摘要
This study aimed to evaluate the external and internal fluxes of nutrients of an urban eutrophic reservoir （lbirit6 reservoir, SE-Brazil）. External loads were estimated in the tributaries （Pintados and Ibirit6 creeks） through nutrient concentrations and discharge measurements. Using Fick＇s law, internal loads were estimated in the reservoir from fluxes across sediment-water interface from nutrient concentration gradients between the pore water and the water. The Ibirit6 creek （urban sewage recipient） contributes with 72%-47% of ammonium （NH4^＋） and 100%-8% of SRP （soluble reactive phosphorus） of the total quantity entering the reservoir, whereas the Pintados creek （oil refinery effluent recipient） contributions are 20%-19% and 44%-100%, respectively. Despite the high external loads （130 and 2.2 ton-yr^-1 of NH4＋ and SRP, respectively）, internal loads （average flux of 120 and 2 mg·cm^-2yr^-1, respectively） correspond to 25% of the total external loads which may sustain a high productivity in the reservoir for a long time even if the external loads are controlled. The stocks of ammonium and SRP of the interstitial water （100 cm of sediment） would be released to the water in six years and five months, respectively, The release time would be extremely larger （〉 3,000 years） considering the stocks of total N and bioavailable P.
