Estuarine influence on survival rates of coho (Oncorhynchus kisutch) and chinook salmon (Oncorhynchus tshawytscha) released from hatcheries on the U.S. Pacific coast     

A. Magnusson  R. Hilborn 《Estuaries and Coasts》2003,26(4):1094-1103

While it has long been known that Pacific salmon use estuarine habitat, it has proven much harder to establish that the loss of estuarine habitat results in reduced survival. We used coded-wire tagging of hatchery fish to estimate the survival from release until maturity and related this survival to several indicators of estuarine condition. We found a significant relationship between the survival of chinook salmon (Oncorhynchus tshawytscha) and the percentage of the estuary that is in pristine condition, but no significant relationship for coho salmon (Oncorhynchus kisutch). This supports field observations that chinook salmon use estuarine habitat much more than coho salmon and confirms that the loss of estuarine habitat results in lower survival of chinook salmon.  相似文献   

An intercomparison of seawater filtration procedures     

J.M. Bewers  P.A. Yeats  S. Westerlund  B. Magnusson  D. Schmidt  H. Zehle  S.S. Berman  A. Mykytiuk  J.C. Duinker  R.F. Nolting  R.G. Smith  H.L. Windom 《Marine pollution bulletin》1985,16(7):277-281

Filtration systems, used for the preparation of coastal seawater samples for trace analysis, have been intercompared to determine the extent of contamination arising during the filtration process. The results show that all the systems intercompared are able to provide uncontaminated filtrates for copper, nickel, cobalt and manganese and, with two exceptions, for cadmium and iron, at levels that would be encountered in uncontaminated coastal waters.  相似文献   

Snow accumulation distribution inferred from time‐lapse photography and simple modelling     

Daniel Farinotti  Jan Magnusson  Matthias Huss  Andreas Bauder 《水文研究》2010,24(15):2087-2097

The spatial and temporal distribution of snow accumulation is complex and significantly influences the hydrological characteristics of mountain catchments. Many snow redistribution processes, such as avalanching, slushflow or wind drift, are controlled by topography, but their modelling remains challenging. In situ measurements of snow accumulation are laborious and generally have a coarse spatial or temporal resolution. In this respect, time‐lapse photography shows itself as a powerful tool for collecting information at relatively low cost and without the need for direct field access. In this paper, the snow accumulation distribution of an Alpine catchment is inferred by adjusting a simple snow accumulation model combined with a temperature index melt model to match the modelled melt‐out pattern evolution to the pattern monitored during an ablation season through terrestrial oblique photography. The comparison of the resulting end‐of‐winter snow water equivalent distribution with direct measurements shows that the achieved accuracy is comparable with that obtained with an inverse distance interpolation of the point measurements. On average over the ablation season, the observed melt‐out pattern can be reproduced correctly in 93% of the area visible from the fixed camera. The relations between inferred snow accumulation distribution and topographic variables indicate large scatter. However, a significant correlation with local slope is found and terrain curvature is detected as a factor limiting the maximal snow accumulation. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

On the dependence of ENSO simulation on the coupled model mean state     

L. Magnusson  M. Alonso-Balmaseda  F. Molteni 《Climate Dynamics》2013,41(5-6):1509-1525

Systematic model error remains a difficult problem for seasonal forecasting and climate predictions. An error in the mean state could affect the variability of the system. In this paper, we investigate the impact of the mean state on the properties of ENSO. A set of coupled decadal integrations have been conducted, where the mean state and its seasonal cycle have been modified by applying flux correction to the momentum-flux and a combination of heat and momentum fluxes. It is shown that correcting the mean state and the seasonal cycle improves the amplitude of SST inter-annual variability and also the penetration of the ENSO signal into the troposphere and the spatial distribution of the ENSO teleconnections are improved. An analysis of a multivariate PDF of ENSO shows clearly that the flux correction affects the mean, variance, skewness and tails of the distribution. The changes in the tails of the distribution are particularly noticeable in the case of precipitation, showing that without the flux correction the model is unable to reproduce the frequency of large events. For the inter-annual variability the momentum-flux correction alone has a large impact, while the additional heat-flux correction is important for the teleconnections. These results suggest that the current forecasts practices of removing the forecast bias a-posteriori or anomaly initialisation are by no means optimal, since they can not deal with the strong nonlinear interactions. A consequence of the results presented here is that the predictability on annual time-ranges could be higher than currently achieved. Whether or not the correction of the model mean state by some sort of flux correction leads to better forecasts needs to be addressed. In any case, flux correction may be a powerful tool for diagnosing coupled model errors and predictability studies.  相似文献   

Trace metals in the Göta river estuary     

Lars-Göran Danielsson  Bertil Magnusson  Stig Westerlund  Kerong Zhang 《Estuarine, Coastal and Shelf Science》1983,17(1):73-85

The concentrations of the trace metals Cd, Cu, Fe, Ni, Pb and Zn in the Göta River estuary have been investigated. The following metal fractions have been determined: acid-leachable, dissolved, labile and particulate.The estuary represents a salt wedge type estuary and is situated in a densely populated region of Sweden. The metal concentrations found for the dissolved fraction is in the range of what can be considered as background levels for freshwater. It is difficult to evaluate any estuarine processes other than conservative mixing for Cd, Cu, Ni and Zn. The dissolved levels in the freshwater end member are Cd, 9–25 ngl^?1; Cu, 1·1–1·4 μgl^?1; Fe, 20–75 μg l^?1: Ni, 0·7–0·9 μg l^?1: Pb 0·09–0·2 μg l^?1; and Zn, 6–7 μg l^?1:The results from the acid-leachable fraction show that at high suspended load the particles sediment in the river mouth. The trace metal levels in this fraction are subject to large variations.  相似文献   

Soil erosion and sediment transport in Tanzania: Part I – sediment source tracing in three neighbouring river catchments     

Maarten Wynants  Linus Munishi  Kelvin Mtei  Samuel Bodé  Aloyce Patrick  Alex Taylor  David Gilvear  Patrick Ndakidemi  William H. Blake  Pascal Boeckx 《地球表面变化过程与地形》2021,46(15):3096-3111

Water bodies in Tanzania are experiencing increased siltation, which is threatening water quality, ecosystem health, and livelihood security in the region. This phenomenon is caused by increasing rates of upstream soil erosion and downstream sediment transport. However, a lack of knowledge on the contributions from different catchment zones, land-use types, and dominant erosion processes, to the transported sediment is undermining the mitigation of soil degradation at the source of the problem. In this context, complementary sediment source tracing techniques were applied in three Tanzanian river systems to further the understanding of the complex dynamics of soil erosion and sediment transport in the region. Analysis of the geochemical and biochemical fingerprints revealed a highly complex and variable soil system that could be grouped in distinct classes. These soil classes were unmixed against riverine sediment fingerprints using the Bayesian MixSIAR model, yielding proportionate source contributions for each catchment. This sediment source tracing indicated that hillslope erosion on the open rangelands and maize croplands in the mid-zone contributed over 75% of the transported sediment load in all three river systems during the sampling time-period. By integrating geochemical and biochemical fingerprints in sediment source tracing techniques, this study demonstrated links between land use, soil erosion and downstream sediment transport in Tanzania. This evidence can guide land managers in designing targeted interventions that safeguard both soil health and water quality.  相似文献   

Soil erosion and sediment transport in Tanzania: Part II – sedimentological evidence of phased land degradation     

Maarten Wynants  Aloyce Patrick  Linus Munishi  Kelvin Mtei  Samuel Bodé  Alex Taylor  Geoffrey Millward  Neil Roberts  David Gilvear  Patrick Ndakidemi  Pascal Boeckx  William H. Blake 《地球表面变化过程与地形》2021,46(15):3112-3126

Soil resources in parts of Tanzania are rapidly being depleted by increased rates of soil erosion and downstream sediment transport, threatening ecosystem health, water and livelihood security in the region. However, incomplete understanding to what effect the dynamics of soil erosion and sediment transport are responding to land-use changes and climatic variability are hindering the actions needed to future-proof Tanzanian land-use practices. Complementary environmental diagnostic tools were applied to reconstruct the rates and sources of sedimentation over time in three Tanzanian river systems that have experienced changing land use and climatic conditions. Detailed historical analysis of sediment deposits revealed drastic changes in sediment yield and source contributions. Quantitative sedimentation reconstruction using radionuclide dating showed a 20-fold increase in sediment yield over the past 120 years. The observed dramatic increase in sediment yield is most likely driven by increasing land-use pressures. Deforestation, cropland expansion and increasing grazing pressures resulted into accelerating rates of sheet erosion. A regime shift after years of progressive soil degradation and convergence of surface flows resulted into a highly incised landscape, where high amounts of eroded soil from throughout the catchment are rapidly transported downstream by strongly connected ephemeral drainage networks. By integrating complementary spatial and temporal evidence bases, this study demonstrated links between land-use change, increased soil erosion and downstream sedimentation. Such evidence can guide stakeholders and policy makers in the design of targeted management interventions to safeguard future soil health and water quality.  相似文献   

Intercalibration of age readings of ling (Molva molva L.) blue ling (Molva dipterygia Pennant, 1784) and tusk (Brosme brosme L.)     

Bergstad  O. A.; Magnusson  J. V.; Magnusson  J.; Hareide  N. -R.; Reinert  J. 《ICES Journal of Marine Science》1998,55(2):309-318

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Mesoproterozoic (1.47–1.44 Ga) orogenic magmatism in Fennoscandia; Baddeleyite U–Pb dating of a suite of massif-type anorthosite in S. Sweden     

Linus Brander  Ulf Söderlund 《International Journal of Earth Sciences》2009,98(3):499-516

The Jönköping Anorthositic Suite (JAS) in S. Sweden has characteristics typical for (Proterozoic) massif-type anorthosites. The interstitial liquid of these plagioclase-porphyritic rocks solidified at 1,455 ± 6 Ma, as determined by U–Pb isotope analysis of baddeleyite. The JAS developed during a regional 1.47–1.44 event in Fennoscandia that generated widespread mafic magmatism (basalts, and diabase dykes and sills) in the north and emplacement of felsic plutons in the south. The event of 1.47–1.44 Ga magmatism in Fennoscandia largely coincides in age with dynamic high-grade metamorphism in SW Sweden and was probably related to convergent active-margin processes during the Danopolonian orogeny.  相似文献   

Brittle-plastic deformation in initially dry rocks at fluid-present conditions: transient behaviour of feldspar at mid-crustal levels   总被引：1，自引：0，他引：1  

Linus Brander  Henrik Svahnberg  Sandra Piazolo 《Contributions to Mineralogy and Petrology》2012,163(3):403-425

We present detailed microstructural and chemical analyses from an initially dry anorthositic rock deformed during wet amphibolite facies conditions. Three different domains representing the microstructural variation of the deformed samples are investigated in detail in terms of fracture morphology and mode, grain characteristics and chemistry of present phases. Results show transient deformational behaviour where a close interaction between brittle, plastic and fluid-assisted deformation mechanisms can be observed. Our analysis allows us to describe the succession, interrelationships and effects of active mechanisms with progressively increasing strain in three so-called stages. In Stage 1, initial fracturing along cleavage planes promoted fluid influx that caused fragmentation and chemical reactions, producing fine-grained mineral assemblages in the fractures. Deformation twins and dislocations developed in clast pieces due to stress relaxation. Passive rotation of conjugate fracture sets and interconnection of intracrystalline fractures formed micro-shear-zones, constituting Stage 2. Microstructures and grain relationships indicate the activity and fluctuation between fracturing, dissolution-precipitation creep, grain boundary sliding and locally dislocation creep, reflecting the transient behaviour of brittle and plastic deformation mechanisms. Further rotation and widening of fractures into overall foliation parallel shear-bands (Stage 3) promoted strain partitioning into these areas through increased fluid influx, influence of fluid-assisted grain boundary sliding, phase mixing and presence of weak phases such as white mica. We suggest that local differences in fluid availability, volume fraction of weak phases produced by fluid present metamorphic reactions coupled with volume increase and local variations in stress concentration induced transient brittle-plastic behaviour. The studied shear-zone represents an example of the transformation of a rigid dry rock to a soft wet rock during deformation through syntectonic fracturing.  相似文献