摘要:

AbstractRiverine fisheries in Brazil are reviewed. There is a broad description of the environment and the fish, and arguments for the high diversity of fish fauna diversity are examined. The country is divided into five large river basins and the fisheries are described in relation to the main fish species caught, the main gear employed, and the fishing strategies. Exotic species introduction is discussed along with strategies for fish stock management. Effects of dams on resident fish stocks and consequences for the small scale fisheries are discussed and compared with the effects of pollution.

ISSN:0886-9375    

DOI:10.1002/rrr.3450040102

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractSpring and summer chinook salmonOncorhynchus tshawytschapopulations from the Snake River have declined precipitously from historical levels. Declines initially were the result of overfishing, but since the late 1950s they have been primarily the result of hydroelectric dams that blocked access to spawning areas, created slack water, and caused mortalities of juvenile outmigrants. Mitigation hatcheries and juvenile collection and bypass systems at dams, transportation of juveniles from upriver dams to a release site on the lower Columbia River, a water budget, allocated spill for fish at main‐stem dams have not increased these populations appreciably. Ocean conditions may have been a factor in the low returns from 1976 through 1984, but the factors currently considered as controlling the viability of the run are the low genetic variability, lack of stress tolerance, and incidence of bacterial kidney disease inherent in the stock. With control of disease, reduced stress at main‐stem projects, and continued efforts to maintain genetic variability, the chinook salmon populations should increase and their long‐term viability should be as

ISSN:0886-9375    

DOI:10.1002/rrr.3450040103

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractAlthough channel change has been documented downstream of urban areas there have been few previous studies which have focused upon the spatial variation of erosion and upon examples of such channel change in tropical areas. In the Avondale stream basin, which includes part of Harare the capital of Zimbabwe the way in which the channel network has evolved from the extensive dambo system in the period 1891 to 1984 is reconstructed showing that drainage density which was initially between 0.35 and 0.80 km km−2has increased to 3.15 km km−2including stormwater drains. Characteristics of erosion of the modified urban channels are described and the downstream reaches indicate an average channel widening of 1.7 times involving average rates of bank erosion of 0.33 m per year. Peak discharge is estimated from channel characteristics to be increased to two times former values and it is concluded that channel type and the relationship of channel change to the accommodation of peak discharges requires further resea

ISSN:0886-9375    

DOI:10.1002/rrr.3450040104

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractNitrate levels which have been rising in many British rivers for at least thirty years have become of particular interest since Britain adopted the EC Drinking Water Directive. The literature examining nitrate trends in the rivers of the U.K. and Eire is reviewed. Long‐term nitrate concentration trends are derived for eight sites in the River Trent drainage system. These include sites on two rural tributaries, two urbanized tributaries, and the main river. Currently, mean annual concentrations for these sites range from about 4.0 mg1−1N in the rural catchments, to 12.4 mg 1−1N in the urbanized tributaries, and to between 8.7 mg 1−1N and 11.0 mg 1−1N along the mainstream. Moreover rates of increase of nitrate concentration of approximately 0.06 mg 1−1N yr−1in the rural catchments, contrast with values up to 0.20 mg 1−1N yr−1in the two urbanized tributaries and River Trent. Long term nitrate loads have been calculated for the River Trent at Nottingham using a discharge weighted mean interval method. This method probably provides the best available estimate of nitrate loads calculable from irregular data of variable sampling frequency for lowland rivers. Annual nitrate loads varied between 10700t yr−1and 29 800t yr−1over the period of record. A rate of increase in nitrate load of 455 t yr−1was obtained. The increases in nitrate concentrations and loads within the Trent basin are matched by similar rates of increase in ot

ISSN:0886-9375    

DOI:10.1002/rrr.3450040105

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractThe Paraná upper reaches, above the confluence with the Paraguay River, drains a predominantly humid, tropical‐subtropical basin that has been extensively altered by anthropogenic activities. Deforestation followed by intense mechanized agriculture has progressively increased in the last decades. Many industrial settlements and hydroelectric impoundments have been developed. Suspended matter, total phosphorus, and inorganic nitrogen exportation rates were estimated at 14 t km−2y−1, 28kg TP km−2y−1and 188kg N km−2y−1respectively. These rates are compartively low when compared to other areas of the world. It was estimated that riverine mass transport represented roughly 6 per cent of the phosphorus and 20 per cent of the nitrogen inputs in the basin. Mass transport of suspended matter and soluble reactive phosphorus are lower and inorganic nitrogen higher than in 1967–1969. Siltation in the man‐made lakes reduced both suspended matter and phosphorus transport. Inorganic nitrogen increase is thought to be related to increased

ISSN:0886-9375    

DOI:10.1002/rrr.3450040106

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractBenthic macroinvertebrates were quantitatively sampled at four sites, one above (T6) and three (T14A, T16, T21A) downstream of the Thomson Dam, Victoria, Australia, for three summers after completion of dam construction in 1983. Community composition was compared with that recorded previously during dam construction to determine the effects of the main environmental consequences of the dam, viz the input of fine sediment (<2mm grain size), the temporary release of cold hypolimnetic water during summer, and altered levels of discharge. Unnaturally low summer water temperatures were only recorded at the two sites immediately downstream of the dam (in order downstream T14A and T16). After water temperatures returned to normal summer levels, species richness increased at these sites. Levels of fine sediment increased in the surface layers of the riverbed at T16 but not at T14A. By the time this study began levels at T16 had been reduced almost to pre‐dam levels. At T21A levels approximately tripled after completion of construction. At T14A and T16 marked increases in species richness occurred during this study whereas at T21A species richness did not change, and was lower than that recorded during dam construction. Ordination and classification of samples clearly displayed these changes in the benthic communities downstream of the dam and the lack of change at T6 above the dam. Altered discharge resulted in some loss of habitable area and thus total standing stock at T14A onl

ISSN:0886-9375    

DOI:10.1002/rrr.3450040107

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractThe composition of epiphytic diatom communities from the cold tailwaters (12°C) of Glen Canyon Dam, Arizona, was analysed after a 2 wk incubation period at 12°C, 18°C and 21°C. There was a significant change in diatom composition between 12°C and 18°C, while no significant changes occurred between 18°C and 21°C. This suggests that a temperature threshold exists between 12°C and 18°C for the diatom flora in the tailwaters of Glen Canyon Dam. At the two higher water temperatures, smaller and closely adnate taxa became more important numerically than larger, upright, cold water stenotherms. The potential importance of this compositional shift in epiphytic diatoms on macroinvertebrate grazers has management implications regarding different release programs from r

ISSN:0886-9375    

DOI:10.1002/rrr.3450040108

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractNavigation dams on the upper Mississippi River have altered the long‐term relationship of river stage to river discharge. Analysis of the 34‐year pre‐dam and 74‐year post‐dam data sets indicated that the completion of Lock and Dam 19 in 1913 increased river width and volume behind the dam. The immediate impact was a higher mean river stage less influenced by changes in river discharge. The dam's long‐term impact was to increase sedimentation causing a steady loss of both river width and volume that resulted in stage/discharge relationships approaching those of the pre‐dam era. The present condition of higher mean river stage coupled with greater stage fluctuation is a major factor in the increased recurrence and duration of floods on the upper Mississippi River in r

ISSN:0886-9375    

DOI:10.1002/rrr.3450040109

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

ISSN:0886-9375    

DOI:10.1002/rrr.3450040110

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

ISSN:0886-9375    

DOI:10.1002/rrr.3450040111

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY