Differences among Aquatic Plant Communities in Irrigation Ponds with Differing Environments

Abstract

Vegetation and environmental conditions of irrigation ponds in the Saijo Basin, Hiroshima Prefecture, were studied to show the differences among aquatic plant communities in ponds with differing environments. The following three communities were found from mountain ponds to ponds in agricultural land : Brasenia schreberi-Nymphaea tetragona community, Trapa japonica-Brasenia schreberi community, and Trapa japonica community. Species-rich ponds were small and had low electric conductivity values ranging from 17.1-50.6 μS cm^-1. Nuphar oguraense var. akiense, Brasenia schreberi and Trapa japonica occurred in the ponds with a wide range of conductivity. Most of the other species were restricted to water with low conductivity values. The temporal vegetation changes in a pond following surrounding land-use change was similar to the spatial distribution pattern of aquatic plant communities. Plant distribution seems to be influenced not only by water quality but also by other factors such as accidental species dispersal, interspecific competition, allelopathy, aquatic animals, substrate types and pond history. To conserve pond life, both the ponds themselves and the catchment areas must be protected.