THE TEMPORALLY INTEGRATED MONITORING OF ECOSYSTEMS (TIME) PROJECT DESIGN .2. DETECTION OF REGIONAL ACIDIFICATION TRENDS

The Temporally Integrated Monitoring of Ecosystems (TIME) project util izes a hybrid sampling approach to achieve its goal of assessing wheth er emissions controls, mandated by the Clean Air Act Amendments of 199 0, have had their intended effect on lakes and streams. A randomly pla ced triangular grid is used to select, with known probability, lakes a nd streams for sampling on either an annual basis (in the case of acid -sensitive sites) or on a 4-year rotation. Data from these sites will be used to detect trends in regional characteristics of the target pop ulations. The ability of TIME to detect trends in acid-neutralizing ca pacity (ANC) and SO42- is dependent on the amount of variability (year -to-year, site-to-site, within-season, and site-by-year interaction) e xhibited by the sites. In particular, high levels of year-to-year vari ability lead to very low power to detect trends. One method to minimiz e year-to-year variability is to group together sites with similar cha racteristics. By performing trends tests on seven separate subpopulati ons the TIME design for northeastern U.S. lakes is predicted to bs abl e to detect trends of the expected magnitudes in ANC (0.5 mu eq L(-1) yr(-1)) and SO42- (1.2 mu eq L(-1) yr(-1)) with power at or above the 0.90 level and alpha = 0.10.