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Environ Monit Assess. 2017 May;189(5):206. doi: 10.1007/s10661-017-5911-9. Epub 2017 Apr 3.

Factors related to Secchi depths and their stability over time as determined from a probability sample of US lakes.

Author information

1
Fisheries and Aquatic Sciences, School of Forest Resources and Conservation, University of Florida, 7922 NW 71 St., Gainesville, FL, 32653, USA. rbach@ufl.edu.
2
Fisheries and Aquatic Sciences, School of Forest Resources and Conservation, University of Florida, 7922 NW 71 St., Gainesville, FL, 32653, USA.

Abstract

A probabilistic sample of lakes in the 48 coterminous US lakes was made by the United States Environmental Protection Agency in the 2007 National Lakes Assessment. Because of the statistical design, the results of our analyses of Secchi depths (SD) apply to a population of 45,265 lakes. We found statistically significant differences in mean Secchi depths between natural (1.57 m) and man-made lakes (1.18 m). The most important variable correlated with SD was turbidity, an optical measure related to suspended particles in the water column. For most lakes, chlorophyll a was highly correlated with both turbidity and SD, but several lakes had more turbidity and lower SD than expected based on chlorophyll a alone, indicating that non-algal suspended solids were an important factor. On an ecoregion basis, the non-algal suspended solids in the lake waters were related to the average levels of suspended solids in streams located in that ecoregion, and the non-algal suspended solids were more important in man-made than natural lakes. Phosphorus and nitrogen were directly correlated with chlorophyll a and turbidity and inversely correlated with SD. Based on diatom-inferred Secchi depths for the tops and bottoms of sediment cores from lakes in Ecoregions VIII and VII (excluding lakes in Minnesota) representing 40% of the natural lakes in the US, there has been no decrease in water transparency in that population of lakes in the past 70 or more years when the US population increased by 134%. We do not have information to determine if the other 60% of lakes have or have not changed.

KEYWORDS:

Diatom-inferred; Man-made lakes; National Lakes Assessment; Secchi; Suspended particles

PMID:
28374189
DOI:
10.1007/s10661-017-5911-9
[Indexed for MEDLINE]

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