NITROGEN-BALANCE IN THE LOWER FRASER-RIVER BASIN OF BRITISH-COLUMBIA

A study was conducted to determine the extent of nitrogen pollution in agricultural lands in the Lower Fraser River basin of British Columbi a, Canada. The specific objectives were to determine the distribution of leachable nitrogen and estimate the nitrogen concentration in groun dwater recharges. Nitrogen and water mass balances were conducted on t he entire basin and on each of the four districts comprising it over t he period 1971-1991 in intervals of five years. The results indicated that the average nitrogen concentration in the groundwater recharge fo r the entire basin rose from nondetectable in 1971 to 6 mg/liter in 19 91. Estimates for the individual districts ranged from 4 to 14 mg/lite r in Central Fraser and from nondetectable to 7 mg/liter in Fraser-Che am and 3 mg/liter in both Greater Vancouver and Dewdney-Alouette. So f ar, excessive levels of nitrogen are confined to Central Fraser. Altho ugh they have remained within the acceptable range, nitrogen concentra tions in the other three districts have definitely increased over the 20-year study period. Sensitivity analyses indicated that animal manur e and fertilizer had the largest contribution in groundwater recharge. Decreasing the rate of manure application to agricultural lands is su ggested as the most practical way of reducing nitrogen pollution in Ce ntral Fraser.