Spillage of wastewater treated in rivers, confluence of rivers, drainage of rainwater, washing the surface of river basins, lakes and rivers, etc. Are processes that lead to the concentration or dilution of components in surface water. The study was carried out by laboratory simulations, which allow us to obtain a dynamics similar to those in the water of aquatic objects, the values of the dynamic parameters of the model differing, however, from the authentic ones in the aquatic objects, keeping the trend of dynamics. The study of the nitrification process in samples with different initial concentrations of ammonium ions and organic matter allows us to estimate the impact of these changes on the dynamics of mineral nitrogen in surface water. Changing the redox-reduced nitrogen / carbon ratio does not obviously change the NH4 + full oxidation time. The initial ammonium ion concentration in the samples has a polynomial correlation with the maximum [NO2 -] with an authenticity factor close to Initial concentrations of NH4 + for the probable maxima of [NO2 -] in the water samples in the Dniester, VadulVoda and Rat river, Floresti are not equal, but they are close to values. Instead, the maximum probable values [NO2 -] are obviously different.