Flow variability and the biophysical vitality of river systems

We illustrate the fundamental importance of fluctuations in natural water flows to the long-term sustainability and productivity of riverine ecosystems and their riparian areas. Natural flows are characterized by temporal and spatial heterogeneity in the magnitude, frequency, duration, timing, rate of change, and predictability of discharge. These characteristics, for a specific river or a collection of rivers within a defined region, shape species life histories over evolutionary (millennial) time scales as well as structure the ecological processes and productivity of aquatic and riparian communities. Extreme events – uncommon floods or droughts – are especially important in that they either reset or alter physical and chemical conditions underpinning the long-term development of biotic communities. We present the theoretical rationale for maintaining flow variability to sustain ecological communities and processes, and illustrate the importance of flow variability in two case studies – one from a semi-arid savanna river in South Africa and the other from a temperate rainforest river in North America. We then discuss the scientific challenges of determining the discharge patterns needed for environmental sustainability in a world where rivers, increasingly harnessed for human uses, are experiencing substantially altered flow characteristics relative to their natural states.     

河口生态需水研究进展

针对陆海交互作用下河口生态需水影响因素多且时空差异性显著的特点,在系统分析淡水输入对河口生态系统水环境过程和生物过程影响的基础上,按生态需水目标的差异,将河口生态需水分析方法划分为基于典型生物资源保护目标、基于生境保护目标以及基于多目标整合分析3种类型。从生态需水目标筛选、生态需水目标对淡水输入响应关系以及生态需水计算方法实用性方面探讨了河口生态需水研究中面临的主要问题。结论认为生态系统健康综合表征指标的确定应成为分析河口生态需水的关键科学基础,筛选控制性生态要素构建河口关键生态水文过程模型可成为有效提高生态需水计算方法实用性的主要技术手段。     

Hydrological responses to rainfall variability and dam construction: a case study of the upper Senegal River basin

The understanding of the spatial and temporal dynamic of river systems is essential for developing sustainable water resource management plan. For the Senegal River, this subject is very complex according to the context of (1) transboundary basin, (2) several contrasted climatic zones (Guinea, South Sudanian, North Sudanian and Sahelian) with high rainfall variability and (3) high human pressures (dam construction and water uses). From 1954 to 2000, 80% (mean value) of the Senegal River flows recorded downstream part of the basin are provided by three majors tributaries (Bafing, Bakoye and Faléme) located in the upstream part. Then, in our study, this upper Senegal River basin was chosen in order to investigate the hydrological responses to rainfall variability and dam construction. Two nonparametric statistical methods, Mann–Kendall and Hubert test, were used to detect the long-term changes in the time series of precipitation and water discharge (1954–2000) at the annual and seasonal scales. The continuous wavelet transform (Morlet Wavelet) was employed to characterize the different mode in the water discharge variability. Flow duration curve and cumulative curve methods were used to assess the impact of dams on the hydrological regime of the Senegal River. Results showed that the Senegal River flows have been changing under the influence of both rainfall variation and dam construction. The long-term evolution of water discharge depend on long-term rainfall variability: The wet periods of the 1950s and 1960s correspond to periods of higher river flows, while the droughts of the 1970s and 1980s led to unprecedented river flows deficits. The new period, since 1994, show a high inter-annual variability of rainfall and discharge without clear trend. At seasonal scale, the results showed also a strong relationship between rainfall and runoff (R ² > 0.8) resulting from alternating wet and dry seasons and rapid hydrological responses according to annual rainfall. Nevertheless, the observed flows during dry seasons highlighted the influence of water storage and restitution of infiltrated waters in soils and surficial formations during wet seasons. In the dry seasons, the water budget of the three upstream tributaries showed a water deficit at the downstream gauging station. This deficit was characterized by water loss to underlying aquifers and highlighted the influence of geological setting on water balance. However, in this context, water restitution during the dry season remained dependent on climatic zone and on the total annual rainfall volume during the previous wet season. The results have highlighted an impact of the Manantali dam previously obscured: The dam has no effect on the regulation of high river flows. That is what explains that since its construction in 1988, flooding of coastal cities, like Saint-louis, by seasonal river floods has not ceased. The flooding risk in coastal cities is not avoided, and the dams caused hyper-salinization of the Senegal lower estuary. The breach created in the coastal barrier of the Langue of Barbary in October 2003 promotes direct export of excess floodwater to the sea and reduces this risk of flooding in the delta area. But, this solution led to considerable loss of potential water resources, and the authors recommend a new water management plan with a global focus. However, this study shows the positives impacts of the two dams. They allow the availability of freshwater in order to support agricultural irrigation in the valley and delta zone, in particular during low flows periods.     

Spatial and temporal variability and drivers of net ecosystem metabolism in western Gulf of Mexico estuaries

Net ecosystem metabolism (NEM) is becoming a commonly used ecological indicator of estuarine ecosystem metabolic rates. Estuarine ecosystem processes are spatially and temporally variable, but the corresponding variability in NEM has not been properly assessed. Spatial and temporal variability in NEM was assessed in four western Gulf of Mexico shallow water estuaries. NEM was calculated from high-frequency dissolved oxygen measurements. Interbay, intrabay, and water column spatial scales were assessed for NEM, gross primary production (GPP), and respiration (R) rate variability. Seasonal, monthly, and daily temporal scales in NEM, GPP, and R were also assessed. Environmental conditions were then compared to NEM to determine which factors were correlated with each temporal and spatial scale. There was significant NEM spatial variability on interbay, intrabay, and water column spatial scales. Significant spatial variability was ephemeral, so it was difficult to ascertain which environmental conditions were most influential at each spatial scale. Significant temporal variability in NEM on seasonal, monthly, and daily scales was found and it was correlated to temperature, salinity, and freshwater inflow, respectively. NEM correlated strongly with dissolved oxygen, temperature, and salinity, but the relationships where different in each bay. The dynamics of NEM on daily scales indicate that freshwater inflow events may be the main driver of NEM in the semiarid estuaries studied. The variable nature of NEM found here is further evidence that it is not valid to use single station monitoring deployments for assessment of whole estuarine ecosystem metabolic rates in large ecosystems. The relationship between NEM and temperature, salinity, and freshwater inflow events could drive predictive models assessing the potential influence of projected climate change and watershed development scenarios on estuarine metabolic rates.     

Groundwater and surface-water interactions and impacts of human activities in the Hailiutu catchment,northwest China

The interactions between groundwater and surface water have been significantly affected by human activities in the semi-arid Hailiutu catchment, northwest China. Several methods were used to investigate the spatial and temporal interactions between groundwater and surface water. Isotopic and chemical analyses of water samples determined that groundwater discharges to the Hailiutu River, and mass balance equations were employed to estimate groundwater seepage rates along the river using chemical profiles. The hydrograph separation method was used to estimate temporal variations of groundwater discharges to the river. A numerical groundwater model was constructed to simulate groundwater discharges along the river and to analyze effects of water use in the catchment. The simulated seepage rates along the river compare reasonably well with the seepage estimates derived from a chemical profile in 2012. The impacts of human activities (river-water diversion and groundwater abstraction) on the river discharge were analyzed by calculating the differences between the simulated natural groundwater discharge and the measured river discharge. Water use associated with the Hailiutu River increased from 1986 to 1991, reached its highest level from 1992 to 2000, and decreased from 2001 onwards. The reduction of river discharge might have negative impacts on the riparian ecosystem and the water availability for downstream users. The interactions between groundwater and surface water as well as the consequences of human activities should be taken into account when implementing sustainable water resources management in the Hailiutu catchment.     

Temporal and spatial variations in water flow and sediment load in Narmada River Basin, India: natural and man-made factors

The Narmada River flows through the Deccan volcanics and transports water and sediments to the adjacent Arabian Sea. In a first-ever attempt, spatial and temporal (annual, seasonal, monthly and daily) variations in water discharge and sediment loads of Narmada River and its tributaries and the probable causes for these variations are discussed. The study has been carried out with data from twenty-two years of daily water discharge at nineteen locations and sediment concentrations data at fourteen locations in the entire Narmada River Basin. Water flow in the river is a major factor influencing sediment loads in the river. The monsoon season, which accounts for 85 to 95% of total annual rainfall in the basin, is the main source of water flow in the river. Almost 85 to 98% of annual sediment loads in the river are transported during the monsoon season (June to November). The average annual sediment flux to the Arabian Sea at Garudeshwar (farthest downstream location) is 34.29×10⁶ t year⁻¹ with a water discharge of 23.57 km³ year⁻¹. These numbers are the latest and revised estimates for Narmada River. Water flow in the river is influenced by rainfall, catchment area and groundwater inputs, whereas rainfall intensity, geology/soil characteristics of the catchment area and presence of reservoirs/dams play a major role in sediment discharge. The largest dam in the basin, namely Sardar Sarovar Dam, traps almost 60–80% of sediments carried by the river before it reaches the Arabian Sea.     

Situated justice in environmental decision-making: Lessons from river management in Southeastern Australia

The practical application of environmental justice in natural resource management depends upon moving beyond generic principles to situated understanding. This understanding in turn requires knowledge of both historical and geographical contexts, including how decision-making frameworks develop and the nature of the biophysical environment itself. This paper examines these requirements based on case material from the Hunter Valley, New South Wales. In the Hunter Valley, the colonial history of river management was one of the creation, and subsequent inclusion and exclusion, of particular ‘stakes’ from the decision-making process, resulting in a narrowly defined ‘community of justice’ that became institutionalised at the catchment scale. However, even within this restricted community, distributive injustices occurred due to a failure of policy to engage with environmental variability at both spatial and temporal scales. This combination of procedural injustice and environmental variability also resulted in ecological injustice - that is a disconnected or even antagonistic human-nature relationship that restricted the opportunity to redress the severe degradation of riverine ecosystems that had occurred since European settlement. In the light of these examples, broader challenges in the application of environmental justice to river management are explored in terms of ecological complexity and contested perceptions of environmental health. Based on this material, a historically and geographically situated, ecologically informed vision of environmental justice is proposed as an essential part of sustainable river management.     

Multivariate Analysis of Water Quality and Plankton Assemblages in an Urban Estuary

Raritan Bay, located between the states of New York and New Jersey, has a long history of cultural eutrophication and associated harmful algal blooms (HABs). Despite striking chemical and biological alterations occurring in Raritan Bay, publications in the early 1960s were the last to report consecutive measurements of both water quality parameters and plankton species composition in this system. The objectives of this study were to characterize water quality trends and plankton composition in a eutrophic estuary, compare current environmental conditions to those documented in Raritan Bay 50 years ago (i.e., at the same six sampling sites), and to further clarify the relationship among nutrients, secondary consumers, and algal bloom generation in this system using ordination techniques. This study (monthly data collected from April 2010–October 2012) indicates that Raritan Bay continues to exhibit numerous symptoms of eutrophication, including high algal biomass, high turbidity, violations of the dissolved oxygen standard to protect fish health, and blooms of potentially harmful phytoplankton species. Altered spatial and temporal patterns for nitrate and soluble reactive phosphorus (SRP) over the past 50 years may suggest new, changing, or expanding sources of nutrients. A total of 14 HAB species have been identified, including Heterosigma akashiwo, which formed a bloom in the upper Raritan Bay during summer 2012 in association with hypoxic conditions. Multivariate analyses indicate that abundance of this species is positively associated with high temperature, salinity, nitrate, and SRP and negatively associated with spring river discharge rates and total zooplankton abundance in Raritan Bay.     

Use of hydrological methods for assessment of environmental flow in a river reach

Environmental flow assessment and maintenance are relatively new practices, especially in developing countries. This paper describes the desktop assessment of environmental flows in a river with insufficient data on ecological features and values. In this study, the potential environmental flows in a typical river reach of the Shahr Chai River in Iran were investigated using a newly developed hydrological method (flow duration curve (FDC) shifting) and Global Environmental Flow Calculator software. This approach uses monthly flow data to develop an environmental FDC and to generate flow requirements corresponding to different features of the river ecosystem. Results were compared with those from four alternative hydrological methods: the desktop reserve model (DRM), Tennant, low-flow index, and flow duration curve analysis (FDCA). Comparisons of these methods indicated that to maintain the basic function of the river ecosystem, the river flows should be managed within an acceptable environmental level. The predictions from the Tennant method and the low-flow index (7-day low flow with a 10-year return period), and from the FDCA (for flows exceeding 90?% of occurrence) are not as reliable as those from the FDC shifting technique and DRM. Comparative results indicate that a minimum flow rate of 1.2?m³/s (equivalent to 23?% of the natural mean annual runoff, or flow with 80?% occurrence depicted from the FDC) is required for the Shahr Chai River to run toward the internationally recognized Urmia Lake in Iran.     

Suspended-Sediment Impacts on Light-Limited Productivity in the Delaware Estuary

The Delaware Estuary has a history of high anthropogenic nutrient loadings but has been classified as a high-nutrient, low-growth system due to persistent light limitation caused by turbidity. While the biogeochemical implications of light limitation in turbid estuaries have been well-studied, there has been minimal effort focused on the connectivity between hydrodynamics, sediment dynamics, and light limitation. Our understanding of sediment dynamics in the Delaware Estuary has advanced significantly in the last decade, and this study describes the impact of spatiotemporal variability of the estuarine turbidity maximum (ETM) on light-limited productivity. This analysis uses data from eight along-estuary cruises from March, June, September, and December 2010 and 2011 to evaluate the impact of the turbidity maximum on production. Whereas the movement of the ETM is controlled primarily by river discharge, the structure of the ETM is modulated by stratification, which varies with both river discharge and spring-neap conditions. We observe that the ETM’s location and structure control spatial patterns of light availability. To evaluate the relative contributions of river discharge and spring-neap variability to the location of phytoplankton blooms, we develop an idealized two-dimensional Regional Ocean Modeling System (ROMS) numerical model. We conclude that high river flows and neap tides can drive stratification that is strong enough to prevent sediment from being resuspended into the surface layer, thus providing light conditions favorable for primary production. This study sheds light on the role of stratification in controlling sediment resuspension and promoting production, highlighting the potential limitations of biogeochemical models that neglect sediment processes.     

滦河下游河道生态需水量

为量化水库下游河道生态修复所需水量,以滦河下游潘家口水库—滦河口为研究样区,采用逐月频率法和生态水力学法估算河道生态需水量,既具有水文学方法的简便,又考虑生物学特性,强调了水文-生态的联系。通过对研究区河道1956~2000年生态、水文及水力资料的分析计算,结果表明:①逐月频率法和生态水力学法在计算滦河下游河道生态需水中均合理;②最小、适宜、理想等级年生态需水量分别为4.29亿,8.93亿和16.29亿m3,分别占河道天然径流量的10.18%、21.21%和38.68%;③年内汛期8月份及生物繁殖期(4~6月)需水量分别达到年度总量的33.5%和11.5%。     

Permafrost degradation and subsurface-flow changes caused by surface warming trends

Change dynamics of permafrost thaw, and associated changes in subsurface flow and seepage into surface water, are analysed for different warming trends in soil temperature at the ground surface with a three-phase two-component flow system coupled to heat transport. Changes in annual, seasonal and extreme flows are analysed for three warming-temperature trends, representing simplified climate-change scenarios. The results support previous studies of reduced temporal variability of groundwater flow across all investigated trends. Decreased intra-annual flow variability may thus serve as an early indicator of permafrost degradation before longer-term changes in mean flows are notable. This is advantageous since hydrological data are considerably easier to obtain, may be available in longer time series, and generally reflect larger-scale conditions than direct permafrost observations. The results further show that permafrost degradation first leads to increasing water discharge, which then decreases as the permafrost degradation progresses further to total thaw. The most pronounced changes occur for minimum annual flows. The configuration considered represents subsurface discharge from a generic heterogeneous soil-type domain.     

Implications of climatic variability and climate change for water resources availability and management in West Africa

The paper examines: (a) trends in climatic variations and variability with particular emphasis on rainfall (b) the characteristics of climatic events, including floods and droughts, (c) seasonal variations in river flows, (d) mean annual trends in river flows and discharges, (e) local variations of extremes of rainfall and river discharges, (f) the effects of climatic variability and climate change on ground water variations, (g) the problems of acute shortage of freshwater, and (h) the prevalence of water stress whose characteristics would be worsened with the projected impacts of climate change. The results show that: (i) there are a lot of spatial and temporal variations in the characteristics of rainfall and the hydrological systems locally and regionally, although in general, there have been downward trends in rainfall and increases in water deficits and drought events, (ii) that flood events, which also have impacted adversely in many parts of the region, have also been witnessed. The paper then produces projections for future urban and rural water supplies in Nigeria, which is an epitome of West Africa and examines the two main categories of adaptation measures needed to improve water management, namely, those involving the water supply and water demand systems in the study region. Finally, the paper discusses the need to address a number of mechanisms for implementation of the various adaptation measures including: (a) building capacity and manpower, (b) promoting education and public awareness, (c) public participation and the involvement of stakeholders, (d) the establishment of both national and regional co-operation, and (e) the need for climatic and other environmental data collection and monitoring. This revised version was published online in July 2006 with corrections to the Cover Date.     

水文网络模型在分布式流域水文模拟中的应用

水文网络模型是地理信息系统对流域实际河网水系的一种规范化描述,它采用拓扑关系来确定流域水流的空间聚合与分散。准确地描述水文网络对成功模拟流域水流的空间分布起着至关重要的作用。水文网络数据模型的关键在于如何表达水文网络的构成要素,以及如何建立要素间的拓扑关系。本文重点阐述了水文网络模型在分布式流域水文模拟中的应用。实例研究证明,采用水文网络模型来表达流域河网水系结构有助于准确地模拟流域上水流的空间与时间分布。     

Rare Earth Element and Yttrium Variability in South East Queensland Waterways

We present data for the rare earth elements and yttrium (REY) in the National Research Council of Canada natural river water reference material SLRS-4 and 19 natural river waters from small catchments in South-East Queensland, Australia, by a direct ICP-MS method. The 0.22 μm filtered river water samples show a large degree of variability in both the REY concentration, e.g., La varies from 13 to 1157 ppt, and shape of the alluvial-sediment-normalised REY patterns with different samples displaying light, middle or heavy rare earth enrichment. In addition, a spatial study was undertaken along the freshwater section of Beerburrum Creek, which demonstrates that ~75% of the total REYs in this waterway are removed prior to estuarine mixing without evidence of fractionation.     

长江上游国土资源,生态环境与灾害防治

长江上游干流流经青、藏、川、滇、鄂、渝6省市,支流涉及甘肃、陕西、贵州3省,流域面积为105.4×104km2,人口1.55亿,占全国国土面积的11.1%.长江上游地区经济发展相对落后,人均国民收入低,少数民族众多,与中下游经济发达地区差距很大.但上游地区蕴藏着巨大的经济开发潜能,丰富的水力和矿产等自然资源,以及农、林、牧等物产,对中下游地区经济发展有着巨大的支援作用.同时,由于自然地理上的相关性,又使上游地区的开发治理,对中下游地区的生态环境和可持续发展有着至关重要的作用.目前,长江上游森林植被大量减少,水源涵养能力下降,水土流失加剧:泥石流、滑坡、崩塌等地质灾害严重,旱、洪灾害频发;沿江大量排放废气、废水、污水,使大气和水体严重污染.随着上游地区生态环境的日益恶化,给中下游地区带来严重危害,河道、湖泊、水库淤积加速,洪涝灾害频繁发生,造成中下游地区经济建设和人民生命财产的重大损失.因此,必须尽快对长江上游地区进行全面综合治理,尽快开展新一轮国土资源大调查,制定各种自然资源的合理开发利用和保护方案;控制沿江污染源的排放,建立大气和水体污染监测系统;运用高新技术,建立上游重点地带地壳形变的动态监测和预警系统,防治地质灾害;充分利用上游地区丰富的水力资源,兴建多级水利设施,对地表水实施人工的时空控制,消除旱、洪灾害.     

Geographic signatures of North American West Coast estuaries

West Coast estuaries are geologically young and composed of a variety of geomorphological types. These estuaries range from large fjords to shallow lagoons; from large to low freshwater flows. Natural hazards include E1 Niños, strong Pacific storms, and active tectonic activity. West Coast estuaries support a wide range of living resources: five salmon species, harvestable shellfish, waterfowl and marine birds, marine mammals, and a variety of algae and plants. Although populations of many of these living resources have declined (salmonids), others have increased (marine mammals). West Coast estuaries are also centers of commerce and increasingly large shipping traffic. The West Coast human population is rising faster than most other areas of the U.S. and Canada, and is distributed heavily in southern California, the San Francisco Bay area, around Puget Sound, and the Fraser River estuary. While water pollution is a problem in many of the urbanized estuaries, most estuaries do not suffer from poor water quality. Primary estuarine problems include habitat alterations, degradation, and loss; diverted freshwater flows; marine sediment contamination; and exotic species introductions. The growing West Coast economy and population are in part related to the quality of life, which is dependent on the use and enjoyment of abundant coastal natural resources.     

Human alteration of groundwater–surface water interactions (Sagittario River,Central Italy): implication for flow regime,contaminant fate and invertebrate response

Many rivers worldwide are undergoing severe man-induced alterations which are reflected also in changes of the degree of connectivity between surface waters and groundwater. Pollution, irrigation withdrawal, alteration of freshwater flows, road construction, surface water diversion, soil erosion in agriculture, deforestation and dam building have led to some irreversible species losses and severe changes in community composition of freshwater ecosystems. Taking into account the impact of damming and flow diversion on natural river discharge, the present study is aimed at (i) evaluating the effects of anthropogenic changes on groundwater/surface water interactions; (ii) analyzing the fate of nitrogenous pollutants at the floodplain scale; and (iii) describing the overall response of invertebrate assemblages to such changes. Hydrogeological, geochemical and isotopic data revealed short- and long-term changes in hydrology, allowing the assessment of the hydrogeological setting and the evaluation of potential contamination by nitrogen compounds. Water isotopes allowed distinguishing a shallow aquifer locally fed by zenithal recharge and river losses, and a deeper aquifer/aquitard system fed by surrounding carbonate aquifers. This system was found to retain ammonium and, through the shallow aquifer, release it in surface running waters via the hyporheic zone of the riverbed. All these factors influence river ecosystem health. As many environmental drivers entered in action offering a multiple-component artificial environment, a clear relationship between river flow alteration and benthic and hyporheic invertebrate diversity was not found, being species response driven by the combination of three main stressors: ammonium pollution, man-induced changes in river morphology and altered discharge regime.     

珠江口的沉积作用和沉积相

珠江口为华南沿海的重要河口,是珠江水(系(西江、北江、东江、流溪河)的受水盆地。珠江流域每年有8000余万吨悬沙。大约3000万吨溶解质和少量底沙进入珠江河口区域,它们在迳流、潮流和其他海洋动力因素共同影响下,沉积作用甚为活跃。但是珠江口水域宽阔,地形复杂,各河口、河口湾或湾外区域的动力背景及泥沙运动不尽相同,因而其沉积作用和沉积特征也具有区域差异。     

Ferry-based monitoring of surface water quality in North Carolina estuaries

Several interrelated factors affect, water quality in the Albemarle-Pamlico Estuarine System (APES) including land use change in the upland and coastal watersheds, legislatively mandated basin-wide nutrient management plans, intense storms, and global and local changes in sea level. Despite its importance as an essential fish habitat, the APES has not been monitored as intensively or extensively for habitat impacts associated with decreased water quality as other estuaries have been, such as with the North Carolina tributary estuaries or Chesapeake Bay. To support the sustainable use of these estuaries, we are developing an automated water quality monitoring system aboard ferries that traverse the APES. This program, FerryMon, provides a unique, long-term, and cost-effective monitoring system to evaluate status and trends in APES water quality. Intensive temporal and spatial data obtained from all ferry routes provide an environmental baseline and are used to assess the patterns and variability in surface water hydrography, dissolved constituents, and particulate matter. The data are useful to calibrate estimates of ocean color and sea surface temperature from aircraft and satellite sensors. We are creating a searchable geographic database that is intended for scientists, managers, and the general public. Using ferries as sampling platforms to monitor estuarine water quality is a tractable approach and FerryMon represents a model for use in other large bodies of water traversed by ferries.