L. Hably szerk.: Studia Botanica Hungarica 23. 1992 (Budapest, 1992)

Stollmayerné Boncz, Emilia: The alga species of the Csömör pool II.

STUDIA BOTANICA HUNGARICA (Antea: Fragmenta Botanica) XXIII. 1992 pp. 17-48 The alga species of the Csömör pool II By E. STOLLMAYER-BONCZ (Received 30 May, 1991) Abstract: Near Csömör (Pest County), a site surrounded by agricultural areas, has been under protection of the county administration since 1977. Part of this area, the so-called Csömör pool is a peaty, marshy area. Higher plants of the region as well as some algal species have already been published by the author, and the consequences of an ecological stress which occurred in February of 1987, were studied with special regard to algal species. Among the 111 species investigated, 17 are registered as definitely rare in Hungary. The species Oedogonium inversum f. subclusum is regarded as a new record, on the basis of the monograph Flora et Iconographia Algarum Hungáriáé. The geographical conditions around the Csömör pool have already been described in two papers STOLLMAYER-BONCZ (1982,1988). The study area is located in the left-side secondary valley of the "Forrás" brook (Csömör brook) in the Pest Plain with varied surface morphology, situated within the riparian floodplain of the River Danube, dissected by talus remnants (Map 1). CHANGES IN THE ECOLOGICAL CONDITIONS OF THE POOL In the years 1984-85, the pH of the water fluctuated between 5.5-6, with a mean value of pH 5.7. The environs of a high voltage electric pole set up in the southern part of the pool is marked by giant specimens of Populus alba and Salix sp. In course of the unusually cold winter of 1987, weather conditions in January and February lead to complete freezing of the pool. The authorities seized the opportunity and had the trees cut. The twigs clipped off detached from the logs were left remaining on the ice. By the end of the season, the vegetation of the pool took flames and was burnt to ashes. By early spring, catastrophic circumstances ruled around the pool. Young trees and bushes of Salix sp. and Populus sp. on the small island in the pool got badly burnt, the thicker pieces remaining in charred state until now. The considerable amount of wooden debris and vegetable ash, resulting mainly from vestiges of Typha species, served as a heavy dose of artificial fertilizer (mainly potassium). Huge amount of snow and early spring precipitation raised the water level to flooding. The island with Sphagnum species could not raise to the elevated water level unlike in previous years. By May, it was already