Estimation of Yearly Changes of Waterchestnut Biomass in Lake North Inbanuma based on Landsat TM data

The waterchestnut (Trapa natans var. japonica Nakai) has been dominating the entire in Lake North Inbanuma, Chiba Prefecture, Japan. In order to investigate the seasonal variation of its surface coverage area, photographic recording of surface areas occupied by waterchestnuts in ten quadrats carried out from a boat every two weeks over a period of two years. In addition, the waterchestnuts were sampled to determine the dry weight of each part of them. The seasonal variation of waterchestnut coverage area in all quadrats appears to be bimodal ; there are two peaks which occurred at the end of June and at the beginning of September. During this period, the total biomass estimated from the laboratory measurements of the dry weight of each part of the waterchestnuts is 320g/m2. The geographical distribution of waterchestnuts over the whole lake can be mapped on the basis of the Landsat TM data. The combination of remotely sensed infestation areas with the directly determined coverage areas and dry weight of waterchestnuts allows us to estimate the total biomass in each component of the waterchestnuts in the whole lake.