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| 2. |
- Dahl, Gudrun
(författare)
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The Beja of Sudan and the Famine of 1984-1986
- 1991
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Ingår i: Ambio. - Dordrecht : Springer. - 0044-7447 .- 1654-7209. ; 20:5, s. 189-191
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Tidskriftsartikel (refereegranskat)abstract
- Howthe Beja, largely apolitical nomadic pastoralists of northeastern Sudan, perceived their profound misfortunes during the drought of the 1 980s is examined. The famine of 1984-1986 was considered neither to have resulted from their own actions nor to be amenable to alleviation by them-both being functions of God, perhaps acting through the central government. Those Beja who were forced by the famine to abandon their traditional ways appear to be ripe for politicization.
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| 3. |
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| 4. |
- Elmberg, Johan, 1960-
(författare)
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Threats to boreal frogs
- 1993
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Ingår i: Ambio. - 0044-7447 .- 1654-7209. - 0044-7447 ; 22:4, s. 254-255
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Tidskriftsartikel (refereegranskat)
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| 5. |
- Granéli, Edna, et al.
(författare)
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Nutrient limitation of primary production in the Baltic Sea area
- 1990
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Ingår i: Ambio. - 0044-7447 .- 1654-7209. ; 19:3, s. 142-151
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Tidskriftsartikel (refereegranskat)abstract
- In the Baltic Sea area, including the Kattegat, the external N/P loadingratios are generally well above the 16:1 Redfield ratio for all subareas (theBothnian Bay, the Bothnian Sea, the Baltic proper and the Kattegat).During winter, the inorganic N/P ratio in surface waters varies. Appreciablyhigher values than the loading ratio are found for the northernmostbasin, the low-saline Bothnian Bay, while lower values than the loadingratio are found for the Baltic proper and the Kattegat. Nutrient enrichmenttests indicate general N limitation in the Baltic proper and the Kattegat,although stimulation of algal growth after P enrichment has been found inthe Baltic proper during summer blooms of blue-green algae. Blooms ofblue-green algae are common in the Baltic proper but hardly ever occur inthe Bothnian Bay and the Kattegat. This has been the case for the lastcentury, indicating natural summer N limitation. Full-scale experimentalmanipulation of the external N/P loading ratio has been carried out in theHimmerfjard basin, south of Stockholm. Results suggest nitrogen as themost limiting nutrient in coastal areas of the Baltic proper, uninfluencedby direct nutrient discharges. The knowledge of the effects of alteredexternal nutrient supplies for nutrient limitation in the Baltic Sea systemas a whole is too limited to allow for reliable predictions. However, theBaltic Sea may have developed towards a more pronounced N limitationdue to a twofold historic increase in P supply relative to N supply. Atpresent, the situation may be reversed as N supply is probably increasingmore rapidly than P supply. Management of the Baltic Sea area cannot bebased on removal of either N or P in sewage, but must take both elementsinto consideration, as well as differences between sub-basins andbetween polluted coastal and offshore areas.
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| 7. |
- Vought, Lena B. M., et al.
(författare)
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Nutrient retention in riparian ecotones
- 1994
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Ingår i: Ambio. - 0044-7447 .- 1654-7209. ; 23:6, s. 342-348
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Tidskriftsartikel (refereegranskat)abstract
- Nutrient retention mechanisms in riparian buffer strips are reviewed with emphasis on surface runoff and subsurface flows, the main pathways of exchanges between the stream and its surroundings. Unique physical and biogeochemical properties prevailing in these riparian ecotones dictate the flux of water, nutrients and other exogenous substances between the upland areas and the stream. Removal of nutrients from surface inflows is induced by deposition of sediment bound nutrients and exchange of dissolved nutrients with the soil/litter surface. Removal of nitrogen in subsurface flows can partly be explained by vegetation uptake, but the main mechanism for removal is usually denitrification. In channelized streams, the subsurface inflows have, in most cases, been altered to discharges via drainage tiles, with the exchange flows (water leaving and re-entering the open-channel via the stream bed and banks) being greatly decreased. Consequently, to improve nitrogen removal in these systems, these flows have to be intercepted or reestablished either through restoration of the old stream valley or through managed structures in the buffer strips.
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| 8. |
- Vought, Lena B. M., et al.
(författare)
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Nutrient retention in riparian ecotones
- 1994
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Ingår i: Ambio. - : Allen Press Inc.. - 0044-7447 .- 1654-7209. ; 23:6, s. 342-348
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Tidskriftsartikel (refereegranskat)abstract
- Nutrient retention mechanisms in riparian buffer strips are reviewed with emphasis on surface runoff and subsurface flows, the main pathways of exchanges between the stream and its surroundings. Unique physical and biogeochemical properties prevailing in these riparian ecotones dictate the flux of water, nutrients and other exogenous substances between the upland areas and the stream. Removal of nutrients from surface inflows is induced by deposition of sediment bound nutrients and exchange of dissolved nutrients with the soil/litter surface. Removal of nitrogen in subsurface flows can partly be explained by vegetation uptake, but the main mechanism for removal is usually denitrification. In channelized streams, the subsurface inflows have, in most cases, been altered to discharges via drainage tiles, with the exchange flows (water leaving and re-entering the open-channel via the stream bed and banks) being greatly decreased. Consequently, to improve nitrogen removal in these systems, these flows have to be intercepted or reestablished either through restoration of the old stream valley or through managed structures in the buffer strips.
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| 9. |
- Weisner, Stefan E.B. 1954-, et al.
(författare)
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Influence of Macrophytes on Nitrate Removal in Wetlands
- 1994
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Ingår i: Ambio. - Dordrecht : Springer Netherlands. - 0044-7447 .- 1654-7209. ; 23:6, s. 363-366
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Tidskriftsartikel (refereegranskat)abstract
- Efficient nitrate removal from wetlands depends on denitrification. Macrophytes support denitrification by supplying organic carbon. Organic carbon available to denitrifying bacteria is released from plant litter and from living macrophytes. Macrophytes offer attachment surfaces for epiphytes, also producing organic matter, and for denitrifying bacteria. Emergent macrophytes are generally more productive than submerged macrophytes, but submerged macrophytes have more epiphytes and offer a larger attachment area in the water column for denitrifying bacteria. Emergent and submerged vegetation differ in their seasonal patterns of release of organic carbon. We conclude that a mixture of emergent and submerged macrophytes may be beneficial for nitrogen removal in wetlands with a surface-flow of nitrate-rich water. The influence of vegetation on wetland hydraulics must also be considered. A wetland design with deeper parts favoring submerged macrophytes alternating, along the water flow, with shallower parts covered by emergent macrophytes, may promote denitrification processes and distribution of water flow.
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| 10. |
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