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Survey design and extent estimates for the National Lakes Assessment
Citation:
PECK, D. V., A. R. OLSEN, M. H. WEBER, S. G. PAULSEN, C. PETERSON, AND S. HOLDSWORTH. Survey design and extent estimates for the National Lakes Assessment. Freshwater Science. The Society for Freshwater Science, Springfield, IL, 32(4):1231-1245, (2013).
Impact/Purpose:
The US Environmental Protection Agency (EPA) conducted a National Lake Assessment (NLA) in the conterminous USA in 2007 as part of a national assessment of aquatic resources using probability based survey designs.
Description:
The US Environmental Protection Agency (EPA) conducted a National Lake Assessment (NLA) in the conterminous USA in 2007 as part of a national assessment of aquatic resources using probability based survey designs. The USEPA Office of Water led the assessment, in cooperation with USEPA regions, states, tribal nations, and the USEPA Office of Research and Development. The NLA used the National Hydrography Dataset (NHD) as the basis for the sample frame, with the target population being all lakes > 4 ha, excluding the Great Lakes and the Great Salt Lake. An unequal probability survey design was used to select 4472 candidate lakes for sampling. The unequal selection depended on 5 lake size classes and 9 aggregated Omernik level III ecoregions. A total of 2034 candidate lakes were evaluated to confirm they met all criteria for inclusion in the target population. The target population (n=1309 lakes), represents ~68,000 lakes in the sample frame. In all, 1028 lakes were sampled, representing ~50,000 lakes. The remaining lakes (n=231, representing ~18,000 lakes) could not be sampled because of access denial or physical inaccessibility. The target population is comprised of natural lakes (41±2% SE) and man-made lakes (59±2% SE). All target lakes in the Southern Appalachian region, and >90% of the target population in the Southern Plains and Xeric regions, are man-made. In the Upper Midwest region, 97±1% SE of the target population are natural lakes. Small lakes (4-10 ha) comprise 47±2% SE of the target population; ~15% of the target population are lakes >50 ha in size. Results from these extent estimates can be used to refine the sampling frame. Identifying target lakes that are not currently represented in NHD and including them in the sample frame, and reducing the number of target lakes in the sample frame that are not sampled, will produce more robust assessments of status and extent in future regional- and national-scale lake surveys. Developing a "master" sample frame of lakes would allow different studies to be easily combined, and provide a consistent basis of lake numbers (or surface area) from which to estimate extent or assess ecological condition.
