2.1. Site Description
 Samples were collected during the growing season of 1999 in Turnagain Bog, which is a 200-ha ombrotrophic convex peatland located in Anchorage, AK, (60°10′N 149°11′W). Summer and winter temperatures in the area vary from 8° to 19°C and from –16° to 6.4°C, respectively, with a mean annual temperature of 2°C. The study area was a Sphagnum moss-Myrica gale (Sweet gale) region in the center of the bog containing plants typical of ombrotrophic bogs. The surface layers (2–4 cm) of the bog contain actively growing Sphagnum moss, whereas the layers below contain brown, decaying peat. The in situ pH is 4.66–5.1. A detailed description of the bog is given by Hogan and Tande . A boardwalk was constructed in July 1998 to provide for minimal disturbance throughout the study area. The bog remained frozen through mid-May, 1999. Within 5 days of spring thaw, temperature sensors, a water level sensor, and pore water samplers were placed in the bog and a barrier put in place to discourage moose traffic.
2.2. In Situ Measurements
 Water level in the bog was determined by using a water level sensor and data logger system (WL300, 0–91.4 cm range, Global Water, Gold River, California) inserted into a well made of slotted PVC pipe (152.4 L × 5.08 cm I.D.). Water level measurements were recorded hourly and are reported as daily averages. The surface of the peat did not change appreciably with respect to the well during the study; therefore no correction for peat movement was made when calculating the water level relative to the peat surface. Temperature was determined at depths of 2, 4, 6, 10, 16, and 26 cm by using temperature sensors and data loggers (Onset Computer Corp., Pocasset, Massachusetts). A sensor was also placed in the shade underneath the boardwalk to record ambient air temperature. Temperature was recorded hourly and reported as daily averages. Precipitation data were obtained near by from the Anchorage International Airport station of NOAA's National Climate Data Center.
2.3. Pore Water Analysis
 Pore water was collected weekly from Teflon "sippers" that consisted of porous filter units designed to filter eluent for ion chromatography (Dionex Corp., Sunnyvale, California). These units were connected to 1/8 inch Teflon tubing and placed within the peat at depths of 2, 4, 6, 10, 16, 20, and 26 cm. The terminal porous portion (4 cm in length) was wrapped in Teflon tape so that water was collected only through a 1-cm window at the tip. Pore water for ion analysis was collected by using a syringe attached to the tubing. After rinsing the tubing and syringe with ∼10 mL of pore water, 1-2 mL of water was collected and filtered through a 0.2-μm syringe filter (13 mm, IC Acrodisc, Pall Gelman Sciences, Ann Arbor, Michigan) into clean distilled H2O rinsed plastic scintillation vials. Vials were held on ice for transport to the lab and analyzed for acetate, SO42− and NO3− concentrations within 5 hours of collection. Water for Fe(II) analysis (1 mL) was immediately filtered through a 0.45-μm nylon filter (13 mm, Acrodisc) into microcentrifuge tubes containing 10 μl of concentrated nitric acid.
 Acetate was measured by injecting 25-μL samples into a Dionex 1200 ion chromatograph with an AS14 4-mm ion exclusion column with suppression and with a sodium carbonate eluent. Acetate standards were prepared fresh in the laboratory from sodium acetate. Sulfate and NO3− were measured in the same samples and concentrations determined by comparison to dilutions of Dionex 5-anion standard. Reduced Fe was measured colorimetrically by using Ferrozine [Stookey, 1970].
2.4. Laboratory Incubation Experiments
 To examine anaerobic microbial activity within the bog, peat was collected periodically (usually 1–2 week intervals) throughout the season in a manner similar to that described by Kiene and Hines . Samples were collected from Sphagnum depressions. Green surficial Sphagnum moss was discarded (upper ∼2–4 cm) and a sample of brown peat (∼5 × 5 x 20 cm) was removed with a knife and placed in a 1-L glass jar. The jar was filled to the top with bog water so that no air pockets were present, and sealed with airtight lids. Jars were placed on ice for transport to the laboratory. Generally, samples were used immediately to create slurries. Occasionally, samples were stored at 4°C for 1–2 weeks prior to use.
 Slurries were prepared by draining excess water from the peat, sorting to remove woody plant roots and green Sphagnum, and placing 100–300 g (wet weight) into a blender. Bog water was added and the mixture homogenized so that a ratio of ∼1:3 wet weight peat:total volume slurry was achieved. Slurries prepared in this manner contained 0.04–0.08 g dried peat mL−1 slurry. Aliquots (50 mL) of slurry were transferred to 72-mL vials, and the vials were sealed with Teflon-lined butyl rubber septa, sealed with aluminum crimps, and flushed with N2 for 5–10 min. Slurries were preincubated in the dark for 12–18 hours. Following preincubation, vials were flushed with N2 again prior to analysis. All incubations were conducted in the dark at in situ temperatures (determined by averaging the 6–26 cm depth temperatures in the bog on the day peat was collected). Vials were incubated in the inverted position to minimize the possibility of oxygen entry through the stoppers. An equal volume of N2 was injected into the vials upon removal of samples for CH4, CO2, acetate and Fe(II) analysis. Replicate vials were amended with 10 mM 2-bromo-ethanesulfonic acid (BES, Sigma-Aldrich, St. Louis, Missouri), a known inhibitor of methanogenesis, by adding 1 mL of a stock solution of BES (500 mM, pH 5.0). Additions of BES had no impact on the pH of the peat slurries, which averaged 5.35 ± 0.2.
 Headspace samples for CH4 analyses (1 mL) were removed by a 1.0-mL plastic syringe. Samples were injected into a Shimadzu GC-9A gas chromatograph equipped with a 6 port valve and sample loop, a flame ionization detector, and a stainless steel column (25°C) packed with Poropak Q. Helium was used as carrier gas at a flow rate of 35 mL min−1. Total CH4 data were corrected for partitioning between gas and liquid phases and are reported as total μmol CH4 L−1 slurry. Carbon dioxide was measured by removing headspace samples (0.5 to 1.0 mL) from vials by a gas-tight Hamilton microsyringe with a side bore needle and injecting into a Shimadzu GC-14A gas chromatograph equipped with a thermal conductivity detector (injector/detector temperature = 90°C; TCD = 80°C) and a Teflon column (1/8 inch, 30°C) containing Poropak Q. Helium was used as carrier gas at a flow rate of 20 mL min−1. Total CO2 was calculated in the manner described for CH4 analysis.
 Slurry samples (1 mL) for acetate analysis were collected from vials by a plastic 1.0-mL syringe. Samples were centrifuged (12,000 × g) for 5 min to pellet peat, and the supernatant was filtered through a 0.2-μm IC syringe filter and frozen until analysis within 1 week of collection. Samples were thawed on ice and analyzed for acetate and other ions as described above. Slurry samples (0.5–1.0 mL) were also removed for Fe(II) analysis. Microcentrifuge tubes (0.6 mL volume) were totally filled and centrifuged to removed peat as described for acetate. The supernatant was filtered through a 0.45-μm syringe filter, fixed in nitric acid, and analyzed for Fe(II) as described above. For all analysis, triplicate vials were sampled at 24- to 48-hour intervals for 5–7 days and rates calculated from linear regression analyses.
 Occasionally, following the incubation of slurries for 5–7 days, vials were opened and contents pooled into a beaker in which the headspace was flushed continuously with N2. While gently mixing, aliquots of slurry (3–4 mL) were transferred to vials (13-mL capacity) that were continuously flushed with N2. After aliquots were transferred, vials were sealed with Teflon-lined gray butyl rubber septa and aluminum crimps and the headspace flushed with N2 for 10 min. The vials were incubated for 12–18 hours at in situ temperature, after which the headspace was flushed with N2 again and 2-14C-acetate (∼0.1 μCi) added. Duplicate or triplicate vials were sacrificed periodically (usually 8- to 24-hour intervals) for 24–48 hours by adding 1 mL of 6N HCl to the vials and shaking overnight. Headspace samples were then analyzed on a GC equipped with a gas proportional counter (RAGA, Raytest Inc., Germany) for 14CH4 and 14CO2.
 A depth profile was conducted in which a peat sample, 5 × 5 × 26 cm, with the green Sphagnum layer intact, was collected and returned to the laboratory. The peat was carefully cut into 6-cm sections representing depths of 0–6, 6–12, 12–18, and 18–24 cm. The 0- to 6-cm-depth section contained green Sphagnum. Each depth section was slurried as described above and incubated anaerobically at 25°C. Slurry samples were removed daily and analyzed for acetate.
 To examine the impact of long term incubation of peat at warmer temperature, the peat was collected and incubated intact with bog water under anaerobic conditions in a 1-L jar at 24°C for 4.5 months. Samples of bog water were removed with a 1.0-mL syringe and analyzed for acetate. The peat was then slurried and transferred to vials as described above and incubated anaerobically at 24°C. Samples of headspace and slurry were periodically removed for CH4 and acetate determinations.