Organic Carbon Data in Water Samples from Minnesota Lakes, 2012 to 2013

The sampling of three hydrologically diverse Minnesota Lakes (Williams Lake, Shingobee Lake, and Lake Manganika) took place during the years of 2012 to 2013. Water samples were collected and filtered in the field using 0.45 micrometer capsule filters (Versapor membrane), silicon tubing, and a peristaltic pump. Water samples were then shipped on ice to the U.S. Geological Survey in Boulder, Colorado and chilled to approximately 4 degrees Celsius until analysis. Dissolved organic matter (DOM) was separated into fractions by an isolation method that passes aqueous sample through Amberlite XAD8 and XAD4 resins using low pressure liquid chromatography. The hydrophobic organic acid (HPOA) fraction is the eluate from the XAD8 fractionation column and the transphilic organic acid (TPIA) fraction is the eluate from the XAD4 fractionation column. Dissolved organic carbon (DOC) was measured on an OI700 Analytical total organic carbon analyzer by wet-oxidation; each sample was measured in replicate and the average was reported. Ultraviolet (UV) absorbance at the wavelength of 254 nm was measured with an Agilent HP8453 UV-Vis spectrophotometer. Specific UV Absorbance (SUVA) at 254 nm is a calculated parameter defined as the UV absorbance at a wavelength of 254 nm in absorbance units per centimeter divided by the DOC concentration in milligrams per liter and then multiplied by 100. SUVA 254 nm is reported in units of liters per milligram carbon per meter and correlates with the percent aromatic carbon of the DOM. Iron(III) absorbs UV light at 254 nm and, if present at appreciable concentration, can influence UV absorbance and calculated SUVA values. Utilizing a Hach spectrophotometer, total iron concentration was measured. The total iron concentrations of filtered whole water samples from each Minnesota Lake site were determined, and were not high enough to significantly influence SUVA 254 nm values. Associated laboratory quality assurance and quality control measures have been taken to produce final data.