Relationship between nitrogen and the Zahuapan River microbasins, Mexico.

Abstract

Agricultural and wastewater discharges are significant sources of nitrogen in streams and rivers. The aim of this study was to spatially and temporally describe the concentrations of nitrogen species in the Zahuapan River and their relationships with some of the attributes of the microbasins, including area, slope, vegetation cover, agriculture, soil erosion, population and pluvial precipitation. The polygons for the Zahuapan River microbasins were defined using the TAS program. The results showed that nitrogen concentrations diminished in the microbasins located near the Atlangatepec dam. The concentrations were highest during the years 2001 and 2002. Concentrations of NT, NTK, N-NH3, and Norg increased during the dry months while N-NO3 and N-NO2 decreased during this period of the year. The relationship between concentrations and monthly precipitation resulted in a greater number of significant coefficient correlations than for daily precipitation. The correlation coefficients for nitrogen species were significant at the 0.05 level. The multiple regression analysis N-NO3 = A0 + A1*NT + A2*N-NH3 + A3*Norg showed coefficients greater than 0.5 in 9 to 12 microbasins. This study concluded that the Atlangatepec dam plays a role in the concentration of nitrogen in the Zahuapan River.