---AUTHORS:
-Jeff Welker (PI), Jace Fahnestock (co-PI)
-Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, CO 80523-1499
-jwelker@nrel.colostate.edu, jace@nrel.colostate.edu
-970)491-1796 (Jeff), 970)491-5262 (Jace), 970)491-1965 (Fax)

---DATA SET OVERVIEW:
-This data represents estimates of wintertime carbon efflux from various tundra and subarctic
soils over several winters. The technique used is static chemical absorption through the use of
sodium hydroxide base traps (NaOH). This technique is very simple to use and requires
virtually no maintenance. However, it is a technique that provides only rough quantitative
estimates at best. We have found that this technique tends to underestimate wintertime fluxes
by as much as 35% when compared to other techniques such as infrared gas analyses.

---DATA COLLECTION and PROCESSING:
-Typically, 500ml of 7N NaOH was placed in a 1 liter open-topped container which in turn was
placed beneath a closed plastic chamber. That is, a chamber was placed over the NaOH
solution such that the solution could absorb CO2 that was emitted only from the footprint of the
chamber. The chamber was sealed to the soil surface with clay to prevent CO2 from entering
the solution from outside the chamber. After the solution had been in the field all winter, it was
collected and diluted with distilled water. In the lab, excess barium chloride was added to the
solution, phenolpthalein indicator was added, and the solution was titrated with HCl on a mixing
table until the desired pH was achieved. The amount of carbon was calculated as:
mg of carbon = (B-V)NE
where B = ml of HCl needed to titrate controls, V = ml of HCl needed to titrate samples,
N = normality of the acid, E = equivalent weight (E = 6 for C; E = 22 for CO2). This was
multiplied by the chamber area and divided by the number of sampling days to yield mg C or
CO2 m-2 d-1.

---DATA FORMAT:
-Data is column delimited ASCII
-Column headers, in order, are: Site, Location, Plant community, Treatment (if any),
Date installed, Date collected, Mean C efflux (g C m-2 season-1), 1 SE of the seasonal mean,
Mean C efflux (mg C m-2 d-1), 1 SE of the daily mean

---DATA REMARKS:
-Keep in mind that these are very rough estimates of wintertime CO2 efflux in accordance with
the limitations of this methodology.