Aquatic systems in semi-arid Brazil include natural shallow lakes, artificial reservoirs and intermittent streams and rivers. These systems are distinctive features in the semi-arid landscape and comprise a range of associated systems functioning as an ever-changing mosaic of dry/wet patches. Lakes and reservoirs in semi-arid Brazil are subject to important periods of water shortages, whereas rivers and streams are characterized as highly variable and driven by the extremes of water flow and its absence. Within this view a catchment-scale approach must be used to create a holistic model to conceptualize and comprehend these aquatic systems, since the aquatic environment types in the semi-arid region of Brazil incorporate broader aspects within the catchment scale such as geomorphology, vegetation, climate and land use. This paper summarizes some of the information on the aquatic systems of the Brazilian semi-arid region and shows the importance of limnological studies in this region. It also attempts to establish perspectives for future research considering the catchment as a scale for surveying biological processes and limnological characteristics of the various aquatic systems. It is presented information on their overall structure and functioning, as well as characteristics of some biological communities, such as phytoplankton, periphyton, aquatic macrophytes, benthic invertebrates and fish. The importance of the understanding of eutrophication in reservoirs and the role of the dry phase in streams is emphasized, and information on possible actions of planning and management to improve water quality of reservoirs are presented.

Avaliou-se neste estudo a eficiência de sistemas compostos de duas espécies de macrófitas aquáticas flutuantes (Eichhornia crassipes e Pistia stratiotes) no tratamento de efluentes gerados por um viveiro de manutenção de reprodutores de camarões-canela (Macrobrachium amazonicum). Os sistemas de tratamento foram constituídos de 12 unidades experimentais com as macrófitas aquáticas e três sem plantas (controle). Foram analisadas amostras da água de abastecimento do viveiro de criação de camarões-d'água-doce, do efluente gerado e dos efluentes tratados. A remoção de nutrientes não diferiu significativamente entre as duas espécies vegetais. As maiores remoções foram obtidas para fósforo total (41,9% pelo controle; 71,6% por E. crassipes; 69,9% por P. stratiotes; 72,5% por E. crassipes + P. stratiotes e 72,1% por P. stratiotes + E. crassipes) e para turbidez (30,6% pelo controle; 80,2% por E. crassipes; 75,2% por P. stratiotes; 79,8% por E. crassipes + P. stratiotes e 81,5% por P. stratiotes + E. crassipes). As macrófitas aquáticas foram eficientes na remoção de nitrogênio e fósforo dos efluentes de criação de M. amazonicum.

Reservoirs play important roles in local socioeconomic development and are particularly relevant in developing countries. The rearing of Nile tilapia (Oreochromis niloticus) in cages is one of the fastest growing activities carried out in reservoirs since it is a strategy to sustain the growing demand for food fish. Most reservoirs are in eutrophic or hypereutrophic conditions in the semi-arid northeast region of Brazil and thus, the expansion of aquaculture endangers the ecological functions of the reservoirs by increasing the eutrophication potential. On the other hand, aquaculture contributes to economic development by generating jobs and income for the population and being an important alternative in the production sector for riverine populations. In this context, we present in this article our opinion about the sustainability of fish farming activities in net cages in reservoirs of the Brazilian semiarid, especially when subjected to extreme drought events.