BG3-2: Contraction of lakes and wetlands accompanied by a declining water table reduces methane emissions and increases CO₂ loss, whereas increases in wetlands and lakes have the opposite effect, especially where sedge is introduced. Spatial and long-term significance of changes to ecosystems and their C budgets depends on permafrost and landscape constraints and on vulnerabilities to disturbance.

Our proposed water table manipulations include both raised and lowered water table treatments, which may be especially important for wetlands with strong topographical and geological variations that control subsurface flow. Correlations between rates of wetland contraction and evapotranspiration in interior Alaska point to important interactions between water availability and temperature in controlling ecosystem structure in Alaska (McGuire unpublished data). To our knowledge, this would be the first study to manipulate both moisture availability and temperature in situ, and to investigate interactions among drainage and warming in boreal wetlands. This work will complement water table drawdown experiments in other regions of the boreal biome, which have been conducted in Finland and in Canada. Such studies have shown that drainage of wetlands can have either negative (cf. Minkkinen & Laine 1998) or positive (cf. Waddington & Price 2000) feedbacks to greenhouse gas emissions depending on site and vegetation characteristics. We will work with Drs. Harri Vasander and Michael Waddington to integrate our results with ongoing drainage but we anticipate a renewed perspective from our inclusion of both wetter and drier manipulations coupled with warming experiments.

Field Experiment

Site Selection and Monitoring- During the summer of 2004, we will locate three wetland sites for manipulations near the Bonanza Creek Experimental Forest. Wetlands in this region tend to be open or sparsely treed sedge tussocks fens with Sphagnum between tussocks. The three sites will be selected based on location, access, and wetland morphology. Specifically, we will choose sites that 1) are similar in vegetation and water chemistry, 2) are large enough to accommodate the 3 separate drainage treatments, and 3) have water inflows that can be diverted with ditches (see details below). We will use satellite imagery and aerial photographs of the area determine wetland type (i.e., bog versus poor fen) and general structure (size, morphology, canopy characteristics) in our site selection process.

Detailed surveys of wetland structure (surface topography, water table height), soil characteristics, and wetland function (moisture, temperature, C fluxes) will be conducted at each site for one year starting in fall 2004. Temporary boardwalks will be constructed during initial site monitoring to limit site disturbance. We will install equipment at each of the three wetland sites, including a small micrometeorology tower at each site to monitor radiation, rainfall, and air temperature. Triplicate pressure transducers will be installed in the soil at each site for baseline monitoring of water table depth. Also, at five locations at each site, we will continuously monitor soil moisture and temperature at three depths above the water table using dielectric constant probes and thermistors, respectively (Yoshikawa and Hinzman in press). The depths of seasonal ice and snow pack will be measured manually every 2 weeks during the winter of 2005. The goals of our baseline monitoring are to assess between-site variability and to provide information on site hydrology that can be used in designing the drainage channels in each site.

Investigators from ongoing drainage experiments in eastern Canada and Finland also will be important in constructing the drainage design (see letters from Drs. Michael Waddington, Harri Vasander, and Jukka Laine). We are requesting travel funds for our international colleagues for at least one site visit and planning session during which co-PIs McGuire, Turetsky, and Harden will present details on the experimental design for discussion.

Experimental manipulations of water tables- We will establish three 80 m² plots within each site. Plots within each site will be assigned to one of three water table treatments (raised, lowered, no change or control) based on water movement at the site. Early in the spring of 2006 while soils are still frozen, we will create channels at each site for moving water away from the lowered water table plots and for irrigating the raised water table plots. A small excavator will be used to construct two main drainage channels surrounding the lowered water table plot at each site. These channels will be narrow (30 cm) and deep (~ 1 m) to facilitate water flow away from the plot. Our goal is to reduce water table inside the plots by an average of 20 cm. This reflects the level of drying predicted for many boreal wetlands under a doubled–CO₂ atmosphere (Waddington, personal communication). We will use chain saws to create several smaller channels that will divert water from the main channels to the raised water table plot at each site. Irrigation pipes of PVC will deliver water evenly to the surface of the raised water table plot. Alternatively, water will be dammed using impermeable layers of mineral soil from a nearby locality. Immediately following the channel construction, boardwalks will be installed at each of the three water table plots (raised, lowered, control) at the three sites. Five frozen soil cores will be extracted along a transect at each water table plot at the three sites using a permafrost auger (5 cores´3 drainage treatments´3 sites). Holes from these soil cores will be used for posts with crossbeams to support the boardwalk. Duplicate soil cores from each water table plot will be transported to U.S. Geological Survey labs in Menlo Park, CA in lengths of PVC tubing for soil and organic matter characterization. The remaining cores from each site will be transported in PVC tubing to the University of Alaska-Fairbanks for whole core incubations (see experiment below).

Experimental manipulation of temperature- At each water table plot at the three sites, we will establish six 3 m² subplots adjacent to boardwalks (total of 54 warming plots). Subplots in each water table plot will be assigned randomly to one of two warming treatments, including no warming (i.e., control) and year-round warming. Thus, warming treatments will be replicated in triplicate within each water table plot at the three sites. Studies have demonstrated that the soil thermal regime in interior Alaska is very sensitive to snow depth (Zhuang et al., 2001; Osterkamp and Romanovsky, 1999), i.e., the degree to which the soil environment is insulated from winter air temperatures depends primarily on the depth of snow, which has low thermal conductivity in interior Alaska. Thus, we will manipulate air and soil temperatures within the warming subplots using 1) open top chambers during the snow-free period following warming experiments at the Toolik Lake LTER site (cf. Welker et al. 2000), and 2) manual snow additions to increase soil insulation during months with snow cover. During our first year of baseline monitoring, we will test the influence of greenhouse height and snow additions on soil temperatures in a nearby wetland site.

In large-scale manipulations, particularly experiments involving full-factorial designs, there is always a compromise between intensity of measurements and the practicality of field logistics. We have built on existing drainage studies in Canada and Finland to include replicate sites for our drainage manipulations. Our design does not include replicate water table plots within a site, but we will examine the influence of water table treatments using site as a blocked effect. To strengthen the power of our drainage´warming analyses, we are including replicate warming subplots within each water table plot.

Thermal and hydrological monitoring

Immediately following soil thaw in 2005, we will begin to measure the influence of the water table and temperature manipulations on thermal and hydrological variables. At each of the three sites (n=3), we will continuously monitor radiation, rainfall, and air temperature using small weather stations. We will install triplicate pressure transducers within each water table treatment at each of the three sites (3 sites×3 water level treatments×3 replicates=27 transducers) to monitor the influence of the water table manipulations.

We will select one of our three sites to monitor physical variables intensively (also for intensive substrate utilization work outlined below). At each warming subplot within the three water table plots at this intensive site (6 warming subplots´3 water table plots´1 site), we will log hourly soil moisture using dielectric constant probes in surface soils and TDR in deeper soils, and soil temperature using thermistors. Soil moisture and temperature probes will be placed 5 cm beneath the vegetation surface, and every 15 cm down to the mineral soil transition. We also will monitor total and photosynthetically active radiation (PAR) using radiometers placed one meter above the vegetation surface and immediately above the moss surface. All data will be logged using Campbell Scientific dataloggers. At every warming plot in the other two sites, we will measure surface soil temperature, soil moisture, relative humidity and PAR using handheld probes during gas flux campaigns. Across all sites, we will manually measure the depths of seasonal ice and snow packs during gas flux campaigns.

Measuring and detecting Changes in carbon

We expect that C fluxes across our experimental treatments initially will be dominated by changes in heterotrophic respiration under the altered thermal and moisture regimes. However, over time, microbial ecology will be moderated by substrate utilization, as shifts in vegetation structure will influence the quality of organic matter inputs to soils. We expect that changes either towards bryophyte communities under saturated conditions (cf. Turetsky 2003) or towards woody vegetation under improved drainage (cf. Minkkinen and Laine 1998) will lead to the accumulation of recalcitrant compounds in soils. To capture these complex responses occurring over different timeframes, we will monitor seasonal C fluxes (CO₂, CH₄, DOC) in relation to temperature, moisture and annual soil inputs (NPP) of moss, vascular litter, and roots. Separating the contributions of NPP and heterotrophic respiration to C fluxes, and the controls over substrate quality and utilization in soils, requires both destructive harvests and nondestructive measures of organic matter quality, DOC, CO₂, and CH₄.

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Hypothesis BG3-2-1: Moisture availability controls vegetation structure and productivity. As a result,

a. Inundation by higher water tables will increase the cover of mosses, particularly Sphagnum species, while soil drainage will favor the invasion of woody species such as Betula nana and Picea mariana.

b. Drainage to lower water tables will increase belowground NPP by favoring vascular productivity over nonvascular mosses.

c. Higher water tables will influence the seasonality of NPP by increasing the productivity of mosses during tail seasons (~May-June; September-November).

NPP as inputs to soil- The focus of our measurements is to assess changes in vegetation structure, function, and seasonality as a function of soil climate manipulations. We expect vegetation, particularly bryophytes, to respond quickly to these manipulations, resulting in changes in species composition and net primary productivity (NPP). We will establish 1 m² permanent quadrats for measuring vegetation composition in all 54 warming subplots following snow melt in 2005. The percent cover of both vascular and nonvascular species will be estimated at the beginning and end of each growing season thereafter. Warming at high latitudes affects plant phenology (Arft et al. 1999); therefore, we will note the timing of phenological events such as leaf budding and senescence, and flower (vascular) and sporophyte (nonvascular) production at each vegetation quadrat.

Since mosses can initiate photosynthesis earlier in the growing season than many vascular species, changes in vegetation structure likely will influence the seasonality of NPP. Following soil thaw in 2006, we will install nondestructive cranked wires (40 wires per plot) within each permanent vegetation quadrat and the vertical growth rates of mosses will be measured each spring, summer, and fall. Within each warming subplot, we will collect destructive litter samples outside of permanent vegetation quadrats annually in the fall, once soils have started to freeze to minimize soil disturbance. These destructive harvests will be used to estimate vascular NPP as well as moss bulk density measurements to use with cranked wire data to estimate nonvascular NPP (Clymo 1970, Rochefort et al. 1990). At each warming subplot, we will assess belowground productivity by installing five root ingrowth bags constructed of commercial peat; ingrowth bags will be sampled each fall. All litter samples associated with destructive harvests will be sorted by plant species and tissue type, including leaves, stems, and roots (vascular only; fine vs. coarse size fractions). For Sphagnum species, we also will separate capitula (0-1 cm section comprised of developing leaves) from other depth intervals. Subsamples will be oven dried, ground on a Cyclotech mill, and analyzed for organic matter content by loss on ignition (550 ºC for 5 hrs), and C and N concentrations using a Carlo Erba.

Hypothesis BG3-2-2: Thermal and moisture regimes interact to control gaseous C fluxes to the atmosphere, largely by controlling rates of heterotrophic respiration. As a result,

a. Lower water tables lead to greater CO₂ fluxes to the atmosphere. If sedges persist under drier soil conditions, improved drainage will not reduce CH₄ fluxes to the atmosphere, as sedge stems serve as conduits for CH₄ to bypass aerobic soil layers. Higher water tables will increase CH₄ fluxes to the atmosphere.

b. Warming will increase CO₂ fluxes to the atmosphere by stimulating heterotrophic respiration, especially in near-surface peat layers. Warming will have less impact on C mineralization in deeper peat layers that is thermally protected from fluctuating air temperatures.

c. Changes in vegetation structure towards bryophyte or woody-dominated communities (Hypotheses 1) will increase the inputs of recalcitrant organic matter to soils, with negative feedbacks to heterotrophic respiration. Thus, over time with improved drainage, increased inputs of woody vegetation to soils offsets increases in aerobic heterotrophic respiration under improved drainage. Under higher water tables, slow heterotrophic respiration in anaerobic soils is exacerbated by increased inputs of recalcitrant bryophyte organic matter to soils.

CO₂ and CH₄ fluxes- Immediately following snowmelt in 2005, we will install replicate aluminum chamber bases in all 54 warming subplots. Clear chambers will be used to measure net ecosystem gas exchange. During our first year of baseline monitoring, we will test various chamber sizes to reduce within-site variability in C fluxes caused by microtopography. CO₂ will be measured with a portable chamber system including a LiCOR 6400 infrared gas analyzer. Chamber designs will follow that of Carroll & Crill (1997). Wetlands in interior Alaska largely are open (treeless) or sparsely treed, but we will design chambers to accommodate shrubby vegetation cover. Removable lids on the chambers will allow headspace equilibration with ambient gas concentrations. Once equilibrated, the chamber lid will be sealed and gas will be continuously sampled over a four-minute sample period. We will monitor air temperature and solar radiation within each chamber over the sampling period. Headspace temperatures will be controlled by running an airline through a cooler packed with ice or frozen soil excavated from a neighboring site.

At the intensive site, a series of opaque shrouds will be placed over the chamber to quantify NEE as a function of light intensity (Bubier et al. 1998). Across all three sites, total ecosystem respiration will be measured under a dark shroud. Net CH₄ flux will be quantified immediately following NEE and respiration measurements at each plot. Four CH₄ samples will be collected sequentially in polypropylene syringes (following Crill et al. 1988) and injected into pre-evacuated Hungate tubes. These gas samples will be analyzed using gas chromatography with a flame ionization detector at the University of Alaska-Fairbanks.

Gas exchange will be conducted weekly to biweekly throughout the growing season and tail seasons, and biweekly to monthly during winter months. We will attempt to randomize time of day and weather conditions among all measurements in order to capture full variations of light and temperature for each collar. Empirical models for ecosystem CO₂ uptake (i.e., gross primary production, GPP), ecosystem CO₂ release (ecosystem respiration), and net CH₄ exchange will be based on gas exchange and environmental measurements (Bubier et al. 1998). Bubier et al. (1998) used dynamic chambers for measurements of net ecosystem exchange (NEE) and found them to be comparable to eddy flux towers and automated chambers.

Hypothesis 3-2-3: Soil thermal and moisture regimes interact to control DOC export to aquatic ecosystems. As a result,

a. Lower water tables lead to greater DOC export, while warming stimulates the production and degradation of labile C (Hypotheses 2) in DOC, leading to increased recalcitrance of DOC compounds.

b. Vegetation controls DOC through the production of soluble compounds; increased belowground productivity (Hypotheses 1) and root exudation under lower water tables stimulates heterotrophic respiration (Hypotheses 2). Increased organic acids and recalcitrant DOC released by bryophytes under higher water inhibits heterotrophic respiration.

DOC flux- Triplicate piezometers and pressure transducers (see section 4) will be used to monitor the position of the water table in each plot at the three sites (site measurement list table). We will install replicate wells along the flow gradients at each plot (control, raised, lowered water tables) following the aquifer gradient outside of the warming subplots (6 replicate wells×3 water table treatment×3 sites). Triplicate transects of wells following the water flow path will be included at the intensive site. From each well, we will sample water at 3 depths below the water table (15 cm increments). Solution chemistry will be analyzed for dissolved organic carbon (DOC) and particulate organic carbon (POC; based on filtration through a 0.45 m filter) using a Shimadzu TOC-A total organic C analyzer. NH₄⁺, NO₃^- and ortho-P concentrations will be determined with a Lachet at the University of Alaska Fairbanks. To assess aromatic-C in DOC samples, absorption of samples at 254 nanometers will be measured on an ultraviolet/visible spectrophotometer. To distinguish between microbial- versus plant or soil- derived DOC, pyrolysis-mass spectrometry will be performed on select freeze-dried subsamples; Turetsky unpublished data, cf. Aiken et al. 1985). To assess DOC cycling within the unsaturated zone above the water table, we will perform laboratory leaching experiments and DOC characterization (UV absorbance and freeze-dried pyrolysis-mass spectrometry as described above) on subsamples of litter collected annually from destructive harvests in the warming subplots following Neff and Hooper 2002. Assessment of DOC flux in the subsurface environment will be achieved using numerical modeling. Neff and Asner (2001) report that the subsurface hydrologic conditions influence the leaching and apparent reactivity of dissolved organic matters and represent one of the most basic but frequently overlooked aspects of soluble element fluxes. The flux and concentration of dissolved inorganic elements are grossly affected by the hydraulic conductivity and the capacity for bypass flow (see for example, Prendergast, 1995). It is most likely that DOC behaves similarly as the dissolved inorganics in the subsurface (Radulovich et al., 1992). Weigand and Totsche (1998) provide evidence of the rate of water flow affecting the physical reactivity of DOC through laboratory experiments. We will use an advective-dispersive transport model that also incorporates sorption and desorption of DOC in porous media. MODFLOW (a modular three-dimensional finite difference based model for fluid flow in porous media, developed by USGS) will be used to estimate water flux through the saturated zone, although unsaturated flow may become important especially in the lowered treatment. There is a combination of transport packages (e.g. MT3D) that are available with MODFLOW to simulate transport of solutes. Besides MODFLOW, other models such as TerraFlux (Bonan, 1995) may be considered for adequacy and adaptability of the simulation regime and parameters, especially for unsaturated flow and flux dynamics. Such parameters will be obtained locally from the experimental sites and laboratory analyses.

Hypothesis BG3-2-4: The zone of water table fluctuation supports high levels of microbial activity, stimulating CO_2, CH₄, and DOC production in soils.

C losses during water table fluctuations - Our field manipulations will alter average water table depths and soil temperatures at three replicate sites. To further examine the influence of fluctuating water tables and temperatures on C fluxes under more controlled conditions, we will perform a 12 month, whole-core incubation in growth chambers at the University of Alaska-Fairbanks. Fifteen cores collected during boardwalk construction will be immediately transported to the University of Alaska-Fairbanks in PVC tubing, and will be placed in growth chambers. For the duration of this experiment, light and temperature conditions will be set to mimic average monthly light and temperature conditions in Fairbanks (approximately 30 miles from the Bonanza Creek Experimental Forest). After an equilibrium period of one month, cores from each site will be randomly assigned to one of three treatments: 1) high water tables held constant at 3 cm beneath the vegetation surface, 2) low water tables held constant at 20 cm beneath the vegetation surface, and 3) water tables fluctuating between 3 and 20 cm beneath the vegetation surface every two weeks. To ensure proper placement of the water table, drain holes will be drilled in the PVC pipe at 3 and 20 cm beneath the vegetation. Cores will receive either rainwater collected from the field site or synthetic rain following the approach of Verry 1983.

We will quantify gas fluxes by fitting a small chamber on top of each core using rubber molding to seal the headspaces. CO₂ and CH₄ production will be quantified using a LiCOR 6400 infrared gas analyzer and gas chromatography following the methods outlined above. DOC concentrations will be quantified in water samples collected at the 20 cm drainage port in each core. Gaseous and dissolved C production under each water level treatment will be quantified each month for one year. Site and vegetation (hummock or hollow) will be tested as covariates for CO₂, CH₄ and DOC fluxes. Information from this experiment, along with seasonal variations in our field data, will be used to investigate the effects of fluctuating temperature and moisture conditions on C losses.

Hypothesis BG3-2-5: Thermal and moisture regimes control organic substrate quality and utilization during heterotrophic respiration:

a. Initially, heterotrophic respiration in response to changing soil climates is controlled by the utilization of organic substrates previously protected by cold or saturated soil conditions. For example, lowering water tables increases acrotelm (peat above the regional water table) thickness, stimulating the aerobic mineralization of some older soil organic matter.

b. Over time, shifts in vegetation structure in response to altered soil moisture and temperature change the quality of organic matter inputs to soils, with potential positive or negative feedbacks to heterotrophic respiration. For example, warming will stimulate microbial activity in surface soils across all moisture regimes. Under higher water tables; however, increased bryophyte cover will lead to more recalcitrant organic matter inputs, potentially inhibiting microbial activity despite the effects of warmer temperatures.

Litter chemistry and substrate utilization- While our experimental design will address the significance of water table changes and warming treatments on C input (NPP) and loss (respiration and DOC flux) components, it may not capture the underlying mechanisms linking C flux to vegetation, microbial ecology, and soil climates, including the biotic (vegetation, microbes) and abiotic (soil climate) controls on substrate quality. Moreover, substrate changes may be small or may counteract one another so that detection of important shifts is difficult. Carbon isotopes of solid and gas phases are especially sensitive to organic matter quality during heterotrophic respiration (Fernandez et al. 2003), and will be a sensitive tool for investigating shifts in substrate utilization during our field manipulations. These analyses will capitalize on samples collected during the destructive harvests once a year in the fall at our intensive manipulation site. Isotope methodologies (Schuur et al, 2003; Gaudinski et al. 2003; Harden et al, 1999) will be conducted in collaboration with Ted Schuur, an LTER affiliate. Using our initial, pre-manipulation measurements (2004) as well as measurements from the control subplots at the intensive site to determine a baseline for change, we will characterize stable and radioactive C isotopes to provide insight into substrate utilization in each experimental treatment. However, we expect early leachate and soil gases to be enriched in radiocarbon as the dying vegetation is replaced and thus will concentrate our ¹⁴C analyses on early changes following the manipulations. Each fall, we will analyze the isotopic signatures of 1) litter components (moss, roots, aboveground vascular litter) from the destructive harvests, 2) surface and deep soil layers from soil cores, 3) DOC from leachates of litter components, 4) DOC from wells representing export from each plot, and 5) gaseous C from field chamber measurements. Together, these measurements will allow us to characterize the signatures of leached and mineralized substrates following our manipulations and also to detect new inputs of soil substrates occurring with shifts in vegetation structure. Isotopic signatures for all samples will be prepared at the U.S. Geological laboratories; stable isotopes will be analyzed in Menlo Park and radiocarbon will be run at laboratories at the University of California Irvine.

We will combine leaching and incubation experiments (following Neff and Hopper 2002) on surface and deep soils collected during the destructive harvests in all warming subplots at the intensive site. Incubations conducted at –10° C, 0° C, +10° C, and +20° C will provide response quotients (Q₁₀) for the temperature and water table manipulations. CO₂ and CH₄ production in aerobic (room air) and anaerobic (N₂) headspaces will be quantified using gas chromatography with thermal conductivity and flame ionization detectors, respectively (Turetsky in press). Ratios of CO₂:DOC will provide an index of relative C loss for each soil profile across the experimental treatments.

Organic matter quality will be quantified by proximate analysis (Turetsky et al. 2000) and pyrolysis-mass spectrometry (Turetsky unpublished data) to document the turnover of organic C compounds in soil in the various experimental treatments and quality of new vegetation inputs entering the soil. Isotopic signals of both labile (i.e., water soluble carbohydrates) and recalcitrant (i.e., acid insoluble material) fractions of soil organic matter samples will be analyzed to investigate isotopic shifts during C turnover. We will use mixing models and multivariate analysis to explore the relationship between isotopic signatures of soil, DOC, and litter components, including shifts in labile (i.e., simple carbohydrates, N-containing compounds) and recalcitrant (i.e., polyphenols such as lignin) compounds through time.

Dynamic modeling: exploring causal links between hydrology, thermal regimes and C cycling

We will synthesize understanding gained from the field and laboratory studies into a site-specific version of a regional-scale model that represents interactions among hydrology, soil thermal regimes, and C cycling. The starting point for the site specific model is a version of the Terrestrial Ecosystem Model (TEM) that represents (1) how soil thermal dynamics influences carbon cycling of ecosystems of interior Alaska and (2) how interactions between water table dynamics and the soil thermal regime influence CH₄ exchange of northern ecosystems. Interactions between soil thermal and carbon dynamics in this version of TEM have been evaluated for black spruce ecosystems in Canada and interior Alaska (Zhuang et al., 2001, 2002, 2003). The dynamics of CH₄ in TEM explicitly considers the processes of methanogenesis and methanotrophy, and the important CH₄ transport mechanisms including diffusion and plant-mediated emissions through hollow stems (Zhuang et al., in review). The model is driven by daily air temperature, precipitation, radiation, and humidity, and soil-water pH must be specified. This version of TEM simulates daily fluctuations in the soil thermal regime, including soil temperature profile, active layer depth, and permafrost dynamics. Soil hydrology is represented by a multiple-layer soil-water module of moss, organic soil, and mineral soil layers that considers fluctuations in water-table depth. The CH₄ dynamics of the model have been evaluated by comparing simulations with CH₄ flux measurements made at the two major field sites of the Boreal Ecosystem-Atmosphere Study (BOREAS) [Sellers et al., 1997; Newcomer et al., 1999], and at the tundra sites at Toolik Lake Field Station, Alaska.

We will enhance this version of TEM to represent DOC dynamics by adding the soil column processes that affect DOC concentration in soil water and by representing the lateral flow of water in our treatments. The soil column processes affecting DOC will be based on Neff and Asner (2001) and the lateral flow of water will be based on simulations using numerical models such as MODFLOW or TerraFlux (discussed before). Losses of DOC from near surface soil regime due to surface-subsurface mixing will be based on Boyer et al. (2000). After incorporating DOC dynamics into TEM, we conduct simulations for each of the treatments by driving the model with daily climate data and by specifying the trends in water table changes that occurred in the lowered and raised water-table treatments. Because our goal is to build realistic dynamics into the model for purposes of conducting regional studies, we will evaluate whether model-data mismatches can be minimized (1) first through parameter adjustments, (2) second through altering formulations in the model, and (3) third through making conceptual changes in the model. The model dynamics will be evaluated for simulating the dynamics of the soil thermal regime, the water-table, net primary production, net ecosystem exchange, ecosystem respiration, CH₄ exchange, and DOC fluxes. Once the model has been evaluated and modified in the context of the experimental data, we will use it to conduct studies that evaluate how changing hydrological and climate conditions in interior Alaska are influencing the regional exchange of CO₂ and CH₄ with the atmosphere (see below).

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