---TITLE:  Winter carbon efflux estimates from NaOH base traps

---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.