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Regional distribution of Secchi disk transparency in waters of the United States

Bigham Stephens, Dana L., Carlson, Robert E., Horsburgh, Christine A., Hoyer, Mark V., Bachmann, Roger W., Canfield, Daniel E.
Lake and reservoir management 2015 v.31 no.1 pp. 55-63
United States Environmental Protection Agency, ecoregions, surface water, turbidity, water distribution, Alaska, Maine, Montana, New Hampshire, Vermont
Individual Secchi disk measurements (975,760) were gathered from across the United States to understand regional distribution in water transparency. Compiled Secchi disk measurements represented 14,421 US waterbodies. Average water transparency ranged from <0.1 to 31.6 m with water transparencies <1.1 m in 25% of the sampled waterbodies, <2.0 m in 50% of the waterbodies, and <3.3 m in 75% of the waterbodies. Of the population of examined waterbodies, 10% had mean Secchi measurements exceeding 4.8 m. US states with the lowest water transparency (<0.7 m) were Delaware, Louisiana, Mississippi, Nebraska, Oklahoma, and South Dakota, while the greatest water transparencies (>3.5 m) were in Alaska, Maine, Montana, New Hampshire, and Vermont. Regional differences in water transparency were identified across the US Environmental Protection Agency ecoregions (Level III), with lower water transparencies occurring in nutrient-rich regions and higher water transparencies occurring in nutrient-poor regions. Regional variability should be considered in the management of waterbodies at local to national levels.