Regional distribution of Secchi disk transparencyin waters of the United States

Abstract

Individual Secchi disk measurements (975,760) were gathered from across the United States to understand regional distribution inwater transparency. Compiled Secchi diskmeasurements represented 14,421 USwaterbodies.Average water transparency ranged from<0.1 to 31.6mwithwater transparencies<1.1min 25% of the sampledwaterbodies, <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 ProtectionAgency 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.