Peterson, Spencer A., David P. Larsen, Steven G. Paulsen, N.Scott Urquhart. 1998. Regional lake trophic patterns in the Northeastern United States: Three approaches. Environmental Management 22(5):789-801.
During the summers of 1991-1994, the environmental Monitoring and Assessment Program (EMAP) conducted variable probability sampling on 344 lakes throughout the northeastern United States. Tropic state data were analyzed for the Northeast as a whole and for each of its three major ecoregions--the Adirondacks (ADI), the New England Uplands (NEU) and the Coastal Lowland and Plateau (CLP)--and inferred to the entire population of lakes <ha (N=11,076). Results were compared to a large, nonrandomly sampled data set for the same area compiled by Rohm and others and contrasted with lake trophic state information published in the National Water Quality Inventory: 1994 Report of Congress 305(b) report. Lakes across the entire Northeast were identified by EMAP data as 37.9% (±8.4%) Oligtrophic, 40.a%(±9.7%) mesotrophic, 12.6%(±7.9%) eutrophic, and 9.3%(±6.3%) hypereutrophic. Lakes in the ADI and NEU generally are at a low, nearly identical trophic state (96% oligotrophic/mesotrophic), while those in the CLP are much richer (45% eutrophic). EMAP results are similar to results of the Rohm data set across the entire region. In the CLP, however, EMAP identified approximately 45% of the lakes as eutrophic/hypereutrophic, while the Rohm data set identified only 21% in these categories. Across the entire Northeast, the 305(b) report identified a much higher proportion (32.2%) of lakes in eutrophic condition and a much smaller proportion (19.8%) in oligotrophic condition than did the EMAP survey data (12.5% ± 7.9% and 37.9% ± 8.5%, respectively ). Probability sampling has several advantages over nonrandom sampling when regional resource condition assessment is the goal.