Relationships between land use and macrophyte infestation in the Tucurui reservoir - Para - Brazil

This paper relates changes in land use to aquatic macrophytes infestation in Tucurui reservoir, a Hydroelectric Power Facility located in Pari State, north Brazil. Remote sensing and geoprocessing techniques were used to map the area occupied by different types of land use and macrophytes stands in 1988 and 1994. Thematic Mapper images were used to map three land use classes: forest and pasture subjected to forest regrowth and clean pasture. The images were also used to map and quantify the area occupied by the aquatic plants. Watersheds were used as analytical units to integrate the terrestrial and aquatic processes. The west margin of the reservoir was selected as test site because of the high diversity of land use and the various degrees of macrophyte infestation found in the region. This area was then divided into seventeen watersheds connected to aquatic compartments. The time change in land use for each watershed was computed and compared to the time changes in macrophyte infestation between 1988 and 1994. The total area occupied by aquatic plants decreased around 31 percent along that period. The results supported the hypothesis that the conversion of forestland into pastureland contributed to the preservation of macrophyte stands over the years. Watersheds where the forest was preserved or where large tracts of pastureland underwent forest regeneration tended to present a steady decrease in macrophyte infestation