Aquatic plant monitoring in the river basin Leira-Nitelva

Summary

The aim of the project was to survey aquatic macrophytes and assess the ecological status of five stations in the lower part of Nitelva and in Svellet. The turbid water affected the distribution and species composition of aquatic macrophytes. Floating leaved species dominated, mainly Nuphar lutea, Sagittaria sagittifolia, Potamogeton natans and Sparganium emersum, and submerged species able to tolerate low light conditions, such as the elodeids and canopy forming Potamogeton obtusifolius and Stuckenia pectinata. Small areas with isoetids were found in shallow water and in areas with better light conditions. The lower part of Nitelva and Svellet were surrounded by large stands of helophytes, dominated by Equisetum fluviatile, Typha latifolia and Schoenoplectus lacustris. Based on the trophic index TIc, ecological status for aquatic macrophytes was assessed as poor or bad for most stations, except for Kjellerholen, which had moderate status. Ecological status in Svellet was poor. Dynea effluent did not seem to have any significant effect on the ecological status of aquatic macrophytes. The macrophytes at D3 (effluent site) did not grow as deep as in the upstream and downstream stations. D3 was a more sheltered site than the main channel of Nitelva, and thus may be more turbid, or had a substrate unsuitable for macrophytes. In general, the species richness was higher in 2020 compared to 2017. Ecological status for aquatic macrophytes showed a small decrease compared to 2017. However, the data were not completely comparable in Svellet due to higher sampling effort in 2020.