Study

Remedial measures connected with aquatic macrophytes in Norwegian regulated rivers and reservoirs

  • Published source details Rørslett B. & Johansen S.W. (1996) Remedial measures connected with aquatic macrophytes in Norwegian regulated rivers and reservoirs. Regulated Rivers-Research & Management, 12, 509-522.

Summary

Action: Actively manage water level (stabilize)

A before-and-after study of an upland reservoir in Norway (Rørslett & Johansen 1996) reported that after reducing the magnitude of water level fluctuations, macrophytes grew in shallower areas and some new species colonized. Between 1915 and mid-1982, the water level in the reservoir fluctuated by around 7 m through the year, with an extensive winter drawdown. Aquatic macrophytes were present only in a zone between 5 and 16 m below the average annual water level (<30% cover). From mid-1982, the water level was stabilized, fluctuating by only 1.6 m through the year. After 11 years, aquatic macrophytes were present between 0 and 12 m below the average annual water level (<4% cover). Shallower zones that were previously scoured by ice in the winter could now support vegetation, but deeper zones now received too little light to support vegetation. New macrophyte species that appeared in the reservoir after stabilization included quillworts Isoetes spp. (at or just above the mean average water level; <15% cover), floating bur-reed Sparganium angustifolium and hooked water starwort Callitriche hamulata. Methods: Macrophytes were surveyed in Hartevatn Reservoir in 1976 and 1993. The study does not report details of survey methods.

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