Effects on fiords of modified freshwater discharge due to hydroelectric power production

Natural freshwater discharge to Norwegian fjords is characterized by low runoff during winter when precipitation is stored as snow and ice, and a marked peak in the discharge due to snow melting in spring. Hydroelectric power production causes a modified runoff pattern with increasing freshwater discharge during winter and reduced flow in spring. The effects of runoff regulations on physical and biological properties of fjords are considered on basis of available litterature. Documented physical effects include changes in salinity, modified current systems and changes in temperature caused by altered mixing depth following a regulation. Oxygen levels of the deeper layers in fjords with shallow sills may be altered. The possibility of changes in the vertical transport of nutrients to the euphotic layer is discussed. Notes are made on changes in temperature, nutrient supply and material load from regulated rivers. In light of these physical changes, possible biological implications are discussed though biological data are insufficient. The differences in characteristics among fjords are stressed, with special emphasis on varying influence by the outer coastal waters