑用地迅速增加。这一变化损害了该区域的生态系统服务功能，使生态系统服务总价值(人民币)从404．22亿元／a下降到370．3亿元／a，损失率达到了8．39％。     

橡胶种植对纳板河流域热带雨林生态系统的影响

通过实地调查数据对云南纵向岭谷区纳板河自然保护区热带雨林生态系统(包括不同海拔高度的3个样地),不同种植年限的人工橡胶林(分别为种植8 a、种植20 a和种植30 a的3个样地)及1个次生林样地,植被和土壤的比较研究,定量分析了橡胶种植对热带雨林生态系统的影响.研究结果表明,①热带雨林随海拔高度的下降,生物量和土壤养分含量均呈增加趋势;中海拔热带雨林物种丰富度最高,群落层次丰富.②热带雨林开采为橡胶林之后,群落层次结构简单化,物种多样性明显下降,地上生物量下降,土壤养分状况变劣,次生林介于二者之间.研究结果可以为该地区土地的持续利用与生物多样性保护提供依据.     

Integrated modelling of the ecosystem of the Niger river inland delta in Mali

The Niger River inland delta in Mali constitutes a vast 36,000 km² area of wetlands, producing numerous natural resources, exploited by fishermen, pastoralists and farmers. It is also a humid zone protected through the Ramsar convention of 1971. To promote the management of its natural resources, an integrated model has been developed in order to simulate the evolution of this ecosystem in relation to different scenarios of population increase, diminishing natural flooding (climatic droughts, construction of dams), increasing stress on land tenure and access to farming areas, technological advances, current administrative decentralisation policy. Possible applications of the model are illustrated through an analysis of the impact of the construction of dams on the traditional farming systems of the delta (fishing, rice cropping, pastoralism), and through a sensitivity analysis of an evolution in the fishing techniques on the revenues of fishermen. The validity of the results of the modelling is discussed and its use for other studies in the field of integrated natural resources management analysed.     

生态系统生物多样性研究及其保护对策

本文综述了生态系统多样性在生物多样性保护中的意义及５个中心研究问题，即生物群落或生态系统关键种、生物多样性关键地区、生态系统多样性的持续性、受害生态系统的恢复生态学、生态系统多样性保护对策及保护途径。文章还分析和讨论当前国际上有关生态系统多样性保护的对策和实践。     

The effect of Po river discharge on phytoplankton dynamics in the Northern Adriatic Sea

An oceanographic transet,, extending from Yugoslavia across the Northern Adriatic Sea to the Po delta in Italy, was occupied during 1972 and 1973 to establish the effect of Po river discharge on the phytoplankton communities of the region. Density distribution showed distinct seasonal features: a winter-spring period of low stability throughout the water column, and a summer period of stratification. The total water-column plant nutrients (nitrate, nitrite, phosphate, silicate) showed a 1.3 to 4.5-fold decrease eastward, with semi-eutrophic conditions restricted to an area off the Po delta. Nannoplankton usually dominated the phytoplankton community, in terms of cell density, surface chlorophyll a concentrations, and surface primary production rates. However, all significant maxima in these characteristics resulted from increases in the microplankton component. Changes in the frequency of major microplankton groups characterized three periods of the annual cycle: September–December, neritic, temperate diatom flora with some littoral elements (e.g. Nitzschia seriata); January–May, neritic, temperate diatom flora of different composition (e.g. Lauderia borealis, Skeletonema costatum); May–August, dinoflagellates (e.g. Prorocentrum micans) at western stations and dinoflagellates plus neritic, warm-water diatoms at eastern stations. The seasonal cycle was characterized by spring and fall maxima tending to coincide with maximum Po river discharge and/or periods of low water-column stability and vertical mixing. The higher nutrient input at western stations was correlated with the co-dominance of only a few species of microplankton during bloom periods, suggesting that these species (S. costatum, N. seriata, and 5 others) can serve as indicators of eutrophic conditions in this region. Assimilation ratios of both the micro- and nannoplankton suggested borderline nutrient conditions. Phosphate was implicated as the limiting nutrient.     

福建洛阳江口红树林湿地恢复对蟹类密度的影响

底栖动物尤其是蟹类对红树林湿地生态系统的生态功能恢复有重要意义,研究检验不同红树林种类及林龄和郁闭度是否对蟹类分布情况存在显著影响。从福建洛阳江口红树林湿地动态变化对蟹类密度的影响可以看出：不同植被类型对蟹类密度的影响达到极显著水平。光滩与成熟的秋茄（Kandelia candel）,桐花树（Aegiceras corniculatum）和白骨壤（Avicennia marina）之间有显著性差异（P〈0.05）,而桐花树、秋茄、白骨壤之间无显著性差异（P〉0.05）。在不同红树林树种和林龄2因素对蟹类密度的影响的双因素分析中：树种、林龄、树种和林龄间互作均对蟹类密度的影响达到极显著水平;在不同红树林树种和郁闭度2因素对蟹类密度的影响的双因素方差分析中：树种对蟹类密度的影响达到极显著水平,郁闭度对蟹类密度的影响达到显著水平;树种和郁闭度之间互作对蟹类密度的影响不显著。     

深圳福田秋茄红树林生态系统碳循环的初步研究

滨海红树林的生产力极高,在全球碳循环中占有重要地位,但是其碳循环的系统测定却鲜见报道。以深圳福田秋茄林为研究对象,2011年4月-2012年4月对内滩天然林、中滩和外滩人工林的植被、凋落物、粗木质残体、土壤的碳密度和净增量,以及植被和土壤呼吸进行了实际观测,并探讨了土壤有机碳来源,初步构建了秋茄林沿不同滩位的生态系统碳循环模式。结果表明,深圳福田秋茄林的碳密度在234.58～694.46 t.hm^-2之间,其中植被碳密度为44.54～239.51 t.hm^-2,凋落物和粗木质残体碳密度为2.02～24.56 t.hm^-2,土壤碳密度（深度为50 cm）为188.02～430.39 t.hm^-2,生态系统碳密度整体上表现为自内滩向外滩降低的趋势。在研究时段内,3个滩位的植被碳密度净增量为4.31～13.28 t.hm^-2.a^-1,凋落物和土壤碳密度没有显著变化。红树林的凋落物生成量为2.17～10.55 t.hm^-2.a^-1,约有49.94～94.01%通过食草动物、冲入海洋和腐烂分解等途径消耗。植被呼吸量为2.20～12.08 t.hm^-2.a^-1,土壤微生物的异氧呼吸量为0.25～1.61 t.hm^-2.a^-1,甲烷排放为0.09～0.31 t.hm^-2.a^-1,土壤有机碳输入约18.99%～44.43%来自植被内源输入,其余来源于海洋碳输入。生态系统的总初级生产力介于8.68～35.91t.hm^-2.a^-1之间,约有47.38%～74.08%转变为净初级生产力（6.48～23.84 t.hm^-2.a^-1）。碳平衡分析表明,在研究时段内,内滩的天然林是个很大的碳汇,约20.08 t.hm^-2.a^-1,中滩和外滩的人工林碳汇量分别为9.98 t.hm^-2.a^-1和4.03 t.hm^-2.a^-1。相对于陆地森林,秋茄红树林有着显著的碳汇效益,在全球碳循环中起着不可忽视的作用。     

Secondary flow within a river bed and contaminant transport

We have developed a numerical method to simulate the transport of non-sorbing contaminants within the sediment layer of a stream and the leaching of these contaminants in the steam. Typical stream bottom surfaces are uneven with triangularly shaped undulation forms. The flow of the water above such triangular surfaces causes external pressure changes that result in a “pumping effect” and a secondary flow within the sediment. The latter causes a significant contaminant advection within the sediment layer. The flow field in the porous sediment layer is obtained by solving numerically Darcy’s equations. The unsteady mass transfer equation is solved by using a finite-difference method with an up-wind scheme. The effects of parameters, such as channel slope, hydraulic head and dispersion, are studied by quantitatively comparing the numerical results of the total mass flow rate from the contaminant source, the concentration front propagation, and the contaminant mass flow rate into the water column. The “pumping effect,” increases the flow in the vertical direction and, thus, enhances the vertical advective mass transport of the contaminant. This bedform-shape induced flow is largely responsible for the mass transfer of contaminants into the water column. The numerical results also show that the mechanical dispersion inside the sediment bed will significantly increase the contaminant mass flow rate from the source.     

The challenge of providing environmental flow rules to sustain river ecosystems.

Accounting for natural differences in flow variability among rivers, and understanding the importance of this for the protection of freshwater biodiversity and maintenance of goods and services that rivers provide, is a great challenge for water managers and scientists. Nevertheless, despite considerable progress in understanding how flow variability sustains river ecosystems, there is a growing temptation to ignore natural system complexity in favor of simplistic, static, environmental flow "rules" to resolve pressing river management issues. We argue that such approaches are misguided and will ultimately contribute to further degradation of river ecosystems. In the absence of detailed empirical information of environmental flow requirements for rivers, we propose a generic approach that incorporates essential aspects of natural flow variability shared across particular classes of rivers that can be validated with empirical biological data and other information in a calibration process. We argue that this approach can bridge the gap between simple hydrological "rules of thumb" and more comprehensive environmental flow assessments and experimental flow restoration projects.     

Modeling ice cover effect on river channel bank stability

Environmental Fluid Mechanics - This paper presents a numerical model study on the ice cover effect on bank stability in non-cohesive alluvial channels. The model consists of a coupled...     

Phosphorus flow analysis of the socioeconomic ecosystem of Shucheng County, China

Human activities disturb the long-term phosphorus (P) cycle in nature, whereby the resulting intensive release of P contributes to the eutrophication of surface water. Hence, a detailed understanding of P flow as it relates to socioeconomic systems is essential for effective nutrient management. This study develops a substance-flow-analysis model for P metabolism for the socioeconomic ecosystem of Shucheng County in Anhui Province in central China as a case study. We estimate P flow using data from questionnaires, face-to-face interviews, published literature, and official statistical databases. Our results show that P flow in Shucheng's current socioeconomic system is linear and openly metabolic. The total P input into Shucheng in 2008 reached 12 748 Mg, mainly as P ores and crops. In all, 43.83% of the total P input was exported, and 30.44% was discharged into surface water. More-balanced nutrient management and options for improving nutrient use efficiency are discussed. The quantifiable, science-based methods used in this study may be applied to neighboring regions of central China for sustainable development and water management.     

Microbial stress-response physiology and its implications for ecosystem function

Microorganisms have a variety of evolutionary adaptations and physiological acclimation mechanisms that allow them to survive and remain active in the face of environmental stress. Physiological responses to stress have costs at the organismal level that can result in altered ecosystem-level C, energy, and nutrient flows. These large-scale impacts result from direct effects on active microbes' physiology and by controlling the composition of the active microbial community. We first consider some general aspects of how microbes experience environmental stresses and how they respond to them. We then discuss the impacts of two important ecosystem-level stressors, drought and freezing, on microbial physiology and community composition. Even when microbial community response to stress is limited, the physiological costs imposed on soil microbes are large enough that they may cause large shifts in the allocation and fate of C and N. For example, for microbes to synthesize the osmolytes they need to survive a single drought episode they may consume up to 5% of total annual net primary production in grassland ecosystems, while acclimating to freezing conditions switches Arctic tundra soils from immobilizing N during the growing season to mineralizing it during the winter. We suggest that more effectively integrating microbial ecology into ecosystem ecology will require a more complete integration of microbial physiological ecology, population biology, and process ecology.     

Modelling the distribution and effect of heavy metals in an aquatic ecosystem

Models are reviewed describing the distribution and effect of heavy metals in an aquatic ecosystem. Since a model used for an impact statement should give the maximum concentration level rather than the seasonal variation, a model focussing on this situation is suggested. The basic differential equations describe (1) the variation in concentration of the toxicant per biomass dry matter in a given trophic level, and (2) the exchange of toxicant between sediment and water. Furthermore, since a substantial part of the heavy metal in an aquatic ecosystem is bound to suspended matter, an equation describing the equilibrium between dissolved and suspended matter must be included.A literature review has been carried out on the parameters used in the above mentioned equations and a demonstration, showing how it is possible to find approximate values for such parameters as excretion coefficient and uptake coefficient on the basis of a relationship between these two parameters and the size of an organism, is given.     

资源型城市土地利用变化及其对生态系统服务价值的影响

东营市是新兴的石油资源城市,土地利用/覆被变化剧烈且具有独特的区域特征。探讨该地区的土地利用变化及其对生态系统服务价值的影响有着重要的现实意义。为此,基于RS和GIS技术,利用Costanza提出的生态系统服务价值评估方法,研究了东营市1986—2008年间的土地利用变化及其引起的生态系统服务价值动态变化。研究结果表明：（1）耕地是东营市主要的土地利用类型,面积有所减少;未利用地和次生盐碱地所占比重较大,居民点及工矿用地大幅增加,油田生产建设和生态环境保护矛盾非常突出。（2）生态系统服务价值减少了6.68%。2008年东营市提供的生态服务仍然以维护原材料、气体调节、食物生产、气候等为主,而废物处理、水源涵养、生物多样性保护、土壤形成与保护和娱乐文化功能是比较弱的。今后应维护生物多样性保护和水源涵养功能,防止土壤盐渍化,提升区域生态系统服务功能;（3）生态系统服务价值对生态价值系数的敏感性指数均小于1,说明研究区内的生态系统服务价值缺乏弹性,研究结果是可信的。     

The impact of detritivorous fishes on a mangrove estuarine system

Sundarban mangrove ecosystem in India is one of the largest detritus based ecosystem of the world and it supplies the detritus and nutrients to the adjacent Hooghly-Matla estuarine complex. In this estuary a group of fish completely detritivorous in nature, belonging to the genus Mugil spp. is present. This group of fish is expected to have important effects on the trophic dynamics of ecosystems, but exact nature of these effects is not known. In order to study the impact that detritivory by fish may have on the estuarine food chain, we developed mathematical formulations. We run two models, one with phytoplankton, zooplankton, carnivorous fish, detritus and nutrient and without this group of fish and a second one after including this fish in the system. In our model this group of fish has no major impact on primary productions of the estuarine system but has extensive role in total fish production. Coexistence of detritivorous fish and carnivorous fish occurs within reasonable parameter range. We have tested different growth rates of phytoplankton, grazing rates and predation rates of zooplankton, detritivorous fish and carnivorous fish for total system equilibrium. Carnivorous fish predation rate on detritivorous fish and detritivorous fish grazing rate on detritus are very important. Different foraging ratios are also tested in this study. Foraging preference of carnivorous fish on detritivorous fish appears significant for the system equilibrium.