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Seasonal and long-term changes in surface cover of aquatic plants in a shallow pond, Abstract Seasonal changes in surface cover and long-term floral changes in aquatic plants of a shallow eutrophic pond, Ojaga-ike, as well as the phenology of each species, were studied . Out of ten floating-leaved and submerged plants, the following five species showed a change in surface cover during 1978 : Potamogeton crispus and Elodea nuttallii occupied 53 .5% of the total pond surface in May, Trapa natans and Nelumbo nucifera 79 .1% in July, N. nucifera and Hydrilla verticillata 62 .0% in September and N. nucifera 41 .2% in November . In addition to dramatic seasonal changes in surface cover, long-term floral changes occurred in this pond from 1971 onwards . While Nymphoides indica, Myriophyllum spicatum and H. verticillata decreased in number and in distribution ranges between 1971 and 1978, two newly established plants, N. nucifera and E. nuttallii, have now become dominant . The alteration in dominance may be due to water level fluctuations and interspecific competition for light . Seasonal changes in water quality during the study period are also summarized .

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