<emphasis role="strong">Study sites</emphasis>
Arco, Budd, Deming, and Josephine lakes lie within Itasca State
Park, which is administered by the Minnesota Department of Natural
Resources (https://www.dnr.state.mn.us/). The lakes formed within
depressions of the Itasca moraine, a >14,000 year old glacial
feature of the Wadena lobe of the latest Pleistocene-aged
glaciations in the area (Wright Jr., 1993). Several studies describe
these lakes as meromictic (Anderson et al., 1985; Baker and Brook,
1971). Deming Lake has been used in paleoclimate studies (Lascu et
al., 2012; McLauchlan et al., 2013).
<emphasis role="strong">Sensors</emphasis>
Multiple systems were used to acquire water column chemical and
physical parameters. These parameters and their units as defined in
the dataset are temperature (degreeCelsius), depth (meters),
specific conductance (microSiemensPerCentimeter), turbidity
(NephelometricTurbidityUnits), pH (pH), dissolved oxygen
(milligramsPerLiter), oxidation-reduction potential (milliVolts),
Chlorophyll a (microgramsPerLiter), and
phycocyanin (microgramsPerLiter). The specific systems were
manufactured by Yellow Springs Instruments (YSI), and included the
models ProDSS, Hydrolab, and 85. Depth was determined manually
through markings on the cables for the Hydrolab and YSI 85, or
integrated pressure transducers for the ProDSS. Calibrations for
specific conductance used two-point calibration buffers obtained
from the manufacturers. Membrane-based and optical dissolved oxygen
sensors were calibrated using a single point calibration with 100%
air-saturated water and/or a two-point calibration with sodium
dithionite as 0%. The pH sensors were calibrated using buffers at pH
4, 7, and 10. The resolution of sensors is given in the QC column
for temperature, depth, dissolved oxygen, specific conductance,
oxidation-reduction potential, pH, and turbidity. Low range is given
for chlorophyll and phycocyanin.
Photosynthetically active radiation (PAR) was quantified using an
underwater spherical quantum sensor (Li-193; 7 μA per 1,000 μmoles
quanta m-2
s-1) coupled to an Li-250A light meter
and deployed on a 2009S lowering frame (Li-COR). All measurements
were taken near mid-day. Measurements in air are denoted as depth of
-1 m.
A BBE Moldaenke Fluoroprobe was used to determine taxon specific
chlorophyll fluorescence [Chlorophyta, Cyanobacteria, diatoms (&
dinoflagellates), and Cryptophya]. The range of chlorophyll is 0-500
microgramsPerLiter with a resolution of 0.01 microgramsPerLiter.
Transmittance is measured in 0-100%. A “yellow substances” or
dissolved organic carbon correction is automatically applied.
<emphasis role="strong">Chemical measurements</emphasis>
Analytical precision was monitored through laboratory replicates.
Replicated analyses are noted in the Comments column of the dataset.
Any different filter pore sizes used to collect samples are also
noted in the Comments column.
Water samples for laboratory-based measurements of dissolved and
gaseous chemical species and were collected with a Mini Monsoon pump
with low-flow controller (Proactive) attached to vinyl tubing and a
cable marked with meter and half-meter depth increments. Water was
filtered in-line through syringe filters affixed to a polycarbonate
luer lock valve attached to the tubing. For measurements of
dissolved inorganic carbon (DIC), a needle was attached to the
filter to introduce filtered samples directly into serum vials.
Samples for total alkalinity were collected and stored at 4°C with
no headspace. They were measured within 24 hours at room temperature
using Hach TNT870 vials and a Hach DR 1900 spectrophotometer. This
method has a range of 25 to 400 milliGramsPerLiter, and all samples
were within range. The coefficient of variation for replicated
samples (in %) is reported in the QC column.
Ion Chromatography (IC) was performed on samples filtered through
0.45 μm PES filters and kept at 4°C until analysis. In 2006-2009
samples were analyzed by the University of Minnesota Department of
Earth Sciences. In 2019 the samples were analyzed at the University
of Minnesota Research Analytical Laboratory. In 2021-2022 the
samples were analyzed by Ion Chromanalytical (St. Paul, Minnesota).
Species analyzed were fluoride (Fl-),
chloride (Cl-), nitrite
(NO2
-), nitrate
(NO3
-), bromide
(Br-), sulfate
(SO4
2-),
thiosulfate
(S2O3
2-),
phosphate (PO4
3-),
acetate and formate. The detection limits are given in the QC
column.
Dissolved cations were first filtered through a 0.45 μm PES filter.
Both dissolved and total (unfiltered) samples were acidified with
nitric acid to a final concentration of 1% and stored at 4°C until
analysis. In 2006-2009 samples were analyzed by the University of
Minnesota Department of Earth Sciences (iCap 7600 Duo) with an
analytical precision of 2% or lower. Metals were analyzed in 2019 by
Q-ICP-MS at Arizona State University (ThermoFisher iCap-Q).
Quantification limits for each element are given in the comment
field of the table. In 2021 samples were analyzed at the Department
of Civil, Construction and Environmental Engineering at Iowa State
University (Shimadzu ICP-OES 9810). The detection limit for each
element is given in the comment field of the table.
In 2006-2009, samples were collected using a van Dorn sampler and
injected into stoppered glass serum vials until no headspace
remained. Samples were refrigerated and kept in dark until injection
of 1-4 ml of sample into evacuated vessels containing 0.3 ml 105%
anhydrous H3PO4 (Myrbo
and Shapley, 2006). These samples were analyzed at the University of
Minnesota Stable Isotope Laboratory on a Finnegan-MAT mass
spectrometer with an analytical precision of 0.2 permil (‰). In
2019-2022, water samples for DIC and
δ13C-DIC were collected with a pump,
filtered in-line (0.45 μm PES) and 4 mL was injected into evacuated,
He-flushed Exetainers (Labco) containing 0.1 ml of 85% phosphoric
acid. Samples were analyzed at the Iowa State University Stable
Isotope Laboratory on a ThermoFinnigan Delta Plus XL mass
spectrometer coupled with a GasBench II with a CombiPal autosampler.
Reference standards (LSVEC, NaHCO3) were used
for isotopic corrections, and to assign the data to the appropriate
isotopic scale. Corrections are done using a regression method. The
analytical uncertainty for δ13C (‰)
relative to V-PDB is in the QC column. Analyses are reported as
δ13C in permil relative to V-PDB.
Samples for water isotopes
(δ2H-H2O and
δ18O-H2O) were
filtered and filled into containers with no headspace and kept at 4
°C until analyses. These samples were analyzed by a Picarro L1102-i
Isotopic Liquid Water Analyzer in the Stable Isotope Laboratory at
Iowa State University. The combined uncertainty (analytical
uncertainty and average correction factor) for
δ18O-H2O is ± 0.05
‰ and δ2H-H2O is ±
0.30 ‰ relative to V-SMOW. These values are provided in the QC
column.
