---TITLE: Alexandra Fiord Wet Tundra Ecosystem

---AUTHORS:
Jeff Welker (PI), Jace Fahnestock (co-PI)
Natural Resource Ecology Lab, Colorado State University, Fort Collins, CO 
80523-1499
telephone 970-491-1796; facsimile 970-491-1965; e-mail 
jwelker@nrel.colostate.edu
data questions: jace@nrel.colostate.edu

---DATA SET OVERVIEW:
The data set presented here represent growing season (late-1999, 2000 and 2001) 
values of net carbon dioxide exchange, photosynthesis, and respiration between 
the atmosphere and wet tundra.  The site is located at Alexandra Fiord on the 
east-central side of Ellesmere Island, Nunavut, Canada at 78.54N 75.55W, 50 m 
elevation asl.  As part of the International Tundra Experiment, Greg Henry of 
the University of British Columbia has been increasing air and soil 
temperatures at this site since 1993 using small open-topped chambers (OTCs).  
These OTCs are hexagonal in shape and are constructed of transparent 
fiberglass.  They typically raise air and soil temperatures by 1 to 4C.  The 
data set shows periodic carbon dioxide exchange data from the end of the 1999 
growing season and throughout the 2000 and 2001 growing seasons in ambient 
plots and long-term (7-9 yrs) warmed (OTC) plots.  The most complete data set 
(2001) begins in spring before winter snowmelt and ends at the end of summer 
when snow has once again covered the ground.  The data are from 199908040800 to 
200108042400 UTC.  

---INSTRUMENT DESCRIPTION:
LI-COR LI-6200 infrared gas analyzer (IRGA) coupled to a transparent 
(225,000cm3; 75 cm x 75 cm x 40 cm tall) chamber.  The chamber is placed on 
pre-selected plots at the time of measurement.  Each plot is surrounded by a 
permanent 75 cm by 75 cm base, inserted into the tundra in late 1999, to which 
the chamber is sealed at the time of each measurement.  Measurements of carbon 
dioxide exchange are corrected for prevailing atmospheric pressure and 
temperature within the IRGA.

---DATA COLLECTION and PROCESSING:
Data are generally collected over 24-hour periods at various dates during the 
growing seasons.  Three consecutive 30-second measurements of net carbon 
dioxide exchange are taken on each plot at the time of measurement to ensure 
steady state conditions within the chamber.  The chamber is subsequently 
covered with an opaque cloth and three more measurements of respiration 
(photosynthesis eliminated by covering the chamber) are taken.  Photosynthesis 
is calculated as the difference between net flux and respiration.  There are 
four replicate ambient and four replicate warmed plots.  The three consecutive 
measurements are averaged for each plot and the data for the plots are 
subsequently averaged to produce a mean carbon dioxide exchange estimate for 
each treatment for each time period.  In this notation, negative numbers 
indicate net carbon loss by the tundra to the atmosphere during the measurement 
time period while positive numbers indicate net carbon gain by the tundra 
during the measurement period.  Thus, respiration is always negative and 
photosynthesis is always positive or zero.

---DATA FORMAT:
Data are column delimited ASCII.  Headings are DATE/TIME (UTC), TRT 
(temperature treatment - ambient or warmed), NET (net carbon dioxide exchange, 
umol m-2 s-1), N_SE (standard error for net CO2 data), Photo (photosynthesis), 
P_SE (standard error for photosynthesis data), resp (respiration), and R_SE 
(standard error for respiration data).  Missing data indicated with 999.99.  
DATA VERSION= 1.0 (30 November 2001) FINAL.

---DATA REMARKS:
Data are initially stored in the LI-6200.  Both BINARY and ASCII versions of 
the data are subsequently transferred to a PC where we primarily use Microsoft 
Excel to manipulate the data.  Because the LI-6200 operating parameters are 
calibrated and set before each measurement period, we do very little 
manipulation of the data following collection except to average the replicate 
measurements and plots. The three replicate measurements on each plot help to 
ensure no outliers.



PI/DATA CONTACT = Welker, Jeff (Colorado State U.)/Fahnestock, Jace (Colorado 
State U.)
DATA COVERAGE  = START: 199908040800; STOP: 200108042400 UTC
INSTRUMENT = LICOR LI-6200 Portable Gas Exchange System
LOCATION = Wet tundra, Alexandra Fiord, Ellesmere Island, Nunavut, Canada, 
78.54N 75.55W
DATA VERSION = 1.0 (30 November 2001) FINAL
REMARKS = Headings are DATE/TIME (UTC), TRT (temperature treatment - ambient or 
warmed), NET (net carbon dioxide exchange, umol m-2 s-1), N_SE (standard error 
for net CO2 data), Photo (photosynthesis), P_SE (standard error for 
photosynthesis data), resp (respiration), and R_SE (standard error for 
respiration data)
REMARKS = Missing data indicated with 999.99