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