This readme.txt file was generated on <2019/01/22> by Patrick Brezonik and Melinda Kernik ------------------- GENERAL INFORMATION ------------------- 1. Title of Dataset: Effect of dissolved iron on CDOM and other optical properties for dissolved organic matter in lakes and rivers of the Upper Great Lakes states 2. Author Information Principal Investigators Contact Information Name: Patrick L. Brezonik, Professor Emeritus, and Raymond M. Hozalski and William A. Arnold, Professors Institution: Dept. of Civil, Environmental, and Geo- Engineering, University of Minnesota Address: Minneapolis, MN 55455 Email: brezonik@umn.edu, hozal001@umn.edu, and arnol032@umn.edu and Name: Jacques C. Finlay, Professor Institution: Dept. of Ecology, Evolution, and Behavior, University of Minnesota Address: St. Paul, MN 55108 Email: finlay@umn.edu 3. Time period of content: 2014-07-03 to 2018-08-06 4. Geographic location of data collection (where was data collected?): The Northern Lakes and Forests (NLF) and the North Central Hardwood Forests (NCHF) ecoregions in Minnesota, Wisconsin and Michigan and the Northern Minnesota Wetlands (NMW) ecoregion of Minnesota -------------------------- SHARING/ACCESS INFORMATION -------------------------- 1. Licenses/restrictions placed on the data: CC0 1.0 Universal (CC0 1.0) Public Domain Dedication 2. Links to publications that cite or use the data: Brezonik, P. L., J. C. Finlay, C. G. Griffin, W. A. Arnold, E. H. Boardman, N. Germolus, R. M. Hozalski, and L. G. Olmanson. 2019. Iron influence on dissolved color in lakes of the Upper Great Lakes states. PLoS ONE. (2019) --------------------- DATA & FILE OVERVIEW --------------------- 1. File List A. Filename: 2014-2016_Fe_CDOM_database.csv Short description: Field and lab data for 450 sets of measurements on 280 lakes across the NLF, NCHF and NMW ecoregions in Minnesota, Wisconsin, and Michigan collected in 2014-2016. Variables include site names, location information (latitude/longitude), ecoregion, and sampling date, Secchi depth, colored dissolved organic matter (CDOM) measured as a(440), dissolved organic carbon (DOC), dissolved iron, chlorophyll-a, specific UV absorbance at 254 nm, SUVA(254), and spectral slopes. B. Filename: Fe-CDOM_addition_expt_11-2015.csv Short description: a(440) and dissolved iron concentrations for six lakes from a laboratory experiment in which known amounts of dissolved iron were added to filtered water samples from six water bodies with a wide range of ambient a(440). C. Filename: UV-vis_Absorbance_Spectra_2015.csv Short description: UV-vis absorbance spectra, 500-250 nm for the six lakes in the iron addition experiment D. Filename:2018_Fe-CDOM_data.csv Short description: Concentrations of total, dissolved and particulate iron fractions in samples from 19 high-CDOM sites (lakes and rivers) in the NLF ecoregion of northern Minnesota collected in 2018 E. Filename:2018_Vertical_Profile_Data.csv Short description: Vertical profile information on a(440), dissolved iron, light penetration, and basic limnological parameters in three NLF lakes with widely varying a(440) levels collected in 2018 2. Relationship between files: (File A) 2014-2016_Fe_CDOM_database.csv contains 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). (File B and C) Fe-CDOM_addition_expt_11-2015.csv and UV-vis_Absorbance_Spectra_2015.csv contain data from an experiment adding known amounts of dissolved iron (Fe(III)) to six of the lake samples. (File D and E) 2018_Fe-CDOM_data.csv and 2018_Vertical_Profile_Data.csv contain additional samples collected from the Northern Lakes and Forests ecoregion in 2018. Lat/long info for sites in 2018_Fe-CDOM_data.csv is given in 2014-2016_Fe_CDOM_database.csv -------------------------- METHODOLOGICAL INFORMATION -------------------------- 1. Description of methods used for collection/generation of data: 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. All 2014-2016 samples were surface water (top ~0.3 m) grab samples. The absorption coefficient at 440 nm, a(440), was calculated from absorbance (A) at 440 nm measured on a spectrophotometer. Absorbance values were blank corrected before a(440) was calculated, and a(440) was calculated as 2.303A(440)/cell path length in m; i.e., values are Napierian absorption coefficients. For the iron addition experiment conducted in 2015, spectra were run on samples 11/25/15, all in a 1-cm cell, and the data in the absorbance spectra file are absorbance (A) at a given wavelngth. Data in the file "Fe-CDOM_addition_expt" are absorbance (A) at 440 nm in a 1 cm cell and dissolved Fe concentrations in the initial samples. For samples collected in 2018, the lakes were sampled July 10-11, 2018, and are located near Side Lake, MN in western St. Louis Cty/eastern Itasca Cty. 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 were collected to evaluate the importance of particulate iron as a component of total iron. Temperature, specific conductance (SC), and pH was measured in situ by YSI Exo2 water quality sonde with 10-m cable. Photosynthetically active radiation (PAR) was measured with Li-cor LI-250A light meter. a(440) and Fe(diss) was measured in laboratory on samples collected at depth by Van Dorn sampler. Additional details on analytical methods for other variables are given in Brezonik et al. PLoS One (2019). 2. Describe any quality-assurance procedures performed on the data: Duplicate analyses were done on some samples, standard analytical methods were used, and good laboratory practice was adhered to. 3. People involved with sample collection, processing, analysis and/or submission: All samples with measured iron data were collected by the coauthors of the PLOS ONE (2019) paper or by students working in their laboratories. Some additional samples for CDOM, DOC and related variables were collected by collaborators; see Readme file associated with a companion data repository file, DRUM record: https://doi.org/10.13020/01WT-JG66 for details on collaborators for sample collection. ----------------------------------------- DATA-SPECIFIC INFORMATION FOR: 2014-2016_Fe_CDOM_database.csv ----------------------------------------- Note: The calculated SUVA value for Clark Lake MI, 7.68, was obviously too high, and the measured DOC concentration likely was erroneously low. The SUVA value for this lake was deleted from SUVA vs. Fe and SUVA vs. a440 plots in Brezonik et al. (2019). 1. Number of variables: 16 2. Number of cases/rows: 451 3. Variable List A. Name: Site_Name Description: Name of water body sampled. Sites in Wisconsin and Michigan are designated by (WI) or (MI) after lake name. Undesignated sites are in Minnesota. For SLRE + St. Louis River Estuary. Site numbers decrease from 10 at upstream near Oliver WI to 2 in Superior Bay and 1 in nearshore Lake Superior B. Name: Sampling_Date Description: Date sample was collected C. Name: Latitude Description: Latitude of sampling location in decimal degrees D. Name: Longitude Description: Longitude of sampling location in decimal degrees E. Name: Ecoregion Description: Ecoregions are the Omernik and Griffith (2014) Level III aquatic ecoregions. Acronyms are as follows: NCHF = North Central Hardwood Forests (MN, WI, MI) NLF = Northern Lakes and Forests (MN, WI, MI) NMW = Northern Minnesota Wetlands (MN) SEWTP = Southeastern Wisconsin Till Plains (WI) SMNIDP = Southern Michigan/Northern Indiana Drift Plains (MI) HELP = Huron/Erie Lake Plains (MI) F. Name: Secchi_depth_m Description: Depth in water column at which a white disk, 20-cm in diameter, or a similar disk divided into black and white quadrants can no longer be seen from above the water surface in a lake. G. Name: a(440)_m^-1 Description:The absorption coefficient at 440 nm i.e., values are Napierian absorption coefficients H. Name: DOC_mg/L Description: Dissolved organic carbon concentration I. Name: SUVA(254) Description: Absorbance at 254 nm, corrected for cell path length to 1 m, divided by DOC concentration (mg/L) of the sample, reported in units of L mg^-1 m^-1. J. Name: Fe_ug/L Description: Total dissolved iron measured on filtered sample using inductively coupled plasma atomic emission spectroscopy (ICP-AES). K. Name: a(440)/DOC Description: Napierian absorption coefficient at 440 nm (m^-1) divided by DOC (mg/L) L. Name: Chl-a_ug/L Description: chlorophyll a concentration in water samples from phytoplankton, corrected for phaeophytin. M. Name: S(275-295) Description: spectral slope, i.e., the slope of a plot of ln A vs. wavelength over the wavelength range 275-295 N. Name:S(350-400) Description: spectral slope, i.e., the slope of a plot of ln A vs. wavelength over the wavelength range 350-400 O. Name:S(400-460) Description: spectral slope, i.e., the slope of a plot of ln A vs. wavelength over the wavelength range 400-460 P. Name:S(r) Description:the slope ratio, i.e., S(275-295)/S(350-400) ----------------------------------------- DATA-SPECIFIC INFORMATION FOR: Fe-CDOM_addition_expt_11-2015.csv ----------------------------------------- Fe(III) addition experiment: absorbance at 440 nm after five increments of Fe(III) additions to six lakes plus ambient a(440) and Fe(diss). 1. Number of variables:8 2. Number of cases/rows: 6 3. Variable List A. Name: Sample Description: Name of lake sampled B. Name: Addn0 Description: Absorbance (A) at 440 nm in 1 cm cell for filtered sample with no Fe(III) addition (ambient sample) C-G. Name: Addn1-5: Description: A at 440 nm in 1 cm cell for filtered sample with each increment adding 92.5 ug/L of Fe(III) to the samples. H. Name: Ambient_Fe, ug/L Description: Dissolved iron concentration, ug/L, in filtered ambient water sample prior to any Fe addition in the laboratory. ----------------------------------------- DATA-SPECIFIC INFORMATION FOR: UV-vis_Absorbance_Spectra_2015.csv ----------------------------------------- 1. Number of columns: 19 2. Number of cases/rows: 251 3. Variable List A. Name: Wavelength Description: UV or visible wavelength in nm B-S. Name: Blank or lake sample name Description: Absorbance (A) in a 1 cm cell at the given wavelength. Addn = addition. Addition 0 = raw (filtered) water sample (ambient value). Addition 1 = sample after first addition of 0.6 mL of dissolved iron (Fe(III)) solution, determined by ICP to contain 77.1 mg/L of Fe(III), thus increasing sample Fe(III) by 92.5 ug/L. Addition 5 = sample after fifth addition of 0.6 mL of same dissolved iron solution, which increased Fe(III) by 460 ug/L over ambient concentration. ----------------------------------------- DATA-SPECIFIC INFORMATION FOR: 2018_Fe-CDOM_data.csv ----------------------------------------- Notes: Lat/long info for sites is given in 2014-2016 database file. (*) The St. Louis River sample site was upstream of Thomson Reservoir. (**) At Embarrass River a large rain event the previous day resulted in very high flow and high turbidity in this sample, such that the inflow plume was visible hundreds of meters into the lake. Although FeT was even higher in this river in the Aug. 6 sample, it was mostly in dissolved form, similar to that for the lake into which the river drains. The low % Fe(diss) for this sample thus likely represents an atypical situation. (***) Fe(T) averages include the two lakes with no measured Fe(diss); % Fe(diss) averages are based on individual % Fe(diss) values in part (A) and not on the ratio of the average Fe(diss) and Fe(T) values. 1. Number of variables: 4 2. Number of cases/rows: 19 3. Variable List A. Name: Sample Description: Name of lake or river sampled B. Name: Sampling_Date Description: Date sample was collected C. Name: Fe(diss)_ug/L Description: dissolved iron concentration, as measured on filtered sample by ICP-AES. D. Name: Fe(T)_ug/L Description: Total iron concentration, as measured on acidified unfiltered samples by ICP-AES E. Name: PctFe(diss) Description: Percent of Fe(T) in dissolved form; that is variable C times 100 divided by variable D. ----------------------------------------- DATA-SPECIFIC INFORMATION FOR: 2018_Vertical_Profile_Data.csv ----------------------------------------- 1. Number of variables: 8 2. Number of cases/rows: 17 3. Variable List A. Name: Lake_name Description: Name of lake sampled B. Name: Depth_m Description: Depth in meters at which variables were measured C. Name: T_°C Description: Temperature in degrees Celcius D. Name: PAR_uM m^-2 s^-1 Description: Photosynthetically active radiation E. Name: SC_uS/cm Description: Specific conductance F. Name: pH_n Description: negative logarithm of hydrogen ion activity G. Name: a(440)_m^-1 Description: The Napierian absorption coefficient at 440 nm H. Name: Fe(diss)_ug/L Description: Dissolved iron concentration, as measured on filtered samples by ICP-AES.