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Wetland Restoration: Contemporary Issues and Lessons Learned
Abstract
Numerous studies have documented the shortcomings of wetland mitigation and voluntary restoration projects to achieve stated goals. However, despite these findings, there is little overall evidence that wetland restoration outcomes have significantly improved - and wetlands continue to be lost. There is general agreement among restoration professionals that the science exists to achieve restoration goals and that wetland restoration performance will improve if certain barriers are addressed. Many lessons have been learned over the past 50 years and there are wetland professionals throughout the country who have found methods to effectively address these barriers. However, much of this information is stored in the minds of those who have learned these lessons over time. This white paper was developed with guidance from a national expert work group in order to share this information, present potential solutions to restoration challenges and barriers, and recommend specific actions that can be taken to improve wetland restoration outcomes.
... Restored wetlands can have impaired C, N, and phosphorus (P) cycling (Hossler et al. 2011) and lower denitrification rates (Bruland et al. 2006). Similar shortcomings have also been reported by federal and state agencies (Fennessy et al. 2004;Stelk et al. 2017). In general, we are falling short of replacing wetland acreage and function (Campbell et al. 2002;Burgin 2009;Hossler & Bouchard 2010;Jones et al. 2018). ...
... Based on these studies we hypothesized that TS would be more favorable than alOM as an organic amendment in wetland restorations. Because all organic amendments provide degraded soils with carbon and nutrients, a common indicator of soil quality (Bünemann et al. 2018), we also hypothesized that amendments would have a greater impact on soils low in organic carbon, as suggested by Richardson et al. (2016) and Stelk et al. (2017). ...
At the present rate of loss (since 1990), half of the remaining wetlands worldwide will be developed within ~140 years, underscoring the importance of improving the creation and restoration of wetlands. Organic amendments are sometimes used during wetland creation. To evaluate the effectiveness of adding organic amendments we used a combined numerical method to assign “scores” on five categories of evaluation metrics: plant growth, soil properties, carbon accrual, denitrification, and anaerobic processes (e.g. redox potential). We found that amendments identified as “topsoil” scored measurably higher and had consistently more positive values with fewer negative results compared to amendments identified as “allochthonous organic matter”. Organic amendments had about the same effect on soils with low soil organic carbon (<2.5%) compared to soils richer in organic carbon. Organic amendments are not uniformly effective, and in some cases may have negative side effects. For example, allochthonous organic matter often resulted in a loss of plant diversity. These outcomes along with site conditions should be evaluated before using organic amendments.
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... Hydrological restoration may require plugging of ditches, removal of berms and dikes, or disabling subsurface drainage systems (e.g., tile drains) [53][54][55][56][57]. Removal of accumulated sediments can also increase wetland area and depth [58]. Sedimentation frequently occurs in agricultural areas, but may also occur in other human-altered landscapes, including via succession in the absence of disturbance [52,[59][60][61]. Artificial methods to extend hydroperiods have been used to protect critical populations from premature pond drying. ...
Geographically isolated wetlands provide a critical habitat for pond-breeding amphibians, a taxa of broad conservation concern. Global wetland loss and degradation has made restoration essential for amphibian conservation. Restoration goals typically include recovering the wetlands’ physiochemical, hydrological, and ecological functions. However, for pond-breeding amphibians, successful restoration should also result in sustained populations, which is difficult to assess and infrequently reported. In this paper, we review the available evidence that restoration of geographically isolated wetlands promotes pond-breeding amphibian occupancy and population persistence. We provide an overview of restoration practices addressing hydrology, vegetation, and ecological processes within these unique environments and across spatial scales. We then summarize the evidence, and discuss the limitations, for evaluating successful restoration within the context of amphibian conservation across these categories. Finally, we provide recommendations for researchers and practitioners to leverage prior successes and establish systematic data collection and dissemination. Moving restoration of wetlands for amphibian conservation forward will require more robust data collection and reporting.
... Comparing baseline data to post-restoration monitoring data can provide additional information regarding time requirements for riparian wetland succession. Commonly, wetland monitoring continues 3-5 years post-restoration to determine restoration success; however, the time required to monitor post-restoration can vary based on the wetland hydrology and structure (e.g., 10-15 years to monitor bogs or fens [108]). With each following year postrestoration, abundance and diversity can be calculated to determine if mitigation efforts need to be modified using an adaptive management framework to ensure the improvement of wetland conditions. ...
Wetland mitigation efforts have increased in numbers over the past two decades to combat wetland loss in the United States. Data regarding wetland function such as biodiversity are required to be collected 5-10 years after a project is complete; however, pre-restoration data that can inform the effectiveness of mitigation are often not collected. We conducted pre-restoration surveys on various taxa along or within Ruby Run, a tributary of Deckers Creek in north-central West Vir-ginia, USA, from 2016 to 2020 to determine the baseline relative abundance and diversity within the stream and the associated riparian zone. In five years, we observed 237 species (154 plant, 58 bird, 13 fish, 6 small mammal, and 6 anuran) and 25 families of macroinvertebrates. Seasonal fluctuations in diversity were present, but mean diversity was relatively consistent among years across taxa, except in anurans, where there was a decrease each year. Wetland mitigation efforts should continue to be monitored for success using multiple taxa, because land use change can affect taxa in different ways, resulting in well-rounded assessments that can improve wetland management practices .
Organic matter is sometimes added to soil in wetland mitigation projects, putatively to improve restoration outcomes. At a freshwater mitigation wetland, built in a former agricultural field to compensate for development-related wetland losses elsewhere, we conducted a manipulative field experiment using organic matter amendments to identify the effects different types and loading rates had on the development of soil (organic matter, bulk density, and hydric soil indicators), vegetation (root and shoot biomass, floristic quality), and methane (CH4) emissions. The amendments included cow manure, composted wood chips, and hay at various loading rates, and municipal wastewater Class A biosolids. We found that there were trade-offs in desired restoration outcomes. Experimental loading rates of hay (226 m³ ha⁻¹) and manure (339 and 678 m³ ha⁻¹) produced more CH4 (78–92 g m⁻² year⁻¹) than unamended plots (28 g m⁻² year⁻¹). These same amendments had little effect on hydric soil indicators (e.g., redox potential and reduced iron). Manure almost doubled vegetation biomass (937 g m⁻² versus 534 g m⁻²) compared to the unamended control, largely due to the growth of Typha sp. (cattail), an undesired plant at this site that resulted in lower floristic quality. Compared to unamended soils, only wood chips appeared to increase soil organic matter after one growing season. All amendments tended to reduce soil bulk density and penetration resistance, but these were not correlated with root growth. Unexpectedly, hydrology varied considerably due to patchy soil characteristics, despite little variation in elevation – this strongly influenced on our results. We qualitatively observed that constantly inundated plots had lower CH4 emissions than areas with wet-dry cycles and that cattail proliferated mostly in wetter areas. Contrary to the prescription of organic matter amendments as a method for accelerating soil and vegetation development in wetland restoration projects, our findings demonstrate that amendments may not be necessary to support vegetation and hydric soil development and might unnecessarily exacerbate atmospheric warming and contribute to invasive species spread.
This chapter discusses restoration of wetlands degraded by oil and gas activities. Restoration involves a synergistic approach that tries to reverse the damage of oil and gas impacts and rebuild a functioning coastal wetland system.
The Second State of the Carbon Cycle Report (SOCCR2) culminated in 19 chapters that spanned all North American sectors – from Energy Systems to Agriculture and Land Use – known to be important for understanding carbon (C) cycling and accounting. Wetlands, both inland and coastal, were found to be significant components of C fluxes along the terrestrial to aquatic hydrologic continuum. In this chapter, we synthesize the role of wetlands in the overall C footprint of North America (from Canada to Mexico) as one metric of the societal values placed on these terrestrial‐aquatic interfaces. We also summarize the effects of management activities and climate change on the wetland C cycle and give some perspectives on the current and future importance of wetlands to society.
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.
Recognition of wetland ecosystem services has led to substantial investment in wetland restoration in recent decades. Wetland restorations can be designed to meet numerous goals, among which re‐establishing a diverse native wetland plant community is a common aim. In agricultural areas, where previously drained wetland basins can fill with eroded sediment from the surrounding landscape, restoration often includes excavation to expose buried seed banks. The extent to which excavation improves the diversity of wetland plant communities is unclear, particularly in terms of longer‐term outcomes. We examined plant species diversity and community composition in 24 restored agricultural wetlands across west‐central Minnesota, USA. In all study wetlands, hydrology was restored by removing subsurface drainage and plugging drainage ditches, thus re‐establishing groundwater connectivity and hydroperiod (“Business As Usual” treatment). In half of the wetlands, accumulated sediment was removed from the basin and redeposited on the surrounding landscape (“Excavated” treatment). Initially, sediment removal significantly decreased invasive species cover, particularly of Typha x glauca (hybrid cattail) and Phalaris arundinacea (reed canary grass), and increased community diversity and evenness. Over time, the effects of sediment removal diminished, and eventually disappeared by ca. six years after restoration. While our results demonstrate that sediment removal improves initial restoration outcomes for plant communities, longer‐term benefits require sustained management, such as invasive species control or resetting of basins through additional excavation. This article is protected by copyright. All rights reserved.
The extent to which ecological properties of restored coastal wetlands in the northern Gulf of Mexico recover to natural wetland conditions has not been synthesized. We conducted a systematic literature review and meta-analysis to evaluate whether vegetation and soil parameters at marsh sites restored through sediment addition recovered to levels found at paired reference sites. From 1342 candidate publications, we identified 25 studies (< 1 to > 30 years since initial restoration) suitable for quantitative meta-analysis. Vegetation cover was 50% lower at restored sites compared to reference sites over the first 5 years of restoration while aboveground biomass was 25% higher. On average, belowground parameters (root biomass and soil organic matter) were 44 to 92% lower at restored sites during the first 15 years of restoration compared to reference sites. Mean recovery trajectories for belowground biomass and productivity, vegetation cover, and soil parameters indicated that mean values for restored sites reached reference site conditions within 30 years following restoration. We also evaluated recovery curves for the 20th percentile of site data, which we suggest provides a valuable perspective for natural resource agencies to consider when evaluating individual projects, as it should ensure higher success rates compared with using mean recovery rates to estimate success. Understanding marsh recovery rates following restoration helps future restoration design and monitoring, but recovery rates vary across measurement endpoints. Deciding on the appropriate response(s) to use as the basis of performance measures and monitoring will influence the apparent success of marsh restoration projects.
When wetland restoration includes re-establishing native plant taxa as an objective, an understanding of the variables driving the development of plant communities is necessary. With this in mind, we examined soil and physiographic characterstics of depressional wetlands of three vegetation types (cypressgum swamps, cypress savannas, and grass-sedge marshes) located in a fire-maintained longleaf pine ecosystem in southwestern Georgia, USA. Our objective was to establish wether plant community development in these wetlands is controlled primarily by hydrogeomorphic features or by different disturbance histories. We did not identify physical features that uniquely separate the wetland vegetation types. Instead, we observed a range of topo-edaphic conditions that likely drive variations in hydrologic regimes, which in turn, are probable influences on fire regime. We propose that several long-term successional trajectories may be initiated in the prolonged absence of fire, altered hydrology, or both, which link the distinctive vegetation types. Thus, a range of vegetation types may be suitable as potential restoration goals for these depressional wetlands. We suggest that the opportunities or constraints for use of prescribed fire in the long-term management of restored wetlands and adjacent uplands should be a significant consideration in the development of restoration strategies targeting specific plant communities.
PURPOSE: Despite substantial national investments in aquatic ecosystem restoration, there is little or no quantitative monitoring of ecological response, and little or no basis upon which to assess project and program success. Moreover, few national databases have been developed for ecosystem restoration projects. Monitoring and assessment efforts within the US Army Corps of Engineers ("the Corps") largely reflect this pattern. Better data and information are needed by the Corps and others to ensure that restoration investments maximize environmental benefits to the Nation.
This report describes the methods and protocol used to develop and evaluate a database of ecosystem restoration projects completed by the Corps. Specific objectives are to evaluate (1) the benefits realized relative to objectives, and (2) the performance of selected restoration techniques and practices with respect to stated objectives as well as to independent ecological criteria. The authors also wish to identify lessons learned and noteworthy projects or practices that can improve the performance and outcomes of future projects or practices. Results will have applications beyond the Corps to practitioners nationwide.
Part 1 of this report summarizes (1) results of a workshop conducted during October 2009 to help formulate and refine the focus and direction of the present study; (2) methods used to develop the database; and (3) questions that ongoing analyses will address in subsequent reports. Part 2 details the database content and development guidelines as well as the protocols used for district review of the database.
The realization of wetland ‘no net loss’ policy under Section 404 of the Clean Water Act remains uncertain, as mitigation practices force a trade-off in on-site mitigation with loss of biological integrity and off-site mitigation with a redistribution of ecosystem services. Wetlands cover 25 % of the Lower St. Johns River Basin (LSJRB), northeastern Florida, a region impacted by urban development. This case study investigated whether impacted wetland area and type of mitigation differ with land use intensity among the years 2006–2013 from a review of 522 Environmental Resource Permits. A Landscape Development Intensity index was used to compare land use as a function of anthropogenic activity for permitted parcels and mitigation banks. Forested wetlands comprised 47–97 % of impacted wetland area/yr and the majority of parcels and mitigation banks were in mid to high development areas (75 % of area). On-site only mitigation (29 % of permits) and use of mitigation banks (27 %) were more common than off-site only mitigation (20 %). Wetland preservation (880 ha/yr) was more common than wetland creation (9 ha/yr). This study puts into question the ‘no net loss’ wetland policy as urban development contributes to cumulative loss, fragmentation, and re-organization of wetlands across the landscape despite compulsory mitigation.