Fig 1.
Map of study area showing ecoregions and sampling sites.
Red circles: sites with Fediss, a440 and DOC data; black circles: additional sites with only a440 and DOC data.
Table 1.
Summary statistics for a440, DOC, and Fediss and two basic limnological variables in the NLF and NCHF ecoregions.
Fig 2.
Plot of eigenvalues for the first two principal components of a principal components analysis of five variables (a440, DOC, Fediss, chl-a, and SD) for the whole data set.
Fig 3.
(a) a440 and (b) DOC vs. Fediss for sampling years 2104–2016; triangles = 2014, squares = 2015, circles = 2016; dashed lines are regression fits for all years (see Table 1 for regression statistics).
Table 2.
Dissolved Fe-CDOM and Fe-DOC relationships.
Table 3.
Simple and multiple regression relationships for a440 vs. DOC and Fediss.
Fig 4.
(a) a440/DOC vs. Fediss for all data, R2 = 0.64; (b) a440/DOC vs. Fediss for sites with a440 > 3.0 m-1, R2 = 0.46. (R2 are for fit of a440/DOC to ln(Fediss)).
Fig 5.
(a) SUVA254,DOM vs. Fediss for sites with a440 > 3.0 m-1, R2 = 0.45 (R2 is for fit to ln(Fediss)); (b) fraction of SUVA254 for all sites caused by DOM (i.e., corrected for FeIII contribution) vs. Fediss.
Fig 6.
a440 vs. Fediss for six waters in iron addition experiment; slopes and statistical information on best-fit lines in Table 4.
Table 4.
Chemical characteristics of lakes and results for iron addition experiment.
Fig 7.
Fediss vs. a440 for 2015 data; best-fit regression line and statistics given in Table 2.
Circled data: outliers examined for effects of Fediss on a440 (S6 Table). Dotted line: best-fit linear relationship: Fediss = 36.8a440−30.7; R2 = 0.79. Dashed lines illustrate change in a440 for some outliers when Fediss was changed to “best-fit” value.