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Dam Construction (dam + construction)
Selected AbstractsRiparian influence on hyporheic-zone formation downstream of a small dam in the Blackland Prairie region of TexasHYDROLOGICAL PROCESSES, Issue 2 2007Jacquelyn R. Duke Abstract Small-order streams have highly variable flows that can result in large temporal and spatial variation of the hyporheic zone. Dam construction along these intermittent headwater streams alters downstream flow and influences the hydrologic balance between stream water and the adjacent riparian zone. A 3-year site study was conducted along an impounded second-order stream to determine the water balance between stream, unsaturated zone, groundwater and riparian vegetation. The presence of the upstream impoundment provided near-perennial water flow in the stream channel. The observed woody plant transpiration accounted for 71% of average annual water loss in the site. The overall contribution of stream water via the hyporheic zone to site water balance was 73 cm, or 44% of total inputs. This exceeded both rainfall and upland subsurface contribution to the site. A highly dynamic hyporheic zone was indicated by high water use from woody plants that fluctuated seasonally with stream water levels. We found leaf area development in the canopy layer to be closely coupled with stream and groundwater fluctuations, indicating its usefulness as a potential indicator of site water balance for small dam systems. The net result of upstream impoundment increased riparian vegetation productivity by influencing movement of stream water to storage in the groundwater system. Copyright © 2006 John Wiley & Sons, Ltd. [source] Do dams increase genetic diversity in brown trout (Salmo trutta)?ECOLOGY OF FRESHWATER FISH, Issue 4 2006Microgeographic differentiation in a fragmented river Abstract , Local genetic differentiation may potentially arise in recently fragmented populations. Brown trout is a polytypic species exhibiting substantial genetic differentiation, which may evolve in few generations. Movement (semi-)barriers in rivers may cause fragmentation, isolation and genetic differentiation in fish. In the Måna River (28 km) flowing from the alpine Lake Møsvatn to the boreal Lake Tinnsjø, construction of four hydropower dams during the period 1906,1957 have fragmented the previously (since last Ice Age) continuous wild resident brown trout population. Samples from the two lakes (N = 40) and six sites in the river (N = 30) isolated at different times were analysed at nine microsatellite loci. All populations showed substantial genetic variation (mean number of alleles per locus 5.3,8.9, observed heterozygosity 0.57,0.65 per population, overall Fst = 0.032). Pairwise multilocus Fst estimates indicated no significant differentiation between populations in the two lakes, and no or little differentiation in the lower river (Fst = 0.0035,0.0091). The microgeographic differentiation among wild resident trout at these sites was less than expected based on similar previous studies. However, results from the upper river, in particular the site immediately below the Lake Møsvatn outlet and dam, indicated isolation (Fst > 0.035). Calculation of genetic distances and assignment tests corroborated these results, as did a significant correlation between years of isolation (since dam construction) and Fst. The population structuring is most likely a result of fragmentation by dams, which has increased overall genetic diversity. This increased local differentiation may be caused by natural selection, but more likely by genetic drift in small, recently fragmented populations. Increased local genetic diversity by genetic drift does not justify conservation measures aiming at preserving genetic diversity. [source] ORIGINAL ARTICLE: Potential for anthropogenic disturbances to influence evolutionary change in the life history of a threatened salmonidEVOLUTIONARY APPLICATIONS (ELECTRONIC), Issue 2 2008John G. Williams Abstract Although evolutionary change within most species is thought to occur slowly, recent studies have identified cases where evolutionary change has apparently occurred over a few generations. Anthropogenically altered environments appear particularly open to rapid evolutionary change over comparatively short time scales. Here, we consider a Pacific salmon population that may have experienced life-history evolution, in response to habitat alteration, within a few generations. Historically, juvenile fall Chinook salmon (Oncorhynchus tshawytscha) from the Snake River migrated as subyearlings to the ocean. With changed riverine conditions that resulted from hydropower dam construction, some juveniles now migrate as yearlings, but more interestingly, the yearling migration tactic has made a large contribution to adult returns over the last decade. Optimal life-history models suggest that yearling juvenile migrants currently have a higher fitness than subyearling migrants. Although phenotypic plasticity likely accounts for some of the change in migration tactics, we suggest that evolution also plays a significant role. Evolutionary change prompted by anthropogenic alterations to the environment has general implications for the recovery of endangered species. The case study we present herein illustrates the importance of integrating evolutionary considerations into conservation planning for species at risk. [source] Fluctuations in European eel (Anguilla anguilla) recruitment resulting from environmental changes in the Sargasso SeaFISHERIES OCEANOGRAPHY, Issue 1 2008SYLVAIN BONHOMMEAU Abstract European eel decline is now widely observed and involves a large number of factors such as overfishing, pollution, habitat loss, dam construction, river obstruction, parasitism and environmental changes. In the present study, we analyzed the influence of environmental conditions in the Sargasso Sea and Atlantic ocean circulation on European glass eel recruitment success. Over a recent 11-yr period, we showed a strong positive correlation between an original index of glass eel recruitment and primary production (PP) in eel spawning area. Moreover, PP was negatively correlated with temperature in the Sargasso Sea. Therefore, we used sea temperature as an inverse proxy of marine production. A close negative relationship has been found over the last four decades between long-term fluctuations in recruitment and in sea temperature. These findings were reinforced by the detection of a regime shift in sea temperature that preceded the start of the decline in glass eel recruitment in the early 1980s. By contrast, variations in integrative indices measuring ocean circulation, i.e. latitude and strength of the Gulf Stream, did not seem to explain variations in glass eel recruitment. Our results support the hypothesis of a strong bottom-up control of leptocephali survival and growth by PP in the Sargasso Sea on short and long time scales. We argue that sea warming in the eel spawning area since the early 1980s has modified marine production and eventually affected the survival rate of European eels at early life stages. [source] Response of waterbird species to fluctuating water levels in tropical coastal wetlandsAFRICAN JOURNAL OF ECOLOGY, Issue 3 2010Francis Gbogbo Abstract Recent upsurges in the incidence of dam construction over rivers for farming and hydro electric power in the West African sub-region is a known promoter of fluctuating water levels on tropical coastal wetlands. Waterbirds, being one of the dominant fauna on wetlands, are key species that can be affected by fluctuating water levels. Waterbird census and water level monitoring at four coastal wetlands in Ghana revealed that different guilds (species assemblages) of waterbirds responded differently to fluctuating water levels. The populations density of birds in guilds 1 (ducks and cormorants), 3 (tactile surface foraging waders), 4 (pelagic foraging waders) and 5 (stalking herons and egrets) significantly (P < 0.05) increased linearly with decreasing water levels. The population density of birds in guilds 2 (visual surface foraging waders) and 7 (fishing terns) responded significantly (P < 0.05) in a second order polynomial function with optimum numbers occurring when water levels were neither too high nor too low. As far as farming and energy requirement are met from these dams, it is important that the ecological needs of waterbirds on wetlands are incorporated into the management of these dams so as to maintain appropriate water levels beneficial to waterbird populations. Résumé En Afrique de l'Ouest, la multiplication récente des constructions de barrages sur des cours d'eau pour les exploitations agricoles et la fourniture d'électricité est un facteur connu des fluctuations du niveau d'eau dans les zones humides côtières tropicales. Les oiseaux d'eau, éléments dominants de la faune des zones humides, sont des espèces clés qui peuvent être touchées par la fluctuation du niveau de l'eau. Les recensements des oiseaux d'eau et le suivi du niveau de l'eau dans quatre zones humides côtières du Ghana ont révélé que des guildes (assemblages d'espèces) différentes répondaient différemment à la fluctuation du niveau de l'eau. La densité de population des oiseaux dans les guildes 1 (canards et cormorans), 3 (échassiers se nourrissant en surface grâce aux corpuscules tactiles du bec), 4 (échassiers se nourrissant en profondeur) et 5 (hérons et aigrettes qui pêchent à l'affût) augmentait significativement (P < 0,05) de façon linéaire lorsque le niveau de l'eau baissait. La population des oiseaux des guildes 2 (échassiers chassant à vue à la surface) et 7 (sternes pêcheuses) répondait significativement (P < 0,05) dans une fonction polynômiale du 2d degré, les nombres optimum s'observant lorsque le niveau de l'eau n'est ni trop haut ni trop bas. À partir du moment où les exigences de l'agriculture et de l'énergie sont satisfaites grâce à ces barrages, il est important que les besoins écologiques des oiseaux d'eau des zones humides soient intégrés dans la gestion de ces barrages de façon à maintenir des niveaux d'eau favorables aux populations d'oiseaux d'eau. [source] Hydrologic Connectivity and the Contribution of Stream Headwaters to Ecological Integrity at Regional Scales,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 1 2007Mary C. Freeman Abstract:, Cumulatively, headwater streams contribute to maintaining hydrologic connectivity and ecosystem integrity at regional scales. Hydrologic connectivity is the water-mediated transport of matter, energy and organisms within or between elements of the hydrologic cycle. Headwater streams compose over two-thirds of total stream length in a typical river drainage and directly connect the upland and riparian landscape to the rest of the stream ecosystem. Altering headwater streams, e.g., by channelization, diversion through pipes, impoundment and burial, modifies fluxes between uplands and downstream river segments and eliminates distinctive habitats. The large-scale ecological effects of altering headwaters are amplified by land uses that alter runoff and nutrient loads to streams, and by widespread dam construction on larger rivers (which frequently leaves free-flowing upstream portions of river systems essential to sustaining aquatic biodiversity). We discuss three examples of large-scale consequences of cumulative headwater alteration. Downstream eutrophication and coastal hypoxia result, in part, from agricultural practices that alter headwaters and wetlands while increasing nutrient runoff. Extensive headwater alteration is also expected to lower secondary productivity of river systems by reducing stream-system length and trophic subsidies to downstream river segments, affecting aquatic communities and terrestrial wildlife that utilize aquatic resources. Reduced viability of freshwater biota may occur with cumulative headwater alteration, including for species that occupy a range of stream sizes but for which headwater streams diversify the network of interconnected populations or enhance survival for particular life stages. Developing a more predictive understanding of ecological patterns that may emerge on regional scales as a result of headwater alterations will require studies focused on components and pathways that connect headwaters to river, coastal and terrestrial ecosystems. Linkages between headwaters and downstream ecosystems cannot be discounted when addressing large-scale issues such as hypoxia in the Gulf of Mexico and global losses of biodiversity. [source] RUNOFF AND SEDIMENT RESPONSES TO CONSERVATION PRACTICES: LOESS PLATEAU OF CHINA,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 5 2003Mingbin Huang ABSTRACT: Soil erosion is the most significant threat to land productivity and environmental quality on the Loess Plateau of China. The annual total sediment load of the Yellow River is 1.6 billion tons, with about 90 percent coming from soil erosion from the Loess Plateau. To reduce soil erosion from the Loess Plateau, conservation practices, including tree planting, ridge construction between fields and around gullies, terrace and ditch construction perpendicular to the main slope, and dam construction are being implemented. An evaluation of these conservation practices is required before they are implemented at the large scale. The objective of this study is to evaluate the effectiveness of conservation practices to control runoff and sediment yield from paired watersheds in the hilly gully region of the Loess Plateau. The advantage of the paired watershed approach is its sensibility in detecting differences in runoff and sediment transport by monitoring both watersheds during two periods, an initial period with no conservation practices and a treatment period with only one watershed subjected to conservation practices. Implementation of the conservation practices resulted in (1) cumulative runoff and sediment yield that were, respectively, 25 and 38 percent less from the treatment watershed than from the control, (2) a decrease in the number of rainfall events producing runoff and sediment transport (94 in the control versus 63 in treatment), and (3) a reduction in the maximum discharge and maximum suspended sediment concentration. [source] Improving public information about large hydroelectric dams: Case studies in France and West AfricaNATURAL RESOURCES FORUM, Issue 1 2003Armelle Faure It is becoming more common for public authorities in charge of dam construction and management to inform the population living in the area soon to be submerged by a proposed dam. However, populations living further downstream along a river to be dammed, have often been left to find out by chance, despite the fact that the changes to the river flow regime will have an important impact on their lives, sometimes serious negative impacts. This article makes a comparison between two dams, one at Bort-les-Orgues across the upper Dordogne River in southern France, the other the Bagré Dam over the Nakambé (or White Volta) River in south-eastern Burkina Faso. The article discusses dam construction and operation from the point of view of the concerned populations living in the reservoir and downstream areas. In 2000, a study was carried out in the Dordogne Valley to ascertain downstream impacts of dam operations and information needs of the population. Suggestions from local river users related mostly to improving public information about predicted and actual flow rates and actual flow in real time along the 300 km course of the Dordogne between the dams and the estuary. Such information should be disseminated as widely as possible through available media, including the Internet, and also displayed visibly in key locations along the length of the river. [source] Rapid Holocene chemical weathering on a calcitic lake shoreline in an alpine periglacial environment: Attgløyma, Sognefjell, southern NorwayPERMAFROST AND PERIGLACIAL PROCESSES, Issue 1 2006Geraint Owen Abstract A small lake (Attgløyma) at an altitude of about 1220,m in the low-alpine zone, southern Norway, has a shore platform in calcitic and quartzitic muscovite-chlorite schists. The platform has recently been exposed by a fall in lake level due to upstream dam construction and exhibits micro-landforms ranging from pits and grooves to upstanding crenulate ridges produced by differential chemical weathering under relatively constant conditions over the last ca. 10,000 years. The maximum surface lowering rate of the calcitic layers estimated from differential weathering is 35,mm,ka,1, which is about an order of magnitude greater than most previous estimates from alpine and polar periglacial environments. Average bedrock surface lowering across the whole platform reached a maximum of 15.5,±,2.2,mm,ka,1 in a vertical zone corresponding with the former lake level, declining to negligible values around 0.7,m below lake level. Differential weathering and bedrock surface lowering were also negligible immediately above lake level. Correspondence of maximum surface lowering rates with the former lake level and a shoreline notch at the back of a platform suggest that the effects of solutional weathering of the calcite have been enhanced by water movement generated by small lake-surface waves. Copyright © 2006 John Wiley & Sons, Ltd. [source] Conservation and management of migratory fauna: dams in tropical streams of Puerto RicoAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 7 2006Effie A. Greathouse Abstract 1.Compared with most other tropical regions, Puerto Rico appears to have dammed its running waters decades earlier and to a greater degree. The island has more large dams per unit area than many countries in both tropical and temperate regions (e.g. three times that of the USA), and the peak rate of large dam construction occurred two or three decades before reported peak rates in Latin America, Asia and Africa. 2.Puerto Rico is a potential window into the future of freshwater migratory fauna in tropical regions, given the island's extent and magnitude of dam development and the available scientific information on ecology and management of the island's migratory fauna. 3.The paper reviews the ecology, management and conservation of migratory fauna in relation to dams in Puerto Rico. It includes a synthesis of recent and unpublished observations on upstream effects of large dams on migratory fauna and an analysis of patterns in free crest spillway discharge across Puerto Rican reservoirs. 4.Analyses suggest that large dams with rare spillway discharge cause near, not complete, extirpation of upstream populations of migratory fauna. They also suggest several management and conservation issues in need of further research and consideration, including research on the costs, benefits and effectiveness of simple fish and shrimp passage designs involving simulating spillway discharge. The appropriateness of establishing predatory fish in reservoirs of historically fishless drainages also needs to be considered. Copyright © 2006 John Wiley & Sons, Ltd. [source] Short-term environmental changes in Lake Morenito (41°S, 71°W, Patagonia, Argentina) from the analysis of sub-fossil chironomidsAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 1 2005Julieta Massaferro Abstract 1.A short sediment core from Lake Morenito was studied to assess the impact of environmental changes on chironomid communities occurring during the last ca 100 yr. 2.Lake Morenito (41°S, 71°W) is located 20 km west of the city of Bariloche, in northern Patagonia, Argentina. Before 1960, this lake was a branch of Lake Moreno; by that time, an artificial dam closed the system, establishing the new lake. Another human disturbance that took place during the time span of the core was the introduction of salmonids to the area ca 1910. 3.The most important natural events that occurred in the area during the last 100 yr were related to volcanic episodes. One of them, occured in Chile in 1960 affecting the Argentinian side, coincided with the dam's construction. 4.Changes in the chironomid community were recorded by studying the sub-fossil remains (the chitinized head capsule of the larvae) present in the sedimentary sequence. The results show that volcanic tephra layers deposited along the core led to a sharp instantaneous drop in the diversity and abundance of chironomid assemblages. Human activities are also associated with a change in chironomid community composition. 5.Chironomus reached its maximum abundance values in 1910 and 1960. The organic matter content also increased at the same time. The increase of Chironomus after 1910 is clearly related to an increase in the trophic status of the lake. However, owing to the synchronicity of events in 1960, i.e. the volcanic event and the dam's construction, it is difficult to establish whether the change in the chironomid assemblage was in response to an increase in trophic enrichment, to natural disturbance, or both. Copyright © 2004 John Wiley & Sons, Ltd. [source] | |||||||||||||||||||