The changing face of the Ethiopian rift lakes and their environs: call of the time

The Ethiopian rift is characterized by many perennial rivers, and a chain of lakes that vary in size, and hydrological and hydrogeological settings. The water resources of the Rift lakes are one of the focal points for large‐scale development in Ethiopia over the last few decades. Some of the lakes and their influent rivers are used for irrigation, soda abstraction, fish farming and recreation, and also support a wide variety of endemic birds and wild animals. Ethiopia's major mechanized irrigation farms and commercial fishery are confined within the Rift region. A few of the lakes have shrunk in surface area because of excessive water abstractions, while others have expanded because of increased surface run‐off and groundwater inflows from percolated irrigation water. Excessive land degradation, deforestation and over‐irrigation have changed the hydrological setting of a few Rift lakes. Human activities, in combination with changes in climate and geology, have influenced the hydrological setting and the water quality of the lakes, with the salinity and major ion composition dramatically changed in some of them. This study tries to address the challenges associated with development of these surface‐water resources, focusing on environmental problems arising over the past few decades on three lakes (Abiyata, Beseka and Ziway) situated along the tectonically active Rift floor. The methods utilized in this study include field hydrological and hydrogeological mapping, supported by aerial photographs and satellite imagery interpretations, as well as hydrometeorological and hydrochemical data analysis, and catchment hydrological modeling. A converging‐evidence approach was adapted to reconstruct the temporal and spatial variations of the lake water levels and surface areas. The study results revealed that the major changes in the Rift Valley are related primarily to recent improper use of water from the large rivers draining the Rift Valley floor and the lake catchments, and from direct lake water abstractions aggravated intermittently by climatic and land use changes. These changes represent grave environmental consequences on the fragile Rift ecosystem that demands urgent intervention in the context of an integrated, basin‐wide water management approach. This study emphasizes lake water level changes and human influences on these changes. It also assesses human interactions and water quality changes, including land use changes and environmental repercussions on the lakes, as well as providing recommendations on how these issues should be addressed.     

Mortalities of lesser flamingos in Kenyan Rift Valley saline lakes and the implications for sustainable management of the lakes

Lesser flamingo populations in the Kenyan Rift Valley saline lakes respond to changes in phytoplankton species’ composition and densities, behavioural needs, breeding cycles and environmental conditions. The numbers of flamingos are high when the density of blue‐green algae Arthrospira fusiformis (Spirulina platensis) is high, stimulating flamingo courtship and display. The numbers decline when lake levels decline, resulting in low phytoplankton densities and a domination by toxic phytoplankton species. In Kenyan saline Rift Valley lakes, heavy metals, pesticides, algal toxins (microcystin), bacterial infection and malnutrition are plausible causes of lesser flamingo mortalities. The production of cyanotoxins by toxic phytoplankton, as a result of declining lake water levels, could be a major factor contributing to the increased mortality of lesser flamingos. Integrated management of the lakes and their catchments is required to ensure the future well‐being of the lesser flamingos.     

Comparative assessment of the water balance and hydrology of selected Ethiopian and Kenyan Rift Lakes

The study area is part of the East African Rift system, characterized by a cluster of lakes occupying an extremely faulted rift floor with geothermal manifestations. Some of the lakes illustrated contrasting water levels and size evolution over the last few decennia, believed to have been caused by various natural and anthropogenic factors. The relative importance of these factors, however, is unknown. This study attempts to present the hydrology of the lakes in a broader context, by giving more emphasis to lake water level fluctuations and to the water balance. These factors have far-reaching implications in regard to future management of the lake basin water. It also provides information on the relation of the groundwater with the lakes, and with the local and regional groundwater flow system from the adjacent highlands to the floor of the Rift. The methods utilized in this study include conventional hydrogeological field surveys, and hydrometeorological and data analyses, coupled with digital image processing and spatial analysis under a Geographic Information System environment. Ancillary supporting information has been obtained from environmental isotopes and hydrochemical data. The study results indicate the terminal Ethiopian lakes changed in size and water level significantly over the last half century. In contrast, the Kenyan lakes only exhibited slight changes. The lakes in both countries exhibit a striking similarity in their subsurface hydraulic connection, and are strongly governed by complex rift geological structures. Groundwater plays a vital role in the water balance of the study lakes. The study results indicate that future sustainable use of the study lakes demands that serious attention be given to the role of the groundwater component of the lake water balances.     

Assessment of lake–groundwater interactions and anthropogenic stresses,using numerical groundwater flow model,for a Rift lake catchment in central Ethiopia

A steady-state groundwater flow model (MODFLOW) was used to study lake and groundwater interactions in a complex rift volcanic catchment. It also was used to assess the effects of water pumping from wells, and of variable recharge rates associated with climate and lake level changes, on the dynamics of the volcanic aquifers surrounding Lake Awassa. The model simulations were made after first developing a reasonable conceptual model, on the basis of conventional hydrogeological mapping, pumping test and hydrometeorological data analyses, and from ancillary information obtained from hydrochemical and isotope techniques. The model results indicated that the lakes and Rift aquifers are fed by large groundwater inputs that originate in the highlands. The lakes and rivers have important roles in recharging the aquifers in some locations. Lake Awassa receives a major groundwater inflow from its southern and eastern shorelines, while substantial water leakage from the lake occurs along the northern shoreline. The annual groundwater outflow from the catchment is estimated to 52.5 × 10⁶ m³. Scenario analyses revealed that increasing the current pumping rate from wells by fourfold will substantially reduce the groundwater level substantially, although the regional flow pattern would remain the same. There appears to be no immediate danger to the Rift aquatic environment from the current water pumping rate. Drying the small Lake Shalo and associated swamps, however, will cause a large change in the water balance of the larger Lake Awassa. Slight changes in groundwater recharge can cause large differences in groundwater levels for most of the Rift caldera floor far from the lake shores. This study provides a reasonable foundation for developing detailed transient predictive models, which can then readily be used as a decision support tool for development and implementation of sustainable water resources practices.     

Modelling natural conditions and impacts of consumptive water use and sedimentation of Lake Abaya and Lake Chamo, Ethiopia

There is few available information regarding the water resource systems of Abaya Lake and Chamo Lake, which are found in the Southern Rift Valley Region of Ethiopia. This paper describes modelling of the water balance components of these lakes, as well as the impacts of water uses, and sediment transport and deposition in the lakes. The various parameters and data needed for the water balance model are derived on the basis of various surveys, analysis of data and modelling efforts. The watershed characteristics are derived using geographical information system, whereas the morphometry of the lakes is investigated by undertaking bathymetry surveys. The hydrometeorological components of this lake system also were investigated through the development of relevant database and information systems, by identifying regional relationships, and by a rainfall‐run‐off model. These information systems have subsequently been integrated to model the water balance of the two lakes, and simulating the in‐lake water levels. Several scenarios reflecting the natural conditions, water consumptive development possibilities, and sedimentation impacts have been investigated in this study. Based on the model simulation results, and on the computation of the life expectancies of the two lakes, it was found that sediment inflow and deposition significantly threaten their existence.     

地下水深循环研究进展

对自然界中地下水深循环的研究进展进行了综述。西藏内流区的湖泊与河流存在渗漏,水量呈现出巨大的不平衡,估算每年通过渗漏流出西藏高原的地下水超过了1 000亿m3;与此同时,中国北方的地下水也呈现出极大的不平衡,降水量较少的火山与裂谷地区有大量的泉水涌出形成了河流与湖泊,内蒙古高原与东北地区的河流与湖泊在北东方向上呈现出串珠状的分布。通过对长白山天池地下水补给源区的各项分析确定,补给天池的地下水来自于外源水,能够同时满足补给源区高程、降水同位素、渗漏等特征条件的地区只有西藏内流区。北方地下水中的锶、氦同位素特征关系揭示了深循环地下水与地幔玄武岩等发生了水岩反应。贝加尔与山西裂谷地区中地壳高导低速层可能是深循环地下水的导水通道,玄武岩孔洞构成了导水构造。深循环水在火山及裂谷附近向地表排泄形成河流与湖泊,河流源头附近的地温梯度偏低。西藏内流区的渗漏水通过深循环方式补给内蒙古高原、鄂尔多斯、阿拉善、华北平原、东北平原、贝加尔湖、东海、南海等地区,地下水的年龄自西向东呈增加趋势,一般在20~40 a之间。     

空间信息技术在水利普查中的应用

2010年开展的全国第一次水利普查是建国以来水利行业水利基础数据全口径调查,分为清查阶段、普查阶段、数据汇总阶段和成果展示及开发利用3个阶段,涉及河湖基本情况普查、水利工程基本情况普查、经济社会用水情况调查、河湖开发治理保护情况普查、水土保持情况普查、行业能力建设情况普查、灌区专项普查、地下水取水井专项普查等8大专项。在3个阶段和8大专项中,空间信息技术都得到了充分利用。特别是河湖基本情况普查和水土保持情况普查调查,主要是依靠空间信息技术,采用内业获取和处理的方式获取相关信息。在成果展示及开发利用方面,以空间信息技术为技术支撑,实现了普查成果“一张图”展示,直观展示了空间信息技术在水利行业中全面和深入的应用。     

河湖普查若干问题的讨论

编制河流名录和水系编码,是河湖普查工作的重要内容之一.提出了甄别和统计河流干支流的原则:①以河流最长的一条为干流,或者以集水面积最大的一条为干流;②各支流的长度、面积接近时,则以水量明显很大的一条为干流;③各支流的长度、面积、水量均接近时,取河道宽广、河谷平缓顺直、上下段自然延伸的一条为干流;④要充分尊重历史上合理的传统称谓.确定河流源头的方法主要有3种:①河流向上溯源交于分水岭,其交点就是河流的源头;②在数字综合水系图上搜索河槽线上端最末端处,其最小集水面积定义为0.2 km2;③河流上源开始有水的地方,"水"包括泉水、小溪、沼泽、湖泊、冰川融水等,但有水即源的方法存在一些缺点.     

平原河网区灌区创新管理模式研究

平原河网区水系纵横交错,河道水流平缓,农田灌溉用水粗放,排水量大,用水效率低下,面源污染严重,灌区长效管理是实施最严格水资源管理制度"三条红线"的重要环节。分析平原河网区灌区特征和存在问题,结合目前农村土地流转工作的开展情况,建立灌区"土地流转+节水控排灌溉"的创新管理模式,改变平原河网区灌区规模小、灌溉田块分散的状况,形成农田规模化种植经营、统一集中灌溉的形式。一方面促进土地集约化和灌区规模化,增加农村效益和农民收入;另一方面提高灌区灌溉效率,减少灌溉排水量,降低进入水体的氮、磷排放量。有效保障灌区的长效管理和运行,提高农业用水效率和效益,改善农村水环境质量。     

Importance of sustainable management of percolation lakes in semiarid basaltic terrain in western India

Sustainable management of percolation lakes or percolation tanks is closely related to the survival of approximately 15 million farmers and an equal number of cattle living in the semiarid basaltic plateau of western India. Here, the monsoonal rains are restricted to a few rainy days between June and September. It is therefore necessary to harvest the monsoon runoff into small percolation lakes in mini‐catchments by constructing earthen bunds on small streams and allowing the stored water in the lakes to percolate and recharge the groundwater body. The residence time of water in the mini‐catchments is thus increased and it is possible for the farmers to dig wells and irrigate the crops in their small farm plots. The efficiency of the percolation lakes is hampered by silt that accumulates in the lake bed or tank bed, year after year. It is therefore necessary for the beneficiary farmers to desilt the lakebed when the lake dries in the summer. Soil conservation practices should be followed in the catchment area in order to reduce the amount of silt entering the lake. Non‐governmental organizations play an important role in this field.     

长江健康评估与保护实践

长江属于大河水系,生物多样性丰富,其健康状态不仅影响流域经济社会可持续发展,也受到国内外广泛关注。综合国内外河流健康评估理论和实践,讨论适合长江特点的健康评估方法和标准;通过水功能区达标率和鱼类多样性2个指标分析长江水环境和水生态近10多年来的变化情况;最后,总结近几年长江大保护系列行动后长江健康进展情况。分析结果表明:长江健康评估可以根据管理需要划分不同时空尺度;根据资料完整性可以采用单指标或者多指标综合评价方法;随着长江系列保护行动的实施,长江河流型水质持续改善,湖库水质和生物多样性开始稳定,人类过度干扰江湖现象得到遏制,但湖库水质改善和生物多样性恢复还需要长期进行。     

水库群联合作用下长江中下游江湖关系响应机制

长江干支流水库群的总库容约占长江入海年均径流量的37.6%,水库群的联合作用改变了进入长江中下游江湖系统的水沙条件,引起江湖系统水沙输移、冲淤演变及江湖关系等发生新的变化,呈现新的特点。本文在综述近年来长江中下游江湖系统水沙输移与冲淤演变特性及江湖关系变化等研究成果的基础上,重点阐述水库群联合作用下长江中下游江湖关系响应机制,形成的主要认识有:水库群联合作用下中下游江湖系统的径流量及比例组成没有明显变化,但输沙量及比例组成发生显著变化,干流宜昌站变化最为明显;中下游河道由自然条件下的中沙河流变为少沙河流,江湖系统由自然条件下的累积性淤积转为持续冲刷,并在较长时期内进行重新塑造与调整;水库群的联合作用对江湖水沙交换与湖区冲淤产生影响,两湖枯水期有所提前,湖区泥沙沉积率显著下降,江湖关系总体趋于向好的方向调整。鉴于长江水沙条件变化的不确定性、人类活动影响的加剧与江湖系统演变的复杂性,今后仍须加强变化环境下中下游江湖系统响应机理研究。     

Landscape integration of North Patagonian mountain lakes: a first approach using characterization of dissolved organic matter

North‐western Patagonia contains a variety of glacially formed mountain lakes located at different positions from the treeline in the Andean Patagonian forest region. Water chemistry of six North Patagonian lakes located in an altitudinal gradient, above, at and below the treeline (~41°S) were analysed in this study. The relative importance of allochtonous to autochthonous carbon inputs along a marked catchment vegetation gradient encompassing altoandino vegetation and Nothofagus forests was addressed. The dissolved organic carbon (DOC) concentration varied among the study lakes, with the lakes located higher in the landscape exhibiting lower DOC concentrations (<1 mg L^?1) than lakes located at or below the treeline (>2 mg L^?1). Analysis of coloured and fluorescent dissolved organic matter (CDOM and FDOM, respectively) followed the DOC pattern, despite the contrasting catchments of the study lakes. The results indicated the CDOM in all the lakes had low molecular weight and low aromaticity. The excitation–emission matrices (EEMs) highlighted three distinctive fluorophores in the FDOM, including two humic‐like (peak A and peak C) revealing the presence of humic terrestrial material, and a protein‐like fluorophore (peak T) generally associated with autochthonous DOM. The increased intensities of the humic fluorophores in the lakes located below the treeline suggest higher allochtonous carbon inputs from their catchments. This evidence collectively suggests that mountain lakes exhibit some heterogeneity in terms of DOM, likely attributable to their position in relation to the treeline, which determines the contribution of the catchment. As remote lakes are extremely sensitive to changes in their catchments, these North Patagonian mountain lakes may accurately track the impact of climate and anthropogenic changes on the landscape.     

FISH DEPTH DISTRIBUTIONS IN THE LOWER MISSISSIPPI RIVER

A substantial body of literature exists about depth distribution of fish in oceans, lakes and reservoirs, but less is known about fish depth distribution in large rivers. Most of the emphasis on fish distributions in rivers has focused on longitudinal and latitudinal spatial distributions. Knowledge on depth distribution is necessary to understand species and community habitat needs. Considering this void, our goal was to identify patterns in fish benthic distribution along depth gradients in the Lower Mississippi River. Fish were collected over 14 years in depths down to 27 m. Fish exhibited non‐random depth distributions that varied seasonally and according to species. Species richness was highest in shallow water, with about 50% of the 62 species detected no longer collected in water deeper than 8 m and about 75% no longer collected in water deeper than 12 m. Although richness was highest in shallow water, most species were not restricted to shallow water. Rather, most species used a wide range of depths. A weak depth zonation occurred, not as strong as that reported for deep oceans and lakes. Larger fish tended to occur in deeper water during the high‐water period of an annual cycle, but no correlation was evident during the low‐water period. The advent of landscape ecology has guided river research to search for spatial patterns along the length of the river and associated floodplains. Our results suggest that fish assemblages in large rivers are also structured vertically. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.     

前郭灌区节水改造工程削减农田面源污染物COD效果分析

水田退水携带的COD是河湖水体的重要面源污染物之一。经过对前郭灌区典型水田、地下潜水、排水干渠水体中COD的监测,并对近两年大规模开展的节水改造工程效果进行了分析,认为水田COD主要是通过地表径流和垂直渗漏两个方式迁移,其中退水导致的地表迁移占较大比例;节水改造工程减少了地表退水量,削减COD的效果较显著,削减率与在排水干渠实测的数据基本吻合,表明节水灌溉工程也是削减农田面源污染物COD的有效方式和可靠手段。     

古芍陂的管护制度对当代治水护水的启发

鉴于芍陂特有的历史地位和非凡价值,挖掘其在治水中的先进性及其对当代治水管理的借鉴性,具有重要的历史意义和实践价值。本文通过查阅古籍、文献等资料,梳理了芍陂灌排工程管理的历史演变,总结了芍陂在历史上的治水管水大事记,阐述了芍陂的兴衰给后人留下的宝贵的治水经验,明确了灌溉管理在水资源综合管理中的突出地位、"双河长制"在河湖治理的显著效率、退田还湖在促进河湖健康发展中的关键作用以及打造幸福河湖、传承治水文化的重要意义与价值引领。以期在芍陂兴废更迭的历史进程中吸取经验,探索灌溉管理与维护制度的发展规律,为当代治水护水提供思路。     

水温变化特性对衡水湖湿地生态环境影响的分析

衡水湖供水水源主要以汛期上游来水和外流域调水为主,调水时段多为每年冬季,水源供给时间相对集中。衡水湖水体水温与其他湖泊有所不同,在秋季、冬季和春季多高于一般性湖泊。通过实测资料对衡水湖内水温及气温变化规律进行分析研究,并与其他河流湖泊水体进行对比,阐明了水温变化对衡水湖湿地生态环境和水质的影响,为制定衡水湖生态系统发展规划提供科学依据。     

浅谈“河长制”在高安市的扎实稳步推进

江西省高安市实施"河长制"近一年多来,开展水污染治理,建立河湖管理长效机制,取得了较好的成效.文章全面细致地阐述了"河长制"在高安市的开展情况,从强化组织领导、严格落实责任、落实保障经费、开展"清河行动"等方面探索出了一些符合自身特点的经验和做法.     

Progressive changes in phytoplankton community structure in urbanized lowland river floodplains—a multivariate approach

Phytoplankton communities along the river Yamuna in Delhi stretch and its associated floodplain lakes showed considerable spatio‐temporal variations. Most of the species identified were cosmopolitan and typical of highly polluted rivers in tropical ecosystems. All the groups of phytoplankton with predominance of Cyanophyceae and some species of Chlorophyceae were distributed within the river stretch though with varying diversity and density. Relatively cleaner sites supported larger phytoplankton assemblages compared to those subjected to sewage outfalls and industrial effluents. Species elimination was observed mainly in the mid‐stretch and downstream of Okhla subjected to high loads of pollution. Co‐inertia analysis indicated significant co‐structures between water quality and species richness and density indicating water quality as the governing factor for phytoplankton distributions in the river stretch. Floodplain plays an important role in regenerating water quality thereby enhancing species richness and density. Floods play an important role in seasonal dynamics through dilution effects and promoting connectivity between river channel and floodplain lakes thereby facilitating species exchanges. Copyright © 2008 John Wiley & Sons, Ltd.     

中国主要河湖水生态综合评价

河湖水生态综合评价是水资源保护规划工作的重要内容之一。本文从水文水资源、水环境、河湖生境形态、生物及栖息地状况等方面,构建了包含生态基流满足程度、水功能区水质达标率、湖库富营养化指数、纵向连通性、重要湿地保留率及鱼类生境等6个指标构成的河湖水生态综合评价体系。在此基础上,对全国673条河流、97座水库和100个湖泊湿地共计1006个规划河段和湖库的水生态状况进行了评价和分类,分析了我国各大流域河湖面临的水生态问题。研究成果对我国主要河湖水生态保护和修复工作的实践具有重要的指导意义。