SEASONAL AND LONG-TERM TEMPORAL PATTERNS IN THE CHEMISTRY OF ADIRONDACK LAKES

There is considerable interest in the recovery of surface waters from acidification by acidic deposition. The Adirondack Long-Term Monitoring (ALTM) program was established in 1982 to evaluate changes in the chemistry of 17 Adirondack lakes. The ALTM lakes exhibited relatively uniform concentrations of SO42-. Lake-to-lake variability in acid neutralizing capacity (ANC) was largely due to differences in the supply of basic cations (Ca2+, Mg2+, K+, Na+; CB) to drainage waters. Lakes in the western and southern Adirondacks showed elevated concentrations of NO3-, while lakes in the central and eastern Adirondacks had lower NO3- Concentrations during both peak and base flow periods. The ALTM lakes exhibited seasonal variations in ANC. Lake ANC was maximum during the late summer or autumn, and lowest during spring snowmelt. In general Adirondack lakes with ANC near 100 mueq L-1 during base flow periods may experience decreases in ANC to near or below 0 mueq L-1 during high flow periods. The ALTM lakes have exhibited long-term temporal trends in water chemistry. Most lakes have demonstrated declining SO42-, consistent with decreases in SO, emissions and SO42-in precipitation in the eastern U.S. Reductions in SO42- have not coincided with a recovery in ANC. Rather, ANC values have declined in some ALTM lakes. This pattern is most likely due to increasing concentrations of NO3- that occurred in most of the ALTM drainage lakes.