Geology topics

Brian Tangen

Publications and source records attributed to Brian Tangen.

At least 19 recordsLinked to original sources

USGS2025

Diurnal patterns of nitrous oxide fluxes from a seasonal prairie wetland

Wetlands have spatially and temporally dynamic nitrous oxide (N 2 O) fluxes. Understanding diurnal patterns in N 2 O fluxes in wetlands can reveal short-term drivers and improve process-based models. An automated chamber system was used to determine N 2 O flux rates every 2.5 to 4 h in a prairie pothole wetland in North Dakota during the 2013 to 2014 growing seasons under ponded, moist, and dry soil conditions. The wetland generally emitted N 2 O under all conditions, although median fluxes during ponded conditions were low over the two-year study. A significant diurnal N 2 O pattern was observed under dry soil conditions, but not in moist soil or ponded conditions. When soils were dry, daytime (~ 10:00–14:00; 2.43 ± 0.31 ng m -2 hr -1 ) and late-day (~ 14:00–18:00; 2.20 ± 0.16 ng m -2 hr -1 ) average N 2 O fluxes were 77% and 61% greater, respectively, than other times during the 24-hr diel cycle (< 1.37 ng m -2 hr -1 ). N 2 O flux was positively correlated to air ( r = 0.58) and soil ( r = 0.49) temperatures under dry conditions, while no significant correlations to environmental factors were observed under ponded and moist conditions. Incorporating diurnal patterns in N 2 O fluxes in wetlands and other ecosystems can improve extrapolations from daily to annual flux calculations and constrain global N 2 O inventories.

North Dakota↗

USGS2024

Visual interpretation of high-resolution aerial imagery: A tool for land managers

Remotely sensed imagery from various collection platforms (e.g., satellites, crewed and uncrewed aircraft) are used by biologists and other conservation personnel to support management activities ranging from monitoring invasive species to assessing land cover and vegetation characteristics. Although remote sensing–based vegetation indices and models have been developed and used for some management applications, straightforward visual interpretation of imagery by on-the-ground personnel may be a pragmatic approach for obtaining time-sensitive and spatially relevant information to support and guide local management activities. Our primary objective was to qualitatively assess our ability to identify patches of target invasive plant species based on simple visual interpretation of high-resolution aerial imagery. We also sought to compare the high-resolution imagery to widely available imagery (e.g., National Agriculture Imagery Program) to determine the efficacy of each for assessing vegetation communities and land-cover features in support of management activities. To accomplish these objectives, we obtained high-resolution imagery and visually scanned and assessed the imagery by using standard geographic information system software. We were able to differentiate patches of crownvetch Securigera varia (L.) Lassen and wild parsnip Pastinaca sativa L., but not spotted knapweed Centaurea stoebe L. or leafy spurge Euphorbia esula L. The relative success in identifying these species had a relationship to plant characteristics (e.g., flower color and morphology, height), time of year (phenology), patch size and density, and potentially site characteristics such density of the underlying vegetation (e.g., grasses), substrate color characteristics (i.e., color contrast with flowers), and physical disturbance. Our straightforward, qualitative assessment suggests that visual interpretation of high-resolution imagery, but not some lower-resolution imagery, may be an efficient and effective tool for supporting local invasive species management through activities such as monitoring known patches, identifying undetected infestations, assessing management actions, guiding field work, or prioritizing on-the-ground monitoring activities.

Journal of Fish and Wildlife Management↗

USGS2023

Practical guide to measuring wetland carbon pools and fluxes

Wetlands cover a small portion of the world, but have disproportionate influence on global carbon (C) sequestration, carbon dioxide and methane emissions, and aquatic C fluxes. However, the underlying biogeochemical processes that affect wetland C pools and fluxes are complex and dynamic, making measurements of wetland C challenging. Over decades of research, many observational, experimental, and analytical approaches have been developed to understand and quantify pools and fluxes of wetland C. Sampling approaches range in their representation of wetland C from short to long timeframes and local to landscape spatial scales. This review summarizes common and cutting-edge methodological approaches for quantifying wetland C pools and fluxes. We first define each of the major C pools and fluxes and provide rationale for their importance to wetland C dynamics. For each approach, we clarify what component of wetland C is measured and its spatial and temporal representativeness and constraints. We describe practical considerations for each approach, such as where and when an approach is typically used, who can conduct the measurements (expertise, training requirements), and how approaches are conducted, including considerations on equipment complexity and costs. Finally, we review key covariates and ancillary measurements that enhance the interpretation of findings and facilitate model development. The protocols that we describe to measure soil, water, vegetation, and gases are also relevant for related disciplines such as ecology. Improved quality and consistency of data collection and reporting across studies will help reduce global uncertainties and develop management strategies to use wetlands as nature-based climate solutions.

Wetlands↗

USGS2023

Large increases in methane emissions expected from North America’s largest wetland complex

Natural methane (CH 4 ) emissions from aquatic ecosystems may rise because of human-induced climate warming, although the magnitude of increase is highly uncertain. Using an exceptionally large CH 4 flux dataset (~19,000 chamber measurements) and remotely sensed information, we modeled plot- and landscape-scale wetland CH 4 emissions from the Prairie Pothole Region (PPR), North America’s largest wetland complex. Plot-scale CH 4 emissions were driven by hydrology, temperature, vegetation, and wetland size. Historically, landscape-scale PPR wetland CH 4 emissions were largely dependent on total wetland extent. However, regardless of future wetland extent, PPR CH 4 emissions are predicted to increase by two- or threefold by 2100 under moderate or severe warming scenarios, respectively. Our findings suggest that international efforts to decrease atmospheric CH 4 concentrations should jointly account for anthropogenic and natural emissions to maintain climate mitigation targets to the end of the century.

North Dakota↗

USGS2022

Lessons learned from wetlands research at the Cottonwood Lake Study Area, Stutsman County, North Dakota, 1967–2021

Depressional wetlands in the Prairie Pothole Region of North America have a long history of investigation owing to their importance in maintaining migratory-bird populations, especially waterfowl. One area of particularly intensive study is the Cottonwood Lake study area in Stutsman County, North Dakota. Studies at the Cottonwood Lake study area began in 1967 and continue through the present (2022). During this period of scientific discovery, meteorological conditions at the Cottonwood Lake study area varied greatly and included one of the most severe droughts of the 20th century and one of the wettest periods in the past 500 years. Persistent wet conditions that began in 1993 have contributed to state changes in many of the study area’s larger wetlands to lake-like conditions, whereas the smaller wetlands returned to seasonally ponded conditions during relatively dry years interspersed within the longer-term wet period. Additionally, some nonwetland areas of the study area developed wetland plant, hydrology, and soil characteristics during the 1993-to-present (2022) wet period. The persistently high stages of water in the larger wetlands since 1993 contributed to a buildup of dissolved solids and increases in salinity with time following an initial decrease in salinity caused by the dilution of dissolved solids within a larger volume of water. During 2021, drought conditions similar to the 1988 to 1992 period may develop if conditions persist. However, meteorological changes during the past 30 years have persisted long enough to be considered a change in climate conditions at the study area and, if such wet conditions continue, would represent a change from conditions that occurred in the past two millennia. During the period of study covered in this report (1967–2021), biotic communities responded in a variety of ways to subtle and marked changes in ponded-water depths, permanence, and salinity among the different wetland types in the study area. This report provides background information on the Cottonwood Lake study area and its context within the Prairie Pothole Region, documents techniques used to quantify environmental conditions and biotic communities, describes major trends that have been observed, presents significant findings as “lessons learned,” discusses recent modeling advances, and highlights key messages to managers. The Wetland Continuum concept was used as a framework to place research findings within an ecological context and to highlight the dynamic nature of prairie-pothole wetland ecosystems.

North Dakota↗

USGS2022

Using a vegetation index to assess wetland condition in the Prairie Pothole Region of North America

Wetlands deliver a suite of ecosystem services to society. Anthropogenic activities, such as wetland drainage, have resulted in considerable wetland loss and degradation, diminishing the intrinsic value of wetland ecosystems worldwide. Protecting remaining wetlands and restoring degraded wetlands are common management practices to preserve and reclaim wetland benefits to society. Accordingly, methods for monitoring and assessing wetlands are required to evaluate their ecologic condition and outcomes of restoration activities. We used an established methodology for conducting vegetation-based assessments and describe a case study consisting of a wetland condition assessment in the Prairie Pothole Region of the North American Great Plains. We provide an overview of an existing method for selecting wetlands to sample across broad geographic distributions using a spatially balanced statistical design. We also describe site assessment protocols, including vegetation survey methods, and how field data were applied to a vegetation index that categorized wetlands according to ecologic condition. Results of the case study indicated that vegetation communities in nearly 50% of the surveyed wetlands were in very poor or poor condition, while only about 25% were considered good or very good . Approximately 70% of wetlands in native grasslands were categorized as good or very good compared to only 12% of those in reseeded grasslands (formerly cropland). In terms of informing restoration and management activities, results indicated that improved restoration practices could include a greater focus on establishing natural vegetation communities, and both restored and native prairie wetlands would benefit from enhanced management of invasive species.

Prairie Pothole Region↗

USGS2022

Prairie wetlands as sources or sinks of nitrous oxide: Effects of land use and hydrology

National and global greenhouse gas (GHG) budgets are continually being refined as data become available. Primary sources of the potent GHG nitrous oxide (N 2 O) include agricultural soil management and burning of fossil fuels, but comprehensive N 2 O budgets also incorporate less prominent factors such as wetlands. Freshwater wetland GHG flux estimates, however, have high uncertainty, and wetlands have been identified as both sources and sinks. Here, we analyzed a regional database of >26,000 N 2 O chamber flux measurements sampled across >150 wetlands from the Prairie Pothole Region (PPR) in the Great Plains of North America. Our goal was to identify important land use and hydrologic drivers of N 2 O flux to help reduce uncertainty in N 2 O models, and to incorporate these drivers into an upscaled estimate of wetland N 2 O emissions from the U.S. portion of the PPR. Within individual wetlands, exposed soils with no standing water, such as along wetland edges, were hotspots that accounted for greater than 90% of wetland N 2 O emissions. In contrast wet (i.e., ponded) areas had minimal or negative N 2 O flux. N 2 O flux from wetlands nested within croplands (16.3–17.3 μg N 2 O m −2 hr −1 ) was, in some instances, nearly double that from wetlands within grasslands (9.2–14.4 μg N 2 O m −2 h −1 ). We estimated that seasonal N 2 O flux from PPR wetlands equated to roughly 0.2% (1.04 Tg CO 2 equivalents) of the U.S. N 2 O budget (c. 2019). Overall, even though PPR wetlands are a small net source of N 2 O to the atmosphere, their emissions are negligible relative to agricultural soil management. Policy and management to restore wetland hydrology and surrounding uplands from cropland to grasslands can reduce landscape N 2 O fluxes. Future activities focused on wetland N 2 O flux would benefit from inclusion of adjacent land use and hydrologic factors, as well as from incorporation of temporally dynamic ponded wetland areas.

Iowa, Minnesota, Montana, North Dakota, South Dako↗

USGS2021

Land management strategies influence soil organic carbon stocks of prairie potholes of North America

Soil organic carbon (SOC) stocks of Prairie Pothole Region (PPR) wetlands in the central plains of Canada and the United States are highly variable due to natural variation in biota, soils, climate, hydrology, and topography. Land-use history (cropland, grassland) and land-management practices (drainage, restoration) also affect SOC stocks. We conducted a region-wide assessment of wetland SOC stocks using data from the Canadian and US portions of the PPR under various management types. Natural wetlands with no disturbance history in the wetland basin or surrounding catchment had considerably greater average SOC stocks in the upper (0–15 cm) soil profile than wetlands surrounded by cropland. Hydrologically restored wetlands did not show significantly greater SOC stocks than drained wetlands, but wetlands surrounded by restored grasslands did have greater SOC stocks in the upper soil profile than those surrounded by croplands. Similarities among cropped and restored wetlands likely were due to insufficient time since restoration, as well as high variability attributable to several environmental factors within the region. We conclude that avoided loss of natural wetlands from drainage and avoided loss of native grasslands from cropping have the most benefit for preserving wetland SOC stocks. Robust PPR SOC models that incorporate multiple abiotic, biotic, and land-use factors are required to determine where and when restoration is most effective for SOC sequestration.

Book chapter↗

USGS2021

Distributions of native and invasive Typha (cattail) throughout the Prairie Pothole Region of North America

The Prairie Pothole Region (PPR) of North America has experienced extreme changes in wetland habitat due to proliferation of invasive plants. Typha × glauca is a highly competitive hybrid between native T . latifolia and non-native T . angustifolia , and it is likely the predominant taxon in PPR wetlands. Genetics-based studies are limited, and distributions are poorly known for the first-generation (F 1 ) hybrid and advanced-generation hybrids from F 1 mating. Information pertaining to the distribution of T . × glauca could benefit efforts to understand the mechanisms of its spread and to develop management strategies to limit hybrid expansion and preserve progenitors. We used microsatellite markers of field-collected tissue samples from 131 wetlands spread over approximately 350,000 km 2 in the PPR to assess the distribution of hybrid T. × glauca relative to its parental species and to examine the prevalence of F 1 hybrids and advanced-generation hybrids. Typha × glauca was found in over 80% of wetlands throughout the PPR, compared to 26 and 18% of wetlands with T . latifolia and T . angustifolia , respectively. Advanced-generation hybrids were more common than F 1 hybrids, suggesting that hybridization is not a recent phenomenon. Hybrids were significantly taller than T . latifolia , indicating heterosis. Only 7% of sampled individual genets were pure T. latifolia . These results suggest that T. × glauca is pervasive throughout the PPR and may spread independently of both parents. In addition, limited prevalence of native T. latifolia indicates the need for active management to preserve the species.

Prairie Pothole Region↗

USGS2021

Preserving soil organic carbon in prairie wetlands of central North America

Wetlands of the Prairie Pothole Region (PPR) in the Great Plains of central North America are numerous, densely distributed, and have highly productive plant and animal communities (Photo 49). When in a natural, unaltered condition, these wetlands store relatively large amounts of organic carbon in their soils (Photo 50). Human alterations, such as extensive drainage and land-use conversion for agriculture (Figure 7), have been linked with the loss of soil organic carbon (SOC) and associated emission of carbon dioxide (CO 2 ), as well as impacts to other ecosystem services provided by these wetlands, such as wildlife and waterfowl habitat, plant biodiversity, flood mitigation, groundwater recharge, nutrient removal and retention, and recreation (Gleason et al., 2011). It has been estimated that more than half of the wetlands of the PPR have been lost due to drainage and other disturbances, with losses approaching 90 percent in some areas (Dahl, 2014; Serran et al., 2018). The goal of this case study was to identify land-management strategies that are consistent with maintaining and increasing SOC stocks of PPR wetlands. Two overarching strategies generally are promoted to preserve and enhance SOC stocks of PPR wetlands: avoided drainage and rewetting or restoration. Avoided drainage involves protecting natural, unaltered wetlands from impacts of human actives with the purpose of retaining wetland functions and services such as carbon storage. Rewetting or restoration involves reestablishing natural hydrology and land use with the purpose of enhancing wetland functions and services that were previously lost due to human activities. Avoided drainage provides immediate and long-lasting benefits, while replenishing SOC through rewetting and restoration requires many decades. Both strategies are associated with higher methane (CH 4 ) emissions but lower CO 2 and nitrous oxide (N 2 O) emissions.

Alberta, Iowa, Manitoba, Minnesota, Montana, North↗

USGS2021

Wetlands

During the last decades, soil organic carbon (SOC) attracted the attention of a much wider array of specialists beyond agriculture and soil science, as it was proven to be one of the most crucial components of the earth’s climate system, which has a great potential to be managed by humans. Soils as a carbon pool are one of the key factors in several Sustainable Development Goals, in particular Goal 15, “Protect, restore and promote sustainable use of terrestrial ecosystems, sustainably manage forests, combat desertification and halt and reverse land degradation and halt biodiversity loss” with the SOC stock being explicitly cited in Indicator 15.3.1. This technical manual is the first attempt to gather, in a standardized format, the existing data on the impacts of the main soil management practices on SOC content in a wide array of environments, including the advantages, drawbacks, and constraints. This manual presents different sustainable soil management (SSM) practices at different scales and in different contexts, supported by case studies that have been shown with quantitative data to have a positive effect on SOC stocks and successful experiences of SOC sequestration in practical field applications Volume 2 includes a description of hot spots of SOC stocks. This manual defines hot spots of SOC as areas that represent a proportionally little of the global land surface but on which SOC storage is highly effective; bright spots as large land areas with low SOC stocks per km2 that represent a potential for further carbon sequestration.

Report↗

USGS2020

Wetland and hydric soils

Soil and the inherent biogeochemical processes in wetlands contrast starkly with those in upland forests and rangelands. The differences stem from extended periods of anoxia, or the lack of oxygen in the soil, that characterize wetland soils; in contrast, upland soils are nearly always oxic. As a result, wetland soil biogeochemistry is characterized by anaerobic processes, and wetland vegetation exhibits specific adaptations to grow under these conditions. However, many wetlands may also have periods during the year where the soils are unsaturated and aerated. This fluctuation between aerated and nonaerated soil conditions, along with the specialized vegetation, gives rise to a wide variety of highly valued ecosystem services.

Book chapter↗

USGS2020

A review of Cattail ( Typha ) invasion in North American wetlands

Overview Cattail ( Typha ) is an iconic emergent wetland plant found worldwide. By producing an abundance of wind-dispersed seeds, cattail can colonize wetlands across great distances, and its rapid growth rate, large size, and aggressive expansion result in dense stands in a variety of aquatic ecosystems such as marshes, ponds, lakes, and riparian areas. Cattail can also quickly dominate disturbed areas with waterlogged soils such as roadside ditches, retention areas, and fringes of stormwater ponds. These dense stands impact local plant and animal life, biogeochemical cycling, and wetland hydrology, which in turn alter wetland functions. Over recent decades, the distribution and abundance of cattail in North America has increased as a result of human disturbances to natural water cycles and increased nutrient loads. In addition, highly competitive nonnative and hybrid taxa have worsened the rapid spread of cattail. Because cattail invasion and expansion often change wetlands in undesirable ways, wetland managers often respond with widespread management efforts, though these efforts may have short-lived or weak effects. Notwithstanding the negative impacts, cattail provides beneficial ecosystem services including the reduction of pollution through bioremediation and the production of biofuel material. Despite the widespread distribution and invasive characteristics of cattail, a comprehensive review and synthesis of past and current research on cattail was lacking. To address this gap, a diverse team of researchers produced a paper that details the spread and management of cattail throughout North America, summarizing 4 decades of research from more than 650 references (Bansal and others, 2019). This fact sheet highlights the primary topics covered in the paper.

Fact Sheet↗

USGS2020

Great Plains

No abstract available.

Kansas, Montana, Nebraska, North Dakota, Oklahoma,↗

USGS2020

Soil organic carbon stocks and sequestration rates of inland, freshwater wetlands: Sources of variability and uncertainty

Impacts of land use, specifically soil disturbance, are linked to reductions of soil organic carbon (SOC) stocks. Correspondingly, ecosystem restoration is promoted to sequester SOC to mitigate anthropogenic greenhouse gas emissions, which are exacerbating global climate change. Restored wetlands have relatively high potential to sequester carbon compared to other ecosystems, but SOC accumulation rates are variable, which leads to high uncertainty in sequestration rates. To assess soil properties and carbon sequestration rates of freshwater mineral soil wetlands, we analyzed an extensive database of SOC concentrations from the Prairie Pothole Region (549 wetlands over 160,000 km 2 ), which is considered one of the largest wetland ecosystems in North America. We demonstrate that SOC of wetland catchments varies among inner, transition, toe slope, and upland landscape positions (LSPs), as well as among land uses and soil depth segments. Soil organic carbon concentrations were greatest in the inner portion of the catchment (66 Mg ha −1 ) and progressively decrease towards the upland LSP (43 Mg ha −1 ). We also conducted a regional extrapolation based on LSP- and land-use-specific SOC stocks, and estimated that wetland and upland areas of PPR wetland catchments contain 141 and 178 Tg of SOC in the upper 15 cm of the soil profile, respectively. Regressing SOC by restoration age (years restored) showed that sequestration rates, which differ by LSP and depth, ranged from 0.35 to 1.10 Mg ha −1 year −1 . Using these SOC sequestration rates, along with data from natural and cropland reference sites, we estimated that it takes 20 to 64 years for SOC levels of restored wetlands to return to natural reference conditions, depending on LSP and depth segment. Accounting for LSP reduces uncertainty and should refine future assessments of the greenhouse gas mitigation potential from wetland restoration.

Iowa, Minnesota, Montana, North Dakota, South Dako↗

USGS2019

Study design and methods for a wetland condition assessment on U.S. Fish and Wildlife Service fee-title lands in the Prairie Pothole Region of North Dakota, South Dakota, and Montana, USA

The U.S. Fish and Wildlife Service (FWS) manages wetlands and grasslands for wildlife habitat throughout the central North American Prairie Pothole Region (PPR). PPR wetlands, or potholes, are widely recognized as critical habitats for North American migratory waterfowl, waterbirds, and other wildlife. Potholes also provide other ecosystem services such as carbon sequestration, flood mitigation, filtration of pollutants, groundwater recharge, nutrient retention, and recreational opportunities. Wetland condition assessments have been completed nationally at coarse scales, but focused, regionwide assessments of the biological condition of potholes managed by the FWS are lacking. Therefore, FWS personnel require information pertaining to the biological condition and status of wetlands on FWS fee-title lands in the PPR to support management, restoration, and acquisition efforts. The biological condition of wetlands typically is reflected by their plant communities, and these communities correspond to past and current management and anthropogenic disturbances; thus, plant communities are a suitable surrogate of wetland condition. This report describes the study design, selection of sample sites, and field survey methods for a wetland condition assessment for FWS fee-title lands in the PPR of North Dakota, South Dakota, and Montana. Various spatial databases were gathered (for example, National Wetlands Inventory) to identify and assess potholes on FWS fee-title lands and to facilitate the selection of study sites. A spatially balanced, site-selection process resulted in the inclusion of 125 temporarily and 125 seasonally ponded potholes distributed across the area of interest; the first 100 for each classification were considered the primary study sites, whereas the remaining 25 were considered an oversample to replace those deemed not appropriate for sampling by field crews. Study sites were within native prairie and reseeded grasslands on FWS National Wildlife Refuges and Waterfowl Production Areas and are distributed among the primary physiographic subregions of the PPR: the Glaciated Plains, Missouri Coteau, and Prairie Coteau; a small number of sites also are within the Lake Agassiz Plain and Turtle Mountains. Site assessment protocols, vegetation survey methods, data analyses, and condition categories (for example, poor, good, very good) for the wetland assessment are based on the North Dakota Rapid Assessment Method and an Index of Plant Community Integrity developed for potholes. Results of the wetland condition assessment will aid FWS staff in assessing past and current management and help to identify priority areas for future management and acquisition.

North Dakota, South Dakota, Montana↗

USGS2019

Typha (cattail) invasion in North American wetlands: Biology, regional problems, impacts, ecosystem services, and management

Typha is an iconic wetland plant found worldwide. Hybridization and anthropogenic disturbances have resulted in large increases in Typha abundance in wetland ecosystems throughout North America at a cost to native floral and faunal biodiversity. As demonstrated by three regional case studies, Typha is capable of rapidly colonizing habitats and forming monodominant vegetation stands due to traits such as robust size, rapid growth rate, and rhizomatic expansion. Increased nutrient inputs into wetlands and altered hydrologic regimes are among the principal anthropogenic drivers of Typha invasion. Typha is associated with a wide range of negative ecological impacts to wetland and agricultural systems, but also is linked with a variety of ecosystem services such as bioremediation and provisioning of biomass, as well as an assortment of traditional cultural uses. Numerous physical, chemical, and hydrologic control methods are used to manage invasive Typha, but results are inconsistent and multiple methods and repeated treatments often are required. While this review focuses on invasive Typha in North America, the literature cited comes from research on Typha and other invasive species from around the world. As such, many of the underlying concepts in this review are relevant to invasive species in other wetland ecosystems worldwide.

Wetlands↗

USGS2019

Hydrologic lag effects on wetland greenhouse gas fluxes

Hydrologic margins of wetlands are narrow, transient zones between inundated and dry areas. As water levels fluctuate, the dynamic hydrology at margins may impact wetland greenhouse gas (GHG) fluxes that are sensitive to soil saturation. The Prairie Pothole Region of North America consists of millions of seasonally-ponded wetlands that are ideal for studying hydrologic transition states. Using a long-term GHG database with biweekly flux measurements from 88 seasonal wetlands, we categorized each sample event into wet to wet (W→W), dry to wet (D→W), dry to dry (D→D), or wet to dry (W→D) hydrologic states based on the presence or absence of ponded water from the previous and current event. Fluxes of methane were 5-times lower in the D→W compared to W→W states, indicating a lag ‘ramp-up’ period following ponding. Nitrous oxide fluxes were highest in the W→D state and accounted for 20% of total emissions despite accounting for only 5.2% of wetland surface area during the growing season. Fluxes of carbon dioxide were unaffected by transitions, indicating a rapid acclimation to current conditions by respiring organisms. Results of this study highlight how seasonal drying and re-wetting impact GHGs and demonstrate the importance of hydrologic transitions on total wetland GHG balance.

Atmosphere↗