Padrões de produtividade primária fitoplanctônica na Lagoa Carioca - parque estadual do Rio Doce (PERD) - MG

Abstract

The study of aquatic ecosystems metabolism is one of the main objectives of the world limnological research. In this case, primary productivity (PPR) is the basis for a detailed study of the mechanisms controlling the energy transfer during the cycle of organic matter. To understand the contribution of phytoplankton in the flow of energy is essential for a sustainable use and management of water systems, reducing the deposition of nutrients and improving water quality. Lake Carioca, chosen as experimental lake for the present work is an environment with relatively small proportions, located in a protected area and, because of that, allows the development of studies capable to identify patterns such as productivity primary rates. The proposed study is based on the analysis of monthly measurements of PPR, performed between August 2004 and September 2007. During this period, the estimate of the PPR was based on the C-14 technique described by Steemann-Nielsen (1952), at a sampling station in the central of the lake. The project aims to: i)identify annual, seasonal and daily patterns of primary production, ii) to correlate the results observed for PPR with other biotic and abiotic variables monitored during in this period, iii) obtain the rate of assimilation for the whole sampling period and compare them with values recorded in the past in order to demonstrate the ecological consequence of a possible change in the structure of the phytoplankton community. The major findings are: i) seasonal variation in several physical and chemical parameters allowing for the characterization of the lake as an oligotrophic one as judged by dissolved nutrients, besides an indication of nitrogen and phosphorus limitation; ii) significant changes in the phytoplankton community in the last decades, probably related to the introduction of exotic fish species; iii) increase in PPR with rates ranging from 0.14 to 1019.5 mgC/m³/h suggesting a clear indication of seasonal and depths variation while there was niether significant variation between periods of the day nor between years; iv) correlation of PPR with pH, temperature, chlorophyll-a, phytoplankton, concentrations of ammonium-nitrogen and soluble reactive phosphorus v) extreme changes in assimilation number, probably due to changes in trophic state of the environment and not the replacement of the phytoplankton community.