| Summary: | In 1992-1994 the local authority of Luleå dammed up the water in the four innermost bays of Luleå (Luleå innerfjärdar). The measures were taken to save the interconnected bays and prevent them become owergrown with aquatic plants and in the long run become svamps and land. The main causes of the succession from aquatic to terrestrial areas were land uplift ( about 1 cm/year), sedimentation eutrophication and owergrowth. A comparison between botanical investigations, including field inventories and analyses of air photgraphs, for the years 1995 and 2004 establish the following facts: In the four dammed up bays, Björkskata-, Björsby-, Sink- and Sörfjärden, the areas of aquatic vegetation are decreased and the density of plants have been reduced. There are much more areas of clean watersurfaces 2004 then 1995. Common Reed (Phragmites australis), which in 1994 made a big contribution to the owergrown situation in the bays, are considrably decreased. Other species that are decreased are Schoenoplectus lacustris, Potamogeton natans, Potamogeton perfoliatus, Sagittaria natans, Ranunculus peltatus and Elodea canadensis The principal cause of the reduction of aquatic vegetation in the innermost bays must be the higher water level during the vegetative period caused by the weirs. In Skurholmsfjärden, outside the weirs, there have been a slight increase of the watervegetation during the ten years period of studies. Here, in opposite to the other bays, the meanwaterlevel have sunk about 10 cm from 1995 to 2004. If it is possible to raise the meanwaterlevel in the innermost bays of Luleå a little bit more (10-20 cm) the reducing effect of the vegetation most likely will be even more noticeable than during 1995-2004. If more reduction of water vegetation in Luleå innerfjärdar is desired take the following measures into consideration: to pump water into the bays to get a higher waterlevel. to reduce the outlet of nutrients from different antropogenic sources. to accept owergrowth in some selected parts of the bays where the ...
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