L. Lőkös szerk.: Studia Botanica Hungarica 25. 1994 (Budapest, 1994)

Ács, Éva, Buczkó, Krisztina; Lakatos, Gyula: Changes in the mosaic-like water surfaces of the Lake Velence as reflected by reed periphyton studies

Studia bot. hung.. 25, pp. 5-19, 1994 CHANGES IN THE MOSAIC-LIKE WATER SURFACES OF THE LAKE VELENCE AS REFLECTED BY REED PERIPHYTON STUDIES É. Ács

1

, K. BUCZKÓ

1 and GY. LAKATOS

2 1 Department of Botany, Hungarian Natural History Museum H1476 Budapest, Pf: 222, Hungary ^Institute of Ecology, Kossuth Lajos University H-4010 Debrecen, Pf: 14, Hungary Long-term changes of the reed cover of the Lake Velence (12 years) were summarised for this paper, with emphasis on the results of investigations in 1989 and 1990. On the basis of the analyses it appeared that the water surface of the lake had lost its former mosaic-like character, which was primarily caused by intensive reed harvesting. Due to the scarcity of water since 1989, the salinity of the lake was increasing, as indicated by the increasing relative abundance of Chaetoceros muelleri as well as other factors. Scarcity of water also explains that algal fields detached from the basement are getting wide-spread even in protected areas (still preserving the water quality characteristic of the dark brown water surfaces), especially species of filamentous blue algae. Key words: algae, periphyton, mosaic-like water surfaces, Lake Velence, Hungary INTRODUCTION Lake Velence is the second largest alkaline lake in Hungary. In the formation of the bed of the 10-15,000 years old lake, tectonic forces, eolian processes, as well as the closing of the outlets contributed most. Sodification of the water was largely promoted by the primeval reed field which practically closed the outlets of the lake (FELFÖLDY 1981). The water level of the Lake Velence had considerable changes from time to time, as it is characteristic of sodaic lakes in general and even went dry once in every 100 years. Currently we have information of 13 dry periods. The last desiccation was registered between 1863 and 1866. By the help of the Dinnyés dam and the Dinynyés-Kajtor channel building at the end of the last century, the water level of the lake became regulable. It was further supported by two additional water reservoirs built on the inlet of the Császárstream (Pátka and Zámoly reservoirs). Due to the originally extent reed cover, the water quality of the lake was mosaic-like (FELFÖLDY 1972). On the SW parts, the small inner lakes surrounded by reed fields were characterised by dark brown water, while the water of the open surface at the middle of the lake was grey due to grains of silt perturbed by the wind. Reed fields at the NE parts of the lake enclosed brownish Studia Botanica Hungarica 25, 1994 Hungarian Natural History Museum, Budapest