STUDYING THE LIMITANT FACTORS TO PRIMARY PRODUCTION OF AQUATIC MACROPHYTES IN BRAZIL.

Abstract

The littoranean ecosystems of Brazil generally present vast areas colonized by aquatic macrophyte plants. In this work we present and discuss a number of studies about the main limitant factors to primary production of aquatic macrophyte plants in Brazil, and the underlying effects of human activities. The limitant factors here discussed would include temperature, photosynthetic active radiation, current speed, and available amounts of nitrogen, phosphorus and inorganic carbon. Studies in the field as well as in the laboratory are discussed. Laboratory studies enable assessing the effects of isolated variations in the rearing conditions over the growth of aquatic macrophytes. Such studies are scant in Brazil. Anthropogenic alterations on aquatic ecosystems affect the growth and primary production of aquatic macrophytes. Humaninduced eutrophication promotes the growth of free-floating, emerged, and submerged algae. The construction of dams also interferes on macrophytes growth, because it causes changes in water flow and levels, which are important factors driving the production of these plants. Knowledge about ecology of aquatic macrophytes and limitant factors to their growth in Brazil is poor, as few environments and species were studied, making it difficult to compare results. We would suggest improving the technical formation of researchers, increasing the area of field investigations, increasing the number of laboratory tests with controlled conditions and promoting more scientific gatherings about aquatic macrophytes to amend that knowledge defficiency.