Oxygen conditions

Abstract

Trophogenic and tropholytic processes in Neusiedlersee proceed in a body of water which, due to morphology and wind conditions, exhibits scarcely any vertical oxygen gradient. On the other hand, very distinct horizontal variations in oxygen content occur, due to the presence of the two sub-biotopes, the open lake and the reed belt, each with its own ratio of oxygen-producing and oxygen-consuming processes. The transitional zone linking these two sub-biotopes coincided with the former macrophyte belt (see Chapter 19) adjoining the reed belt on its lakeward fringe, although its position depends upon the wind direction. It can thus shift at times into the reed belt or even be displaced to the open water beyond the former macrophyte belt. At the same time wind conditions determine the intensity with which the transitional zone is developed. As Table 11.1 shows, the oxygen content of the water of the open lake is near to saturation level or even slightly above it (88–105 per cent). Values measured in the bays are usually similar to those found at points remote from the shore. Only in the Hungarian part of the lake is the influence of reed water observable in places remote from the reed fringe. Due to breakdown processes the oxygen content of the reed water is lower than in the lake and is subject to much greater fluctuations (0–70 per cent). Values recorded for the open lake zone in front of the reed fringe (0–1 km) clearly reflect the alternating effects of reed and lake water in addition to the macrophytes (24–125 per cent).