bluuebunny/crossref_metadata_2025_split huggingface dataset:
Life cycle and production of Baetis rhodani in a regulated river in Western Norway: Comparison of pre‐ and post‐regulation conditions
Authors: Raddum Gannur G. , Fjellheim Arne 
Published: February 2007

AbstractThe benthic invertebrate fauna of the lowland part of the Aurland River was investigated in 1966–7 over a full year cycle. The watershed was built out for hydropower production during 1979–83. In this study the life cycle and production of Baetis rhodani from pre‐regulated conditions (1966–7) was compared with two types of post‐regulation streams (1988–9). Before regulation the water flow was high during May‐June and in autumn, combined with heavy rainfall. The lowest flow was in winter and early spring. The pre‐regulated temperature was low in winter, increasing from April to a maximum in August (10–14°). After regulation one part of the river received reduced flow and increased summer temperatures (upper part) and one received hypolimnion release and reduced summer temperatures (lower part). In the upper part the density of B. rhodani increased between 10 and 20 times. The reason for this seems to be increased temperature, reduced accidental drift of larvae and increased amount of stored organic material on the bottom. In the lower part the density increase was two to five times and the production two times higher after regulation. The lower increase in production than density was due to a much higher proportion of small larvae. B. rhodani had mainly an univoltine life cycle before regulation, but a small part of the population was bivoltine. After regulation the species was univoltine in the lower part. In the upper part the life cycle was about one month faster, but no clear indication of bivoltinism was seen. The absence of the second generation is due to low temperatures and probably a lack of signals connected with temperature.
Impact of combined sewer overflows on the water quality of an urban watercourse
Authors: Rees Adrian , White Keith N. 
Published: February 2007

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 flow per 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 promising solutions.
Environmental effects of flow regulation on the lower river Murray, Australia
Authors: Walker K. F. , Thoms M. C. 
Published: February 2007

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 forms of disturbance.
Effects of increased discharge on benthic invertebrates in a regulated river
Authors: Fjellheim Arne , Håvardstun Jarle , Raddum Gunnar G. , Schnell Øyvind A. 
Published: February 2007

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 m3 s−1 in 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 m 2 and from 8.0 to 0.8 g dw m−2 at 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 chironomids Stictochironomus pictulus and Chironomus melanotus. The mean autumnal densities of these two species were reduced from 4400 to 170 ind. m2 and from 876 to 2 ind. m2, respectively. An increase in the biomass was recorded for rheophilic insect larvae, such as the stoneflies Leuctra fusca and Capnia pygmaea. On the other hand lentic caddis larvae such as Apatania spp. and Oxyethira spp. were reduced. Mean benthic animal production of the weir basin was reduced from 22.3 g dw m−2 yr−1 in 1988 to 12.5 g dw m −2 yr−1 in 1989. In a riffle upstream of the weir basin the production was reduced from 9.1 to 3.9 g dw m−2 yr −1 in the same period. The faunal change is explained by an altered physical environment and destruction of lentic habitats.
Effects of river bed restructuring on fish and benthos of a fifth order stream, melk, Austria
Authors: Jungwirth Mathias , Moog Otto , Muhar Susanne 
Published: February 2007

AbstractStudies conducted on 15 sections of seven different epipotamal streams between 1981 and 1984 established the impact of river bed structures on fish communities. Reduced spatial heterogeneity due to river straightening resulted in decreasing numbers of fish species, stock density and biomass. The variance of maximum depths (VMD) used as a measure of habitat structure showed a highly significant correlation with the number (NFS) and diversity of fish species (DFS). In 1987 these models were used for the evaluation of a planned restructuring project on a channelized section of the Melk River, which was realized in 1988. During a three year investigation of the response of the fish fauna and benthic community to changed hydraulic and morphometric conditions within the restructured river bed section the validity of the VMD/NFS model could be verified. The number offish species increased from 10 to 19. Fish density and biomass as well as annual production of 0+ fish increased three‐fold. In contrast the DFS did not reach expectations, suggesting that more time is needed to establish a balanced fish community. The newly created riparian zones (e.g. shallow water lagoons, pioneer vegetation of gravel banks, etc.) provided important refuge regions during flooding, places for hatching or emerging, and nursery grounds for younger benthic instars and fish fry, indicating the positive effects of a complex water‐land ecotone. Owing to the increasing habitat variability, including riffle‐pool sequences, more and diverse specific benthic communities with many epipotamalic species developed. The number of benthic invertebrate taxa increased from 202 in the channelized section to 273 in the restructured area (in total 347 taxa were recorded). The benthic drift decreased significantly in the restructured river section, suggesting unfavourable conditions for many benthic invertebrates in the straightened section. Terrestrial invertebrates, however, occasionally entering the water body, showed a ten‐fold increase in drift in the channelized reaches.
Research needs in regulated river ecology
Authors: Ward J. V. , Stanford J. A. 
Published: February 2007

AbstractThe general effects of single dams on the downstream ecology of temperature lotic systems are predictable, although some underlying causal mechanisms remain elusive. Few quantitative data of an ecological nature are available for regulated tropical rivers, however, and it would not be prudent to uncritically apply principles and patterns developed from temperate rivers to fluvial systems of the tropics. New techniques of gradient analysis appear especially suited to examining spatial recovery gradients below dams at any latitude and portend to provide considerable insight into the mechanisms responsible for such patterns. Few studies have specifically examined the influence of regulation on interactions between the river channel and the floodplain and virtually nothing is known of channel‐aquifer interactions. A fuller understanding of these interactive pathways is necessary to effectively regulate discharge as part of river restoration strategies. Viewing regulated streams as experimental systems for addressing ecological questions has proved to be useful and should be further exploited. It is concluded that research and expertise in regulated stream ecology will increasingly be needed as the rational basis for flow criteria to conserve, protect and enhance the societal values of regulated rivers world‐wide.
Short communication. Pipelines as a refuge for freshwater snails
Authors: Sheldon F. , Walker K. F. 
Published: February 2007

AbstractIn the lower River Murray, Australia, populations of gastropods have declined markedly over the past 40 years. Of the native fauna of about 18 species, only the ancylid Ferrissia petterdi remains common (but in patches), and another five species feature in sporadic local resurgences. Until recently the viviparid Notopala was thought to be extinct. The introduced physid Physa acuta is widespread, but in low numbers. The decline probably is associated with flow regulation, high turbidity and the introduction of common carp. Snail populations have persisted, however, in irrigation pipelines fed from the river, where they periodically cause blockages. This paper reports the discovery of the only known populaion of Notopala hanleyi in a pipeline where the inner wall accumulates microbial and other organic matter, providing high quality food for snails. In the Murray before regulation most of the periphytic biomass was probably microbial, as fluctuating water levels would have maintained littoral communities in a highly productive, early state of succession his postulated that, by stabilizing seasonal water levels, regulation has promoted the production of filamentous green algae, an inferior food source, and so displaced snail populations from the open aquatic environment.
Implications of the annual macrophyte growth cycle on habitat in rivers
Authors: Hearne John W. , Armitage Patrick D. 
Published: February 2007

AbstractThe continuity equation, Manning's equation and an empirically determined relationship between channel roughness and the biomass of macrophytes were used to simulate the effects of weed growth in contrasting channels. Two indices of wetted available habitat, velocity and depth were chosen to illustrate the role of macrophyte in maintaining and modifying instream habitat with particular reference to chalk streams. Plant growth maintained depth within the channels and its effect was modified by channel shape and slope. Weed cutting resulted in very sudden changes in depth and velocity and the loss of a large volume of water from the river. The results indicate that macrophyte growth could be used to maintain wetted habitat while allowing more abstraction, but more data are required on the long‐term effects of implementing such policies.
Changes in fish communities of the Phongolo floodplain, Zululand (South Africa) before, during and after a severe drought
Authors: Merron Glenn , Bruton Michael , De Lalouviere Philippe La Hausse 
Published: February 2007

AbstractThe Pongolapoort Dam in Zululand, South Africa has regulated the flow of the Phongolo River to its floodplain downstream since 1970. Ecological surveys of the floodplain fish communities were conducted before (1974–6), during (September 1983) and after (August 1984) a severe drought to assess the response of the fish stocks. During the three study periods the floodplain lake communities varied. Fish populations were markedly reduced during the drought. The redistribution offish on the floodplain after the drought was rapid. Colonization of previously dry lakes was mainly by juvenile fish and the mean size of the fish was lower in these lakes than in the refuge lakes. A few species successfully spawned during the drought, although the natural mortality of the young of the year was probably greater due to increased competition and predation in restricted habitats. Large scale spawning in most species occurred immediately after the drought was broken by a large flood.
Fine sediment infiltration into gravel spawning beds within a regulated river experiencing floods: Ecological implications for salmonids
Authors: Sear D. A. 
Published: February 2007

AbstractInfiltration rates into eight gravel spawning beds were monitored over a range of discharges including compensation flows, peak hydropower generation and floods of up to bankfull capacity. The results indicate that the interrelationship of sediment supply and discharge influence both the rate and grain size composition of infiltrated sediments, with maximum rates experienced during bankfull floods when sediments are scoured from upstream pools. The effects of river regulation for hydropower are shown to produce a finer matrix infill in the absence of unregulated tributary sources, although the rates of infiltration are much lower than for sites downstream of unregulated tributaries. Values for infiltration rates are shown to be detrimental for small salmonid spawning redds during post‐flood conditions when sediment transport is not restrained by supply.
Experimental measurements of river‐bank erosion caused by boat‐generated waves on the gordon river, Tasmania
Authors: Nanson Gerald C. , Von Krusenstierna Axel , Bryant Edward A. , Renilson Martin R. 
Published: February 2007

AbstractErosion of natural river banks by boat‐generated waves is an increasingly serious problem on the navigable reaches of many rivers, particularly on the middle and estuarine reaches. An experiment designed to link bank erosion rates with easily measured wave characteristics, conducted on the scenic lower Gordon River in Tasmania, provides information useful for river management. Within a boat‐generated wave train a number of characteristics were measured and most showed a high correlation with measured rates of bank retreat. Maximum wave height within the train is the simplest measure and is associated with a major threshold in erosive energy on unconsolidated sandy alluvium at wave heights of 30 to 35 cm. At maximum wave heights above 35 cm all but the most resistant bank sediments erode. Reducing maximum wave heights to < 30 cm by limiting boat speeds, and reducing the frequency of boat passages, caused a dramatic decline in bank erosion along the river.
Stability of the pool‐riffle sequence in changing river channels
Authors: Gregory K. J. , Gurnell A. M. , Hill C. T. , Tooth S. 
Published: February 2007

AbstractThe pool‐riffle sequence as an important feature of river channels was described by Leopold et al. (1964) to occur with a spacing of five to seven times the channel width. Subsequent work has generally confirmed this spacing, although more closely spaced pools and riffles are quoted for some channels in woodland basins and for some channelized streams. Although few detailed empirical studies have been made of adjustments of the pool‐riffle spacing, a detailed survey of a 6 km channel reach containing over 300 riffles in the New Forest, southern England indicates that despite the influence of woody debris and channelization, the interriffle distance generally falls within the range of five to seven channel widths. As substantial adjustments in channel dimensions have been widely observed downstream of channelization schemes, land‐use changes, and dams and reservoirs, the associated adjustments in pool‐riffle spacing should be a consideration in channel management and an ingredient of design for channel restoration.
Ecological effects of river regulation on mammals and birds: A review
Authors: Nilsson Christer , Dynesius Mats 
Published: February 2007

AbstractAlthough most of the world's river systems are regulated, the effects of river regulation on mammals and birds are little known. In fact, speculations are more common than empirical data. A review of this topic is presented, emphasizing northern rivers where most impacts have been described. Effects are related to the major causes of change. It is concluded that the two most disastrous effects of river regulation on mammals and birds are the permanent inundation of vast areas of land, and the disruption of the seasonal flood regime along the river. The design of future investigations to improve our knowledge is considered.
Role of the floodplain and riparian zone in suspended matter and nitrogen retention in the adour river, south‐west France
Authors: Brunet R. C. , Pinay G. , Gazelle F. , Roques L. 
Published: February 2007

AbstractThe retention capacity of the floodplain and riparian zone for suspended matter and nitrogen has been investigated in the Adour River, a seventh order stream in south‐west France. Suspended matter and nitrogen fluxes through a 25 km meandering stretch of the river were measured during two flood events and compared with the amount of sediment trapped in the riparian zone (1.1 km2) and the major floodplain (16.8 km2) of the studied area. It was estimated that the floodplain and the riparian zone together retained between 10 and 20% of the suspended matter entering the stretch under study during the two main floods (138 700 Mg). Moreover, they retained about 11% of the total particulate nitrogen fluxes (640 Mg). Although the riparian zones are 15 times smaller than the major floodplain, the total suspended matter and particulate nitrogen deposition were, 50 and 17 times, respectively, larger in the riparian zone. The results obtained on the Adour River floodplain show that large river systems should not be considered only as export systems as riparian zones can retain a significant amount of suspended organic and mineral matter during floods.
Environmental and biological responses of former channels to river incision: A diachronic study on the upper rhǒne river
Authors: Bornette Gudrun , Heiler Gudrun 
Published: February 2007

AbstractThe impacts of river incision should be a lowering of the river level, which would increase the rate of water flow from the hillslope aquifer to the river and its former channels. If this aquifer is nutrient‐poor, it should favour the oligotrophication of the former channels. However, if the lowering of the water‐table exceeds the depth of the former channels, then it should lead to the drainage of these channels. These hypotheses were tested on two former channels located in a degrading reach of the Rhǒne River (France); the former channels were influenced by floods, seepage water from the river and hillslope groundwater in 1989. The rate of river incision in this reach has increased since 1980 because of gravel extraction from the river bed (0.5 m between 1989 and 1993). Between 1989 and 1993, the reduction of river infiltration and the increase in the amount of water from the hillslope aquifer in the former channels were demonstrated by the decrease in the phosphate and ammonia content of the water, and its increased alkalinity and conductivity. The responses of aquatic vegetation to river incision depended on the vegetation zone investigated. Two floristic zones that were frequently flooded and species‐poor in 1989 remained species‐poor in 1993. Two floristic zones, which were species‐rich and patchily organized, became dry or very shallow in 1993; as a consequence, aquatic vegetation disappeared, and was replaced by helophytes and terrestrial species. In the last vegetation zone, the increase in the amount of water coming from the hillslope aquifer caused the appearance and development of Chara hispida, an oligotraphent species. Unforeseen impacts of river incision were a decrease in the spatial and temporal heterogeneity of the former channels and lower aquatic macrophyte richness.