INTERREGIONAL COMPARISON OF PATTERNS AND TRENDS IN SURFACE-WATER ACIDIFICATION ACROSS THE UNITED-STATES

Temporal trends in acid-base chemistry are reported for surface waters in 6 regions of the United States. The lakes and streams are low ANC, dilute systems, selected to represent acid-sensitive aquatic resource s in the 6 regions. The predominant trends observed were decreases in lake and stream SO42- concentrations in sites east of the Mississippi River, and increases in NO3- in the Adirondack lake and Catskill strea m sites (both located in eastern New York State). Correlations of tren d results from all sites with other factors indicated that trends in p recipitation volume were highly correlated with the observed trend pat terns. From the surface water trend results, three distinct clusters w ere identified that corresponded to three trend patterns: 'dilution,' 'recovery,' and 'acidification.' These were distributed across the LTM regions, with no particular geographic patterns.