Duration: 10/01/2024 to 09/30/2029

Administrative Advisor(s):

NIFA Reps:

Non-Technical Summary

Wetland soils are one of the largest reservoirs of soil organic carbon storing up to 20-30% of the planet’s terrestrial carbon pool. Hydrology is a primary factor controlling wetland carbon storage since wet soils have less oxygen causing slow rates of decomposition of plant tissues (leaves, roots, etc.). Depressional wetlands occur in landscape positions where water collects, resulting in wet conditions that promote soil carbon accumulation. Our goal is to study depressional wetlands across 11 different states with varying climates from Northeast Region across the Midwest and into the Mountain West in order to document soil carbon storage. Our primary objectives are to quantify the carbon pools in depressional wetlands and the range in characteristics that occur within these 11 sites. Our target audiences for the results from this research include the soil science and ecology scientific communities, students, policy makers, conservationists, and others interested in soils and carbon. Our activities in this collaborative project will facilitate research that is difficult to perform alone or in small research teams. Further, the results from this work will inform the management and conservation of depressional wetlands as well as greenhouse gas models used to predict soil carbon dynamics.

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 nine years members of the NE-1438 multistate project and subsequent NE-1938 multistate project have been studying the hydrology, redox processes, and carbon dynamics occurring in vernal pool wetlands (seasonally wet depressional wetlands). These studies have mostly occurred across the northeast region from Massachusetts to Virginia, with three study sites in the west (Wyoming, Kansas, and Nebraska). These depressional wetlands represent a suite of wetlands with similar hydrologies, yet vary in  temperatures, parent materials, vegetation, and other soil forming factors which leads to variation in  wetland C stocks. Further, notable amounts of recalcitrant carbon, sometimes known as “black carbon”, have been observed in some of the sites. Goldberg (1985) stated that black carbon is formed through the incomplete combustion of wood, vegetation, and fossil fuels as well as certain industrial processes. Kuhlbusch (1998) describes black carbon as a potential sink for atmospheric carbon. Black carbon is a mechanism of long-term carbon storage that was not explored in NE-1438 or NE-1938. 

Our goal is to  determine the range in C stocks across a set of 11 depressional wetlands. In concert with accounting the labile, recalcitrant, and mineral 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 measurements 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 these  multistate project sites, while exhibiting similar hydrologic conditions, will have varied carbon storage, and differing rates of soil C additions, decomposition, and losses. By quantifying C dynamics of these understudied wetland ecosystems we will gain a better understanding of the vulnerability of stored C to losses due to increasing temperatures as well as the potential for C sequestration 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 percentage 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 rather 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).

We previously studied decomposition at the soil surface in NE-1938, and will continue that research and methodology going forward. We will minimize the soil effects by studying decomposition at the soil surface with both leaves and sticks. 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 gasses (GHG). Thus, understanding how differences in organic matter sources, losses, degree of soil saturation, and temperature control decomposition processes and the production of greenhouse gasses 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.

During the preceding multistate project, NE-1938, several collaborators noted the presence of black carbon at their sites. At the site in West Virginia the source of black carbon is coal in residual soils. At the site in Pennsylvania the black carbon is attributed to charcoal hearths used for making charcoal for making iron in the late 1700s. Further, two new tallgrass prairie sites from the Great Plains were added to the project – bison wallows in the Flint Hills of Kansas and depressional wetlands in southeast Nebraska. Prairie ecosystems are fire-dependent and are likely to have significant pools of black carbon present. Black carbon included in total carbon measurements. However, the recalcitrance of this pool of carbon complicates carbon dynamics of these depressional wetlands. Thus, we propose to quantify the presence of black carbon at all of our sites using the temperature ramp dry combustion method, a novel analytical method that quantifies soil organic carbon (SOC), soil inorganic carbon (SIC), and black carbon.  

Previous multistate projects, NE-1021, NE-1038, and NE-1438 helped establish 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-1938 (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 to understand the range in hydroperiods in the depressional wetlands across these 11 sites. 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. 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 11 multistate project sites 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 documentation of ranges in depressional wetland properties in a way that is  not possible for a single investigator working within a single state. This information is critical for providing baseline data to document if and how these systems are changing with increased temperatures as well as comparisons with depressional wetlands in other regions of the world.  Achieving this within a multi-state framework is also critical because the major agencies that use the soil information that pedologists collect, such as USDA-NRCS, USACE, 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 (http://www.neiwpcc.org/), need soils information that is not restricted by state boundaries. Recent focus of the USACE 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.

Through multistate projects NE-1021, NE-1038, NE-1438, and NE-1938 the original members of our team established eight depressional wetland study sites that span different temperature regimes across the Northeast with one site in Wyoming. Since NE-1938 began, we have added two collaborators with respective sites in Kansas and Nebraska. Those collaborators are in the process of characterizing their sites and implementing protocols established in NE-1938. In addition, one new collaborator will be joining the project in 2024 and will need to implement a newly established study site in Michigan. These additional sites expand the range of depressional wetland characteristics observed, thus expanding the applicability of our results to other regions. Disruptions of research caused by the Covid-19 pandemic limited certain aspects of the NE-1938 research, especially the measurement of greenhouse gasses. In addition, observations of black carbon at some sites during the NE-1938 project helped identify the need for quantifying black carbon and documenting that carbon pool as an important component of the carbon dynamics story of these depressional wetlands. Due to the differences in time of establishment across our 11 sites, the disturbances caused by the Covid-19 pandemic, and the observation of black carbon at multiple sites, we propose a continuation of the research initially proposed for NE-1938 with the addition of an assessment of black carbon pools at all sites. 

Objectives

1. To better understand the hydrological, biogeochemical and pedological properties and processes that affect SOM decomposition, CO2 and CH4 greenhouse gas fluxes, and C sequestration in depressional wetland ecosystems.
   
2. To document the range in accumulated soil C stocks and fluxes across these 11 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 quantify black carbon in depressional wetland systems.
   

Methods

Site Selection

Eleven sites will be used in this study (Figure 1). Those sites include eight that were previously selected across the Northeast region for study by the PIs and generally characterized, and three new sites in Kansas, Michigan, and Nebraska. 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, three 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 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 m intervals along the transects.

Hydrology

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 USACE Wetland Delineation Manual (Environmental Laboratory, 1987) and the appropriate regional supplement (USACE, 2010a; USACE, 2010b; USACE, 2010c; USACE, 2012a; USACE, 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 the 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 based on the equivalent soil mass calculation by Ellert and Bettany (1995)

Further, pools of soil carbon can be thermodynamically subdivided into easily oxidized organic carbon (SOC), inorganic carbon (SIC), and less easily oxidized organic carbon (presumably “black carbon”) via the process of temperature ramp dry combustion. This will be performed in collaboration with Tiffany Carter at the National Soil Survey Center in Lincoln, Nebraska using the “soli TOC^® cube”, a commercially available combustion analyzer by Elementar Americas which has been used across various studies for the speciation and quantification of SOC and SIC (Zethof et al., 2019; Natali et al, 2020; Wenzel et al., 2023). The commercial analyzer is equipped with an analytical method that utilizes both temperature ramping and carrier gas alteration to separate carbon pools. During the analysis the initial instrument temperature rises from 150°C to 400°C where it plateaus for 2 minutes utilizing O₂ as the initial carrier gas. After the 2-minute plateau at 400°C, the O₂ is switched off and replaced with nitrogen (N₂). The temperature then rises and plateaus at 900 °C for 4 minutes under N₂. At the conclusion of the 4-minute plateau at 900°C, the O₂ is switched back on and the temperature remains at 900°C for an additional 2 minutes. In principle, easily oxidized soil organic carbon, soil inorganic carbon, and less easily oxidized soil organic carbon (presumably “black carbon”) are respectively quantified during the ramps to 400°C (under O₂), to 900°C (under N₂), and then at 900°C (under O₂) (Zethof et al., 2019; Natali et al, 2020; Wenzel et al., 2023).

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 (USACE, 2010a; USACE, 2010b; USACE, 2010c; USACE, 2012a; USACE, 2012b). 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 over a 12 month period with focused collection between the months of September to November using plastic devices to collect litter. This focused sampling period was 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 input plots for  deadfall will be determined in each zone. 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. Over the course of a year deadfall that has accumulated in the plots will be collected. Leaves and deadfall will be dried to a constant weight at 60oC, 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 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 extracted 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 (60^oC) and mass loss will be calculated by comparing with initial weights. Two sets of five replicate pre-weighed northern white birch (Betula papyrifera) dowels (30 cm in length and either 9.5 mm 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 one 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. Corrections for soil contamination within the litterbags will be made using the standard methods for ashing and the recommended correction equation (Harmon et al., 1999). 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 each day 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 contains 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 growing degree days 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). Greenhouse gas sampling will occur at least once per season for the spring, summer, and fall.

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).

Site History

We will investigate site history for each of the 11 sites. This will be done through several means. First, we will explore the recent history of each site using available aerial imagery. Second, we will identify the current state within the Ecological Site Description (ESD) state and transition model using the respective ESD key for each Major Land Resource Area, soil data collected as part of this study, and plant survey data from this study. This will allow inferences to be made on historic land use. Lastly, for sites where it is available, records associated with each property will be reviewed and used to supplement ESD and aerial imagery information.

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). Total areas represented by the three zones will be determined based on Goldman et al. (2020). Temperature and hydrology will be continuously measured. Gas fluxes will be measured from two chambers from each plot for three seasons (18 data points/zone/year). Total annual CO₂-C flux from the soil surface will be estimated by developing CO₂vs. 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 be used to extrapolate annual CO₂emissions 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 net 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.

Current Site Status

As shown in Table 1, original sites that participated in NE-1021, NE-1038, NE-1438, and NE-1938 are ahead of recently established (KS and NE) and to-be-established (MI) sites. Thus, for the original sites, efforts during the proposed research will be focused on measurement of greenhouse gas fluxes and assessment of soil black carbon concentrations. For recently- and newly-established sites, research efforts will include completing all aspects of the project originally proposed for NE-1938 as well as assessing black carbon pools.  

 

 

 

Measurement of Progress and Results

Outputs

• 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 Field Indicators of Hydric Soils in the United States, 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.
• A summary of Outputs from NE1438 and NE1938 are included below. Comments: Peer-reviewed Publications (1) Rabenhorst, M.C., P.J. Drohan, J.M. Galbraith, C. Moorberg, L. Spokas, M.H. Stolt, J.A. Thompson, J. Turk, B.L. Vasilas, and K.L. Vaughan. 2021. Mn‐Coated IRIS to document reducing soil conditions. Soil Science Society of America Journal, 85(6):2201-2209. https://doi.org/10.1002/saj2.20301. Conference Oral and Poster Presentations (4) Rabenhorst, M.C., P.J. Drohan, J.M. Galbraith, B.A. Needelman, L. Spokas, M. Stolt, J.A. Thompson, B.L. Vasilas, and K.L. Vaughan. 2017. Comparing Performance of Mn-Coated and Fe-Coated IRIS Devices. Poster presentation at the 2017 American Society of Agronomy-Crop Science Society of America-Soil Science Society of America International Annual Meeting, Tampa, FL, October 22-25, 2017. Rabenhorst, M.C., P.J. Drohan, J.M. Galbraith, L. Spokas, M. Stolt, J.A. Thompson, B.L. Vasilas, and K.L. Vaughan. 2019. Biogeochemistry of Vernal Pools Assessed Using IRIS Film Technology. Poster presentation at the 2019 Soil Science Society of America International Soils Meeting, San Diego, CA, January 6-9, 2019. Rabenhorst, M.C., P.J. Drohan, J.M. Galbraith, L. Spokas, M. Stolt, J.A. Thompson, B.L. Vasilas, and K.L. Vaughan. 2019. Using Mn IRIS (Indicator of Reduction In Soils) for early growing season redox assessment. Oral presentation at the 2021 National Cooperative Soil Survey (NCSS) National Conference, Virtual, June 8-10, 2021. Vaughan, K.L., P.J. Drohan, J.M. Galbraith M.C. Rabenhorst,, L. Spokas, M. Stolt, J.A. Thompson, and B.L. Vasilas. 2019. Redoximorphic Feature Expression in Seasonally Inundated Soils Reveals Belowground Climatic Influence on Development. Poster presentation at the 2019 Soil Science Society of America International Soils Meeting, San Diego, CA, January 6-9, 2019.

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 or the Field Indicators of the United States.
• External funding for proposals drafted by members of the multistate project. With the NE-1438 project we leveraged funds ($100,000) from USDA-NRCS to complete some of our current work. We plan 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 of 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 being 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 affect the C balance toward sequestration.
• Our previous soil morphology and soil carbon investigations revealed sites in West Virginia and Pennsylvania contained measurable amounts of black carbon that resulted in abnormally high total carbon concentrations. We have also added two prairie sites that are expected to have some black carbon due to prairie fires. By incorporating a novel method for quantifying black carbon, we will attribute carbon storage to biologic and pyrogenic processes and provide much needed context for wetland carbon processes.
• One of the main advantages to studying carbon accounting in similar soil conditions on a regional scale is 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.

Milestones

(2025):Collect climate and hydrological data for newly-established sites. 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. Collect soil carbon cores for carbon and nitrogen stock and black carbon analysis for recently established sites or for original sites where archived soil samples are not available. Submit all soil carbon samples to Tiffany Carter at the USDA NRCS Kellogg National Laboratory for analysis.

(2026):Initiate decomposition for newly-established sites. Initiate GHG studies for all sites. Visit selected sites during biannual Northeast Pedology Fieldtrip. Meet to further discuss coordination and strategies for instrumentation, mapping, and sampling. Update web page to include site information and discussions during the regional field trip to selected sites.

(2027):Maintain monitoring, decomposition, and GHG experiments. Describe and sample soils within various hydropedological entities (i.e. upland, wetland, inundated) for newly and recently-established sites. Meet to discuss greenhouse gas flux and black carbon data from the first two years of project and initial results from the recently-established sites. Visit selected sites during region soil survey work planning conference tours. Update web page to include site and monitoring information and discussions during the field trip to selected sites.

(2028):Complete monitoring, decomposition, and GHG experiments. Complete 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.

(2029):Complete analysis, synthesize results across all study sites, 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 and research, graduate student advising, 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.

Organization/Governance

The core membership in the multi-state project will likely come from the current NE-1938 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). Vasilas and Spokas have since retired and will not be directly participating in the project organization or governance, but we have access to their respective study sites for resampling for black carbon. New members since the start of NE-1938 include Colby Moorberg (Kansas State University), Judy Turk (University of Nebraska - Lincoln), and Barret Wessel (Michigan State University). 

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. 

Literature Cited

Ågren, A., Buffam I., Berggren M., Bishop K., Jansson M., and H. Laudon. 2008. Dissolved organic carbon characteristics in boreal streams in a forest-wetland gradient during the transition between winter and summer. J Geophys Res 113:G03031.

Altor, A.E., and W.J. Mitsch. 2008. Methane and carbon dioxide dynamics in wetland mesocosms: effects of hydrology and soils. Ecological Applications 18:1307-1320.

Amador, J.A., and E.J. Avizinis. 2013. Response of Nitrous Oxide Flux to Addition of Anecic Earthworms to an Agricultural Field. Open Journal of Science 3:100-106.

Austin, A.T., and P.M. Vitousek. 2000. Precipitation, decomposition and litter decomposability of Metrosideros polymorpha in native forests on Hawai’i. Journal of Ecology 88:129-138.

Baker, T.T., B.G. Lockaby, W.H. Conner, C.E. Meier, J.A. Stanturf and M.K. Burke. 2001. Leaf Litter Decomposition and Nutrient Dynamics in Four Southern Forested Floodplain Communities. Soil Sci. Soc. Am. J. 65:1334-1347. doi:10.2136/sssaj2001.6541334x.

Bontti, E. E., J.P. Decant, S.M. Munson, M.A. Gathany, A. Przeszlowska, M.L. Haddix, and M.E. Harmon. 2009. Litter decomposition in grasslands of central North America (US Great Plains). Global Change Biology 15:1356-1363.

Borken, W., K. Savage, E.A. Davidson. 2006. Effects of experimental drought on soil respiration and radiocarbon efflux from a temperate forest soil. Global Change Biology 12:177–193.

Bridgham, S.D., J.P. Megonigal, J.K. Keller, N.B. Bliss, and C. Trettin. 2006. The carbon balance of North American wetlands. Wetlands 26: 889-916.

Brinson, M.M. 1993. A hydrogeomorphic classification for wetlands. East Carolina Univ. Greenville, NC

Brown, P. T. and K. Caldeira. 2017. Greater future global warming inferred from Earth’s recent energy budget. Nature 552:45.

Capps, K. A., R. Rancatti, N. Tomczyk, T. B. Parr, A. J. K. Calhoun, and M. Hunter, Jr. 2014.

Biogeochemical hotspots in forested landscapes: the role of vernal pools in denitrification and organic matter processing. Ecosystems 17:1455-1468.

Chmura, G. L., S. C. Anisfeld, D. R. Cahoon, and J. C. Lynch. 2003. Global carbon sequestration in tidal, saline wetland soils. Global Biogeochem. Cycles 17:1-22.

Covich, A.P., Palmer, M.A., and T.A. Crowl. 1999. The role of benthic invertebrate species in freshwater ecosystems: Zoobenthic species influence energy flows and nutrient cycling. BioScience 49 (2): 119–127. https://doi.org/10.2307/1313537

Davidson, E.A., and I.A. Janssens. 2006. Temperature sensitivity of soil carbon decomposition and feedbacks to climate change. Nature 440:165-173.

Davis, A.A., J.E. Compton, and M.H. Stolt. 2010. Soil respiration and ecosystem carbon stocks in New England forests with varying soil drainage. Northeastern Naturalist, 17:437-454.

Douglas, C.L., and R.W. Rickman. 1992. Estimating crop residue decomposition from air temperature, initial nitrogen content, and residue placement. Soil Science Society of America Journal 56:272- 278.

Ellert, B. H., and J. R. Bettany. 1995. Calculation of organic matter and nutrients stored in soils under contrasting management regimes. Canadian Journal of Soil Science 75(4):529–538.

Environmental Laboratory. 1987. Corps of Engineers Wetland Delineation Manual. Tech Report Y-87-U.S. Army Engineer Waterways Experiment Station. Vicksburg MS. (http://el.erdc.usace.army.mil/wetlands/pdfs/wlman87.pdf)

Gala, T.S., and D. Young. 2015. Geographically Isolated Depressional Wetlands – Hydrodynamics, Ecosystem Functions and Conditions. Applied Ecology and Environmental Sciences 3:108-116.

Goldberg, E.D. 1985. Black carbon in the environment: properties and distribution. https://www.osti.gov/biblio/5473086.

Goldman, M.A., B.A. Needelman, M.C. Rabenhorst, M.W. Lang, G.W. McCarty, et al. 2020. Digital soil mapping in a low-relief landscape to support wetland restoration decisions. Geoderma 373: 114420. doi: 10.1016/j.geoderma.2020.114420.

Harmon, M.E., K.J. Nadelhoffer and J. M. Blair. 1999. Measuring decomposition, nutrient turnover, and stores in plant litter. Stand Soil Methods for Long-Term Ecological Research. Oxford University Press, New York, NY.

Gulis, V., A.D. Rosemond, K. Suberkropp, H.S. Weyers and J.P. Benstead. 2004. Effects of nutrient enrichment on the decomposition of wood and associated microbial activity in streams.

Freshwater Biology 49:1437-1447.  doi:10.1 111 /j.1365-2427.2004.01281.x.

Huntington, T.G. 1995. Carbon sequestration in an aggrading forest ecosystem in the southeastern USA. Soil Science Society of America Journal 59: 1459-1467.

IPCC. 2007. Climate change 2007: the physical science basis. Cambridge University Press, New York, NY.

Jaffé, R., Ding, Y., Niggemann, J., Vähätalo, A.V., Stubbins, A., Spencer, R.G.M., Campbell , J., Dittmar, T. Global charcoal mobilization from soils via dissolution and riverine transport to the oceans (2013) Science, 340 (6130), pp. 345-347.

Janzen, H.H. 2006. The soil carbon dilemma: Shall we hoard it or use it? Soil Biology & Biochemistry 38: 419-424.

Kagotani, Y., E. Hamabata, and T. Nakajima. 2001. Seasonal and spatial variations and the effects of clear-cutting in the methane absorption rates of a temperate forest soil. Nutrient Cycling in Agroecosystems 59: 169-175.

Kuhlbusch, T.A.J. 1998. Black Carbon and the Carbon Cycle. Science 280(5371): 1903–1904. doi: 10.1126/science.280.5371.1903.

Kuhn, M. 2015. Methane Dynamics in Vernal Pools. Doctoral Dissertation. Department of Environmental Science, Wheaton College, Norton, MA.

Mausbach, M.J. and J.L. Richardson. 1994. Biogeochemical processes in hydric soil formation, Current Topics in Wetland Biogeochemistry 1:68-127.

McClain, M.E., E.W. Boyer, C.L. Dent, S.E. Gergel, N.B. Grimm, P.M. Groffman, and W.H. McDowell. 2003. Biogeochemical hot spots and hot moments at the interface of terrestrial and aquatic ecosystems. Ecosystems 6: 301-312.

Mitsch, W.J., B. Bernal, A.M. Nahlik, Ü. Mander, L. Zhang, C.J. Anderson, and H. Brix. 2012.

Natali, C., Bianchini, G., Carlino, P., 2020. Thermal stability of soil carbon pools: Inferences on soil nature and evolution. Thermochimica Acta, 683. https://doi.org/10.1016/j.tca.2019.178478

Wetlands, carbon, and climate change. Landscape Ecology 28: 583-597.

Nelson, E.W., and L.E. Sommers. 1996. Total Carbon, Organic Carbon, and Organic Matter. Methods of soil analysis. Part 3-Chemical methods. Soil Science Society of America Inc., Madison, WI

O'Lear, H.A., T.R. Seastedt, J.M. Briggs, J.M. Blair, and R.A. Ramundo. 1995. Fire and topographic effects on decomposition rates and N dynamics of buried wood in tallgrass prairie. Soil Biology and Biochemistry 28: 323-329.

Ostertag, R., E. Marín-Spiotta, W.L. Silver and J. Schulten. 2008. Litterfall and Decomposition in Relation to Soil Carbon Pools along a Secondary Forest Chronosequence in Puerto Rico. Ecosystems 11:701-714.

Rabenhorst, M.C. 2008. Protocol for Using and Interpreting IRIS Tubes. Soil Survey Horizons 49:74- 77.

Rabenhorst, M.C. 2012. Simple and Reliable Approach for Quantifying IRIS Tube Data. Soil Sci. Soc. Am. J. 76:307-308.

Rabenhorst, M.C. 2018. A System for Making and Deploying Oxide-Coated Plastic Films for Environmental Assessment of Soils. Soil Sci. Soc. Am. J. 82:1301-1307 doi: 10.2136/sssaj2018.05.0178

Rabenhorst, M.C. and S.N. Burch. 2006. Synthetic iron oxides as an indicator of reduction in soils (IRIS). Soil Science Society of America Journal 70:1227-1236. doi:10.2136/sssaj2005.0354.

Rabenhorst, M.C. and K. A Persing. 2017. A Synthesized Manganese Oxide for Easily Making Durable Mn-Coated IRIS Tubes. Soil Sci. Soc. Am. J. 81:233–239.  doi: 10.2136/sssaj2016.10.0348

Rabenhorst, M.C. and J. Post. 2018. Manganese Oxides for Environmental Assessment. Soil Sci. Soc. Am. J.  82:509-518. doi:10.2136/sssaj2017.08.0256.

Rabenhorst, M.C., D.W. Ming, R.V. Morris, and D.C. Golden. 2008. Synthesized iron oxides used as a tool for documenting reducing conditions in soils. Soil Science 173:417-423. doi:10.1097/SS.0b013e31817751b17.

Ricker, M.C., M.H. Stolt, & M.S. Zavada. 2014. Comparison of soil organic carbon dynamics in forested riparian wetlands and adjacent uplands. Soil Science Society of America Journal 78:1817-1827.

Rohde, R., R.A. Muller, R. Jacobsen, and E. Mulleret. 2013. A New Estimate of the Average Earth Surface Land Temperature Spanning 1753 to 2011. Geoinfonnatics ana Geostatistics: An Overview 1:1.

SAS Institute, Inc. 2004. SAS, Version 9.0.1. Statistical Analysis Systems Institute, Inc., Cary, NC, USA.

Schoeneberger, P.J., D.A. Wysocki, D.A. Benham, and W.D. Broderson. 2012. Field Book for Describing and Sampling Soils. Ver. 3.0. Natural Resources Conservation Service, National Soil Survey Center, Lincoln, NE, USA.

Segers, R. 1998. Methane production and methane consumption: a review of processes underlying wetland methane fluxes. Biogeochemistry 41: 23-51.

Six, J., R.T. Conant, E.A. Paul, and K. Paustian. 2002. Stabilization mechanisms of soil organic matter: Implications for C-saturation of soils. Plant Soil 241:155–176.

Smith, R.D., A. Ammann, C. Bartoldus, and M.M. Brinson. 1995. An approach for assessing wetland functions using hydrogeomorphic classification, reference wetlands, and functional indices.

Technical report WRP-DE-9, U.S. Army Engineer Waterways Experiment Station, Vicksburg, MS.

Spokas, L.A., P.L.M. Veneman, S.C. Simkins, and S.C. Long. 2010. Performance Evaluation of a Constructed Wetland Treating High-Ammonium Primary Domestic Wastewater Effluent. Water Envir. Res. 82:592-600.

USACE. 2010a. Regional Supplement to the Corps of Engineers Wetland Delineation Manual: Great Plains Region (Version 2.0) ERDC/EL TR-10-1. U.S. Army Engineer Research and Development Center, Vicksburg, MS.

USACE. 2010b. Regional Supplement to the Corps of Engineers Wetland Delineation Manual: Midwest Region (Version 2.0), ERDC/EL TR-10-16. U.S. Army Engineer Research and Development Center, Vicksburg, MS.

USACE (2010c). Interim Regional Supplement to the Corps of Engineers Wetland Delineation Manual: Eastern Mountains and Piedmont Region (Version 2.0), ERDC/EL TR-10-9, U.S. Army Engineer Research and Development Center, Vicksburg, MS.

USACE (2012a). Regional Supplement to the Corps of Engineers Wetland Delineation Manual: Northcentral and Northeast Region (Version 2.0), ERDC/EL TR-12-1, U.S. Army Engineer Research and Development Center, Vicksburg, MS.

USACE (2012b). Regional Supplement to the Corps of Engineers Wetland Delineation Manual: Eastern Mountains and Piedmont Region (Version 2.0), ERDC/EL TR-12-9, U.S. Army Engineer Research and Development Center, Vicksburg, MS.

Vasilas, B., M. Rabenhorst, J. Fuhrmann, A. Chirnside, S. Inamdar. 2013. Wetland Biogeochemistry Techniques. In J. Anderson and A. Davis (eds.) Wetland Techniques. Volume 1, pp. 355-442. ISBN 978-94-007-6860-4 (eBook) Springer Dordrecht Heidelberg, New York, London.

Waggoner, A. 2016. Effects of residual waste material as agricultural soil amendments on soil greenhouse gas fluxes. M.S. Thesis. Department of Natural Resources Science, University of Rhode Island, Kingston, RI.

Wellborn, G. A., D. K. Skelly, and E. E. Werner. 1996. Mechanisms creating community structure across a freshwater gradient. Annual Review of Ecology and Systematics 27:337-363.

Wentzel, W.W., Philipsen, F.N., Herold, L., Kingsland-Mengi, A., Laux, M., Golestanifard, A., Strobel, B.W., Duboc, O., 2023. Carbon sequestration potential and fractionation in soils after conversion of cultivated land to hedgerows. Geoderma. 435, 116501. https://doi.org/10.1016/j.geoderma.2023.116501

West, T.O., and J. Six. 2007. Considering the influence of sequestration duration and carbon saturation on estimates of soil carbon capacity. Climate Change 80:25–41.

Whiting, G.J., and J.P. Chanton. 2001. Greenhouse carbon balance of wetlands: methane emission versus carbon sequestration. Tellus B, 53: 521-528.

Wiggins, G.B., R.J. Mackay, and I.M. Smith. 1980. Evolutionary and ecological strategies of animals in annual temporary pools. Archiv fur Hydrobiologie, Supplement 58:97-206.

Zethof, J. H. T., Leue, M., Vogel, C., Stoner, S. W., and Kalbitz, K.: Identifying and quantifying geogenic organic carbon in soils – the case of graphite, SOIL, 5, 383–398. https://doi.org/10.5194/soil-5-383-2019

Attachments

Land Grant Participating States/Institutions

KS, MD, NE, PA, RI, VA, WV

Non Land Grant Participating States/Institutions