NE1938: Carbon Dynamics and Hydromorphology in Depressional Wetland Systems

(Multistate Research Project)

Status: Active

NE1938: Carbon Dynamics and Hydromorphology in Depressional Wetland Systems

Duration: 10/01/2019 to 09/30/2024

Administrative Advisor(s):

NIFA Reps:

Non-Technical Summary

Statement of Issues and Justification

The complexity of the carbon (C) cycle, and the potential for soil to act as both a C source and sink, have made projections of terrestrial C dynamics in light of global change difficult to determine with high confidence (Jaffe et al., 2013). The debate on whether soil is a net source or sink of C is ongoing because soil organic matter is a fundamental dynamic soil property that is capable of varying on human-time scales with changes in climate (Six et al., 2002; Janzen, 2006; West and Six, 2007; Ågren et al., 2008). If the United States is to manage and/or diminish future C emissions, scientists and policy makers must have dependable and accurate information on C stocks and fluxes (NOAA, 2013).

Of the landscapes that exist around the globe, wetland soils are one of the largest reservoirs of soil organic C (Chmura et al., 2003). Mitsch et al. (2012) estimated that wetlands store 20-30% of the earth’s terrestrial C pool; which makes them one of the landscape types under scrutiny in an attempt to mitigate the impacts of global climate change (IPCC, 2007). The primary factor controlling the quantity of C in the wetland soil reservoir is the hydrology that promotes saturation and anaerobic conditions. In soils that are saturated to the surface or inundated, (i.e. hydromorphic soils), the soil environment is anaerobic for much or all of the year. In such cases, soil organic matter (SOM) decomposition is a function of microbial activity (Borken et al., 2006). Fewer microbes are involved, and they are much less efficient at decomposing SOM into organic C compounds under anaerobic conditions than under aerobic conditions, and thus C stocks are typically greater in hydromorphic soils (Mausbach and Richardson, 2000). Carbon dioxide (CO2) is a byproduct of SOM breakdown via aerobic and anaerobic respiration, while methane (CH4) is produced via fermentation of SOM under anaerobic conditions. A secondary but important factor in SOM decomposition is soil temperature; with an increase in temperature typically leading to an increase in decomposition (Davidson and Janssens, 2006).  Significant increases in temperature have been recorded over the last couple decades and are expected to continue to increase (Rohde et al., 2013). Recent models suggest global temperature increases of 15% (approximately 3.9℃) by the next century (Brown and Caldeira, 2017), which should accelerate microbial activity and the rate of SOM breakdown in soils. The question is: How such an increase in temperature will affect C stocks in wetlands (Davidson and Janssens, 2006). One way to answer this question is to find wetlands to study with similar soils, hydrologies, and geomorphic settings but a range in temperatures.

Depressional wetlands occur worldwide. In the United States there are a range of depressional wetlands including prairie potholes, kettle holes, and Carolina Bays (Brinson, 1993). Over a short distance depressional wetlands have areas that are inundated, saturated, and unsaturated (Gala et al., 2005). The areas that are inundated and saturated change over the seasons resulting in a full range of hydrologic conditions every year. Thus, the unique hydrologic characteristics of depressional wetlands allow for a diagnostic investigation of how hydrology influences the magnitude of the biological and chemical interactions that take place in the soil such as C fluxes in all types of wetlands. Over the last four years members of the NE-1438 Multistate project have been studying the hydrology and redox processes occurring in vernal pool wetlands (seasonally wet depressional wetlands). These studies have mostly occurred across the northeast region from Massachusetts to Virginia, with one study site in the mountains of Wyoming. Even with the exclusion of the site in Wyoming, the range of soil temperatures among sites span the expected change over the next century (Table 1). Thus, these depressional wetlands represent a suite of wetlands with similar soils, hydrologies, and geomorphic settings that have a range in temperatures that can be used to understand the effects of increased temperature on wetland C stocks.

In this study, we will determine C stocks across depressional wetlands having a range of temperatures. In concert with accounting the C stored in these systems, we will measure inputs of C through litter and dead fall, rates of decomposition of these C sources, and the fluxes of C via carbon dioxide (CO2) and methane (CH4) that occur in these soils. We will make these measures in, or adjacent to, each of the two zones of these wetlands (seasonally inundated, seasonally saturated), and the adjacent uplands. Our working hypothesis is that since the multistate sites will have similar hydrologic conditions, relationships between soil temperature and soil C additions, decomposition, and losses can be identified. These relationships can be used to understand the effect of increasing temperatures on C stocks and fluxes in wetlands over the next century.

Related, Current and Previous Work

Because soil is the of Earth’s large terrestrial C pool, the topic of soil C budgets for different landscapes is being increasingly debated within the scientific community (Smith et al., 1995; Huntington, 1995; Bridgham et al., 2006; Mitsch et al., 2012; Ricker et al., 2014). In soils, C sequestration (a net gain in C over time), is a function of a larger contribution of C primarily from plant inputs relative to a smaller amount of losses primarily through microbial decomposition. Over long periods of time (100’s to 1000’s of years) C builds up in soils if the balance is positive. This is particularly true in wetlands because they develop anaerobic conditions due to saturation for extended periods compared to adjacent upland soils. The anaerobic conditions that develop in saturated soils slow the rates of SOM decomposition (Whiting and Chanton, 2001; Altor and Mitsch, 2008). These relatively high soil C stocks (200- 600 Mg ha-1) are often cited as evidence of the effectiveness of wetlands to serve as a C sink.

With increasing global temperatures, the question becomes: has the net positive balance between C inputs and losses shifted so that now (or in the near future) the C stored in these wetlands will serve as a net source of C to the atmosphere in response to rising temperatures?

Studies on the variation in organic matter decomposition rates across hydrologic gradients of depressional wetlands have produced conflicting results (McClain et al., 2003; Capps et al., 2014). In C sequestration studies, sources of C are typically associated with leaf litter, deadfall, and roots. Decomposition rates of these sources have been studied in a number of different ways. Mesh litter bags filled with leaves or tea bags may be used to represent leaf litter deposited in the field, while wooden dowel rods placed at the soil surface may represent deadfall, and wooden dowel rods inserted into the soil may represent coarse roots (O’Lear et al., 1995; Austin and Vitousek, 2000; Bontti et al., 2009; Capps et al., 2014). Fibrous root decomposition could also be studied by inserting dead roots into mesh bags buried in the soil. One study by Capps et al. (2014) examined differences in leaf litter decomposition across a hydrologic gradient in a forested depressional wetland. This study reported that the percent of leaf litter lost over approximately three months was significantly higher in the vernal pool basin (~38%) and transitional edge zone (~45%) than in the upland area (~28%). These results are counter- intuitive; we expect decreased SOM decomposition in wetlands than uplands. The 1-cm mesh bags used in the study were very large and the losses in the wetlands may have been due to increased scavenging of leaf tissue by macroinvertebrates such as aquatic larvae of winged insects, other insects, earthworms, and arachnids, rather than decomposition by microbes. Benthic macroinvertebrates are estimated to consume 20-73% of leaf litter inputs to riparian wetlands (Covich et al., 1999), which could explain higher losses in wetlands with standing water. Replication of this study using a finer (closer to 1 mm) mesh size to exclude large macroinvertebrates is necessary to refute or accept the Capps study results as representative in wetland systems.

Studies have also simulated deadfall and woody root decomposition through the examination of above-ground and below-ground dowel rod decomposition in a variety of different environments. These studies focused on precipitation, temperature, and landscape disturbance as the variables relative to dowel decomposition.  After a span of approximately three months, several studies found that dowel decomposition did not exceed 10% (O’Lear et al., 1995; Austin and Vitousek, 2000; Bontti et al., 2009). Parts of these results both match and also are in conflict with data from our studies as part of the NE-1438 multistate project. In our present study, we found significant site, zone, and year effects on dowel rod decomposition in the soil. Annual decomposition ranged from 0.2% to 18% mass loss in zone 1, 0.3% to 27% in zone 2, and from 0.6% to 48% in zone 3. We are still analyzing the data, and expect most of these differences to be a function of temperature, especially when the soil wasn’t saturated. Other effects, however, could be related to the characteristics of the soils in which the decomposition sticks were placed. This could include presence of easily soluble C that the microbes could use instead of the C in sticks, soil pH affecting the microbial community, and soil texture which controls factors such as moisture content during unsaturated conditions and how much direct contact occurs between the soil and the sticks (finer textures will have greater contact).

In our proposed work, we will minimize the soil effects by studying decomposition at the soil surface with both leaves and sticks and focus on temperature affects across sites. Deadfall and litter fall are by far the largest source of C to the wetland soils making up approximately 80% of the contributions (Davis et al., 2010; Richardson and Stolt, 2012; Ricker et al., 2014) and were not measured in the previous study. Within sites temperature is controlled, thus decomposition of leaves and sticks at the surface is a function of duration of inundation (water over the soil surface). Zones 2 and 3 are not inundated, thus, we can test temperature effects among sites by focusing on these two zones.  In addition, we will deploy a second set of sticks and litter bags in early summer after ponding in Zone 1 has ceased. These sticks and leaves will be left for the 3 summer months (before fall inundation in Zone 1) which is the warmest time of year where most decomposition is expected. Lastly, we will include Zone 1 in a multiple regression analysis of yearly decomposition to explain the contributions of both temperature and inundation.

Decomposition of organic matter is primarily the result of heterotrophic respiration from microbial mineralization of organic matter. Soil microbes decompose SOM in order to utilize it as an energy source. Through respiration, C is released into the atmosphere as CO2. Depending on environmental conditions, microorganisms will respire either aerobically (via the tricarboxylic acid cycle) or anaerobically (via fermentation). Wetland soils play a key role in the global C cycle not only by contributing CO2, but also through the process of methanogenesis to produce CH4. Both CO2 and CH4 are important greenhouse gases (GHG). Thus, understanding how differences in organic matter sources, losses, degree of soil saturation, and temperature control decomposition processes and the production of greenhouse gases is of the utmost importance.

Methanogenesis is an anaerobic process in which microorganisms first degrade organic matter present in the soil. Methanogenic microorganisms utilize the acetate or hydrogen produced by this decomposition in order respire, thus producing CH4 which can then be emitted into the atmosphere (Segers, 1998; Altor and Mitsch, 2008). Although fluxes of CH4 are much lower than CO2, CH4 is 25 times more effective as a GHG. There is a positive correlation between the amount of C fixed in wetlands to the amount of CH4 emitted into the atmosphere (Whiting and Chanton, 2001). Although depressional wetlands tend to be small, CH4 concentrations tend to be high in these wetlands as aerobic soil becomes inundated, reducing the soil’s ability to oxidize CH4. When CH4 oxidation exceeds CH4 production through methanogenesis, the area is considered to be a sink of CH4 rather than a source (Kuhn, 2015; Holgerson, 2015). Thus, this absorption of CH4 is typical in aerobic soil environments (Kagotani et al., 2001). Considering how potent a greenhouse gas CH4 is, the release or sorption of CH4 in wetlands under different temperatures and degrees of saturation/inundation needs further study.

Previous multistate projects, NE-1021 and NE-1038, helped established a framework for the systematic study of hydromorphic, hydric, and subaqueous soils. These efforts pointed to the need to establish studies focused on wetlands with similar hydrologic conditions of national importance and debate (vernal pools). In multistate project NE-1438 (2015-2019), we instrumented 8 depressional wetlands (vernal pools) and studied their hydrology and redox status, soil morphology, and simulated rates of root decomposition with dowel rods. Although we are still analyzing these data sets, several things became clear. In particular, our understanding of carbon dynamics in these soil systems was incomplete. We focused on root decomposition, but roots only make up about 20% of the carbon additions to the systems. We had no measures of other carbon inputs (litter and dead fall), nor actual measures of carbon losses as either CO2 or methane. Although our studies pointed to the importance of temperature in decomposition, since our studies were of below-ground decomposition there were several confounding soil factors that clouded our interpretations of the results. Considering the role of wetlands in carbon storage and cycling, and the possible effects of rising temperatures on carbon pools and cycles, we need a much better understanding of wetland C-budgets in a changing climate.

For ecologists, understanding the duration of inundation (hydroperiod) is critical to determining whether a depressional wetland will serve as an effective wetland breeding habitat for important amphibians. One of our goals was the understand the range in hydroperiods in the depressional wetlands and to develop a soil hydromorphic predictor of hydroperiod. Likewise, one of our interests was to relate inundation and saturation, relative to the criteria used for identifying hydric soil conditions, to test hydric soil morphologic indicators.  Although we now have several years of hydrologic data for our range of depressional wetlands, considering the recent large variability in precipitation, additional hydrology data for these sites would be valuable in reaching our soil hydromorphic indicator goals. A continuation of this project will provide a forum to advance our knowledge of these systems and the associated soils and provide an outlet for the dissemination of our knowledge to stakeholders that are seeking answers to their use, management, and restoration questions.

The depressional wetland systems identified across the region are distributed across climatic gradients, across parent material types (coastal plain, residual, and glacial), and among different geomorphological settings. This multi-state project will permit the development and testing of hypotheses in a way that is not possible for a single investigator working within a single state. Addressing these questions within a multi-state framework is also critical because the major agencies that use the soils information that pedologists collect, such as USDA-NRCS, USACOE, and USEPA, all work across state and regional boundaries. In addition, working groups such as the New England Hydric Soil Technical Committee and Mid-Atlantic Hydric Soils Committee, who offer guidance to regional regulatory bodies like the New England Interstate Water Pollution Control Commission (, need soils information that is not restricted by state boundaries. Recent focus of the USACOE and other federal agencies to develop amendments to the 1987 Wetlands Delineation Manual (Environmental Laboratory, 1987) provide additional incentive to work region-wide in applied research. This project will enhance current collaborations and will foster and facilitate new collaborations.


  1. To better understand the hydrological, biogeochemical and pedologcial properties and processes that affect SOM decomposition, CO2 and CH4 greenhouse gas fluxes, and C sequestration in depressional wetland ecosystems, as expressed across geographical and climatic gradients.
  2. To determine the relationship between soil and air temperature and accumulated soil C stocks and fluxes in depressional wetland systems.
  3. To determine the relationship between hydroperiod (i.e. duration of saturation and inundation) and accumulated soil C stocks and fluxes in depressional wetlands.
  4. To seek to develop morphological indices of the hydroperiod within depressional wetlands in order to estimate or predict C stocks.


Site Selection

Sites previously selected across the region for study by the PIs and generally characterized, will be utilized (Figure 1). Each site includes a depressional wetland having three clearly-identifiable hydrological zones (ponded, saturated, and unsaturated) with gradual boundaries between the zones (Figure 2).

Plot Layout and Experimental Design

In each wetland study site, 3 hydrological zones were identified, corresponding to the predominant soil, plant, and water characteristics at each location (Figure 2). Zone 1 is seasonally ponded, and typically contains hydrophytic vegetation (emergent, shrub or woody). Zone 1 usually becomes ponded in the Winter and early Spring and then dries out sometime before or during the Summer season. Zone 2 is a wetland zone marked by saturation, but not significant ponding. It contains hydrophytic vegetation (woody) and hydric soils. Zone 3 is the upland area beyond the wetland boundary. Hydric soils are not present in zone 3, although in some cases hydrophytic vegetation can be observed adjacent to, and outside the boundary of, the wetland zones.

Within each site, nine research plots have been identified along three transects as illustrated in Figure 3. Each of the transects extends radially outwards from the center of the vernal pool (zone 1) through zone 2 and into the upland. Along each transect, a single plot was centrally located within each of the hydrological zones. Locations of the transects were randomized based upon compass orientation. Elevations along each transect will be measured using appropriate tools such as a level or total station. Microtopographic differences will be documented by recording elevations at 1 meter intervals along the transects.


The depth of ponded water or the depth to the water table (below the surface) will continue to be recorded at each site. Depth of ponded water is measured using a staff gauge. Monitoring ports consisting of a well screen installed to a depth of 100 cm have been placed at each plot and water tables will continue to be measured periodically (Figure 3). Along a single transect at each site, water table recording devices have been installed and programmed to record water table levels daily. The detailed (daily) data set from the recording devices will be extended to the other transects based on the periodic observations in the monitoring ports.

Soil Morphology

In the vicinity of each plot, a soil profile description has been made to a depth of 1 to 2 m according to standard protocols (Schoeneberger et al., 2012). Samples collected from each horizon have been stored for laboratory analysis. Morphological descriptions will be compared with approved field indicators of hydric soils to determine whether there is any need for additional hydric soil indicators for use in depressional wetlands (USDA-NRCS, 2017).

Vegetation Analysis

Plant communities in each of the three zones will be assessed by methods outlined in the 1987 USACOE Wetland Delineation Manual (Environmental Laboratory, 1987) and the appropriate regional supplement (USACOE, 2010, USACOE, 2012a, USACOE, 2012b).

Weather and Climate Data

In order to generalize and extend hydrological observations from the period of this study to the broader context, weather data will be obtained from the nearest weather station that maintains a long term (30+ years) record of daily precipitation and air temperatures. Daily records of precipitation and of minimum and maximum temperatures will be collected for the period of this study and will also be obtained for a minimum of the previous 30 years.

Quantification of Carbon and Nitrogen Stocks

Carbon and nitrogen stocks will be determined at plots along each transect (Vasilas et al., 2013). A soil core will be collected from the upper 50 cm in a way that permits simultaneous calculation of horizon thickness and soil bulk density. While most approaches to calculating carbon stocks generate independent errors associated with determining bulk density and measuring horizon thickness, this approach decreases sampling error by combining these two components. Within each plot, a section of aluminum tubing (sharpened on the leading edge) (60 cm long and 5 cm diameter) will be driven 50 cm into the soil. The tube will then be excavated and capped. Upon return to the lab, cores will be frozen to assist in extrusion (alternatively, cores will be opened with sheet metal shears). Once opened, the cores will be divided into vertical sections based on observed soil horizons, and the thickness of each horizon will be carefully measured. All soil material from each horizon will then be homogenized and weighed. The bulk density of each horizon will then be calculated as the weight of the horizon divided by the horizon volume (calculated from the thickness of horizon multiplied by the cross-sectional area of the tube). The soil organic C percentage will be determined using a homogenized subsample of each horizon. Total carbon will be determined in duplicate by dry combustion (Nelson and Sommers, 1996) using a high temperature CNH Analyzer with an IR detector. These data will be used in conjunction with measurements of horizon thickness and bulk density to calculate the total C stocks in the soil to a depth of 50 cm.

Soil Inorganic Nitrogen

Soil nitrate and ammonium will be measured on samples collected from each plot in the middle to end of the aerobic phase (August -September). Four to six replicate cores will be collected using a 30 cm push probe, and will be aggregated into a single composite homogenized sample for analysis. Samples will be analyzed using the HACH 8171 method, similar to that used by Spokas et al. (2010). These data will be used to provide insight into OM decomposition data.

Soil Redox Assessment

IRIS (indication of reduction in soil) films will be used to assess the reducing soil conditions within each plot (Rabenhorst, 2008, 2018; Rabenhorst and Burch, 2006; Rabenhorst et al., 2008; Vasilas et al., 2013). Both traditional Fe-coated and newly developed Mn-coated devices will be utilized (Rabenhorst and Persing, 2017; Rabenhorst and Post, 2018). Five replicate IRIS films of each type (Fe and Mn) will be deployed at each plot to a depth of 50 cm. IRIS films will be deployed for one month periods in the Spring when water tables are expected to be high. Deployment dates at the various sites will be scheduled to follow local weather conditions and will target the beginning of the growing season as determined by US Army Corps of Engineers guidance (USACOE, 2010; USACOE, 2012; USACOE, 2012). The extent of reduction on IRIS films will be assessed using digital image analysis (Rabenhorst, 2012). Mn- coated IRIS devices may also be deployed prior to the normal growing season in an attempt to document biogeochemical conditions during colder, but saturated, periods.

Carbon Inputs

Replicate measurements of litterfall will be made within each plot along the central transect at each site. Leaf litter deposition will be measured between the months of December to August, and September to November using plastic devices to collect litter. These selected sampling periods were chosen to align with the period of major leaf fall in the forested wetlands of the eastern United States (September to November) (Ricker et al., 2014). Three randomly placed C inputs as deadfall will be determined in each plot. Deadfall will be considered as any woody debris greater than 1 cm in diameter. Existing deadfall and leaf litter will be cleared from the forest floor upon delineation of each plot. Flags, placed at the corners of each plot, will be left in place throughout the study. Each year deadfall that has accumulated in the plots will be collected. Leaves and deadfall will be dried to a constant weight at 60o C, in order to determine carbon contributions at the various hydrologic zones throughout the sites. Carbon inputs will be estimated assuming a concentration of 0.50 g C g-1 of leaf litter (Davis et al., 2010).

Organic Matter Decomposition

During the previous study northern white birch (Betula papyrifera) sticks (9.5 mm dowels, 30 cm long) were inserted into the soil and then extracting following one year of burial in order to assess the relative rates of organic matter decomposition. This approach was based upon other studies showing that wooden sticks can be used to indicate organic matter decomposition rates in several different types of settings (Baker et al., 2001; Gulis et al., 2004; Ostertag et al., 2008). To complement these data already collected, metrics of leaf litter and woody deadfall decomposition will be examined at each study plot. Five replicate nylon mesh leaf-litter bags will be filled with dried, pre-weighed leaves of species native to each site (such as White Oak (Quercus alba), Black Oak (Quercus velutina), or Red Maple (Acer rubrum)) and secured at the soil surface in each zone. After retrieval, the bags will be rinsed and dried to a constant weight (60oC) and mass loss will be calculated by comparing with initial weights. Two sets of five replicate pre-weighed northern white birch (Betula papyrifera) dowels (15 cm in length and either 1 cm or 2 cm in diameter) will be secured at the soil surface at each research plot at the same time as the leaf litter bags. The bags and dowel rods will be left on the soil surface for a year (May to May), dried in the oven, and the difference in weight before and after will be calculated as a measure of degree of decomposition. We will repeat this measure of decomposition for three years to document and understand temporal variability. We will use the number of growing degree days for each year, and among the study sites, to identify any difference in energy in the soil system between the sites and years and relate those differences to decomposition rates. Growing degree days are an index of solar energy a given site receives eachday and is based on air temperature. It is strongly correlated with soil heat which in turn is an index related to soil microbial activity (Douglas and Rickman, 1992). We will compare the decomposition rates to organic inputs from leaf and woody deadfall studies to understand net carbon fluxes from the primary sources of SOC to each system and how temperature, inundation, and soil surface saturation control carbon fluxes in wetlands.


Greenhouse Gas Flux

Flux rates of major greenhouse gasses will be measured at each research plot on each of the three transects at each site, using a closed chamber approach, thus providing data for each of the three hydrologic zones. Two cylindrical plastic chambers (16 cm in height, 20 cm in diameter) will be placed at each site and pushed approximately 2.5 cm into the soil. Using a 20 ml gas-tight syringe, an initial gas sample will be collected after securing the chamber’s lid, which contained a rubber septum to allow for sampling, followed by samples taken 15 and 30 minutes after the initial sample. The headspace of the chamber will be mixed prior to sampling. After sample collection, syringe contents are immediately transferred into a 15 ml evacuated tube (Amador and Azivinis, 2013). In each sample, CO2, CH4, and N2O will be determined.

Sampling date will be based on GDD in the spring, summer, and fall. In the field, internal chamber temperatures are measured when each gas sample is collected and averaged in order to obtain the average chamber temperature during the sampling period. Soil temperature and moisture content at a depth of 10 cm, and specific chamber volume (m3) will be recorded at each sample period (Ricker et al., 2014; Waggoner, 2016).

Gas concentrations (CO2, CH4, and N2O) will be measured with a Shimadzu gas chromatograph and recorded in units of ppm (Altor and Mitsch, 2008). Concentrations are plotted against time and fitted with a linear regression in order to calculate the CO2 flux rates. The mass of each gas present in the sampling chamber, or n (mol), is calculated using the Ideal Gas Law, n=PV/RT, where n=mol CO2 per mol air, R=universal gas constant (0.0821 L atm/mol K), T= chamber internal temperature (K), P=atmospheric pressure (atm), and V= chamber volume (L).  The rate of GHG production per unit area is calculated using the slope of the best- fit line, cross-sectional area of the chamber, and volume of air in the chamber (Waggoner, 2016).

Data Analysis

The project design has three plots for each of three hydrologic zones at each depressional wetland:  basin (zone 1), transition (zone 2), and upland (zone 3). Temperature and hydrology will be continuously measured. Gas fluxes will be measured from 2 chambers from each plot for 3 seasons (18 data points/zone/year). Total annual CO2-C flux from the soil surface will be estimated by developing CO2 vs. temperature regressions for each chamber. This approach will allow us to calculate standard errors and make comparisons across sites for each season and year. Daily average soil temperature for each site will used to extrapolate annual CO2 emissions from each chamber (Davis et al., 2010; Ricker et al., 2014). Mean comparisons for the point-in-time values will be assessed using repeated measures analysis of variance. We will use multiple regression to test the effects of soil temperature and moisture on CO2, CH4, and N2O fluxes. Leaves and deadfall additions will be collected within specified areas at each plot and averaged across zones and years. Five decomposition litter bags and coarse woody debris sticks will be placed at each plot each year and loss of C determined after averaging within plots and within zones. Analysis of variance will be used to test for differences in decomposition in leaves and deadfall among zones within sites and by zone among sites. Effects of temperature on decomposition across sites will be assessed using regression analysis, with total degree days as the independent variable and average decomposition at zones 2 and 3 (zones that are not inundated) within sites as the dependent variable. Decomposition rates per year will be applied to leaves and dead fall additions to estimate annual CO2 additions (g m-2 yr-1) to the atmosphere from each zone and site. Our previous in-the-soil decomposition rates (simulated root decomposition) can be applied to estimated root additions (i.e. 20% of the mass of leaves plus deadfall) to roughly estimate total yearly addition of CO2 to the atmosphere. Total yearly CO2 loss will be compared to our yearly CO2 efflux measures as a ballpark check on our analysis.  Carbon additions from litter, deadfall, and roots (estimated) will be compared with C losses as CO2. Zones with nets gains in carbon will serve as a sink while zones with a net C-loss will serve as a source of CO2 to the atmosphere.

Measurement of Progress and Results


  • An annual project report highlighting the results for the previous year will be made available on the project website, and forwarded to participants in the related project focus areas.
  • Participants will submit appropriate research findings for publication in peer reviewed journals and make presentations at local, regional, and national meetings.
  • Any amendments related to National Indicators of Hydric Soils, or related documents, will be composed and submitted for consideration and final approval.
  • Research sites will be incorporated into bi-annual Soil Survey Work Planning Conference fieldtrips and Northeast Graduate Student Pedology Field Tours. These field trips and tours rotate throughout the region and run on opposite years.

Outcomes or Projected Impacts

  • This research will result in improved region-wide understanding of the soils, hydrology, and carbon accounting of depressional wetlands. We will use the depressional wetlands as surrogates for a range of wetlands that have both inundation and saturation and that these conditions vary seasonally. This research will be a continuation of our region-wide focus on hydric soils and hydric indicators to determine if there is a need for additional hydric soil indicators. If needed, new hydric soil indicators may be proposed and submitted for inclusion as part of the National Indicators of Hydric Soils for the Northeast Supplement.
  • External funding for proposals drafted by members of the multistate project. With our current NE-1438 project we leveraged funds ($100,000) from USDA-NRCS to complete some of our current work. We already have plans to approach USDA-NRCS in their next call for soils related research to seek additional funding.
  • Our previous research showed that there is significant variation in soil climate within depressional wetlands over a 4 year period. Considering that variability, the additional data from our region-wide approach (temperature gradient) to measure reducing conditions with IRIS tubes may have significant impact on how (when and for how long) reducing conditions within wetlands are measured and evaluated.
  • Carbon accounting requires measures of inputs and losses of carbon. Our studies will provide metrics of main sources carbon to the soil (litterfall and deadfall) and the rates that these soil carbon sources decompose. We can assume that decomposition results in an equivalent amount of CO2 is lost to the atmosphere. We will measure GHG fluxes at the same time as a check of the release of carbon from these systems. These inputs and losses will provide an estimate of the amount of C that is sequestered in these soils yearly and how inundation and saturation effect the C balance toward sequestration. .
  • One of the main advantages to studying carbon accounting in similar soil conditions over a region is the differences in temperature. The differences in temperature among our sites represents the projected change in temperature in the next century. Thus, our study will provide an estimate of how wetland soils will react to an increase in temperature as a result of global warming.


(2020):Collect climate and hydrological data. Organize research so that all participants are on the same page. Develop training materials (video) for measuring GHG. Purchase and prepare materials for experiments in future years. Organize a meeting for all participants to attend.

(2021):Initiate decomposition and GHG studies. Visit selected sites during biannual Northeast Pedology Fieldtrip. Meet to further discuss coordination and strategies for instrumentation, mapping, and sampling. Update web site to include site information and discussions during the regional field trip to selected sites.

(2022):Maintain monitoring, decomposition, and GHG experiments. Describe and sample soils within various hydropedological entities (i.e. upland, wetland, inundated). Meet to discuss first two years of project and initial results. Consider additional questions and studies. Visit selected sites during region soil survey work planning conference tours. Update web site to include site and monitoring information and discussions during the field trip to selected sites.

(2023):Continue the monitoring, decomposition, and GHG experiments. Continue the soil characterization efforts. Continue to analyze the morphologic data from the inundated, hydric, and seasonally saturated soils relative to inundation, saturation, temperature, redox potential, data. Continue to collect and analyze GHG and decomposition data. Meet to discuss the initial three years of the project and to begin to develop and construct research proposals and peer- reviewed papers based on the project. Visit selected sites during biannual Northeast Pedology Fieldtrip. Update web site to include new monitoring and analytical information and discussions during the regional field trip to selected sites.

(2024):Complete analysis, synthesize results across the region, and write final report and other output works.

Projected Participation

View Appendix E: Participation

Outreach Plan

Results from the proposed multistate project activities will be published as project reports, on the project web site, and as peer-reviewed publications. Participating members involved in undergraduate teaching, graduate student advisement, and extension activities associated with Land Grant Universities will promote the general dissemination of knowledge developed from the proposed project activities. Research sites will be visited on local, regional, and national pedology, hydric soil, and soil-environmental science field trips and workshops.

Northeast Pedology Field trips have been run at least every two years since 1985. Participants include National Cooperative Soil Survey personnel from the NE region and graduate students from participating schools. Field trips are run every other year during the region soil survey work planning conferences. Annual field trips are also run by the New England Hydric Soils Technical Committee and the Mid-Atlantic Hydric Soils Committee. These committees are made up of university faculty, consulting soil scientists, NRCS soil scientists, and state and regional regulators.


The core membership in the multi-state project will likely come from the current NE- 1438 Multistate project including: Patrick Drohan (Penn State University), John Galbraith (Virginia Tech), Martin Rabenhorst (University of Maryland), Mark Stolt (University of Rhode Island), James Thompson (West Virginia University), Bruce Vasilas (University of Delaware), Mickey Spokas (University of Massachusetts), and Karen Vaughan (University of Wyoming).

A Chair, a Chair-elect, and a Secretary will be selected from the above participants. Representatives from the member institutions will meet at least annually to assign tasks and review progress on the current research project. Additional participants with expertise in pedology, mineralogy, soil ecology, hydrology, soil-environmental science, and other related disciplines will be invited to join the project. We have already contacted Matt Ricker at the North Carolina State University, Matt Levi at Georgia, and Judy Turk at Nebraska and they are considering joining the project. This would give us sites with a much larger range in temperatures.

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