Cassava and caesar weed are among the mainly products of the familiar agriculture in the Northeast of the Pará State. To treat these products the small farmers used to sink amounts of cassava and caesar weed in small streams (regionally named as "igarapés"), to make peal softer and remove its toxic compounds, in the case of cassava, or to promote defibrating in the case of the caesar weed. The effects of these practices to the stream water quality are poor known. In this context, this study aimed to evaluate the potential impacts of these practices to the fluvial hydrobiogeochemistry in the "igarapés" of these region. We adopted the strategy of collect stream water samples before the washing point of these products, in the washing point, and ten meters after this point. For a clearer understanding of the feasible alterations of the water chemistry due to cassava and caesar weed washing it was conducted besides the field monitoring a controlled input and output discharge tank experiment. In both approaches it was measured in the dissolved material the following hydrobiogeochemical: pH, electric conductivity, dissolved oxygen, calcium, magnesium, potassium, sodium, chloride, sulfate, phosphate, nitrate, ammonium, as well as total nitrogen total and organic and inorganic carbon. Our results point out that these cassava and caesar weed washing processes contribute to alter the fluvial hydrobiogeochemistry of these small streams only locally. However, some of the observed local alterations remained along at least ten meters downstream the products washing points. In the tank experiments the alteration were observed clearer and a cluster analysis confirmed the hypotheses that these rude treatments of the studied agriculture products contributes to change the fluvial hydrogeochemistry of the monitored small streams. The study recommends some precautions regarding to the evaluated products treatments and also the adoption of some parameters measurements to monitor these impacts.
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