摘要:

AbstractIn a river reservoir, the Ishitegawa Dam Reservoir in Japan, sites of abundant phytoplankton growth were investigated in connection with the water movement in the reservoir from January 1982 to January 1984 by comparing the distributions of chlorophylla, water temperature, and coliform bacteria (Project A). The results distinguished three types of phytoplankton growth, of which one type, the abundant surface growth at the head of the reservoir, was most frequently observed. This case was considered to be caused by mixing of the surface lake water with the inflowing nutrient‐rich river water at the shallow lake‐head. Subsequently the effects of dissolved calcium and magnesium on the chlorophyllaand phytoplanktonic particulate phosphorus concentrations at the head of the reservoir were investigated until December 1987 (Project B). A trophic index, named the Ca‐Mg index, was found which correlated positively with the chlorophyllaand phytoplanktonic particulate phosphorus concentrations in a logarithmic scale and varied in relation to the changes in the same index of the inflowing river water. Based on the ecological results of these two projects, two proposals are presented for inhibiting abundant phytoplankton growth at the head of a river reservoir. Proposal A: make the head deep and, in addition, create a strong near‐bottom underflow of the inflowing river water. Proposal B: make a bypass in order to cut off the inflow of river water in the case of a high Ca

ISSN:0886-9375    

DOI:10.1002/rrr.3450030112

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractIn this paper a method for measuring discontinuities in the spatial organization of a river produced by disturbances is presented. First of all, a way of doing comparable environmental gradients defined by different variables is proposed. To do so, all the variables have been transformed by means of the equation:Pi' =Pi‐Pmin/Pmax‐Pmin, as a previous measure of the parametric distances (Pij') between sites. When these parametric distances are plotted in relation to the geographical ones, the distortion between both river images appears as an expression of the changes occurring in each stretch, and the derivative dPij'/dx is a measure of its rate of change. To define a river gradient, we need to calculate the general trend of a variable, using direct gradient analysis. The fit of the results obtained from an undisturbed stretch to an empirical curve for all the river gives us a measure of the expected values for that river. The difference between expected and observed values can be a measure of the discontinuity. The same procedure has been used for an overall environmental and biological data. To this end, the Euclidean distance (ED) and a distance obtained from Factor score of a Principal Components analysis (PCA) have been calculated. Only the second method seems to be of general interest for studying discontinuities. Finally, the results of the first score loadings obtained from PCA of three groups of variables (physical and chemical, physiographical and morphological, and phytobenthic) have been used to do a comparison between the parametric images of the River

ISSN:0886-9375    

DOI:10.1002/rrr.3450030113

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractSamples were collected year‐round over a one‐year period at sites 250m, 500m, 1000m, 2300m, 5200m, and 11000m downstream from a hypolimnetic‐release reservoir on the Blue River, Colorado, to examine biotic and abiotic gradients induced by river regulation. The impoundment had only minimal effects on river chemistry and chemical variables failed to exhibit discernible downstream patterns. The temperature regime was markedly altered by regulation and exhibited a distinct downstream recovery gradient. The progressive downstream increase in zoobenthos species diversity is attributed, in part, to the thermal recovery. The average size of mineral substratum particles was greater at sites nearest the dam, although cobble and pebble predominated at all sites. A downstream decrease in bed stability was accompanied by decreased water clarity and increases in scour and ice action. These factors may have accounted for the higher standing crops of periphyton near the dam and a shift from filamentous chlorophytes to a predominance of diatoms with increasing distance downstream. The amount of leaf detritus in the substratum increased downstream. The abundance of shredders, zoobenthic species that feed on leaf detritus, tracked the downstream increase in coarse sedimentary detritus. Spatial patterns of organic seston within the study reach, influenced partly by sloughing of periphyton, are thought to account for the downstream species replacement patterns exhibited within the filter‐feede

ISSN:0886-9375    

DOI:10.1002/rrr.3450030114

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractThe aim of the study was to evaluate the impact of an upland storage reservoir, typical of the series of reservoirs in the Golan Heights basaltic plateau, on structural and functional properties of the downstream ecosystem, in the vicinity of the reservoir, shortly after damming.The effect of impoundment on water quality conditions may be divided into winter‐spring, and summer periods. In the former, the impoundment seems to lengthen the period of flow of runoff quality water. This is evident by the elevated winter and spring turbidities and the higher concentrations of suspended solids below the reservoir. In summer, water quality below the reservoir is controlled by the consequences of stratification in the reservoir. The hypolimnial release results in depression of the maximal temperature and narrowing of the daily and seasonal temperature variations. It supplies water enriched in nutrients and low in oxygen, suspended solids and turbidity. The macroinvertebrate community responds to impoundment in density changes and shifting of dominance. We hypothesize that the thermal effect of hypolimnial release from warm monomictic reservoirs on the invertebrate community of warm streams will differ from an equivalent thermal change caused by cold dimictic reservoirs in cold, temperate zone, streams.The effect of impoundment on functional properties of the ecosystem are most pronounced. The rate of production of benthic algae biomass below the reservoir increased by more than two orders of magnitude, but the effect diminished downstream. The rate of processing of plant material below the reservoir was lower than above the reservoir. Further investigation is needed to clarify this effect. Changes in reservoir operation are recommended to diminish the effects of impoundmen

ISSN:0886-9375    

DOI:10.1002/rrr.3450030115

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractSamples were taken year‐round at eleven sites along the altitudinal profile (2900‐1400 m a.s.l.) of the Gunnison River, a 329 km tributary of the Colorado River, to document the distribution of the Plecoptera and to evaluate responses to hypolimnial‐release dams in the headwaters and middle reaches. Twenty‐two species were present, with the greatest species richness occurring in an unregulated segment upstream of the middle reach dams; average nymphal biomass over the study period (175 organisms, 395 mg dry mass m−2) was also greatest in this segment. Only four species (58 organisms, 48 mg m−2) were present in the tailwaters of the headwater dam and values were greatly reduced (nine species; 35 organisms, 180 mg m−2) below the middle reach dams. The stonefly community recoveredca.80 km downstream from the last dam (15 species; 244 organisms, 250 mg m−2), apparently in response to natural resetting of environmental conditions corresponding to those above the middle reach dams. At the most downstream site (11) only four species (four organisms, 16 mg m−2) were present. The observed distributional pattern is a classic serial discontinuity in response to hypolimnial stream regulation in a tempera

ISSN:0886-9375    

DOI:10.1002/rrr.3450030116

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractRiver regulation in the headwaters and middle reaches of the Gunnison River, Colorado, significantly altered distributions and abundances of Trichoptera fauna. Twenty‐five species were collected from mainstream samples, with the greatest species richness occurring at an unregulated, rhithron segment above the central reach dams. At sites immediately below the three hypolimnial‐release dams and a reregulation dam, species richness was reduced 35–90 per cent and abundance>95 per cent. Net‐spinning caddisflies were the dominant trichopterans at unregulated sites;Arctopsyche grandisin the upper reaches (218 organisms, 586 mg dry mass m−2) andHydropsyche cockerelli, H. occidentalisandCheumatopsyche pettitiin the lower river (9041 total organisms, 6621 mg m−2), downstream from the last dam. The observed distributional pattern of low trichopteran densities in dam tailwaters and high hydropsychid densities at sites 60–80 km below the central reach dams is a classic expression of continuum resets and adjustments in response to stream regulation as predicted by the Serial Disconti

ISSN:0886-9375    

DOI:10.1002/rrr.3450030117

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractBenthic animal production was studied in a weir basin area of western Norway in 1984, eleven years after construction of the basin and eight years after the first benthic study. Compared to estimates from 1976, a marked change in production and species composition had occurred. Benthic animal production at two stations inside the basin was 199 and 169 KJ m−2yr−1, an increase of 440 and 270 per cent respectively compared to 1976. In a riffle upstream of the basin, the production estimate was 50 KJ m−2yr−1, a decrease of 40 per cent since 1976. Chironomids formed the main contribution to the increased production in the weir basin, mainly through increased abundance of larger species likeStictochironomus pictulusandMicropsectraspp. Also other species more adapted to lentic water, like the ephemeropteransSiphlonurus aestivalisandAmeletus inopinatus, showed increased density. The fauna succession and increased production in the weir basin was mainly due to improved habitats and food conditions, as the amount of organic sediments had increased since the first productio

ISSN:0886-9375    

DOI:10.1002/rrr.3450030118

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractImpoundment and diversion of watercourses for power production and water supply can have profound effects on the mayfly fauna. To explain such effects a species‐specific approach is adopted on account of differing habitat requirements and life histories in the order and even within genera. Environmental conditions such as discharge and flow patterns, temperature, food availability, and predation may be changed. This leads to changes in the density and species composition of the mayfly community, especially when there is a hypolimnion drain from reservoirs. Temperature changes below such reservoirs may remove obligatory life cycle thresholds. Prolonged periods of low discharge lead to the dominance of genera, such asParaleptophlebia, Choroterpes, Siphlonurus, andPseudocloen, typical of slow‐flowing and lentic habitats.The life cycle plasticity and opportunism shown byBaetis rhodaniin Europe andB. tricaudatusin North America have undoubtedly contributed to their success in regulated rivers. The life history characteristics ofTricorythodesare also advantageous below dams. The increased growth of periphyton and mosses below many dams favour certain Ephemerellidae, but restrict or eliminate many Heptageniidae. In order to survive adverse conditions, flexible life cycles or a short period of rapid nymphal growth coupled with a long period of egg development, are advantage

ISSN:0886-9375    

DOI:10.1002/rrr.3450030119

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractFish in south‐central African freshwaters are governed by biological rhythms. First, these are associated with the markedly seasonal summer annual rainfall when breeding takes place with an initially high mortality among newspawned juveniles. Second, a longer term rhythm of annual rainfall variability occurs in cycles up to or more than a decade. These cause water levels to vary from exceptionally high levels to near desiccation in endorheic systems.Studies of the shallow endorheic lakes Mweru Wa'Ntipa (Zambia), Ngami (Botswana), and Chilwa (Malawi) are cited showing that species diversity rapidly increases by colonization from adjacent ‘inocula’ (relict communities surviving in more permanent nearby water bodies, e.g. deep pools in perennial streams) when filling starts. During the drydown phase of the cycle, diversity decreases through lack of annual breeding environment and diminution of water quantity and quality. A few, usually three, species remain longer which, being physiologically hardy or showing phenotypic plasticity, are tolerant of higher salinity, temperature, etc., conditions associated with dry‐out. Despite the lakes' wide geographical separation these taxa in every case are a single species of the tilapia, genusOreochromis, the catfishClarias gariepinus, and the minnowBarbus paludinosus, which build up large populations valuable to local fisheries.Evidence from the Pongolo River, Zululand, regulated by a large dam, shows that fish of downstream endorheic lakes react similarly to artificial water deprivation, with mainly the same taxa persisting. Managed water releases timed to coincide with breeding rhythms largely restore the conditions which previously prevailed. Data from Zambezi impoundments indicate conversely that reaction of previously riverine fish to large man‐made lakes is for previously sparse lentic taxa likeOreochromisto proliferate greatly while lotic forms likeLabeoare reduced in number.Since fish stocks are a valuable natural resource, such basic scientific results may be applied with great advantage. The collaboration between engineer, biologist, and management authority can minimize adverse environmental effects and predict better opportunity cost assessments of a projected river man

ISSN:0886-9375    

DOI:10.1002/rrr.3450030120

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractAn investigation of the spawning sites of European grayling,Thymallus thymallus(L.), in two Swedish rivers revealed narrow range in their physical parameters.The bottom substrate was composed of 10–20 per cent sand, 50–70 per cent gravel (10cm in diameter). Eggs were found only where the gravel thickness was more than 5 cm. The depth varied between 30–50cm. Mean depth for 22 different spawning sites was 36cm. The water velocity varied between 23–90cm s−1, average 54 cm s−1. The temperature at the start of spawning was 3.9°C and at the end it was about 9°C.The results indicate the narrow range in physical parameters at the spawning sites. Small changes in the environment caused by regulation of river flow or water level may disturb the spawning behaviour of grayling and cause a decrease in population size o

ISSN:0886-9375    

DOI:10.1002/rrr.3450030121

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY