摘要:

AbstractDam removal has received increasing attention over the last several years as a viable alternative to rehabilitation of unsafe dams and as an alternative for consideration as many hydroelectric dams come up for relicensing in the USA. The environmental impacts of dams on river ecosystems have been studied far more extensively than have the impacts of removing dams. Comprehensive environmental research is currently being conducted, assessing both the positive and negative impacts of the possible removal of Rodman Dam on the Ocklawaha River, Florida. The 2073 m long and 6·7 m high dam was constructed in 1968, impounding 3642 ha on this 125 km long river. The impacts of dam removal are compared with those expected by retaining and actively managing the reservoir for fish and wildlife. The research approach described here for addressing alternatives is recommended as a holistic procedure in which to make an environmentally based decision regarding dam removal

ISSN:0886-9375    

DOI:10.1002/rrr.3450110302

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractReservoirs comprise an expanding proportion of global freshwater resources. New multimetric approaches to biological monitoring, such as the index of biological integrity, have been useful in streams; similar approaches in reservoirs might aid managers concerned about the reservoirs they manage. Electrofishing data from Tennessee Valley Authority reservoirs were used to evaluate the applicability of biomonitoring to those reservoirs. Individual metrics and overall index scores exhibited substantial annual variation. Within‐year variation in scores from a supplemental data set suggests that annual changes in scores may not represent real fluctuations in resource condition. Species accumulation curves demonstrate that standard samples consisting of ten timed runs were not adequate; the sample error was high. Some metrics are useful, but they require more testing; other metrics are clearly not appropriate for use in a integrative multimetric index. Finally, the reservoirs included in this study may be similarly degraded; independent data from separate regions and watersheds are needed to resolve this and other issues. Although attaching qualitative judgements (e.g. excellent to poor) is premature, the concept of a reservoir biomonitoring index deserves more study, especially the development of more comprehensive and systematic sampling programmes designed to resolve sample adequacy and sources of variation in sample dat

ISSN:0886-9375    

DOI:10.1002/rrr.3450110303

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThe objectives of the study were to measure the effects of an experimental flood on : (1) leaf litter production by the riparian forest; (2) leaf decomposition; and (3) the amount of forest floor organic matter. The study area is located at Bosque del Apache National Wildlife Refuge, approximately 160 km south of Albuquerque, New Mexico. Experimental and reference study sites of about 3·1 ha were both located in cottonwood (Populus fremontii) riparian forests that had not been flooded for approximately 50 years. The experimental and control study sites were sampled for two years before flooding the experimental site. The experimental flood peaked on about 31 May, the average date of peak flow in the 100 year hydrograph for the USGS gauging station on the Rio Grande at Embudo, New Mexico. Litter fall was lower at the flood site than at the control site, whereas the rate of leaf decomposition was higher at the flood site during the period of inundation. However, the flood did not produce a measurable response in standing stock of forest floor litter. This pool of carbon may require the cumulative effects of several years of flooding to show a measurable response

ISSN:0886-9375    

DOI:10.1002/rrr.3450110304

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractA measure of stream quality, the index of biotic integrity (IBI), was adapted to great rivers (>3226 km2) and calibrated using a variety of spatial scales. Fish fauna was sampled at 60 localities within 15 impoundments of the Ohio River drainage, eastern Ohio, West Virginia and Pennsylvania, with boat electroshocker methods during the summers and autumns of 1990–1993 to provide biological information for the IBI. Significant correlation was not found between ecoregion or differing reservoirs; however, the IBI was sensitive to differences in land use and variable industrial and municipal loadings. Species richness, the percentage large river faunal group, the proportion of round‐bodied sucker species, the number of centrarchid species, the number of sensitive taxa and the proportion of simple lithophilous spawning species showed the greatest change between riverine and lacustrine habitats within an impoundment. The percentage large river faunal group metric was not significantly different between riverine, transitional and lacustrine habitats; however, the metric reflected significant differences when evaluated with habitat information. The number of centrarchid species was higher in lacustrine habitats, whereas round‐bodied sucker species were highest in transitional habitats. The inherent variation of proportional metrics was significantly reduced with the removal of gizzard shad. This modification of the IBI will enhance assessment sensitivity over the original approach designed for wadable streams and r

ISSN:0886-9375    

DOI:10.1002/rrr.3450110305

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractHistorically the hydrograph of the Missouri River had high and low discharge components. Low flows occurred from July through to early March. The period was characterized by declining thalweg velocity, reduced depth and exposed sand bars. Flood control was initiated as early as 1937 when the first mainstem dam was completed: however, it was not until after 1944 that a rigorous effort to control the wild Missouri River occurred. By 1954 sufficient reservoir storage had been built to allow complete re‐organization of the hydrograph to minimize floods and facilitate navigation. The present managed hydrograph (plan III) is compared with four operational alternatives. Plan I was selected by a team of environmental advisers and it was patterned after the natural hydrograph, but with some adjustments to minimize flood damage and to provide only minimal benefits to navigators. Plan II was selected as the preferred alternative in the environmental impact analysis and it was much more sensitive to the preservation of flood control and navigation benefits. Plan IV was a run of the river alternative, but with the reservoirs present, and, finally, plan V was a true run of the river under pre‐dam conditi

ISSN:0886-9375    

DOI:10.1002/rrr.3450110306

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractFocusing on the ecological integrity of large river systems has suggested the rethinking of the entire issue from a landscape perspective. Ecological integrity is impossible without biological integrity. However, it appears improbable that highly localized measures of biological integrity can be used for effective, scientifically justifiable extrapolations to landscape‐ or system‐level ecological integrity. It may be more reasonable to make measurements at the level of organization of interest, i.e. larger spatial and temporal scales. In addition, human society and natural systems have been coevolving since the agricultural revolution and, arguably, well before then. Two types of coevolution between human society and natural systems appear possible: (1) an ‘arms‐race’ in which human society ignores changes in natural systems—essential ecosystem services are lost, resulting in unpleasant consequences for society; or (2) mutualism in which environmental literacy and a feeling of responsibility for natural systems motivate rapid societal response to ecosystem changes and the preservation of ecological integrity.The simplest measures of ecological integrity may be the actions of human society likely to minimize or markedly reduce negative impacts on natural systems. This does not mean substituting such measures for more customary ecological measures, but rather using both types of measurements sim

ISSN:0886-9375    

DOI:10.1002/rrr.3450110307

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractAn attempt is made to evaluate the present environmental impacts of the Tucuruí dam on the fisheries and ecological integrity of the Araguaia—Tocantins basin. Management and research needs to minimize the impacts from future hydroprojects and increased human activities in the basin are also addressed. The Tocantins and Araguaia fish fauna is not especially rich by Amazonian standards (about 300 species). Total yields are also rather low (about 8800 t/y) in a river stretch of about 2500 km and unique for being concentrated (90%) in the main channel. Fisheries are heavily dependent on migratory fish and may be severely damaged as a consequence of river regulation. Downstream from the Tucurui Dam important fisheries have been drastically reduced (70%), probably by recruitment failure, lower productivity and overfishing. Upstream from the dam, however, fisheries have benefited from the higher productivity of the artificial lake, although this has not compensated for the regional economic shortages. Management based on ‘basinwise’ catch statistics and fish migration research should take account of likely future disruptions of commercial fisheries by the synergistic effects of other planned impoundments, mining, deforestation and uncontrolled sport fisheries in the middle and upper

ISSN:0886-9375    

DOI:10.1002/rrr.3450110308

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractPreparations are currently under way to establish a river restoration concept for the free‐flowing section of the Austrian Danube downstream of Vienna. This should serve as a basis for a National Park management. Studies have been initiated to assess the effects of hydrological connectivity, flood pulses and successional processes on backwaters with regard to their hydrochemistry and suspended solid load. Water level fluctuations in the ground‐ and surface waters of the floodplain are dynamic because of the porous aquifer structure and several inflow areas. In a lateral transect, increasing distance from the Danube correlates with decreasing connectivity. Different influences in a longitudinal transect are due to the positions of the inflow areas. At low water level, the Danube and its backwaters have no surface connection. Internal processes determine the conditions within the backwaters, which are typically characterized by low concentrations of inorganic nutrients and particles versus the Danube. At higher water levels, local surface inflow and seepage water lead to periodic nutrient pulses and eutrophication. The input of inorganic nutrients and particles, as well as the flushing of phytoplankton during floods, establish an initial setpoint in the backwaters. The significance of flood pulses for the dynamics of biological processes is emphasized by short‐term changes, e.g. in the relationship between nutrients, inorganic particles and chlorophyll. The response in different water bodies depends on the grade of connectivity to the D

ISSN:0886-9375    

DOI:10.1002/rrr.3450110309

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractFish communities from four catchments in the Murray—Darling river system were analysed in relation to climate, hydrology and river regulation. Using the annual proportional flow deviation as a measure of river regulation, the Paroo River catchment was assessed as unregulated, the Darling River catchment as mildly regulated and the Murrumbidgee River and River Murray catchments as highly regulated. A total of 11010 fish, representing nine native and three alien species, was caught during high and low flow seasons in the four catchments. Native species, such as golden perchMacquaria ambigua(Percichthyidae), bony herringNematalosa erebi(Clupeidae) and spangled perchLeiopotherapon unicolor(Teraponidae), dominated fish communities in the Paroo and Darling catchments, but alien species, mostly carp,Cyprinus carpio(Cyprinidae), were also abundant. Both native and alien species were more abundant in these catchments after flooding, but there was little change in species composition between high and low flow seasons at the catchment level. Carp dominated communities in the Murray and Murrumbidgee catchments. There was a significant trend for reduced species diversity in increasingly regulated catchments. River regulation may alter the relative abundance of native and alien fish by desynchronizing environmental cycles and the reproductive cycles of native species. Ordination of species abundances showed discrete fish communities that reflect the geographical separation between catchments. Differences between communities are related to opportunities for dispersal, the environmental tolerances of dominant species and the modifying effects of river regulation. Fish communities in lakes exhibited less seasonal variation than riverine communities within the same catchment, indicating the greater seasonal stability of lakes compared with regulated and unregulated river reaches. Management of fish resources needs to include catchment‐specific strategies within current State and basin‐wide management progr

ISSN:0886-9375    

DOI:10.1002/rrr.3450110310

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThe River Rhine has suffered because of numerous drastic environmental changes — for example, the regulation of the river bed and the construction of weirs and dams. Furthermore, discharges of agricultural, industrial and municipal wastewater have caused a deterioration in the water quality. This problem became particularly acute in the 1960s and 1970s. After the Sandoz accident in Basle in November 1986, the states bordering the River Rhine agreed the Rhine Action Programme for its ecological rehabilitation. This programme has the following four aims, which should be realized by the year 2000: (1) to create conditions which will enable the return of higher species (such as salmon); (2) to safeguard Rhine water as a source for the preparation of drinking water; (3) to abate the contamination of sediments due to toxic compounds; and (4) to fulfil the requirements of the North Sea Action Plan, as the River Rhine flows into the North Sea. Water quality criteria have been developed for about 50 contaminants or contaminant groups and for phosphorus and ammonium. Early signs of the ecological recovery of some aquatic communities in the River Rhine have been observed, but eutrophication and pollution by micropollutants, in particular polychlorinated biphenyls found in suspended matter, sediments and biota, still form a serious threat. In addition to further improving the water quality, river habitats must be improved, reversing the artificial river control measures taken in the past for the return of a number of characteristic riverine organisms such as migratory fish. The ‘Ecological Master Plan for the River Rhine’ aims to restore the mainstream, along with the main tributaries, as habitats for migratory fish (e.g. salmon). This involves protecting, preserving and improving ecologically important reaches of the River Rhine and the Rhine valley. The first steps for realizing the hydrological and morphological modifications have been taken, starting with the development of a specific ecological network focusing on the most important floodplain areas along the Rhine. Habitat improvement measures started later than the pollution abatement measures and, so far, relatively few studies on the effectiveness of the ecological rehabilitation techniques concerning habitat improvements in the Lower Rhine have been published. A major task for research programmes will be to identify the detailed quantifiable and verifiable ecological objectives (e.g. water quality criteria, hydrological and morphological targets) to guarantee the actual ecological rehabilitation of the River

ISSN:0886-9375    

DOI:10.1002/rrr.3450110311

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY