Aquatic macrophytes in lake Svanevatn

Summary

Svanevatn is part of the Nautå Nature reserve and is a “selected habitat type” according to the Nature Diversity Act. The lake is affected by the upgrading of the Evenes air base. The aim of the project has been to survey the aquatic macrophytes, with special focus on the status of charophytes, and assess if the development of the air base has affected the charophytes. The charophytes in Svanevatn grew in large, healthy stands when examined in September 2020, dominated by Chara hispida. Most charophyte species, particularly C. hispida, were heavily encrusted with lime, which seemed to have developed naturally due to intense photosynthesis. Based on the trophic index TIc, ecological status for aquatic macrophytes is assessed as high. However, the index value was somewhat decreased compared to earlier years. Dense covers consisting of diatoms and the cyanobacterium Phormidium sp. were observed on both plants and lake sediment. While these generally occur naturally in highly calcareous lakes, when increased growth is observed, it may also indicate some nutrient enrichment. The occurrence of Chara contraria indicates that the lake still is a “selected habitat type”. The stone filling in the southwestern part of the lake seems to have had little impact on the macrophytes. Because of the decreased TIc, combined with the observation of dense covers of diatoms and cyanobacteria, which both could indicate some nutrient enrichment, a monitoring program should be developed for Svanevatn, which includes biology and water chemistry surveys, in addition to mapping the pressures from the catchment.