Rivers In Norway Research Articles

A theoretical approach to using faecal indicator data to model norovirus concentration in surface water for QMRA: Glomma River, Norway

Monitoring of faecal indicator organisms, such as Escherichia coli, in environmental and drinking waters is inadequate for the protection public health, primarily due to the poor relationship between E. coli and the occurrence of human pathogens, especially viruses, in environmental samples. Nevertheless, measurements of faecal indicator organisms within the risk based approach, can provide valuable information related to the magnitude and variability of faecal contamination, and hence provide insight into the expected level of potential pathogen contamination. In this study, a modelling approach is presented that estimates the concentration of norovirus in surface water relying on indicator monitoring data, combined with specific assumptions regarding the source of faecal contamination. The model is applied to a case study on drinking water treatment intake from the Glomma River in Norway. Norovirus concentrations were estimated in two sewage sources discharging into the river upstream of the drinking water offtake, and at the source water intake itself. The characteristics of the assumed source of faecal contamination, including the norovirus prevalence in the community, the size of the contributing population and the relative treatment efficacy for indicators and pathogens in the sewage treatment plant, influenced the magnitude and variability in the estimated norovirus concentration in surface waters. The modelling exercise presented is not intended to replace pathogen enumeration from environmental samples, but rather is proposed as a complement to better understand the sources and drivers of viruses in surface waters. The approach has the potential to inform sampling regimes by identifying when the best time would be to collect environmental samples; fill in the gaps between sparse datasets; and potentially extrapolate existing datasets in order to model rarer events such as an outbreak in the contributing population. In addition, and perhaps most universally, in the absence of pathogen data, this approach can be used as a first step to predict the source water pathogen concentration under different contamination scenarios for the purpose of quantifying microbial risks.

The vgll3 Locus Controls Age at Maturity in Wild and Domesticated Atlantic Salmon (Salmo salar L.) Males.

Wild and domesticated Atlantic salmon males display large variation for sea age at sexual maturation, which varies between 1–5 years. Previous studies have uncovered a genetic predisposition for variation of age at maturity with moderate heritability, thus suggesting a polygenic or complex nature of this trait. The aim of this study was to identify associated genetic loci, genes and ultimately specific sequence variants conferring sea age at maturity in salmon. We performed a genome wide association study (GWAS) using a pool sequencing approach (20 individuals per river and phenotype) of male salmon returning to rivers as sexually mature either after one sea winter (2009) or three sea winters (2011) in six rivers in Norway. The study revealed one major selective sweep, which covered 76 significant SNPs in which 74 were found in a 370 kb region of chromosome 25. Genotyping other smolt year classes of wild and domesticated salmon confirmed this finding. Genotyping domesticated fish narrowed the haplotype region to four SNPs covering 2386 bp, containing the vgll3 gene, including two missense mutations explaining 33–36% phenotypic variation. A single locus was found to have a highly significant role in governing sea age at maturation in this species. The SNPs identified may be both used as markers to guide breeding for late maturity in salmon aquaculture and in monitoring programs of wild salmon. Interestingly, a SNP in proximity of the VGLL3 gene in humans (Homo sapiens), has previously been linked to age at puberty suggesting a conserved mechanism for timing of puberty in vertebrates.

A vertical axis hydrodynamic turbine with flexible foils, passive pitching, and low tip speed ratio achieves near constant RPM

A full-scale vertical axis turbine with flexible foil blades and a passive spring-loaded pitching mechanism was tested in the Glomma River in Norway, demonstrating a maximum turbine efficiency of 37% (0.79 m/s, 3.7 RPM), 25% (1.18 m/s, 4.2 RPM), and 20% (1.55 m/s, 4.7 RPM). The turbine rotational speed showed a limited revolutions per minute (RPM) variation (increasing by only a factor of 1.3) with a doubling of inflow speed. The turbine RPM and load variations were controlled using five wings, double-cambered morphing blades with a relatively high blade lift/drag ratio over a wide range of angle of attacks, and passive spring-controlled blade pitching. The inherent passive blade pitching demonstrated a distinct flopping motion around the nominal (non-pitched) position at ∼0° azimuth angle and a less distinct motion at ∼180° for each revolution around the axis. The turbine's high solidity design, morphing blades, and Knoller-Betz effect limited the RPM variations over a wide range of water velocities. The flex foil turbine had higher power coefficients at lower tip speed ratios compared to typical lower solidity turbines with fixed blades, higher tip speed ratios, and no blade pitching and/or flopping.

Increased abundance of European eel (Anguilla anguilla) in acidified Norwegian rivers after liming

AbstractThe prevalence and abundance (density 100 m−2) of European eel (Anguilla anguilla) were studied by means of electrofishing in 13 acidified rivers in Norway that had been limed to restore acceptable water quality for Atlantic salmon (Salmo salar). Status of Atlantic salmon in these rivers varied prior to liming, from being entirely lost in six highly acidified rivers and in different stages of decline in seven less acidified rivers. Four of the rivers are heavily affected by hydropower development. The abundance and prevalence of European eel increased significantly during the study period. The best model for predicting eel abundance was that with four explanatory variables: time after liming, time after liming squared, status of salmon stocks and hydropower regulation. The eel density was expected to increase by a factor of almost 5 after 10 years of liming. The model also predicts that a river with a formerly reduced Atlantic salmon stock has a 2.8 times higher density of eel than rivers with formerly lost salmon stocks. Before liming, European eel were on average recorded at 15 and 41% of the sampling stations in rivers with formerly lost and reduced Atlantic salmon populations, respectively, increasing to 49 and 68% in individual rivers, respectively, after 10 years of liming. The recovery of European eel in these formerly acidified rivers by means of liming took place during the same period as their abundance declined in other parts of their distribution area in Norway and elsewhere in Europe.

Effects of Rotenone Treatment on Lotic Invertebrates

AbstractTwo rivers in Norway were treated with rotenone in an effort to eradicate the salmon parasite, Gyrodactylus salaris. Rotenone induced an immediate catastrophic invertebrate drift, mainly of dead individuals. The response to rotenone with respect to degree and timing varied widely. Baetis rhodani, Isoperla sp. and Rhyacophila nubila displayed a strong increase in drift densities early in the treatment. Baetis niger, Ameletus inopinatus, Heptagenia sp. and Agapetus ochripes showed a delayed response. Ephemerella aurivillii, E. mucronata, Taeniopteryx nebulosa and Elmis aenea drifted at low densities throughout the treatment. Early larval instar tended to be more sensitive to rotenone than later instar, and the toxic effect of rotenone tended to increase with increasing water temperature. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Dynamic rating curve assessment in unstable rivers using Ornstein‐Uhlenbeck processes

The procedure of fitting rating curves in channels where the stage‐discharge relationship is subject to changes driven by morphological processes remains one of the major unsolved problems in hydrometry. This paper addresses this issue by formulating the stage‐discharge relationship as a steady flow, one‐segmented power law model with parameters that are viewed as stochastic processes with characteristics associated with the temporal instabilities of the channel elements governing the stage‐discharge relationship. A Bayesian analysis with informative priors and time‐stage‐discharge measurements as forcing data is used to determine the most plausible model and its posterior parameter distributions using Markov chain Monte Carlo simulation techniques and particle filtering. The proposed framework is applied to data from gauging stations in two unstable rivers and one stable river in Norway.

Quantification of free-living Gyrodactylus salaris in an infested river and consequences for inter-river dispersal

Gyrodactylus salaris is a major threat to wild populations of Atlantic salmon Salmo salar in Norway. Inter-river dispersal of this parasite is considered to be mainly linked to infested fish. Dispersal through movement of contaminated water is considered possible but has not been quantitatively evaluated. To approach this problem, we built a simple model to estimate (1) the water concentration of free-living G. salaris and (2) the probability that given water volumes would contain free-living parasites. The concentration was back-estimated from reported experimental observations on the number of salmon juveniles found to be infected after being caged in a heavily infested river in Norway, protected from direct contact with the substrate or fish. Monte Carlo simulation was used to account for uncertainty and variability. The average concentration of G. salaris in the water column during the experiment was estimated to be 0.12 m(-3) (95% CI = 0.05 to 0.24). The probability that a given volume would contain at least 1 parasite was 1.2 x 10(-4) (95% CI = 5 x 10(-5) to 2.4 x 10(-4)) for 1 l, increasing to 0.67 (95% CI = 0.39 to 0.91) for 10,000 l. Thus, only high volumes were likely to represent a significant risk. Since we used data from a heavily infested spot, and despite the fact that time and space variations in water concentration of G. salaris may occur, we conclude that the risk of inter-river dispersal due to transfer of infested water through common river activities by humans is probably low.

Monthly indices of the post‐smolt growth of Atlantic salmon from the Drammen River, Norway

Indices of the monthly post‐smolt growth of three maturity groups of Atlantic salmon Salmo salar from the Drammen River in Norway were examined. Scale samples were collected from 1983 to 2003, providing a retrospective growth history for 2854 individuals. Overall post‐smolt growth of all three maturity groups decreased throughout the study period. When the post‐smolt year was segmented into 8 monthly indices, there was a significant decline in growth during the fourth and fifth month, typically months of maximum growth. The pre‐fishery abundance of one and two sea‐winter fish from Norway also showed a decline throughout the study period and was positively correlated to the post‐smolt growth of fish returning to the Drammen River. Freshwater growth was negatively correlated to the pre‐fishery abundance, thus indicating that factors affecting post‐smolt growth during the fourth and fifth months at sea may be responsible for declining return numbers in Norway.

Liming of acidified lakes and rivers in Norway

Acidification is one of the most serious environmental problems in Norway. International agreements to reduce emissions are the only acceptable solution to the acidification problem. The “Sulphur Protocol”, signed in Oslo in 1994, will certainly improve matters, but southern Norway will have large acidified areas for decades. Norwegian environmental authorities therefore carry out liming as a temporary alleviatory measure to reduce damage for freshwater ecosystems. In 1995, about NOK 92 mill, was spent on liming. Acidification has wiped out the salmon in 25 rivers, and they are threatened in another 28 rivers. Because of varying water flow and rapidly changing water quality, liming a Norwegian salmon river is a huge operation demanding sophisticated equipment. Eleven rivers carrying anadromous fish are being limed in 1995. The largest is the River Audna where liming has meant that a salmon stock could be reintroduced. Most rivers are limed using automatic lime dosers. The most sophisticated ones control the amount of lime using pH sensors and water flow to neutralize major episodes of acidic water flow, which regularly occur in Norwegian rivers.

Water quality requirement of Atlantic salmon (Salmo salar) in water undergoing acidification or liming in Norway

Atlantic salmon are severely affected by acidification in Norway. Water quality criteria for the salmon have to be based on the most sensitive stage, the smolt stage. The sensitivity to acidic water increases enormously during smolting, the seawater tolerance being especially vulnerable. Even moderately acidic water (pH about 6) with low inorganic monomeric aluminium (LA1) concentrations (<20μg. L−1) and short-term episodes may be harmful. Mixing zones in limed or unlimed rivers may also represent a problem for seaward migrating smolts. In limed salmon rivers, the national liming goal has been increased to pH 6.5 during smolting (1 February to 1 July) and to 6.2 the rest of the year as a result of our experiments. In contrast to what has been found for brown trout, salmon strains originating from watercources undergoing acidification were not more tolerant than those from non-acidic watercourses. At the moment no such “tolerant” strains are available for restocking limed rivers in Norway.

Homing and straying of hatchery-reared Atlantic salmon, Salmo salar L., released in three rivers in Norway

Releases of hatchery-reared smolts of Atlantic salmon, Salmo salar L., in the Rivers Orkla, Gaula and Alta, Norway yielded large percentages of strays (194, 13.7 and 13.8% respectively), based on recaptures from anglers. Homing precision to the rivers of release was independent of the release site on the river. Distribution of recaptured adult salmon within the rivers was dependent on the release site; upstream releases yielded more upstream recaptures than did downstream releases.

Oceanic migration in homing Atlantic salmon

Abstract. There appear to be two phases to the homing migration of maturing Atlantic salmon, Salmo salar, from feeding areas in the north Norwegian Sea to the home rivers in Norway: a first phase with crude navigation from the feeding areas towards the Norwegian coast and a second phase with more precise navigation in coastal and estuarine waters towards the home river. This was indicated by recaptures of Atlantic salmon individually tagged as: (1) smolts released in four Norwegian rivers; (2) smolts released on the Norwegian coast; (3) post-smolts transported from Norway and released in the feeding area north of the Faroe Islands during winter; (4) adults captured, tagged and released in the feeding areas in the Norwegian Sea outside northern Norway; and (5) maturing adults captured, tagged and released on the Norwegian coast and at the mouth of fjords. Experience gained as outward migrating smolts was required for salmon to navigate precisely along the coast, into the fjords and towards the home river, but not for the crude, eastward navigation from the feeding grounds towards Norway. Ocean currents appeared insignificant for the precise homing in coastal waters. Migration speed in the ocean increased with time during spring. Fish moving in the coastal current swam faster than those approaching the home stream in fjords. The return migration of Atlantic salmon is an active process where more than one set of navigational cues are needed.

A review of the inter- and intraspecific variability in salmonid hosts to laboratory infections with Gyrodactylus salaris Malmberg

Host specificity tests in the laboratory have demonstrated that Gyrodactylus salaris Malmberg can attach to and reproduce on species of Salmo, Salvelinus, Thymallus and Oncorhynchus. Inter- and intraspecific variations in host specificity and transmission capacity of G. salaris are described briefly. All Norwegian salmon individuals were initially susceptible and under 10% were later able to mount a response against the infection. Generally, heterogeneity in susceptibility/resistance to G. salaris seem less prominent in the Norwegian salmon stocks tested, than the Baltic salmon. Laboratory experiments indicate no correlation between temperature and host specificity, but positive correlations between temperature and the innate capacity for increase and the transmission rate. The results presented support the view that heavy salmon epidemics in G. salaris-infected rivers in Norway may occur because of this parasite. However, the importance of temperature on G. salaris reproduction and transmission suggests seasonal differences in the development and outcome of the colonization of infected rivers in Norway, along e.g. the north-south gradient.

Farmed Atlantic salmon (Salmo salar) in fisheries and rivers in Norway

The proportion of reared Atlantic salmon in Norwegian marine and freshwater fisheries was estimated using a combined method of examining external body morphology and scale patterns of the salmon. The point estimates suggested a high proportion of reared salmon both in the fisheries and in salmon spawning populations. During the fishing season in summer, the proportion of reared salmon was higher in the outer coastal areas than in fjords and rivers. Near spawning, the proportion of reared salmon in many rivers increased considerably, indicating that these fish ascend the rivers late in the season. Several sources of error affect the estimates, but there are strong indications that the proportion of reared salmon in nature has increased considerably in recent years. This is probably a result of the increased salmon farming activity in Norway, and the subsequent increase in number of salmon escaping from fish farms.

Chemical and Sensory Analysis of Off-Flavours in Fish from Polluted Rivers in Norway

Fish caught in waters polluted with paper mill effluents have been analysed by a gas chromatographic headspace technique in order to identify the organic compounds causing the strong off-flavour present in the fish. Both chemical and sensory analyses were done and the results compared. The concentrations of off-flavour volatiles present in the different fish samples showed good correlations with the degree of off-taste found by sensory analyses. Typical organic compounds from paper mill effluents such as terpenes and their derivatives caused strong off-flavour, whilst low concentrations of haloforms and other halogen-containing compounds were found.