PRODUCTION AND REDUCTION OF GEOSMIN AND 2-METHYLISOBORNEOL DURING STORAGE OF RIVER WATER IN DEEP RESERVOIRS

The Water Storage Corporation Brabantse Biesbosch manages three interconnected deep reservoirs in the south western part of The Netherlands. These reservoirs, with a total retention period of five to six months, are employed for storage and upgrading of polluted and eutrophic water from the River Meuse. In the first two reservoirs, with a total retention period of 4-5 months, probably due to adsorption/settling and biodegradation there is a reduction of geosmin and 2-methylisoborneol (2-MIB) down to 1-2 ng/l, i.e. 60-70% of the concentration in the river water. In the last reservoir Petrusplaat a large benthic cyanobacterial population consisting of various Oscillatoriaceae produces geosmin from February till June. In 1984 this production resulted in an average concentration of 6 ng/l, i.e. 5-6 times the concentration of the inlet of this reservoir. Since 1985 cyanobacterial growth is controlled by rooting up the bottom with a harrow. This resulted in average concentrations of 1-3 ng/l, i.e. twice the average concentration of the inlet. No further reduction of 2-MIB has been observed in this reservoir. It is concluded that storage of eutrophic river water in deep reservoirs reduces the concentration of geosmin and 2-MIB. Autochthonous production however may interfere with this water quality improvement.