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Lakeshore and littoral physical habitat structure: A field survey method and its precision

Abstract Measures of near-shore physical habitat structure have only recently been employed in large-scale assessments of lake ecological condition. We outline and evaluate a rapid approach for quantifying lake physical habitat structure and disturbance that was piloted in the Northeast United States by the US Environmental Protection Agency in its Environmental Monitoring and Assessment Program (EMAP-NE), then improved and applied in the 2007 National Lakes Assessment (NLA). This approach measures littoral habitat complexity, fish cover, substrate, aquatic macrophytes, riparian vegetation, and human disturbances. Of 46 NLA physical habitat metrics, 34 had repeat-visit standard deviations <10% of their potential ranges, indicating repeatability sufficient to distinguish 4 to 5 levels of habitat condition within that range. For 23 metrics, the signal to noise ratio (S/N) of among-lake to same-year repeat-visit variance was moderate to high (3–10), indicating that noise variance was a relatively small confounding factor in their interpretation. Most NLA metrics were 30–40% more precise than those of EMAP-NE, largely because NLA used a greater number of habitat percent cover classes. We conclude that the metrics and indices derived from the NLA physical habitat field approach are precise enough to quantify near-shore habitat structure for contributing to national, state, and ecoregional assessments of lake condition.