SUBMERSED MACROPHYTES OF 2 HABITATS IN LAKE CONSTANCE (UNTERSEE) AND THEIR RELATIONS TO CHEMICAL-COMPOSITION OF SURFACE AND SEDIMENT INTERSTITIAL WATER

Habitat conditions of two macrophyte stands in Lake Constance with dif ferent species composition were investigated to find out determinating factors. The results of surface water analyses hardly showed any diff erences. Marked differences were found in chemical composition of sedi ment interstitial water. This was explained by different wind expositi on of the two habitats. One is exposed to the main wind direction and can be characterized as erosion shore, the other one is mostly protect ed against wind and can be characterized as sedimentation shore. In fi rst case, locally produced organic matter is transported away from lit toral zone by autumn storms onto the shore or to deeper sites of the l ake, where decomposition of organic matter takes place. In the other c ase, decomposition of locally produced organic matter takes place dire ctly al production site. This results in high concentrations of ammoni um and sulfid in sediment interstitial water showing strictly anaerobi c conditions, whereas at the wind exposed site only little concentrati ons of ammonium and no sulfid was detectable. Apart from different res istence against wave action of the macrophyte species, different sedim ent interstitial water quality is considered to be the reason for the differences in species composition of the two macrophyte habitats.