The process of biomass formation as the key point in the restoration of tropical eutrophic lakes

Abstract

The paper presents initially some specific features of tropical lakes (high recycling rates, elevated primary production during the whole year, high nutrient assimilation, high settling velocity of nutrients, intense organic matter decomposition, high grazing rates), which leads to the establishment of a very dynamic ecosystem. Due to these characteristics the warm water lakes show completely different reactions to the impacts derived from the phenomenon of eutrophication in comparison with lentic systems situated in temperated regions. Moreover in shallow lakes occurs an almost permanent mixing process, which in its turn allows the resuspension of nutrients and a consequent increase in the primary productivity. The key point at the study of the eutrophication of tropical lakes is the comprehension of the complex relationship between nutrient concentration and biomass formation. The paper presents the result of some studies carried out by the author in Brazilian lakes and reservoirs, leading to the conjecture that the nutrient mass in a water body is often not directly linked with the phytoplankton growth. The strategies for the recovery of degraded tropical lakes should hence be directed towards a control of the formed biomass and not to a limitation in the nutrient input, as is usually the case in cold water lakes.