Monitoring bulbous rush, yearly report 2017

Summary

Four years of monitoring Juncus bulbosus and parameters influencing plant growth at 18 sites in the three rivers Mandalselva, Otra and Tovdalselva show that none of the investigated parameters alone can explain the large differences in biomass between sites with nuisance growth compared to reference sites. Combinations of water chemistry and pore water chemical parameters also cannot explain this difference. The conclusion is therefore that a combination of chemical and physical factors over time has led to the development of the nuisance biomasses we observe today. It is also clear that hydropower not only affects the hydrological regime in these rivers, but also changes the water chemistry; with higher concentrations of the major plant nutrients ammonium and CO2. To better understand and predict the development of nuisance growth in the future, we recommend analyzing ecosystem functions and processes that work in combination and over time. This way, we can better prevent the development of nuisance growth, and also adapt the measures implemented to increase the cost-effectiveness and reduce regrowth after removal.