ACID PRECIPITATION-RELATED CHEMICAL TRENDS IN 18 RIVERS OF ATLANTIC CANADA - 1983 TO 1992

Using non-parametric techniques, we studied water chemistry changes fr om 1983 to 1992 in 18 rivers located at the extreme northeastern porti on of North America. This period was marked by a decrease in sulfate ( SO4-2) production in eastern Canada from 1982 to 1986, followed by a l evelling off from 1986 to 1992. Nitrate (NO3-) production and depositi on generally increased over this whole period. We used two time window s, 1983 to 1989 and 1983 to 1992, to determine if changes in river aci dification variables occurred over the ten year period. We found signi ficant trends of increasing pH and acid neutralization capacity (ANC) concentrations at eight sites using both time windows, while SO4-2 inc reased at five and seven sites during the same two time periods. Nitra te concentrations showed few consistent trends, while base cations sho wed increases in the earlier part of the data set and total organic ca rbon (TOC) showed long-term decreases. There were few significant tren ds in hydrogen (H+), and a slight decrease in SO4-2 exports as opposed to increased concentrations over the same period. We attribute the di screpancy between SO4-2 concentration and export trends to be due to e vapotranspiration in the basins, causing a concentration of ions in wa ter. Nitrate and calcium exports showed no trends, while TOC decreased at four or five sites, depending on the time window used. Longer data sets tended to produce more detectable trends. Overall, water chemist ry in the region is showing the effects of reduced SO4- loads and is n ot yet being affected by the increases in NO3- deposition.