Iron influence on dissolved color in lakes of the Upper Great Lakes States

PLoS One. 2019 Feb 13;14(2):e0211979. doi: 10.1371/journal.pone.0211979. eCollection 2019.

Abstract

Colored dissolved organic matter (CDOM), a major component of the dissolved organic carbon (DOC) pool in many lakes, is an important controlling factor in lake ecosystem functioning. Absorption coefficients at 440 nm (a440, m-1), a common measure of CDOM, exhibited strong associations with dissolved iron (Fediss) and DOC in 280 lakes of the Upper Great Lakes States (UGLS: Minnesota, Wisconsin, and Michigan), as has been found in Scandinavia and elsewhere. Linear regressions between the three variables on UGLS lake data typically yielded R2 values of 0.6-0.9, suggesting that some underlying common processes influence organic matter and Fediss. Statistical and experimental evidence, however, supports only a minor role for iron contributions to a440 in UGLS lakes. Although both DOC and Fediss were significant variables in linear and log-log regressions on a440, DOC was the stronger predictor; adding Fediss to the linear a440-DOC model improved the R2 only from 0.90 to 0.93. Furthermore, experimental additions of FeIII to colored lake waters had only small effects on a440 (average increase of 0.242 m-1 per 100 μg/L of added FeIII). For 136 visibly stained waters (with a440 > 3.0 m-1), where allochthonous DOM predominates, DOM accounted for 92.3 ± 5.0% of the measured a440 values, and Fediss accounted for the remainder. In 75% of the lakes, Fediss accounted for < 10% of a440, but contributions of 15-30% were observed for 7 river-influenced lakes. Contributions of Fediss in UGLS lakes to specific UV absorbance at 254 nm (SUVA254) generally were also low. Although Fediss accounted for 5-10% of measured SUVA254 in a few samples, on average, 98.1% of the SUVA254 signal was attributable to DOM and only 1.9% to Fediss. DOC predictions from measured a440 were nearly identical to those from a440 corrected to remove Fediss contributions. Overall, variations in Fediss in most UGLS lakes have very small effects on CDOM optical properties, such as a440 and SUVA254, and negligible effects on the accuracy of DOC estimated from a440, data for which can be obtained at broad regional scales by remote sensing methods.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Carbon / analysis
  • Color*
  • Coloring Agents / analysis*
  • Ecosystem
  • Environmental Monitoring
  • Iron / chemistry
  • Iron / pharmacology*
  • Lakes / chemistry*
  • Michigan
  • Minnesota
  • Organic Chemicals / analysis*
  • Rivers / chemistry
  • Solubility
  • Water Pollutants, Chemical / analysis*
  • Wisconsin

Substances

  • Coloring Agents
  • Organic Chemicals
  • Water Pollutants, Chemical
  • Carbon
  • Iron

Grants and funding

PLB received a grant from the University of Minnesota Office of the Vice President for Research and the University of Minnesota's Faculty Retirees Association, no grant number provided (https://umra.umn.edu). RMH, PLB, and JCF received a grant from the National Science Foundation, CBET 1510332 (www.nsf.gov). JCF, PLB, LGO, and RMH received a grant from the Minnesota Environmental and Natural Resources Trust fund, as recommended by the Legislative-Citizen Commission on Minnesota Resources, no grant number provided (https://www.lccmr.leg.mn/). JCF received a grant from the Minnesota Sea Grant, no grant number provided (www.seagrant.umn.edu). LGO also received salary support from the University of Minnesota’s U-Spatial Program and Agricultural Experiment Station. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.