Hydropower is the main source of energy supply in Norway and is predicted to increase by 73 % worldwide in the next 10-20 years. Adverse environmental impacts from hydropower production, such as fish migration barriers, changes in sediment dynamics and altered discharge regimes,are known and addressed in Norway. However, impact caused by supersaturation of dissolved gasses (TDGS) is mostly overlooked. It occurs when entrained air dissolve in water under high pressure in the tunnel system of hydropower plants. The water becomes supersaturated when the hydrostatic pressure decreases as the water exists the tunnel.

Exposure to TDGS negatively affects aquatic biota primarily through the formation of bubbles (gas bubble disease). This causes acute fish kills or sub-lethal effects, such as increased susceptibility to diseases and changes in behaviour and habitat use. During the most recent years, TDGS has been detected in several Norwegian rivers and preliminary studies indicate adverse effects on the fauna. However, the extent and biological effects in Norway and most other parts of the world are unknown. Especially, little ittle is known about the effects and the sensitivity involved for species in European rivers.

The overall aim of SUPERSAT was to reveal biological impacts of gas supersaturation at the individual and community scales and identify effective mitigation measures. We analyzed the extent of TDGS in Europe and identify hydrological events causing TDGS in hydropower plants with the aim of improving technical solutions to avoid TDGS. Hence, the project delivered the basis for mitigation and improved solutions supporting a more sustainable and environment-friendly development of the hydropower industry.

Project PIs: A. Lorke (co-PI)

Key publications:

• Pulg, U., Lennox, R. J., Enqvist, M., Stranzl, S. F., Espedal, E. O., Schwarz, M., Lorke, A., Flödl, P., Hauer, C., Schletterer, M., Halleraker, J. H., & Velle, G. (2024). Assessing the potential for gas supersaturation downstream of hydropower plants in Norway, Austria and Germany. Science of the Total Environment, 948, 174645. https://doi.org/10.1016/j.scitotenv.2024.174645