The expansion of the agricultural frontier in the west of Pará in recent decades has changed the landscape once occupied by family agriculture or forests, causing environmental changes impacting on water resources. The study evaluated the quality of water of 24 micro watersheds under different land uses: natural/reference area (Flona Tapajós), traditional agriculture (PA - Moju) and recent mechanized farming and old soybean crops (Highways Curuá-Una and BR-163, respectively), based on Conama Resolution nº357/05, in Santarém and Belterra (PA). The samples were collected in October/11 and April/12. Analyzed parameters: pH, color, turbidity, TDS, DO, BOD, nitrate, nitrite, ammonia nitrogen, total phosphorus, chlorophyll-a and fecal coliform. Comparing the results to the resolution, it was found that in the dry period six micro watersheds from Flona Tapajós and one from PA-Moju had concentrations below the permissible limits for DO. Only one micro watershed (BR-163) showed pH within the acceptable range, and all the micro watersheds from PA-Moju exceeded the limit for chlorophyll-a. The color showed inconsistency in four micro watersheds of Curuá-Una, during the rainy season. Human activities are causing siltation and supply of compounds and nutrients to water resources, promoting their degradation. Resolution nº 357/05 needs to be adjusted for the Amazon region, since some parameters that presented values in violation of the law reflect natural conditions of the region.
Water resources; Land use; Limnology
