Foliar element determination from field survey in association with an Analytical Spectral Device Fieldspec3 survey, East River, CO 2023

Abstract

Foliar elements were determined for samples collected in the field during a 2023 survey in Gunnison County, CO that also included paired data collection using an ASD FieldSpec3 spectrometer. Sampling locations were selected based on metal hotspots identified using remote sensing data and foliar elemental data from the 2018 National Ecological Observatory Network (NEON) Airborne Observation Platform (AOP) imaging spectroscopy and lidar surveys in Gunnison County, CO. The samples collected across the East River, Washington Gulch, Slate River, and Coal Creek watersheds include a mixture of vegetation including meadow, shrub, and tree foliar samples. Foliar samples underwent aqua regia digestion for elemental determination on inductively coupled plasma optical emission spectrometry (ICP-OES). This data package contains the raw foliar elemental data for all foliar samples, metadata associated with the foliar samples collected, and a certificate of analysis for this project. 

Methods

Foliar metal maps were produced using remote imaging spectroscopy data paired with in situ foliar measurements and subsequently loaded on GPS capable iPads to geolocate individual plants within targeted metal hotspots areas. For trees and shrubs within identified metal hotspots, samples were collected from sun-lit leaves, with enough sample for 30-40 g of fresh leaf material (not including stem or woody material). We identified branches that were sunlit and cut 2-3 small branches by slingshot or pole clippers depending on canopy height. We assessed samples to avoid excessive herbivore damage, discoloration, or epiphylls. Samples were placed in a gallon polyethylene bag and as much air as possible was removed from the bag before sealing, while being careful that leaves were not crushed or folded, and placed in a cooler with ice. For the meadow sampling sites, teams collected the top 10-20 cm of vegetation within a given square meter plot. We collected samples representative of the foliar coverage within the designated plot and placed them in a gallon polyethylene bag. We removed as much air as possible from the bag before sealing, while being careful that leaves were not crushed or folded, and placed them in a cooler with ice. At the end of each sampling day, fresh foliar samples were transferred to pre labeled paper bags and placed in an oven at 65 degrees Celsius for 72 hours. After 72 hours in the oven, the samples remained in the paper bags and were vacuum sealed in dry, labeled Ziploc bags. Then, they were placed in dry coolers and transported as personal luggage back to the University of Southern California.

Once in the lab at the University of Southern California, all samples were immediately dried again at 65 degrees C for at least 24 hours. The samples were kept out of sunlight and under consistent temperatures. Then, the samples were first processed by removing all woody material, stems and petioles before grinding each sample in an automatic mill. The ground samples were then homogenized and divided so that each sample had a corresponding working sample that was stored in a separate working vial. Between each sample, the mill and all parts that had been in contact with the sample were cleaned with kim wipes and ethanol. Leftover ground samples were placed in respective storage boxes with desiccant and sealed. Each specimens’ working sample was powdered using a custom ball mill, then placed in trays to dry again at 65 degrees C for at least 24 hours before elemental analysis. 

The dried and powdered foliar samples were sent to ALS Geochemistry where they were dried once more, then weighed out at 0.4 g 0.005 g and transferred into a microwave digestion vessel. A CEM MARS Xpress Microwave Digester enabled aqua regia digests for foliar elemental determination on a Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES). The outlined methods above are consistent with the methods used to process all foliar elemental data associated with the NEON AOP surveys in 2018. Raw elemental data, quality control (QC) certificates of analysis, and certificates of analysis were emailed to us by ALS Geochemistry. These raw data (csv), metadata associated with the foliar samples collected (csv), and the certificate of analysis (pdf) are contained in this data package.