Estratégias para o monitoramento da qualidade da água em bacias rurais de cabeceira

Abstract

Quality of natural waters is dependent on geomorphological and edaphoclimatic characteristics of each watershed. These characteristics provide a pattern of regularity in water quality over time, affected by season and rain intensity. The variation in water quality is influenced, mainly, by anthropic actions. The population development is conditioned to the presence of water, negatively impacting the environmental quality, due to high polluting loads that return to water courses. In the agricultural environment, application of high doses of inputs may degrade water quality since these inputs can be lost by leaching or surface runoff. The objective of this dissertation was to understand hydrosedimentological factors and processes that influence water quality of a small rural watershed with intense changes in land use and management, to search for monitoring techniques capable of better identifying spatiotemporal changes in the evaluated parameters. Monitoring was divided into three strategies. The first one had the objective of evaluating surface and groundwater characteristics of the rainy season, with a monthly interval for approximately one year. During this period, water supplied to the rural community was also evaluated, comparing the characteristics of water from three sources with the national legislation standards. Considering the influence of surface runoff on water quality, the second period had the objective of identifying changes in water quality characteristics during rainfall events, also characterizing the scale effect during monitoring. The third period was to evaluate historical data of the long period, low sampling frequency monitoring in the watershed. The parameters that most interfere in the variation of the surface and ground water quality during the base flow were the biological parameters, phosphorus and the turbidity, which are above the standard established by the current legislation CONAMA 357 for most of the analyses. During rainfall events, the behavior of some parameters of water quality changes significantly with the hydrograph and sedimentograph, also varying according to the area of contribution for each sampling point. The main parameters that increased along with the hydrograph rise were turbidity, total and soluble P, Fe and K; Cu and Zn parameters showed no variation during the event; while total dissolved solids and oxidation potential presented a dilution behavior. The identification of changes in water quality according to changes in soil use and management for the studied basin was not possible through the use of low-frequency monitoring. Studies using the monitoring of variable scales, with multiparameter probes, sub-daily discretization and during events are stimulated by allowing the best characterization of the process, allowing modeling to propose scenarios indicating the main sources of pollution and helping in the definition of practices capable of reducing environmental degradation