Stream and River Chemistry in Watersheds of Northwestern Alaska, 2015-2019

Stream water quality parameters (temperature, specific conductivity, pH, and dissolved oxygen) were measured in situ using a YSI Professional Plus multi-parameter instrument. All probes were regularly calibrated following standard methods.

Samples were collected in the field using a peristaltic pump. Silicon tubing (size 15) was connected to a Geotech 2 peristaltic pump to collect water samples, approximately 25-50 cm below the stream surface in a well-mixed location. A Geotech disposable capsule filters (0.45-micron) was used to filter water for dissolved constituents. Samples were filtered for all analysis except Total Iron, Unfiltered Total Nitrogen (UTN), Unfiltered Total Phosphorus (UTP), Total Organic Carbon (TOC), and Alkalinity. Samples for dissolved organic carbon concentration and dissolved organic matter composition were collected in 125-mL amber glass bottles. Dissolved inorganic carbon samples were collected unfiltered and without headspace in 60-cc luer-lock syringe with 3-way stopcocks with luer fittings. Water isotope samples were collected unfiltered in 12-mL borosilicate glass vials. All other dissolved constituents were collected in 500-mL HDPE Nalgene bottles. Unfiltered samples for analysis of UTN, UTP, TOC, and alkalinity were collected in 250-mL HDPE Nalgene bottles. A detailed SOP for stream water collection can be found in O'Donnell and Miller (2018).

All DOC concentration and DOM composition parameters (UV Absorbance 254 nm, SUVA 254 nm) from 2015-2019 were analyzed at USGS Organic Matter Laboratory in Boulder, CO by Kenna Butler or Brett Poulin. DOC concentrations were determined using an O.I. Analytical Model 700 TOC analyzer via the platinum catalyzed persulfate wet oxidation method. UV-visible absorbance was measured on filtered stream samples at room temperature using a quartz cell with a path length of 1 cm on an Agilent Model 8453 photodiode array spectrophotometer. Specific UV absorbance at 254 nm (SUVA254) was determined for all stream samples by dividing the decadal UV–visible absorbance coefficient at k = 254 nm by DOC concentration. SUVA254 is typically used as an index of DOC aromaticity and provides an average absorptivity at k = 254 nm of the DOM (Weishaar and others 2003).

All other stream water constituents were analyzed at Oregon State University’s Cooperative Chemical Analytical Laboratory (CCAL; http://ccal.oregonstate.edu/).