| Abstrakt: |
An account is given of changes in water chemistry and algal vegetation in one Thailand deepwater rice field (Huntra) through the 1983—1984 flood season, together with comparative observations at this and two other sites in September 1982. The Huntra field had standing water for almost six months (July—January), reaching a maximum depth of 175 cm in late October. The attached algal vegetation was dominated by heterocystous species of blue-green algae throughout the period, suggesting the importance of nitrogen fixation; the most abundant genera were Nostoc, Gloeotrichia, Aulosira and Anabaena, (in decreasing order). Green algae were the next most important phylum, with Bulbochaete and Oedogonium predominant. Diatoms showed an obvious increase in abundance in October, but even then formed a small part of the algal biomass in comparison with blue-green and green algae. The algal vegetation at two other sites, including one on acid sulphate soil, had a quite similar algal vegetation, in spite of obvious differences in water chemistry. Azolla pinnata reached a density of 223 individuals m-2 at one site, but was absent at the other two sites. |
