Maximum allowable phosphorus load in the Piraquara II reservoir, a TMDL process application

For the implementation and operation of the Brazilian Federal law on water resources of 1997 it is indispensable to use planning tools that take into account the effect of all activities or processes that cause or contribute to the loss of quality of a waterbody. For this purpose, the nutrient phosphorus was evaluated by the TMDL (total maximum daily load) process developed by the United States Environmental Protection Agency - EPA in the drainage area of contribution to the future Piraquara II Reservoir, Piraquara River Watershed, Paraná State, Brazil. The TMDL process determines the maximum amount of a pollutant load a waterbody can receive without violating the established water quality standards, and allocates loads of this pollutant between point and nonpoint sources. In the present research the TMDL methodology was used to demonstrate its usefulness in the management of water resources. Sceneries of soil use were simulated by mathematic modeling to define a total phosphorus concentration in the reservoir under the limit range for eutrophication established in the study (0.025-0.10 mg L-1 of P). The current soil use was simulated aiming to foresee the initial condition of water quality in the waterbody. The data obtained indicate that the resulting total phosphorus concentration in the reservoir did not meet the established standard. In a second simulation with adoption of potential control measures, such as recomposed riparian areas and no-till systems, the exportated total phosphorus load from the watershed decreased. With adoption of such conservation measure the simulated water quality of the reservoir improved and attained the established standard, demonstratig the applicability of the methodology.

water quality; water resource planning; watershed management

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