Plot location was chosen based on dominate vegetation type (T or W). The tussock tundra plots are located near the Moist Acidic Tundra plots characterized by Shaver and Chapin (1991). The wet sedge plots are located near the outlet of Toolik Lake; all plots have been used by the Arctic LTER project at Toolik Lake.

In wet sedge tundra, three 1 m2-sized plots were positioned randomly in each of two treatments of block 2 of the LTER wet sedge scheme (outlet site), control and N+P-fertilized , respectively, in 2000. Paired control and fertilized plots were labelled with 14C and 15N at one of three different dates of the summer season 2001.

In moist acidic tussock tundra six 1 m2 sized plots were positioned in three of the "X" (=extra") blocks of the LTER scheme, in 2001, inside an area extending 5 m from the boardwalks and, positioning plots so that similar area shares between tussocks and intertussock areas was achieved. In each of the three X blocks two 1m2-sized plots were established. The whole 5 m area of the X blocks extending from the board walks was divided into two halfs, each containing one of the 1m2 sized plots. One half was set aside as the control and the other half was designated to be fertilized. Fertilization with a Hoagland solution (see protocol) started in late summer 2001, and was repeated annually after that , early in the summer season. Paired control and fertilized plots were labelled with 14C and 15N of the summer season 2002; all three pairs were labelled as closely together in time as logistically possible.

For 14CO2 and 14CH4 determinations, dissolved gas (d-gas) and dissolved inorganic carbon (d-dic) samples were ran on Oxidation Line I, and bag samples were processed on Oxidation Line II. Both oxidation lines first trap CO2 in NaOH, oxidize residual CH4 to CO2 in an 800 ºC oven, then trap the CH4-derived CO2 in a 2nd NaOH solution (Whalen and Reebugh 1990). All scint vials from the oxidation lines were filled with 4mL of NaOH sample and 12mL of Scintiverse II cocktail. Solutions are then analyzed for 14C by a Beckman™ LS3801 Liquid Scintillation Counter (LSC).

1. Dissolved Gas Sampling Description:
Using soil sampling needles and a 60 mL syringe, we pulled 40 mL of bubble-free water out of the ground. We then pulled 20 mL of ambient air and vigorously shook the syringe for 2-3 minutes. After the shaking period, the gases in the headspace should be in equilibrium with the dissolved gas content. We transfered ~10-15 mL of the headspace air into a nylong, airtight syringe (Kling et al. 2000). The syringes were returned to the laboratory at the Toolik Field Station and were ran on the oxidation line.

2. Dissolved Inorganic Carbon (DIC) Sampling Description:
After the gas samples were analyzed, we expelled all air and bubbles from the water syringe to a standard volume of 38mL. The remaining water was acidified with 0.5 mL of 0.2N HCl through the stopcock, which converts DIC to Carbon Dioxide. We then added nitrogen gas headspace to 60 ml, and shook vigorously to equilibrate the headspace and DIC content (Stainton 1973). We split the headspace gas – 8 ml to a syringe for the GC (CO2 only); and the remainder to the oxidation line.

3. Dissolve Organic Carbon Sampling Description:
Using soil sampling needles and a 60 mL syringe, we pulled 40 mL of water out of the ground and filtered it through a Whatman GF/F filter (0.7μm pore size, nominal). At the laboratory, we pipetted 4 mL of the pore water and 12 mL of Scintiverse scint cocktail into a scint vial. We shook the solutions for 2 minutes on a shaker table, and then put the vial onto the LSC to determine the concentration of labeled DOC.

4. Bag Sampling Description:
During the system flux measurements, a bag is attached to the flux chamber though a battery operated pump. 15 minutes after the methane flux sampling, the pump was activated and the chamber headspace was pumped into the sample bag. Upon returning to the lab, the carrier line was disconnected from the oxidation line and a bag sample was attached. The bag was allowed to empty for 2 hours. Bag volumes were measured by displacement of water. 4mL of NaOH from the second trap was mixed with
scint cocktail and 14CO2 and 14CH4 were measured by LSC.

5. Soil Respiration Sampling Description:
After a flux measurement, we allowed the CO2 concentrations to build-up in the head space of the soil collars for 40 minutes. We evacuated a butyl stopper sealed glass serum vial with a hand vaccuum pump. We then added 15 mL of Carbo-sorb through the septum. We took a 120 mL gas sample from the soil collar and injected/bubbled it into the Carbo-sorb. Upon returning to the TFS lab, we transfered 10mL by syringe of the Carbo-Sorb into 10mL of Permafluor scint cocktail in a scint vial. The 14CO2 was determined by LSC.

Kling, G. W., G. W. Kipphut, M. M. Miller, and W. J. O'Brien. 2000. Integration of lakes and streams in a landscape perspective: The importance of material processing on spatial patterns and temporal coherence. Freshwater Biol. (43): 477–497.

Shaver, G.R. and F.S. Chapin. 1991. Production - biomass relationships and elemental cycling in contrasting arctic vegetation types. Ecological Monographs 61(1): 1-31.

Stainton, M.P. 1973. A syringe gas-stripping procedure for gas-chromatographic determination of dissolved inorganic carbon and organic carbon in fresh water and carbonates in sediments. J. Fish Res. Bd. Canada 30:1441-1445.

Whalen S.C. and W.S. Reeburgh. 1990. Consumption o f atmospheric methane by tundra soils. Nature 346:160-162.