This readme.txt file was generated on <2019/01/22> by Patrick Brezonik and Melinda Kernik ------------------- GENERAL INFORMATION ------------------- 1. Title of Dataset: Combined UMN-MPCA 2014-2017 lake data on Secchi depth, CDOM, Chlorophyll and total suspended solids 2. Author Information Principal Investigators Contact Information Name: Patrick L. Brezonik, Professor Emeritus, and Raymond M. Hozalski, Professor Institution: Dept. of Civil, Environmental, and Geo- Engineering, University of Minnesota Address: Minneapolis, MN 55455 Email: brezonik@umn.edu and hozal001@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 2017-09-20 4. Geographic location of data collection (where was data collected?): Lakes in Minnesota (primarily) and also in Wisconsin and Michigan -------------------------- 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, Bouchard, Finlay, Griffin, Olmanson, Anderson, Arnold and Hozalski, Color, chlorophyll, and suspended solids effects on Secchi depth in lakes: implications for trophic state assessment. Ecological Applications 2019; 29. -------------------------- METHODOLOGICAL INFORMATION -------------------------- 1. Description of methods used for collection/generation of data: Sampling and analytical methods for a(440), chl-a, SD, and TSS are described in Brezonik et al. Ecological Applications 2019: 29,. In brief, UMN water samples were collected from ~ 0.25 m below the lake surface, and the MPCA collected a 0-2 m integrated sample of the epilimnion. Samples were stored in acid-washed and triple-rinsed polycarbonate or high-density polyethylene bottles and filtered for chl-a and dissolved constituents within 24 h of collection. Chl-a was filtered from water with 0.22 um cellulose nitrate filters (0.45 um glass fiber filters for MPCA) and stored frozen until analysis by fluorometry after 90% acetone extraction. Total suspended solids (TSS) was measured as the additional dry weight after filtration and drying at 105 degrees C, normalized by volume. Water for CDOM analysis was filtered through 0.45 um Geotech High Capacity filters and stored in the dark at 4 °C in pre-ashed 40 mL amber glass bottles until analysis within 1 month of collection. Absorbance at 440 nm, measured using a Shimadzu 1601UV-PC dual beam spectrophotometer through 1 or 5 cm quartz cuvettes against a nanopure water blank, was converted to Napierian absorption coefficients by the formula 2.303 times absorbance divided by cell path length (in meters). Absorbance scans were blank-corrected before conversion. CDOM values are reported as a(440). 2. Describe any quality-assurance procedures performed on the data: Various samples were analyzed in duplicate or triplicate; standard analytical procedures were used. 3. People involved with sample collection, processing, analysis and/or submission: Lakes identified by the System Locator Code in column A were sampled by Minnesota Pollution Control Agency staff as part of their annual lake assessment program. Lakes identified by name in column A were sampled by the Remote Sensing Group at the University of Minnesota or by collaborating agencies or colleagues at other universities who agreed to follow our sampling protocol and provide us with samples. Collaborating agencies and organizations in 2016 were: Minnehaha Watershed District; University of Michigan Biological Station; Michigan DNR; Minneapolis City Parks; Red Lake Nation; Three RIvers Park District; University of Wisconsin Trout lake Field Station and LTER Program, especially Luke Loken; Voyageurs National Park; Wisconsin DNR. Collaborating agencies, organizations, and individuals in 2017 were: Minneapolis Parks; Red Lake DNR; research group of Prof. Jim Cotner, Dept. of EEB, UMN; St. Croix Field Station of the Minnesota Science Museum; UMN Lake Itasca Field Station, Leslie Knoll; and several unnamed volunteers. ----------------------------------------- DATA-SPECIFIC INFORMATION FOR: Effects_of_CDOM_chl-a_andTSS_on_SD.csv ----------------------------------------- 1. Number of variables: 12 2. Number of cases/rows: 1460 4. Variable List A. Name: SysLocCode_or_LakeName Description: System locator code or lake name Lakes listed by name were sampled by our group or by our collaborators, as identified in #3 above. The System Locator Code is a unique lake identier code used by the Minnesota Pollution Control Agency to identify the location of their sampling sites. The first two digits identify the county from an alphabetical list of MN counties. The next four digits is a unique id for each lake from a Minnesota DNR list of lakes, available at: https://www.dnr.state.mn.us/waters/watermgmt_section/pwi/bulletin25.html, and the next two digits define the embayment number for lakes with complicated morphometry. The last three digits are an MPCA code defining the sampling location in the lake/embayment. Alternatively, lakes can be found entering the lake's DNR id (first 8 digits of the system locator code with no dashes) into the Lake ID search box in DNR’s lake finder website: https://www.dnr.state.mn.us/lakefind/index.html. B. Name: Date Description: Sampling dates C. Name: Ecoregion Description: from Level III delineation described in Omernik and Griffith, Environmental Management 54(6):1249–1266 (2014). NCHF = North Central Hardwood Forests (MN, WI, MI) NLF = Northern Lakes and Forests (MN, WI, MI) NMW = Northern Minnesota Wetlands (MN) WCBP = Western Corn Belt Plains (MN) RRV = Red River Valley (MN) NGP = Northern Glaciated Plains (MN) SEWTP = Southeastern Wisconsin Till Plains (WI) SMNIDP = Southern Michigan/Northern Indiana Drift Plains (MI) D. Name: a(440)_m^-1 Description: Napierian absorption coefficient at 440 nm in reciprocal meters (m^-1; m = meters) E. Name: Chl_a_corr_ug/L Description: chlorophyll-a concentration corrected for phaeophytin in μg/L F. Name: SD_m Description: Secchi depth in meters G. Name: 1/SD_m^-1 Description: The reciprocal of Secchi depth with units of reciprocal meters (that is, meters to the power of minus one). H. Name: TSS_mg/L Description: Total suspended solids retained by 0.45 μm filter in mg/L I. Name: log_chl_a Description: base 10 logarithm of data in column E (Chl a, corr. ug/L) J. Name: log_SD Description: base 10 logarithm of data in column F (SD, m) K. Name: log_a(440) Description: base 10 logarithm of data in column D (a(440), m^-1) L. Name: log_TSS Description: base 10 logarithm of data in column H (TSS, mg/L)