Research was carried out in Udorn Thani beginning in September, 1975, in order to elucidate the effects of seasonal changes on the aquatic community of a rice field. Physical and chemical changes that occur during the course of a year were recorded and related to the structure and activity of the aquatic biological com munity. A rice field was selected that is typical of the countless habitats of this kind that are found in Northeastern Thailand (Fig. 1). For a variety of reasons these habitats and their location are of special interest (Fig. 2). Figure 1. The rice field investigated, north...