Carbon content and composition of zooplankton fractions in two reservoirs of Central Brazil: Serra da Mesa and Manso

At present, large reservoirs in many watersheds o f all continents number more than 50 000. Many smaller reservoirs (volume: 106-108 m3 and area: 1-102 km2) have been built in semiarid regions of both tropical and temperate latitudes, in rural as well as urban areas, to collect surface water for multiple uses. Reservoirs interfere with al! major biogeochemical cycles such as that of nitrogen, phosphorus and carbon, in addition to the cycles of other elements such as Fe, Mn, Ca and Mg. Reservoirs also interfere with gas exchange between the atmosphere and water and can be a source of gas emissions to the atmosphere, especially in regions where vegetation from the watershed was not previously removed. Some studies on gas emission by reservoirs (DucHEMIN et al. 1995, MATVIENKO et al. 2000, ROSA et al. 2002, 2004) demonstrated a need to further understand the carbon cycle in reservoirs and the nature and amount o f gas emissions from these artificial ecosystems. In addition to the water/atmosphere interaction and the CH4 and C02 emission amounts coming from reservoirs, the ro le o f organisms in this cycle must be evaluated, especially in the case o f planktonic organisms due to their capacity for rapid cycling o f carbon, and also to the relationship of carbon to the trophic state o f the reservoir. Ihis paper describes and discusses the ro le o f zooplankton biomass and its carbon content in the carbon cycle as well as gas emissions o f two reservoirs in the tropical region ofBrazil.