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21.
Seasonal behaviour of NO3 - in surfacewater is often used as an indicator on a catchment's ability toretain N from atmospheric deposition. In this paper, weclassify 12 pristine sites (five streams and seven lakes) insouthernmost Norway according to the N saturation stageconcept. All examined sites were acid-sensitive and had annualmean NO3 - concentrations in the range 6–36 μeqL-1. At lake sites with relatively long water residencetimes, hydrology will have a damping effect on the seasonalNO3 - oscillations in the outlet streams. Under givenrunoff conditions (1.0–2.2 m yr-1), the seasonalNO3 - pattern was clearly affected when lake:catchmentarea ratios exceeded 0.15 and the total residence time of lakesin the catchments exceeded 0.3 yr. In such cases, annualmean NO3 - concentration rather than seasonalvariations may be the better indicator of N saturation. Toaccount for this we propose a set of supplementary criteria forsuch lake systems, defining limit values for annual meanNO3 - concentrations within each stage class. Beforebeing applied on a broader scale, however, we recommend anexamination of additional lake-dominated catchmentsrepresenting a larger gradient in ecosystem types, N depositionlevels and hydrologic regimes. When applying the supplementarycriteria on the Norwegian sites, two were classified as stage 0(no saturation), five as stage 1 (early stage of saturation)and five as stage 2 (saturated – moderate N loss). No siteswere showing symptoms of stage 3, which characteriseswatersheds that are net sources of N, rather than sinks. Theresults indicate a great variability in N retention capacity inthe study region, despite the fact that many of the catchmentsexperience relatively uniform N deposition amounts and climaticconditions. This suggests that much of this variability must bedue to specific catchment characteristics as e.g. soil type,soil depth, and vegetation cover. 相似文献
22.
Arne Linløkken 《Water, air, and soil pollution》1988,40(1-2):203-213
Brown trout (Salmo trutta) and perch (Perca fluviatilis) had different vertical distributions throughout the year in the acidified lake Gjerstadvann. During summer, the brown trout lived in the 0 to 16 m depth interval, whereas the perch lived in the 0 to 8 m interval. In Gjerstadvann, the thermocline lies at 8 to 10 m depth. The epilimnion pH was usually > 5.6, and the thermocline pH was about 5.2. Brown trout and perch in Gjerstadvann, thus experienced different chemical environment during summer-stratification. Two rivers, one of them acidified, the other circum-neutral, were the most important spawning areas for the Gjerstadvann brown trout. Brown trout parr in the acidified river migrated to the lake and matured at younger ages than the brown trout spawning in the non-acidic river. The brown trout stocks were juvenilized because of low survival rate of adult fish (S = 0.15 to 0.19). The short life span was probably dus to low pH and elevated Al. The perch in Gjerstadvann showed fluctuating year class strength but the survival rate of adult perch (S = 0.57) did not seem to be affected by acidification during this investigation. This may due to its vertical distribution during summer. 相似文献
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Andersen CB Holst-Jensen A Berdal KG Thorstensen T Tengs T 《Journal of agricultural and food chemistry》2006,54(26):9658-9663
We have tested and compared the performance of 12 different assays representing four different real-time polymerase chain reaction (PCR) chemistries in the context of genetically modified organism detection. Several different molecular beacon, SYBR Green, TaqMan, and MGB assays were designed for the event specific detection and quantification of the 3' integration junction of GTS 40-3-2 (Roundup Ready) soybean. Sensitivity as well as robustness in the presence of background DNA were tested. None of the PCR-based approaches appeared to be significantly better than any of the other, but the molecular beacon assays had the lowest efficiency and also seemed more sensitive to changes in experimental setup. 相似文献
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Moisture-induced stresses resulting from climate variations of the environment can induce cracks in timber members and thus affect the safety and serviceability. The present study highlights—by means of numerical simulations—the distribution and development over time of moisture-induced stresses in various glulam cross sections during wetting. The results show that local stresses may be significantly larger than average stresses, the extent of which strongly depends on the geometrical configuration of the glulam laminates. Suggestions are made on the design of glulam cross sections to minimize the arising local stresses. Furthermore, the studied wetting exposure results in local tensile stresses that exceed the tensile strength of the material. In smaller cross sections, this is the case within few days, while more time is required in wider cross sections. 相似文献
27.
Kevin Alan Glover Øystein Skaala Anne Grete Eide Søvik Tor Arne Helle 《Aquaculture Research》2011,42(9):1323-1331
Seven samples, each consisting of approximately 50 Atlantic salmon, were collected from five marine farms in Norway. These farms reported to rear fish originating from the same commercial breed; however, all samples followed a unique route of production from breeder to marine farm via egg, fry and smolt producers. A group of farmed escapees (n=50) were also captured. Following genotyping with 18 microsatellite loci, the global FST was 0.083, and pair‐wise values were as high as 0.158. Four clusters, with varying degrees of genetic differentiation, were identified among samples from the farms, and the source of the escapees was identified successfully. It is suggested that the genetic differences observed among samples from the farms were created through the process of genetic drift, facilitated by parallel sub‐strains, extensive within‐strain selection and low to moderate numbers of adults contributing to batches of eggs. In conclusion, this study has demonstrated that genetic identification of escaped Atlantic salmon, back to the farm of origin, may be possible even when farms rear fish reported to originate from a single breeder. 相似文献
28.
Magnus Vikan Rsg Espen Rimstad Arne Guttvik Brd Skjelstad Eldar sgard Bendiksen se Helen Garseth 《Journal of fish diseases》2019,42(1):97-108
Salmonid alphavirus (SAV) causes pancreas disease (PD) in farmed Atlantic salmon (Salmo salar L.), and exocrine pancreas tissue is a primary target of the virus. Digestive enzymes secreted by the exocrine pancreas break down macromolecules in feed into smaller molecules that can be absorbed. The effect of SAV infection on digestion has been poorly studied. In this study, longitudinal observations of PD outbreaks caused by SAV subtype 2 (SAV2) in Atlantic salmon at two commercial sea sites were performed. The development of PD was assessed by measurement of SAV2 RNA load and evaluation of histopathological lesions typical of PD. Reduced digestion of both protein and fat co‐varied with the severity of PD lesions and viral load. Also, the study found that during a PD outbreak, the pen population comprise several subpopulations, with different likelihoods of being sampled. The body length of sampled fish deviated from the expected increase or steady state over time, and the infection status in sampled fish deviated from the expected course of infection in the population. Both conditions indicate that disease status of the individual fish influenced the likelihood of being sampled, which may cause sampling bias in population studies. 相似文献
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