COLONIZATION OF SUBMERGED MACROPHYTES IN SHALLOW FISH MANIPULATED LAKE VAENG - IMPACT OF SEDIMENT COMPOSITION AND WATERFOWL GRAZING

The impact of sediment composition and waterfowl grazing on colonizati on of submerged macrophytes in shallow biomanipulated Lake Vaeng was s tudied by means of growth experiments: curly leaved pondweed (Potamoge ton crispus L.) was transplanted to separate pots containing each type of sediment found in Lake Vaeng, and the pots were planted at two loc ations, one sheltered and one exposed. Half of the macrophyte pots wer e behind a fence to protect them against grazing by water-fowl (mainly coots, Fulica atra L.). Sediment composition had some impact on macro phyte growth, being highest on mud from the centre of the lake. The fe nced-in macrophytes became up to 6.5 times longer than the unfenced ma crophytes. It was concluded that macrophytes were able to grow on all substrates present in Lake Vaeng, but waterfowl grazing probably contr olled and delayed macrophyte colonization.