Distribution and biomass of submerged macrophytes in Neusiedlersee

Within the area of the open, reed-free zone in Neusiedlersee there exists a clearly defined region with Myriophyllum spicatum L. and Potamogeton pectinatus L. Phytosociological estimates, quadrat counts and direct harvest methods have been combined over a 3-year period in order to estimate the extent, density and production characteristics of the zone. Quantitative studies have been concentrated on the northern part of the lake which the previous survey (Schiemer and Weisser, 1972) had indicated as the major zone of macrophyte growth. Evidence is presented for a distinctive inshore-offshore distribution of M. spicatum. The interaction of wave action and sedimentation rates of fine inorganic material is considered to be principally responsible for this pattern as well as for the overall distribution of both species. However, the distribution pattern of P. pectinatus shows a lesser degree of dependence upon such factors. Computations of the total biomass and annual production of macrophytes within the lake are presented and a comparison is attempted between the status of macrophyte production within Neusiedlersee and that estimated for other shallow lakes. The constant reduction in extent of the macrophyte belt during the observation period is discussed in relation to the artificial increase in water level and eutrophication phenomena (significantly increased phytoplankton and epiphytic algae) during recent years.