These files contain the raw field and lab data collected during sampling of lakes and a few rivers in 2014-2016 to evaluate the importance of dissolved iron concentrations in affecting apparent levels of colored dissolved organic matter (CDOM), as measured spectrophotometrically by light absorption coefficient at 440 nm, a(440), with additional sampling in 2018 for more specific purposes. Approximately 450 sets of measurements were made on 280 lakes/rivers during the field seasons of 2014-2016, with most of the sampling in two ecoregions of Minnesota -- the Northern Lakes and Forests (NLF) and the North Central Hardwood Forests (NCHF). Additional samples collected in these two ecoregions in neighboring Wisconsin and Michigan in 2016 and in the Northern Minnesota Wetlands (NMW) ecoregion of Minnesota also are in the database. Data collected in 2018 included depth profiles of a(440), iron, dissolved organic carbon (DOC), and basic water quality parameters on three NLF lakes and samples on about 20 colored lakes and rivers to evaluate the importance of particulate iron as a component of total iron. Experimental data for addition of dissolved iron (Fe(III)) to six lakes also is included.
Three data files are included. The first contains the 2014-2016 field and lab data for 450 sets of measurements on 280 lakes across the NLF, NCHF and NMW ecoregions in Minnesota, Wisconsin, and Michigan. In addition to site names, location information (latitude/longitude), ecoregion, and sampling date, the file contains data on Secchi depth, CDOM measured as a(440), DOC, dissolved iron, chlorophyll-a, specific UV absorbance at 254 nm, SUVA(254), and spectral slopes. The second contains data on concentrations of total, dissolved and particulate iron fractions in 2018 samples from 19 high-CDOM sites (lakes and rivers) in the NLF ecoregion of northern Minnesota plus vertical profile information on a(440), dissolved iron, light penetration, and basic limnological parameters in three NLF lakes with widely varying a(440) levels. The third file contains a(440) and dissolved iron concentrations for six lakes from a laboratory experiment in which known amounts of dissolved iron were added to water samples from six water bodies with a wide range of a(440) levels plus additional spectral absorbance information from the samples.
Sponsorship: National Science Foundation, Legislative-Citizen Commission on Minnesota Resources, University of Minnesota