River Flow Alterations Research Articles

Evaluating the relationship between basin‐scale fish species richness and ecologically relevant flow characteristics in rivers worldwide

Summary1. River flow alterations due to climate change and increasing water usage affect freshwater biodiversity including fish species richness. Here, we statistically explored the relationships of fish species richness to 14 ecologically relevant flow metrics as well as basin area and latitude in 72 rivers worldwide.2. The statistical models best supported by the data included three variables with positive coefficients (mean river discharge, basin area and the maximum proportion of no‐flooding period) and three variables with negative coefficients (latitude, coefficients of variation in the frequency of low flow and the Julian date of annual minimum flow).3. The model outputs have provided the first empirical indication that specific low‐ and high‐flow characteristics may be important in explaining variations in basin‐scale fish species richness. Our findings can be useful in identifying high‐risk basins for conservation of fish species diversity.4. The results not only support the adoption of mean discharge as a predictor, but also suggest the importance of basin area in predicting basin‐scale fish species richness around the world.

Engineering the North American waterscape: The high modernist mapping of continental water transfer projects

Starting in the late 1950s, at least fifteen separate proposals to radically alter the North American waterscape emerged. These proposals typically sought to bring water from northern regions (especially in Canada) to southern ones in the United States and Mexico through canal construction, the massive alteration of river flow, and (in some cases) nuclear excavation. This study analyzes the cartographic strategies used in support of re-engineering the continent’s water flow. The project maps promoted a specific political agenda that sought to redistribute North America's water resources by transcending political boundaries and physical barriers. Furthermore, conventions of cartographic representation, particularly the need for generalization and simplification, worked to reinforce and heighten the original modernist, engineering ethos. This led to representations that de-emphasized political communities and boundaries, that both assumed and hid nuclear technology, and that ultimately removed water from the natural environment by treating it as a purely abstract resource.

Impact analysis of the Three-Gorges Project on the spawning of Chinese sturgeon Acipenser sinensis

Summary The spawning run of adult Acipenser sinensis was blocked by the Gezhouba Dam in 1982 and the flow line was altered again in October and November, when during the spawning period the Three Gorges Project (TGP) started to fill the reservoir with water. This alteration of river flow may affect spawning of A. sinensis. By comparing historical river flow records at spawning dates and outflow at the design year from TGP, we found that A. sinensis spawning in the Yangtze river took mostly place below the Gezhouba Dam on the flood receding period, and discharge volumes of about 7110 m3 s−1 were at the minimum for the spawning of A. sinensis. The Three Gorges reservoir operation as designed would satisfy the spawning flows for A. sinensis except in low-flow years. Once low flow years occur, an adaptive operational procedure should be taken to meet the A. sinensis spawning requirements for hydrodynamics. This can be achieved by impounding water early on and taking rapid responses to meet the flow at the spawning time of A. sinensis.

Assessing effects of flow alteration on macroinvertebrate assemblages in Australian dryland rivers

Summary1. Possible impacts of water‐resource development on assemblages of freshwater macroinvertebrates were investigated in the upper Darling River and some of its tributaries in north‐western New South Wales (Australia), an arid and semi‐arid region of low relief where alteration of river flows has intensified through expansion of irrigated agriculture.2. Study sites were grouped into four hydrological regimes resulting from impoundment, flow regulation, water abstraction and natural variation, namely (i) intermittent flow with relatively little hydrological alteration from water‐resource development, (ii) intermittent flow with substantial alteration, (iii) near‐perennial flow with substantial alteration but unimpounded and (iv) near‐perennial flow with substantial alteration plus impoundment by weirs that stabilise water levels.3. Macroinvertebrates were sampled with three methods (a quantitative cylinder sampler, handnet sampling and baited traps) in three periods with differing hydrology (recessional low flow in June 2003, high flow in March 2004 and increasing flow after drought in December 2004).4. Taxonomic richness, assemblage composition and catch per unit effort of the crayfish Cherax destructor differed significantly among the site groups, but total macroinvertebrate density and the AUSRIVAS O/E (Australian River Assessment System observed‐over‐expected) index did not. The principal spatial differences were between the intermittent and near‐perennial rivers, and apparent effects of water‐resource development and impoundment were more subtle. Temporal differences in richness, abundance and composition were substantial and appeared to be related mainly to variations in discharge and temperature.5. Current macroinvertebrate‐based methods for assessing the ‘condition’ or ‘health’ of Australian dryland rivers are inadequate. Such assessments might be improved with (i) reference data that take adequate account of antecedent hydrological conditions, (ii) consideration of long‐term taxonomic richness as well as richness on individual sampling occasions, (iii) evaluation of invertebrate population sizes, (iv) analysis of assemblage data by trait composition and (v) adoption of the genus as the default level of taxonomic resolution.

Impact of climate change on freshwater ecosystems: a global-scale analysis of ecologically relevant river flow alterations

Abstract. River flow regimes, including long-term average flows, seasonality, low flows, high flows and other types of flow variability, play an important role for freshwater ecosystems. Thus, climate change affects freshwater ecosystems not only by increased temperatures but also by altered river flow regimes. However, with one exception, transferable quantitative relations between flow alterations and ecological responses have not yet been derived. While discharge decreases are generally considered to be detrimental for ecosystems, the effect of future discharge increases is unclear. As a first step towards a global-scale analysis of climate change impacts on freshwater ecosystems, we quantified the impact of climate change on five ecologically relevant river flow indicators, using the global water model WaterGAP 2.1g to simulate monthly time series of river discharge with a spatial resolution of 0.5 degrees. Four climate change scenarios based on two global climate models and two greenhouse gas emissions scenarios were evaluated. We compared the impact of climate change by the 2050s to the impact of water withdrawals and dams on natural flow regimes that had occurred by 2002. Climate change was computed to alter seasonal flow regimes significantly (i.e. by more than 10%) on 90% of the global land area (excluding Greenland and Antarctica), as compared to only one quarter of the land area that had suffered from significant seasonal flow regime alterations due to dams and water withdrawals. Due to climate change, the timing of the maximum mean monthly river discharge will be shifted by at least one month on one third on the global land area, more often towards earlier months (mainly due to earlier snowmelt). Dams and withdrawals had caused comparable shifts on less than 5% of the land area only. Long-term average annual river discharge is predicted to significantly increase on one half of the land area, and to significantly decrease on one quarter. Dams and withdrawals had led to significant decreases on one sixth of the land area, and nowhere to increases. Thus, by the 2050s, climate change may have impacted ecologically relevant river flow characteristics more strongly than dams and water withdrawals have up to now. The only exception refers to the decrease of the statistical low flow Q90, with significant decreases both by past water withdrawals and future climate change on one quarter of the land area. However, dam impacts are likely underestimated by our study. Considering long-term average river discharge, only a few regions, including Spain, Italy, Iraq, Southern India, Western China, the Australian Murray Darling Basin and the High Plains Aquifer in the USA, all of them with extensive irrigation, are expected to be less affected by climate change than by past anthropogenic flow alterations. In some of these regions, climate change will exacerbate the discharge reductions, while in others climate change provides opportunities for reducing past reductions. Emissions scenario B2 leads to only slightly reduced alterations of river flow regimes as compared to scenario A2 even though emissions are much smaller. The differences in alterations resulting from the two applied climate models are larger than those resulting from the two emissions scenarios. Based on general knowledge about ecosystem responses to flow alterations and data related to flow alterations by dams and water withdrawals, we expect that the computed climate change induced river flow alterations will impact freshwater ecosystems more strongly than past anthropogenic alterations.

Global-scale analysis of river flow alterations due to water withdrawals and reservoirs

Abstract. Global-scale information on natural river flows and anthropogenic river flow alterations is required to identify areas where aqueous ecosystems are expected to be strongly degraded. Such information can support the identification of environmental flow guidelines and a sustainable water management that balances the water demands of humans and ecosystems. This study presents the first global assessment of the anthropogenic alteration of river flow regimes, in particular of flow variability, by water withdrawals and dams/reservoirs. Six ecologically relevant flow indicators were quantified using an improved version of the global water model WaterGAP. WaterGAP simulated, with a spatial resolution of 0.5 degree, river discharge as affected by human water withdrawals and dams around the year 2000, as well as naturalized discharge without this type of human interference. Compared to naturalized conditions, long-term average global discharge into oceans and internal sinks has decreased by 2.7% due to water withdrawals, and by 0.8% due to dams. Mainly due to irrigation, long-term average river discharge and statistical low flow Q90 (monthly river discharge that is exceeded in 9 out of 10 months) have decreased by more than 10% on one sixth and one quarter of the global land area (excluding Antarctica and Greenland), respectively. Q90 has increased significantly on only 5% of the land area, downstream of reservoirs. Due to both water withdrawals and reservoirs, seasonal flow amplitude has decreased significantly on one sixth of the land area, while interannual variability has increased on one quarter of the land area mainly due to irrigation. It has decreased on only 8% of the land area, in areas downstream of reservoirs where consumptive water use is low. The impact of reservoirs is likely underestimated by our study as small reservoirs are not taken into account. Areas most affected by anthropogenic river flow alterations are the Western and Central USA, Mexico, the western coast of South America, the Mediterranean rim, Southern Africa, the semi-arid and arid countries of the Near East and Western Asia, Pakistan and India, Northern China and the Australian Murray-Darling Basin, as well as some Arctic rivers. Due to a large number of uncertainties related e.g. to the estimation of water use and reservoir operation rules, the analysis is expected to provide only first estimates of river flow alterations that should be refined in the future.

Biodiversity and the Three Gorges Reservoir: a troubled marriage

The Three Gorges region, located on the upper reaches of the Yangtze River in central China, is considered one of the most important biodiversity hotspots in China. It harbours more than 6000 plant species, over 500 terrestrial vertebrates, and about 160 species of fish. In addition to this taxonomic richness, the region is home to many endemic and threatened taxa, which may be the result of its role as a glacial refuge. The construction of the Three Gorges Dam may have serious consequences for this biodiversity. The flooding of more than 600 km2 together with massive population resettlement will involve the loss and/or fragmentation of many terrestrial habitats in the reservoir area, affecting both plant and animal species. Furthermore, negative effects on downstream terrestrial biodiversity are expected due to the regression of floodplains and riparian wetlands after the dam is completed. The alteration of river flow caused by the dam will also have a severe impact on freshwater biodiversity throughout the whole Yangtze River system, especially on migratory fish but also on other aquatic life, such as the emblematic Yangtze River dolphin. The conservation measures implemented by the authorities, although valuable, may well be insufficient to mitigate the negative effects of the dam on biodiversity.

Similarity in Taxonomic Composition of Benthic Macroinvertebrate Communities in the Blagoevgradska Bistritsa River

ABSTRACTBenthic macroinvertebrate communities in the Blagoevgradska Bistritsa River were examined as a part of a complex study of the river and its basin. Monthly in 2002 and seasonal in 2003 handnet samples were taken from seven stations along the river length. The similarity of the benthic communities at different stations—along the river continuum and at each station—in different months was determined in order to study the taxonomic (species) composition dynamics and to identify the main factors affecting it. Generally the species composition along the river continuum was changed slightly, which confirms the results about the dominant structure of benthic macroinvertebrate communities and the conclusion that the whole river possesses characteristics typical of upper river courses. Both in 2002 and 2003 the similarity in species composition between sampling stations from 1 to 6 was high (above 50% almost in all cases) but comparatively low (from 21.6 to 41.1%) between the first six stations and the last one where the saprobic pollution was quite high. The seasonal changes in composition between the stations and at each station were determined mainly by the river flow alterations. In periods with prolonged high flow (2002) the species composition similarity along the river continuum increased while in low flow period (summer-autumn 2003) the tendency was the opposite. During the summer-autumn low flow period in 2003 the composition of macrozoobenthos in the lower river course was strongly influenced by the altered characteristics of the basic hydrological parameters (velocity, temperature etc.) and was considerably changed.

Impact of the Mekong River Flow Alteration on the Tonle Sap Flood Pulse

Rapid development in the upper reaches of the Mekong River, in the form of construction of large hydropower dams and reservoirs, large irrigation schemes, and rapid urban development, is putting water resources under stress. Recent studies have concluded that these developments will lead to flow alterations in the Mekong River. These flow alterations would threaten the sensitive ecosystems downstream, particularly Tonle Sap River, Tonle Sap Lake, its floodplain, and its gallery forest and protected areas, by changing the flood-pulse system of the lake. This article estimates the changes in parameters of the Tonle Sap flood pulse due to the aforementioned flow alterations. The impacts on the flooded area and loss of gallery forest and protected areas were analyzed using geographic information system-based methods. Relatively small rises in the dry-season lake water level would permanently inundate disproportionately large areas of floodplain, rendering it inaccessible to floodplain vegetation and eroding the productivity basis of the ecosystem. It is highly important to maintain the natural hydrological pattern of the Mekong River, particularly the dry-season water levels, to preserve Tonle Sap Lake's ecosystem productivity.

Quenching Urban Thirst: Cities and Their Effects on Freshwater Ecosystems

This article discusses potential ecological degradation that could result from future expansion of urban water supplies and assesses the history of water resource development for five large U.S. cities including Los Angeles, Phoenix, New York, San Antonio, and Atlanta. The article demonstrates the ecologic impacts of water development practices commonly used in the twentieth century, and discusses options to increase water supply in less ecologically damaging ways than have been used in the past. They include: water conservation programs that reduce per capita water use; storing and extracting water in less ecologically damaging ways; and, limiting human alteration of river flows to protect ecosystems.

Regional‐scale effects of flow regulation on lowland riverine fish communities in New South Wales, Australia

AbstractLowland reaches of 40 rivers in New South Wales, Australia, were designated as ‘regulated’ or ‘unregulated’, depending upon the degree to which flows were modified by the operation of a dam upstream. Five replicate rivers of each type were selected from the North Coast, South Coast, Darling and Murray regions in the State. Fish communities in each river were sampled in summer and winter in two consecutive years. Regulated and unregulated rivers contained significantly different fish communities, although communities in each region retained characteristic features. The proportion of native species in the total catch was greater in unregulated rivers in all regions, ranging from 27% in the Murray region to 100% in South Coast rivers. In regulated rivers, native species made up 20% of the catch in the Murray region compared with a maximum of 99% in the North Coast. Carp, Cyprinus carpio, were the main alien species contributing to changes in the proportional abundance of native fish. Native species most affected by river regulation were western carp gudgeons, Hypseleotris spp., bony herring, Nematalosa erebi, and striped gudgeons, Gobiomorphus australis. Fifteen native species showed some effect of river regulation on their population structures. Individual species showed positive, negative or mixed positive and negative, effects of regulation, at population, species or community levels. Three abundant alien species and seven native species showed only positive or mixed responses, whereas 13 native species exhibited only negative effects. Flow regulation has reduced the resilience of New South Wales rivers and native fish communities to invasion by alien species. New research has commenced to investigate whether recently introduced environmental flow rules are effective in reducing the effects of river flow alteration on fish communities in New South Wales rivers. Copyright © 2001 John Wiley & Sons, Ltd.