pCO2 (partial pressure of carbon dioxide) was monitored in late summer
(late July to mid-August) over a period of 4 years (2013, 2015, 2017,
2018) from open water areas of a variety of aquatic habitats. pCO2 was
monitored for a minimum of 30 minutes, to allow measurements to
stabilize, up to a maximum of nearly 3 weeks of diel monitoring,
depending on the site. At sites monitored on a diel basis, aquatic CO2
was logged every minute using an NDIR CO2 sensor (Vaisala GMM 222)
enclosed in a PFTE membrane (sensu (Hari et al. 2008, Johnson et al.
2010, Bass et al. 2012) linked to a Campbell Scientific CR1000
datalogger. At sites where continuous stations were not installed, a
portable NDIR CO2 sensor (Vaisala GMT220) was allowed to stabilize for
at least 30 minutes before a value was recorded. Data were converted
to pCO2 using water temperature and pressure logged with a HOBO U20
logger. CO2 flux (g C/m2/day) was calculated following corrections for
diffusive exchange with the atmosphere estimated using wind-derived
gas transfer co-efficients (k) (Wanninkhof 2014).
DOC was measured on either a Lachat IL-550 or a Shimadzu TOC-V
analyzer. DOC was measured as non-purgeable organic carbon (NPOC) on
the Shimadzu instrument; data from the Lachat were converted to NPOC
based on samples run on both machines (n=86; range 1.9 to 68 mg/L
NPOC; r2=0.98).
Downward total solar irradiance data were retrieved from Barrow
Atmospheric Baseline Observatory (NOAA ESRL) prior to 2017. Post-2017,
these data were acquired from NEON's Barrow Environmental Observatory
Site (National Ecological Observatory Network 2018). A comparison
between the 2 sites in 2017 was used to standardize the data among
years (r2=0.97). Photosynthetically active radiation (PAR), air
temperature and rain data were collected from a HOBO weather station
installed near IBP Pond C until 2013. Starting in 2015, rain data were
retrieved from the National Weather Service, Barrow Airport; air
temperatures and atmospheric CO2 were from NOAA ESRL. For
identification of unusual temperature and radiation conditions, we
calculated the 95th percentile of each of these based on all data from
July and August in the 4 study years (2013, 2015, 2017, 2018); as
such, this is not meant to be representative of a long-term analysis,
but rather represents the study period in general.
A YSI 6920 V2 multiparameter water quality sonde was deployed into
IBP-C throughout the summers (early June- late August) of 2010-2013,
and also for 3 weeks in late summer 2015, to record temperature and
dissolved oxygen (DO) every 15 minutes. Data from the optical DO
sensor was used to continually estimate NEP at IBP-C using a
free-water metabolism (FWM) technique (Cole et al. 2000, Pace and
Prairie 2004, Staehr et al. 2010), where hourly NEP is expressed as a
function of the change in O2 minus diffusion. Diffusion and other
parameters were calculated using formulae and steps described in
detail elsewhere (Staehr et al. 2010). Even though there is no period
of darkness in June-July in Utqiaġvik, we assumed that PAR at 2am was
sufficiently low (Median = 35) to allow for estimation of respiration
(R), prior to the sun setting in early August; however, it is worth
noting that this assumption may be less robust at the beginning of the
summer when the sun does not set. Sensor-based DO was validated
against lab analyses using the Winkler method (Wetzel and Likens
2000).
Bass, A. M., M. I. Bird, M. J. Morrison, and J. Gordon. 2012. CADICA:
Continuous Automated Dissolved Inorganic Carbon Analyzer with
application to aquatic carbon cycle science. Limnology and
Oceanography-Methods 10:10–19.
Cole, J. J., M. L. Pace, S. R. Carpenter, and J. F. Kitchell. 2000.
Persistence of net heterotrophy in lakes during nutrient addition and
food web manipulations. Limnology and Oceanography 45:1718–1730.
Hari, P., J. Pumpanen, J. Huotari, P. Kolari, J. Grace, T. Vesala, and
A. Ojala. 2008. High-frequency measurements of productivity of
planktonic algae using rugged nondispersive infrared carbon dioxide
probes. Limnology and Oceanography-Methods 6:347–354.
Johnson, M. S., M. F. Billett, K. J. Dinsmore, M. Wallin, K. E. Dyson,
and R. S. Jassal. 2010. Direct and continuous measurement of dissolved
carbon dioxide in freshwater aquatic systems-method and applications.
Ecohydrology 3:68–78.
National Ecological Observatory Network. 2018. Data Products:
D18.BARR.DP1.00014.001. Provisional data downloaded from
http://data.neonscience.org on 10/15/2018. Battelle, Boulder, CO, USA.
Pace, M. L., and Y. T. Prairie. 2004. Respiration in lakes. Pages
103–121 in P. J. le. B. Williams and P. A. del Giorgio, editors.
Respiration in Aquatic Ecosystems. Oxford University Press.
Staehr, P. A., D. Bade, M. C. Van de Bogert, G. R. Koch, C.
Williamson, P. Hanson, J. J. Cole, and T. Kratz. 2010. Lake metabolism
and the diel oxygen technique: State of the science. Limnology and
Oceanography-Methods 8:628–644.
Wanninkhof, R. 2014. Relationship between wind speed and gas exchange
over the ocean revisited. Limnology and Oceanography: Methods
12:351–362.
Wetzel, R. G., and G. E. Likens. 2000. Limnological Analysis.
Springer-Verlag, New York.
