Effects of a new bridge on an intertidal mudflat in the Outer Barsnesfjord, Western Norway

Abstract

A new bridge is going to be built in Sogndal (west-Norway) over the sill of Barsnesfjord which is a part of the Sognefjord due to the fact that the current bridge is no longer safe nor able to deal with the increasing traffic. This research is a pilot study and uses macro-benthos from the intertidal mudflat to qualify the ecosystem and make a status quo of the ecosystem before the bridge is build. The samples (4 samples of 0.1 and 4 of 0.01 ) were taken on the first of March, meaning that it are winter values. 7 species and 173 individuals were found in the 6 analysed samples. The Shannon-Wiener index, commonly used for ecosystem qualification, showed that the status of the ecosystem is ‘bad’ or ‘very bad’. This is most likely due to natural causes such as a change in salinity throughout the year. The EU Water Framework Directive contains a list of indexes that should be used but no index have been developed to describe natural ecosystems this extreme. The predictions are that the new bridge is not going to influence this. What could be influenced is the renewal of the deep water of the Barsnesfjord due to the design of the new bridge. The size of this possible effect depends on how much the water is constricted and on how much the sill is swallowed. Due to the fact that no research has been done on the macro-benthos of this intertidal mudflat further research is recommended.