摘要:

AbstractThe lowermost 20 km of the River Surna, northwestern Norway receives cool water during summer from a hypolimnetic release mountain reservoir. In this part of the river, yearlings of both Atlantic salmon and brown trout are significantly smaller compared with those in the upper section of the river, which is unaffected by the cold water release. The slower growth below the power station causes both Atlantic salmon and anadromous brown trout to smoltify one year later compared with fish in the upper section of the river. This leads to higher mortality and therefore lower production of both adult salmon and trout.

ISSN:0886-9375    

DOI:10.1002/rrr.3450050402

出版商:John Wiley&Sons, Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractThe Burgomillodo Dam, located in the middle Rio Duraton (north Spain, Duero Basin), has created a small eutrophic reservoir with a capacity of 15 × 106m3and a maximum depth of 40m. Burgomillodo Reservoir is solely used for producing hydroelectric power. The regulated flow pattern of hypolimnial waters is characterized by higher daytime flows than those by night, with low flows at weekends all the year round. The environmental impact generated by this hydropower scheme on the river downstream was assessed by comparing physiochemical characteristics and aquatic communities of an upstream site (reference station) with those of three downstream stations, which were located 0–2, 2–5, and 7–6 km below the dam.Water temperature, pH and dissolved oxygen were significantly lower downstream from the reservoir. Hardness, alkalinity, suspended inorganic matter, and conductivity had reduced annual variability below the dam. Photosynthetic activity was directly involved in the recovery of dissolved oxygen and pH values.Species richness and abundance of macrophytes increased just below the dam. Macrobenthic and fish communities were composed of higher numbers of potamic species. Number of taxa, density, biomass, and diversity were higher at the reference site, recovering their values as the distance below the reservoir increased. Macrobenthic trophic structure was changed by an increase in predators and filter feeders and a decrease in shredders. Environmental impact values for the macrobenthic community living just below the dam were higher than those for the fish community.It is concluded that the main physiochemical factors involved in environmental impacts were dissolved oxygen deficit and short‐term flow fluctuations for the macrobenthic community, and oxygen deficit for the fish fauna. Benthic macroinvertebrates appear to be the best aquatic organisms for detecting changes and for reflecting the spatial recovery of environmental co

ISSN:0886-9375    

DOI:10.1002/rrr.3450050403

出版商:John Wiley&Sons, Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractChanges in the faunal composition and density of communities of chironomid larvae were studied over a four year period in a newly regulated stream and compared with those in an adjacent unregulated stream, with a view to examining “stability” in contrasting environments. A total of 68 chironomid taxa were recorded from all sites. Faunal diversity was lowest closest to the dam and highest in the unregulated site. Within the study period values of H were highest in the fourth year of study (five years after dam closure). Species increments were tending to level out at the three totally regulated sites whereas at the partially regulated and unregulated sites new taxa continued to be recorded in samples.Clustering techniques and similarity indices clearly separated the study sites based on the composition of the chironomid fauna and there were indications that the unregulated sites were more variable in faunal composition between years than the regulated sites. The data are used to develop a conceptual model of fluctuations in faunal parameters under steady or reduced flow regimes. It is suggested that environmental stability brought about by regulation has structured the composition of the chironomid community and further that the changes occur very rapidly after impoundment. The model identifies key areas of faunal change and the question of environmental stability is discussed in relation to the scale of observat

ISSN:0886-9375    

DOI:10.1002/rrr.3450050404

出版商:John Wiley&Sons, Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractEleven physicochemical variables (pH, temperature, oxygen, percentage of oxygen saturation, orthophosphate, nitrite, nitrate, ammonium, orthosilicate, organic matter and organic matter in sediment) have been analysed in 175 sampling sites during four seasons in 1985. A principal component analysis has been applied after standardization of the density function of the variables, according to skewness and kurtosis. Four main groups of sites have been differentiated. These groups represent different degrees in the redox process of organic matter. (A) Very oxygenated sites with high pH values indicating that the mineralization process prevails. Organic matter appears in low concentrations and a reduced state. (B) Sites nutrient enrichment where elements with high oxidation number prevail (nitrite, nitrate, and orthophosphate). (C) Sites supporting high organic pollution. (D) Sites subjected to heavy urban and/or industrial dumping.

ISSN:0886-9375    

DOI:10.1002/rrr.3450050405

出版商:John Wiley&Sons, Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractYoung Atlantic salmon appear to occupy similar suitable stream habitats year round. The salmon is stationary, often associated with “home stones”. At low water temperatures in winter, the fish seek shelter in the substrate, which has to be coarse enough to provide interstices for the fish to hide in. In summer, salmon select habitats within tolerable ranges of habitat variables, rather than narrow optima. It is suggested that a genetic basis to habitat evaluation allows incorporation of the full range of behavioural responses. This is important as partially different habitats may be selected in diverse streams. Habitat availability influences both habitat use and habitat preferences. Suitable summer habitats have depths in the range 5–90 cm; mean water velocities 10–80 cm s−1, and gravel‐to‐boulder substratum. Fish size affects habitat use, as young of the year are found in the more shallow habitats closer to the stream banks, whereas the older parr use a wider range of habitats. In the absence of brown trout, the Atlantic salmon parr, and especially young of the year, use habitats otherwise inhabited by brown trout. Water velocities are in many cases the principal physical habitat variable determining the distribution of Atlantic salmon in streams, but other variables are also important. Depth is more important in small streams than in

ISSN:0886-9375    

DOI:10.1002/rrr.3450050406

出版商:John Wiley&Sons, Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractIn order to test the effect of regulated water temperature on the development of eggs and alevins of three salmonid species, deep and surface water from an oligotrophic lake was pumped into a hatchery. Atlantic salmon (Salmo salar) clearly needed the highest number of degree‐days to reach the different developmental stages while brown trout (Salmo trutta) needed just a little more than the brook trout (Salvelinus fontinalis). Eggs and alevins developed in the surface water, which was colder in winter, needed a lower number of degree‐days to reach the hatch and swim‐up stages. In spite of this there was a considerable difference in time for hatching and start of feeding of fish in the two temperature regimes. This might have consequences for the reproduction success and competition between species in regulated r

ISSN:0886-9375    

DOI:10.1002/rrr.3450050407

出版商:John Wiley&Sons, Ltd    

年代:1990

数据来源: WILEY

ISSN:0886-9375    

DOI:10.1002/rrr.3450050408

出版商:John Wiley&Sons, Ltd    

年代:1990

数据来源: WILEY

ISSN:0886-9375    

DOI:10.1002/rrr.3450050409

出版商:John Wiley&Sons, Ltd    

年代:1990

数据来源: WILEY

ISSN:0886-9375    

DOI:10.1002/rrr.3450050401

出版商:John Wiley&Sons, Ltd    

年代:1990

数据来源: WILEY