ABSTRACT:

This resource contains the results from a set of whole-stream isotopically-label dissolved organic carbon (13C-DOC) addition experiments conducted in August 2019 to directly trace the uptake and mineralization of DOC into the stream DIC pool. These experiments were conducted in Blaine Creek, an open-canopy, agricultural, spring-fed stream located a the Montana State University Northwestern Agricultural Research Center in Creston, Montana, USA. Between 8 and 15 August 2019, we conducted three separate pulse releases of NaCl (used as a conservative solute tracer) and a reactive 13C-labeled DOC substrate, either 13C-labeled glucose on 8 and 15 August 2019 (as 3 grams of D-glucose dissolved in 100 mL of deionized water) or 13C-labeled leaf leachate on 9 August 2019. The 13C-labeled leaf leachate was prepared following Kaplan et al. (2008) using uniformly labeled 13C red fescue in deionized water. During each pulse release, we sampled for DOC, pH, alkalinity and CO2 at two sampling stations 41 (denoted as "upstream") and 61 meters (denoted as "downstream") downstream of the addition site, respectively. We also deployed sensors to collect dissolved O2 and temperature (PME miniDOT) and dissolved CO2 (Eosense eosGP) sensors at 10 minute intervals throughout the study period to estimate CO2 emission fluxes and daily rates of of ecosystem metabolism (i.e., gross primary production and ecosystem respiration). The file "blaine_65_oxy.csv" contains the 10-minute interval temperature and dissolved O2 sensor data from the downstream sampling station, which was used to estimate daily rates of metabolism.

The file "pco2_blaine.csv" contains the 10-minute interval temperature and dissolved CO2 data from both the upstream (denoted as "white" in column names) and downstream (denoted as "bela" in column names) sampling stations. The file "site_data.csv" contains relevant information to each pulse release such as reach length (in meters), mean wetted width (in meters), conservative and reactive tracer masses (in grams for "salt_mass" and "sugar mass", in milligrams for "doc_mass_13C_mg"), alkalinity, travel time between addition and sampling station (in minutes), as well as velocity (v.ms, in meters per second) and discharge (Qest.Ls, in liters per second) estimated from the conservative tracer during each addition.

For samples collected throughout each pulse release, we quantified 13-CO2 from headspace equilibrated samples immediately following the experiments using a Cavity Ring-Down Spectrometer (CRDS; Picarro), alkalinity via end-point titration, and DOC concentrations and del13C-DOC using a TOC analyzer (Aurora 1030, OI Analytical) coupled to a Picarro CRDS. The folder "DOC_runs" contains individual CSV files for each pulse release with the DOC concentration ("DOC_conc", in milligrams per liter), del13C-DOC ("Delta 13C"), and alkalinity (in meq/L) for each sampling timepoint. The folder "picarro_runs" contains individual CSV files for each pulse release with the CO2 and CH4 concentration ("CO2" and "CH4" in ppm), del13C-CO2 ("delCO2"), and del13C-CH4 ("delCH4") values for each sampling timepoint.

All file and column names are preserved to ensure coding and modeling workflows associated with this resource function, which can be found at https://github.com/robohall/DOC_uptake

References

Kaplan, L. A., T. N. Weigner, J. D. Newbold, P. H. Ostrom, and H. Gandhi. 2008. Untangling the complex issue of dissolved organic carbon uptake: a stable isotope approach. Freshwater Biology, 53:855–864.