---TITLE: Toolik Moist Tundra Ecosystem Flux ---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 (1996, 1997, 1998, and 2000) values of net carbon dioxide exchange, photosynthesis, and respiration (plant and soil) between the atmosphere and moist tussock tundra at Toolik Lake, Alaska (61.41N 39.42E). Climate change scenarios were experimentally implemented at this site in fall 1995. The first is an increase in wintertime snow accumulation that is achieved through the use of a 60 m long by 3 m tall snowfence (built in 1994). This fence increases wintertime snow accumulation in drifts on the lee side of the fence. The snowdrift is approximately 60 m long, 15 m wide, and 3 m deep at its deepest point. Ambient snow accumulation ranges from a few cm to 60 cm. The second climate change scenario is increased growing season air and soil temperatures. This is accomplished by setting out multiple 1 m2 open-topped chambers (OTCs) over Eriophorum vaginatum tussocks. These OTCs are hexagonal in shape and are constructed of transparent fiberglass. They typically raise air and soil temperatures by 1 to 4°C. The third climate change scenario at this site is a combination of the first to whereby winter snow accumulation and summer temperatures are both increased. The data set shows periodic CO2 gas exchange data throughout four summers in each of the four treatments - ambient temperature with ambient snow levels; ambient temperature with increased snow levels; elevated temperature with ambient snow levels; and elevated temperature with increased snow levels. The data are from 199606041600 to 200009181800. ---RELATED DATA SET: Toolik Dry Tundra Ecosystem Flux, which contains similar data for an identical experiment that was carried out in dry heath tundra at Toolik Lake, Alaska. ---INSTRUMENT DESCRIPTION: LI-COR LI-6200 infrared gas analyzer (IRGA) coupled to a transparent (37000cm3 for 1996-1998 measurements, 225,000cm3 for 2000 measurements) chamber. The chamber is placed on pre-selected plots at the time of measurement. Each plot is surrounded by a permanent 30cm by 30cm (1996-1998) or 75 cm by 75 cm (2000) base, inserted into the tundra in late 1994 (for the smaller bases) or late 1999 (for the larger bases), 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 three replicate plots in each of the four treatments. 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: Headings are DATE/TIME (UTC), TRT (-S-T = ambient winter snow and ambient summer temperatures, -S+T = ambient winter snow and elevated summer temperatures, +S-T = increased winter snow accumulation and ambient summer temperatures, and +S+T = increased winter snow accumulation and elevated summer temperatures), N_Net (number of replicate samples for net carbon dioxide exchange) NetFlux (net carbon dioxide exchange, umol m-2 s-1), StdDev_Net (standard deviation for net CO2 data), N_Ps (number of samples for photosynthesis), Photo (photosynthesis), StdDev_Ps (standard deviation for photosynthesis data), N_R (number of samples for respiration), Resp (respiration), and StdDev_R (standard deviation for respiration data). Data are ASCII space delimited. Missing data indicated with -99.99. ---DATA VERSION= 2.0 (11 March 2002) 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. ---REFERENCES: Additional information on site description, methodology, and analyses and interpretation of these data can be found in the following publications: Jones, M.H. et al. 1998. Arctic and Alpine Research 30(4):373-380. Welker, J.M. et al. 2000. Climatic Change 44:139-150.