We present the original results of set of toxicity tests of the herbicide Paraquat, used in sugar cane fields, and the cultivation of pineapple and ,i>Eucalyptus, on zooplankton and benthos organisms from reservoirs of the Brazilian Northeast Littoral Zone. We demonstrate that Macrobrachium amazonicum (prawn), Pomacea lineata (snail) and Daphnia similis (cladoceran) are several orders of magnitude more sensitive than test organisms (aquatic insects, amphipods, and cladocerans) classically used in temperate regions. Combining typical herbicide application data together with rainfall and water level seasonality of Gramame Reservoir, we emphasize highly fluctuation patterns of toxicity for the other reservoirs in the region. Therefore, they urge the enforcement of management policies based on the implementation of a watershed-scaled biomonitoring program using the here employed test organisms. Reservoirs of the Brazilian Northeast was deteriorating (eutrophication, pollution; including frequent cyanobacteria blooming, often toxic), and multi-use management, particularly to meet the water drinking demand of rural and urban populations, is now a crucial need. The suggestion of implementing a biomonitoring program based on toxicity tests of particularly sensitive organisms are then more appropriate than a costly large-scale high technology program. The use of locally dominant organisms instead of temperate standards is essential. The demonstrated high sensitivity of Daphnia species to Paraquat may well explain why rotifers often dominate the zooplankton in reservoirs of this region, as herbicides and pesticides are widely as well as intensively used in the Northeast Semi-Arid Regions (e.g. Agreste and Sertão).
