Focused groundwater discharge of phosphorus to a eutrophic seepage lake (Lake Væng, Denmark): implications for lake ecological state and restoration   总被引：1，自引：0，他引：1  

Jacob Kidmose  Bertel Nilsson  Peter Engesgaard  Mette Frandsen  Sachin Karan  Frank Landkildehus  Martin Søndergaard  Erik Jeppesen 《Hydrogeology Journal》2013,21(8):1787-1802

A study on Lake Væng in Denmark demonstrates a high potential for loading of phosphorous via groundwater to seepage lakes. Groundwater discharges are displayed as an important source of phosphorous to a lake due to: (1) high concentrations in the aquifer just below the lake, and (2) the main flow paths through the aquifer–lakebed interface either being overland flow through a seepage face, or focused in zones with very high discharge rates. In-lake springs have measured discharge of up to 7.45 m³ per m² of lakebed per day. These findings were based on seepage meter measurements at 18 locations, stable isotope (δ¹⁸O) analyses, temperature profiles and mapping of ice cover distribution. Groundwater–lake interaction was modelled with a 2D conceptual flow model (MODFLOW) with hydrogeology interpreted from catchment multi electrode profiling, on-lake ground-penetrating radar, well logging and borehole data. Discharge was found to be much focused and opposite to expected increase away from the shoreline. The average total phosphorus concentration in discharging groundwater sampled just beneath the lakebed was 0.162 mg TP/l and thereby well over freshwater ecological thresholds (0.043–0.612, median = 0.117 mg TP/l). The study illustrates a direct link between groundwater and lake chemistry.  相似文献   

A poly morphological landform approach for hydrogeological applications in heterogeneous glacial sediments     

Knud Erik S. Klint  Bertel Nilsson  Lars Troldborg  Peter Roll Jakobsen 《Hydrogeology Journal》2013,21(6):1247-1264

The ‘poly morphological (PM) concept’ is used to assess geological heterogeneity in glacial sediments and to evaluate groundwater recharge to aquifers, especially those underlying clay till. The novelty of the PM concept is that it enhances the knowledge of, especially, heterogeneity of till units in geological models by using superimposed geomorphological units with typical sediment types related to the individual landforms. The PM concept is demonstrated through the construction of a poly morphological map for Zealand in Denmark and an aggregated map comparing clay-till-thickness distribution within individual PM types. The hydrogeological applicability of the PM concept was tested with a physical-based distributed 3D hydrological model. The aggregated PM map was compared with fracture and redox conditions at 21 field sites to evaluate the PM-type correlation to: (1) till thickness, (2) thickness of the reduced-till zone, and (3) depth to the zone with fracture spacing >1 m The results show that the till thickness is a critical parameter for the formation of fracture networks in clay till, and that fracture density decreases in till thicker than 8–10 m. However, the amount of data is still inadequate for statistically proving the PM concept.  相似文献   

A new early Holocene shoreline displacement record for Blekinge,southern Sweden,and implications for underwater archaeology     

Anton Hansson  Dan Hammarlund  Giacomo Landeschi  Arne Sjstrm  Bjrn Nilsson 《Boreas: An International Journal of Quaternary Research》2019,48(1):57-71

We present evidence of a submerged early Holocene landscape off the Blekinge coastline in the Baltic Sea, dating to the Yoldia Sea and Initial Littorina Sea Stages when the water level was lower than at present. ¹⁴C dated wood remains obtained by surveillance diving and new archaeological findings in combination with bathymetric analyses and interpolations between other sites across the Baltic Sea were used for refinement of the shoreline displacement history of the region. The new results reveal a Yoldia Sea lowstand level at 20 m b.s.l., a subsequent Ancylus Lake highstand at 3 m a.s.l., and then a period of relatively stable water level at about 4 m b.s.l. during the Initial Littorina Sea Stage, several metres lower than previously concluded. The refined shoreline displacement record was used for palaeo‐reconstructions of the study area during four key periods, the Yoldia Sea lowstand phase, the Ancylus Lake transgression phase, the Ancylus Lake highstand phase and the Initial Littorina Sea lowstand phase, using elevation data and map algebra functions. A flow accumulation algorithm was used for reconstruction of the now submerged prehistoric river network in order to identify areas of high archaeological potential. Our revised shoreline displacement record, and especially its lowstand period during the Initial Littorina Sea Stage around 9500–8500 cal. a BP, raises future demands not only for specific archaeological shallow‐water surveys down to 4 m b.s.l. in the area, but also for a renewed cultural heritage management strategy. The results of this study fill an important gap in the early Holocene part of the shoreline displacement history of Blekinge, contributing to its completion since the deglaciation, which is unique for the Baltic Sea.  相似文献   

Integrated environmental assessment of fisheries management: Swedish Nephrops trawl fisheries evaluated using a life cycle approach     

Sara Hornborg  Per Nilsson  Daniel Valentinsson  Friederike Ziegler 《Marine Policy》2012

Fisheries management needs to broaden its perspective to achieve sustainable resource use. Life cycle assessment (LCA) is an ISO standardized method to evaluate the environmental impacts of products using a broad and systematic approach. In this study, the outcome of a management regime promoting species-selective trawling in Swedish Nephrops trawl fisheries was studied using LCA methodology by quantifying the impacts per kilogram of landing using two different fishing methods. Demersal trawling has previously been found to be both energy intensive and destructive in terms of seafloor impact and discards. It is demonstrated that species-selective trawling fulfils management objectives, although with tradeoffs in terms of fuel consumption and associated GHG emissions. To prioritize between impacts, one must be aware of and quantify these potential tradeoffs. LCA could be an important tool for defining sustainable seafood production as it can visualize a broad range of impacts and facilitate integrated, transparent decision making in the seafood industry. It is also concluded that, with current LCA methodology, use of total discarded mass could increasingly be distinguished from potential impact by applying two new concepts: primary production requirements and threatened species affected.  相似文献   

Simultaneous measurements of Martian plasma boundaries by Rosetta and Mars Express     

N.J.T. Edberg  A.I. Eriksson  U. Auster  S. Barabash  A. Bößwetter  C.M. Carr  S.W.H. Cowley  E. Cupido  M. Fränz  K.-H. Glassmeier  R. Goldstein  M. Lester  R. Lundin  R. Modolo  H. Nilsson  I. Richter  M. Samara  J.G. Trotignon 《Planetary and Space Science》2009,57(8-9):1085-1096

We present the first two-spacecraft near-simultaneous observations of the Martian bow shock (BS), magnetic pileup boundary (MPB) and photo-electron boundary (PEB) obtained by the plasma instruments onboard Rosetta and Mars Express during the Rosetta Mars flyby on February 25, 2007. Our observations are compared with shape models for the BS and MPB derived from previous statistical studies. The MPB is found at its expected position but the BS for this event is found significantly closer to the planet than expected for the rather slow and moderately dense solar wind. Cross-calibration of the density measurements on the two spacecraft gives a density profile through the magnetosheath, indicating an increasing solar wind flux during the Rosetta passage which is consistent with the multiple BS crossings at the Rosetta exit.  相似文献   

Understanding Lyα emitters     

Kim K. Nilsson  Guest Editors  Klaus Meisenheimer 《New Astronomy Reviews》2009,53(3):37

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Comparison of preparatory signal analysis techniques for consideration in the (post-)Kyoto policy process   总被引：2，自引：2，他引：0  

Matthias Jonas  M. Gusti  W. Jęda  Z. Nahorski  S. Nilsson 《Climatic change》2010,103(1-2):175-213

Our study is a preparatory exercise. We focus on the analysis of uncertainty in greenhouse gas emission inventories. Inventory uncertainty is monitored, but not regulated, under the Kyoto Protocol to the United Nations Framework Convention on Climate Change. Under the Convention, countries publish annual or periodic national inventories of greenhouse gas emissions and removals. Policymakers use these inventories to develop strategies and policies for emission reductions and to track the progress of these policies. However, greenhouse gas inventories contain uncertainty for a variety of reasons, and these uncertainties have important scientific and policy implications. For most countries, the emission changes agreed under the Protocol are of the same order of magnitude as the uncertainty that underlies their combined (carbon dioxide equivalent) emissions estimates. Here we apply and compare six available techniques to analyze the uncertainty in the emission changes that countries agreed to realize by the end of the Protocol’s first commitment period 2008–2012. Any such technique, if implemented, could “make or break” claims of compliance, especially in cases where countries claim fulfillment of their commitments to reduce or limit emissions. The techniques all perform differently and can thus have a different impact on the design and execution of emission control policies. A thorough comparison of the techniques has not yet been made but is needed when expanding the discussion on how to go about dealing with uncertainty under the Kyoto Protocol and its successor.  相似文献   

Ion escape from Mars as a function of solar wind conditions: A statistical study     

Hans Nilsson  Ella Carlsson  Masatoshi Yamauchi  Stas Barabash  Yoshifumi Futaana 《Icarus》2010,206(1):40-49

The influence of solar EUV and solar wind conditions on ion escape at Mars is investigated using ion data from the Aspera-3 instrument on Mars Express, combined with solar wind proxy data obtained from the Mars Global Surveyor (MGS) spacecraft. A solar EUV flux proxy based on data from the Earth position, scaled and shifted in time for Mars, is used to study relatively long time scale changes related to solar EUV variability. Data from May 2004 until November 2005 has been used. A clear dependence on the strength of the subsolar magnetic field as inferred from MGS measurements is seen in the ion data. The region of significant heavy ion flows is compressed and the heavy ion flux density is higher for high subsolar magnetic field strength. Because of the difference in outflow area, the difference in estimated total outflow is somewhat less than the difference in average flux density. We confirm previous findings that escaping planetary ions are mainly seen in the hemisphere into which the solar wind electric field is pointed. The effect is more pronounced for the high subsolar magnetic field case.The average ion motion has a consistent bias towards the direction of the solar wind electric field, but the main motion is in the antisunward direction. The antisunward flow velocity increases with tailward distance, reaching above at 2 to 3 martian radii downtail from Mars for O⁺ ions. Different ion species reach approximately the same bulk flow energy. We did not find any clear correlation between the solar EUV flux and the ion escape distribution or rate, probably because the variation of the solar EUV flux over our study interval was too small. The results indicate that the solar wind and its magnetic field directly interacts with the ionosphere of Mars, removing more ions for high subsolar magnetic field strength. The interaction region and the tail heavy ion flow region are not perfectly shielded from the solar wind electric field, which accelerates particles over relatively large tail distances.  相似文献   

Relationships between drainage area characteristics and lake water quality   总被引：1，自引：0，他引：1  

Ake Nilsson  Lars Håkanson 《Environmental Geology》1992,19(2):75-81

The aim of this work is to quantify some of the complex relationships between drainage area characteristics (such as bedrocks and quaternary deposits) and lake water quality (pH, alkalinity, conductivity, and hardness). Seventysix drainage lakes, mainly oligotrophic, are described with respect to drainage area characteristics, morphometry, and water chemistry. The DAZ (drainage area zonation) method has been used to describe the drainage areas. The method utilizes a weighting system to reduce the impact of land types with increasing distance from the lake. The most significant parameter governing the water chemistry parameters seems to be the percentage of open land (cultivated land and/or meadows) in the drainage areas. High percentage leads to high pH, alkalinity, conductivity, and hardness. The correlations concerning alkalinity and pH are improved using the DAZ method. No significant relationships between bedrock geology of the drainage areas and lake water chemistry have been recorded.  相似文献   

Situational and cognitive obstacles to political consensus on climatic change     

Lars J. Nilsson 《Climatic change》1993,25(2):93-96

The discussion draws on results from the project entitledCultural and Techno-Ecological Constraints and Opportunities for Natural Resources Management, financed by the Swedish Council for Planning and Coordination of Research.  相似文献