Charcoal counts, stable isotopes, and elemental chemistry of particulate materials after the 2020 CZU Wildfire

SAMPLE COLLECTION. Stream sediment was collected by hand from recently deposited fine-grained material on stream banks and stored in wire-top polyethylene bags. Charcoal samples were collected in duplicate or triplicate in sandy material on the stream bank using a one-quarter teaspoon scoop and stored in falcon vials. Ash, soil, and mixed samples were collected from undisturbed forest sites by hand, stored in combusted 500 milliliter glass jars, and sieved to remove particles greater than 2 mm in diameter.

CHARCOAL COUNTS. Sediment was gently agitated with bleach at room temperature for two hours without changing particle sizes. Stainless steel sieves were used to separate particles greater than or equal to 0.125 mm in diameter. The retained particles were rinsed in a water bath. Particles were transferred to a petri dish and dried completely at 45 degrees Celsius. Charcoal particles were counted under a stereo-microscope.

CARBON CONTENTS. Carbon analysis was performed at the PCMSC Carbon Laboratory by combustion, acidification, and coulometric detection using a UIC CM5015 Coulometer. Approximately 1 gram of sediment was dried overnight at 80 degrees Celsius and pulverized by hand in a mortar and pestle. 20 milligrams of sediment for total carbon (TC) were combusted at 950 degrees Celsius (UIC CM 5230 furnace) and quantified with a coulometric titration. 20 milligrams of sediment for total inorganic carbon (TIC) were digested with perchloric acid (UIC CM 5130 acid digester) and quantified with a coulometric titration. Total organic carbon (TOC) was calculated as the difference between TC and TIC. Average values of process duplicates are reported.

STABLE ISOTOPE RATIOS OF CARBON 13/12 (d13C) and NITROGEN 15/14 (d15N). Bulk sedimentary d13C and d15N were determined at the Washington State University Stable Isotope Core Laboratory using an elemental analyzer (Costech Analytical) interfaced with a Delta PlusXP isotope ratio mass spectrometer using a Santrock correction (ThermoFinnegan). Ratios of d13C ratios were referenced to the Vienna PeeDeeBelemnite (VBPD) using NBS 19 and LSVEC as anchor points. Ratios of d15N were referenced to air.

ELEMENTAL CHEMISTRY. Bulk sediment was oven-dried at 60 degrees Celsius and disaggregated gently with a mortar and pestle to avoid changing grain sizes. Disaggregated sediment was dry-sieved through stainless steel sieves to obtain 2 grams of the less than 0.063 millimeter fine fraction. Fine sediments were sent to the Analytical Chemistry Project of the USGS Geology, Geophysics, and Geochemistry Science Center (GGGSC), which contracted AGAT and SGS Labs, both nationally accredited, for analyses of major, minor, and trace element contents using two methods: a near-total four-acid digestion (labeled multi-acid in the table of data) and a total digestion with a sodium peroxide fusion (labeled fusion in the table of data) for elements hosted in acid-resistant minerals. Quantification was performed by inductively coupled plasma atomic emission spectroscopy (ICP-AES) for major and some minor elements and by inductively coupled plasma mass spectroscopy (ICP-MS) for some minor and all trace elements.