摘要:

AbstractThe lower Irwell/upper Manchester Ship Canal is a canalized waterway in the north‐west of England with a catchment area of 700 km2. A 12 month study established a baseline of key chemical and physical parameters (dissolved oxygen, biological oxygen demand, temperature, pH, conductivity, NO−3, NO−2, PO3‐4, NH+4, suspended solids) with which episodic deteriorations in water quality along the river could be compared. The relative importance of changes in flow, and the impact of the tributaries on water quality in the Irwell, was assessed by mass balance calculations and multivariant analysis. Particular attention has been given to the interactions between sediments and the chemistry of the water column. The main conclusions to emerge are that: (i) the lower Irwell/Ship Canal is subject to significant organic pollution from storm water overflows discharging directly to the river above the study area and via its major tributaries, the Irk and Medlock; (ii) the Irk and, to a lesser extent, the Medlock have an adverse effect on water quality in the Irwell‐increases in mass flux below the confluences above that attributable to direct loading suggest that sediment interactions with the water column are partly responsible; (iii) high flowper se, rather than combined sewer overflows in storm events, may be causing deteriorations in water quality due to the release of pollutants from resuspended sediments; and (iv) limited storm data appear to show a readily‐soluble ‘first flush’ of pollution to be followed by a delayed impact caused by degradation of newly introduced material. The feasibility of short‐term restorative measures such as the installation of oxygen/air injection systems and the provision of weirs are examined in the context of river management; weirs do not appear to be pr

ISSN:0886-9375    

DOI:10.1002/rrr.3450080112

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe River Suldalslågen, which holds a population of large Atlantic salmon, has been regulated twice for hydropower production. The first regulation occurred in 1968 and the second in 1980. Present problems include the reduced density of benthic fauna, the reduced growth rate of young salmon, the low survival of 0+fish and the increased time required for smoltification. A programme of habitat restoration includes building a rearing channel system where water flow and the substrate can be controlled. The salmon fry are stocked in the rearing channel and in an adjacent tributary stream. The effects on macrobenthos of introduced dead organic material were also studied. Improvement of physical habitat increased the density of benthic animals, and the survival of 1+salmon was about 30%. Experiments that included adding of 115g wheat/m2resulted in a threefold increase in benthic fauna compared with a control area. The largest increase in numbers was in Chironomidae in August‐September, when benthic Crustacea also showed a significant increase. An increase in macrobenthos is expected to increase the growth and survival of young salmon f

ISSN:0886-9375    

DOI:10.1002/rrr.3450080113

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractBefore regulation flows in the lower Murray were highly variable, as for most rivers in semi‐arid regions. Major floods promoted large‐scale recruitment of flora and fauna in riverine and floodplain communities, and seasonal floods maintained lower levels of recruitment. The regime changed with the construction of 10 low‐level weirs in 1922–35, supplemented by the effects of dams in upstream areas. Flows remain variable but are much reduced in volume (about 44%). Low flows (100–300 Gl per month) have decreased five‐fold and moderate flows (500–1500 Gl per month) have increased two‐fold. Although the magnitude of peak seasonal flows has been diminished, the timing of flows is unaffected. The effects differ in the Valley and Gorge sections of the river, depending on local development of the floodplain and associated wetlands. The weirs have flooded once‐temporary wetlands and contributed to problems of salinization. Weir operations cause daily stage fluctuations that diminish downstream, and the channel is developing a stepped gradient as a consequence of active deposition and erosion. Regulation has limited exchanges between the river and its floodplain, changed the nature of the littoral zone and generally created an environment inimical to many native species, notably fish. The key to rehabilitation may be to restore a more natural balance of low and medium flows, but this may be unrealistic given the needs of irrigators and other water users. Despite its evolutionary history of wide spatial and temporal variation, the Murray river‐floodplain ecosystem evidently cannot accommodate these f

ISSN:0886-9375    

DOI:10.1002/rrr.3450080114

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe invertebrate communities and environmental characteristics of three English chalk streams; the rivers Wissey, Rhee and Pang, were investigated to determine the effects of groundwater abstraction. The data were collected as part of a larger study of 21 UK rivers subject to a variety of types of abstraction. A variety of analytical techniques, including a novel multivariate analysis (co‐structure analysis), and the use of species profiles, showed significant physical and biotic differences between the three rivers and between impacted and natural sites on each river. The observed faunal differences are discussed in relation to existing data on the impact of natural droughts on chalk streams, and the problems associated with determining the effects of non‐point source abstractions (such as from groundwater) are conside

ISSN:0886-9375    

DOI:10.1002/rrr.3450080115

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractRegulation of the catchment area of the Norwegian river Gudbrandsdalslågen began in 1919. The lowermost power station on the main river was completed in 1964 and is situated about 10 km above the large Norwegian lake, Mjøsa. The lake is the foraging area of the Hunder strain of brown trout, the fastest growing of all Norwegian trout. The running of the power plant has led to a severe reduction in water flows below the dam, and the most important spawning and nursery areas of the Hunder strain has been affected. The natural smolt production has been permanently reduced. The rehabilitation programme has included the construction of a fish ladder through the dam and a fixed minimum flow. A hatchery was built and a stocking programme using the local strain was implemented. The effect of stocking has been the easiest of the relief measures to evaluate. Hatchery reared fish constitute a growing share of the spawning population. During the last three years their share has been close to 60%. Reared fish constitute 30–40% of the trout caught in Lake Mjøsa. The average and best returns of tagged groups have been 25 and 50%, respectively, but return rates are highly dependent on release length and time and place of stoc

ISSN:0886-9375    

DOI:10.1002/rrr.3450080116

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThis study was carried out to assess the efficiency of eight fishways constructed in connection with hydroelectric dams in the Glomma river system in south‐eastern Norway. The fishways were of the pool and weir type, except for one which was of the counter current (Denil) type, and had a discharge of 0.5–1.0 m3/s. During 1985–8 3077 grayling and 2995 brown trout were captured in traps in the fishways, measured and floy‐tagged before being released in the river upstream of the fishways. The number of fish captured in two of the fishways were compared with estimated fish stocks in the areas around the fishways. Migrations began in May or June when the water temperature was>5–6°C. Spawning migration of grayling occurred in May. During May more than 200 grayling may enter a single fishway within a week. In other fishways grayling occur only sporadically before late June or early July, when they migrate upstream to feed. Brown trout migrate during late spring, summer and autumn. The spawning migration takes place more or less during the whole summer, but mostly in late July and August. Immature brown trout also pass through the fishways, with a peak in October in three fishways. This migration is probably an ascending emigration from recruitment areas located downstream of these fishways. The efficiency of these fishways appears low, as the number of fish ascending was less than 2% of the estimated stock within the stretches where 90% of the recaptures occurred. The discharge in the fishway relative to the total discharge seemed to be of great importance, and to achieve efficient fishways they should be constructed for higher discharges, compared with river discharge, than the fishways in this area. The longest migration of grayling was 100 km, whereas the longest migration of brown trout was 122 km. The fish seemed to exploit shorter river stretches in areas influenced by several dams/fishways than fish in an area influenced by on

ISSN:0886-9375    

DOI:10.1002/rrr.3450080117

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractChannelization of the Kissimmee River in central Florida destroyed or degraded most of the fish and wildlife habitat once provided by the river and its floodplain wetlands. Between 1984 and 1989 a demonstration project was conducted to evaluate the feasibility of restoring the river's biological resources. Reintroduction of flow through remnant river channels improved river channel habitat diversity and led to favourable responses by fish and invertebrate communities. However, results indicated that more complete restoration of biological attributes will require the re‐establishment of historical inflow characteristics. Owing to the flood control regulation schedule of its headwater lakes, current river discharge regimes are pulse‐like, include extended periods of low or no flow, and have high and low flow periods which are out of phase compared with typical seasonal patterns that occurred before channelization. These flow characteristics will preclude effective river restoration by contributing to chronic low dissolved oxygen regimes and repetitive fish kills, interfering with fish reproduction and limiting floodplain inundation. Simulation modelling was used to develop a modified headwater lakes regulation schedule which re‐establishes season flow patterns, smooths discharge peaks and maintains base flows for a greater portion of the year. Implementation of the new schedule, combined with extensive canal backfilling, will lead to discharge and stage characteristics that meet established criteria for achieving ecosystem restoration

ISSN:0886-9375    

DOI:10.1002/rrr.3450080118

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractDownstream variations of benthic macroinvertebrate communities on the River Rede below Catcleugh Reservoir, impounded in 1905, are related to a simple index of regulation magnitude, related to hydrological, water quality and trophic changes, and variations of channel morphology. The river is divided into five sectors on the basis of network morphometry and channel form. Channel change to flow regulation is confined to a short (1.6 km) reach immediately below the dam within which channel width and conveyance have been reduced by 53 and 75%, respectively. Downstream, siltation has occurred, but it is patchy and average levels of sediment finer than 2 mm are less than 10%. The main faunal responses — increased abundance and number of taxa — are also confined to the first sector below the dam. Ephemeroptera are shown to be the best describers of the downstream pattern. Variations of the fauna between riffles within sectors are shown to relate to site‐specific hydraulic conditions, especially bed shear s

ISSN:0886-9375    

DOI:10.1002/rrr.3450080119

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractBenthic animal densities, biomass and production were studied in a weir basin and the upstream adjacent riffle area in a regulated west Norwegian river in 1988 and 1989. In years of normal discharge, such as 1988, water from a large part of the catchment area is transferred to a hydroelectric power station in another watershed, and the discharge at the study site is low. In 1989 heavy precipitation and a mild winter climate caused surplus production of hydroelectric power. Consequently large amounts of stored water had to be released as overflow at the dam. On a yearly basis the discharge at the study site was 4.8 times higher in 1989 than 1988, whereas peak values were 12.0 and 54.0 m3s−1in 1988 and 1989, respectively. The change in flow regime resulted in reduced biomass and faunal changes. Biomass was high during 1988 and the first months of 1989. Corresponding to the flow increase in June 1989 the biomass in the weir basin was reduced from 7.1 to 2.2 g dw m2and from 8.0 to 0.8 g dw m−2at the two studied transects. The mean biomass in the autumn period was 270 and 800% higher at the two transects in 1988 compared to 1989. A great part of the biomass reduction was caused by reduced densities of the chironomidsStictochironomus pictulusandChironomus melanotus. The mean autumnal densities of these two species were reduced from 4400 to 170 ind. m2and from 876 to 2 ind. m2, respectively. An increase in the biomass was recorded for rheophilic insect larvae, such as the stonefliesLeuctra fuscaandCapnia pygmaea. On the other hand lentic caddis larvae such asApataniaspp. andOxyethiraspp. were reduced. Mean benthic animal production of the weir basin was reduced from 22.3 g dw m−2yr−1in 1988 to 12.5 g dw m−2yr−1in 1989. In a riffle upstream of the weir basin the production was reduced from 9.1 to 3.9 g dw m−2yr−1in the same period. The faunal change is explained by an altered physical environment and destruction of

ISSN:0886-9375    

DOI:10.1002/rrr.3450080120

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractTechniques for reducing adverse effects of river and lake regulation are being developed and tested within the framework of the Norwegian Biotope Adjustment Programme. The programme is illustrated by studies of a river flowing through the wetland area, Lesjaleirene, which has been drained and channelized to provide additional agricultural land. The channelized river has a homogeneous sand substrate. Experimental placement of rocks and stones increased brown trout densities, especially in areas in contact with the river banks. The new areas of rocks and stones provide cover for fish as well as a greater variation in depth and flow conditions.

ISSN:0886-9375    

DOI:10.1002/rrr.3450080121

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY