ABSTRACT:

This resource specifically includes the Membrane Inlet Mass Spectrometer (MIMS) dissolved gas seasonal (approach 2) and synoptic (approach 3) sample datasets collected in our Talladega research watershed, including Argon (Ar), Oxygen (O2), Nitrogen (N2), N2:Ar ratio, and O2:Ar ratio. Approach 2 and approach 3 sampling campaigns conducted in Talladega research watershed were designed in support of the sampling goals of the NSF funded Aquatic Intermittency effects on Microbiomes in Streams (AIMS) project (EPSCoR funded project, OIA 2019603). Specifically, the MIMS dissolved gas data was collected by the biogeochemistry team to better understand the effects of stream drying on dissolved gases in the southeastern US. The Talladega National Forest (Cleburne County, AL, USA; Watershed Outlet Lat/Long: 33.76219799, -85.59550775) contains a non-perennial unnamed tributary of Pendergrass Creek, where our study sites were located, as well as 0.92 km^2 of mixed coniferous and deciduous forest in the Piedmont Upland physiographic section. The research watershed also spans an elevation range from 345 to 456 m above sea level and is a tributary to the Coosa River (within the larger Mobile-Tombigbee basin). The region has a humid subtropical climate, with mean daily January and July air temperatures of 5.3°C and 25.3°C respectively, and mean annual precipitation of 1,400 mm/yr.

On six different occasions from March 29, 2022 to January 29, 2024, we collected dissolved gas (MIMS) samples seasonally across 7 sampling locations (approach 2). On one separate occasion during June 2022, we collected MIMS samples from 49 sampling locations (approach 3) within the same Talladega research watershed. For the approach 3 sampling campaign, the sites were selected to balance multiple competing priorities: (i) strategically targeting existing monitoring infrastructure with long-term data; (ii) including sites near several known springs and tributary junctions; and (iii) including a range of drainage area and topographic wetness index (TWI) values, both of which have been correlated with flow permanence. Briefly, the sites selected based on drainage area and TWI were chosen by binning drainage area into 10 bins and then binning TWI into quintiles within each drainage area bin. We then randomly selected a point in each bin after accounting for points selected based on existing infrastructure, springs, and tributaries, as well as enforcing a minimum spacing of 100 m between locations. We then made minor adjustments to points to account for field conditions, for instance adjusting locations with respect to a road crossing.

Included in the Content section is the sampling datasheet that was used during field collection, as well as one compiled excel file containing approach 2 and 3 MIMS TAL data. Within the compiled excel file, the 'Working Files' tab contains the processed MIMS data before taking averages of all the replicates. The 'Final Data' tab has the data that should be used for analyses with the averages of all 3 replicates and standard deviations (sd) in uM units. Also, there are columns regarding whether the sample was from approach 2 or 3. Approach 1 samples were any MIMS samples collected at Talladega watershed outlet site (TLMO1) during approach 2 or 3 sampling campaigns. The raw MIMS data was processed and calculated via the package 'MIMSY' (R Package; M. Kelly (2020), https://cran.r-project.org/package=mimsy) and has 3 data points per replicate.

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.