A technique for building of generalized intra-annual dynamics of biogenic elements concentrations in river run-off is presented. The dynamics is necessary as external factor for simulation of aquatic ecosystems functioning. Algorithms of determination of degree of anthropogenic influence upon the biogenic elements concentrations in river water and revealing of natural part of total biogenic run-off are considered. A method of intra-annual hydrological phases revealing and the data assignment to the phases is presented. Statistical analysis of the data statistical homogeneity is discussed.