Restoration Of Freshwater Wetlands Research Articles

Freshwater wetland restoration and conservation are long-term natural climate solutions

Freshwater wetlands have a disproportionately large influence on the global carbon cycle, with the potential to serve as long-term carbon sinks. Many of the world's freshwater wetlands have been destroyed or degraded, thereby affecting carbon-sink capacity. Ecological restoration of degraded wetlands is thus becoming an increasingly sought-after natural climate solution. Yet the time required to revert a degraded wetland from a carbon source to sink remains largely unknown. Moreover, increased methane (CH4) and nitrous oxide (N2O) emissions might complicate the climate benefit that wetland restoration may represent. We conducted a global meta-analysis to evaluate the benefits of wetland restoration in terms of net ecosystem carbon and greenhouse gas balance. Most studies (76 %) investigated the benefits of wetland restoration in peatlands (bogs, fens, and peat swamps) in the northern hemisphere, whereas the effects of restoration in non-peat wetlands (freshwater marshes, non-peat swamps, and riparian wetlands) remain largely unexplored. Despite higher CH4 emissions, most restored (77 %) and all natural peatlands were net carbon sinks, whereas most degraded peatlands (69 %) were carbon sources. Conversely, CH4 emissions from non-peat wetlands were similar across degraded, restored, and natural non-peat wetlands. When considering the radiative forcings and atmospheric lifetimes of the different greenhouse gases, the average time for restored wetlands to have a net cooling effect on the climate after restoration is 525 years for peatlands and 141 years for non-peat wetlands. The radiative benefit of wetland restoration does, therefore, not meet the timeframe set by the Paris Agreement to limit global warming by 2100. The conservation and protection of natural freshwater wetlands should be prioritised over wetland restoration as those ecosystems already play a key role in climate change mitigation.

Preserving La Mancha’s Wetland Avian Heritage with a Community-Driven Bird Monitoring Initiative

The region of La Mancha includes several bodies of water and communities of wetlands and jungles. It has a rich flora and fauna, and its wetlands are a Ramsar site (La ManchaEl Llano no 1336). Since 1999, there has been a community ecotourism group made up of farmers, ranchers, and fishermen who actively participate in research projects at CICOLMA (a reserve and field station of the Instituto de Ecología A.C., a public research center). They supported the restoration of freshwater wetlands, and since then, one of their members has been monitoring monthly the birds that arrive at the restored wetland. He has recorded 200 species, including aquatic, wading, and terrestrial birds. His training and enthusiasm have allowed him to constantly support data collection and generate this list, showing the role of a small wetland in bird richness. The group’s activity has also resulted in greater community interest in conservation and becoming a livelihood.

Correction: Jobe et al. Herbivory by Geese Inhibits Tidal Freshwater Wetland Restoration Success. Diversity 2022, 14, 278

In the original publication [...]

Herbivory by Geese Inhibits Tidal Freshwater Wetland Restoration Success

Experimental results from a multi-year exclosure study (2009–2015) demonstrate strong effects of geese on plant cover and species diversity in an urban, restored tidal freshwater wetland. Access by geese inhibited plant establishment and suppressed plant diversity, particularly of annual plant species. Our experimental results demonstrate that the protection of newly restored tidal freshwater wetlands from geese is a make-or-break management activity that will determine the composition and long-term persistence of vegetation at the site. The causal herbivore, in this case, was resident, non-migratory Canada geese (Branta canadensis), which have increased dramatically over the last several decades and had high population densities throughout the study period. These findings suggest that management activities to reduce the population sizes of non-migratory goose populations will support greater wetland plant diversity.

Successional dynamics of a 35 year old freshwater mitigation wetland in southeastern New Hampshire.

The long-term ecological success of compensatory freshwater wetland projects has come into question based on follow-up monitoring studies over the past few decades. Given that wetland restoration may require many years to decades to converge to desired outcomes, long-term monitoring of successional patterns may increase our ability to fully evaluate success of wetland mitigation projects or guide adaptive management when needed. In Portsmouth, New Hampshire a 4 ha wetland was constructed in an abandoned gravel quarry as off-site compensatory mitigation for impacts to a scrub-shrub swamp associated with property expansion. Building upon prior evaluations from 1992 and 2002, we conducted a floral survey in 2020 to compare results with prior surveys to document vegetation successional trends over time. In addition, we monitored the avian community throughout the growing season as a measure of habitat quality. The plant community mirrored documented successional trends of freshwater wetland restoration projects as native hydrophytes dominated species composition. Plant species composition stabilized as the rate of turnover, the measurement of succession, declined by nearly half after 17 years. Researchers should consider long-term monitoring of specific sites to better understand successional patterns of created wetlands as we documented long time frames required for the development of scrub-shrub swamps, red maple swamps, and sedge meadows. High species richness was attributed to beaver activity, topographic heterogeneity from Carex stricta tussocks, and the seed bank from the application of peat from the original wetland. Habitat heterogeneity of open water, herbaceous cover, and woody vegetation supports a diverse avian community including 11 wetland dependent species. Although the mitigation project has not created the full area of lost scrub-shrub swamp after 35 years, it has developed a structurally complex habitat and diverse avian community that effectively provides the functions and values of the impacted system.

Quantifying effects of increased hydroperiod on wetland nutrient concentrations during early phases of freshwater restoration of the Florida Everglades

Wetland restoration requires managing long‐term changes in hydroperiod and ecosystem functions. We quantified relationships among spatiotemporal variability in wetland hydrology and total phosphorus (TP) and its stoichiometric relationships with total organic carbon (TOC:TP) and total carbon (TC:TP) and total nitrogen (TN:TP) in water, flocculent organic matter (floc), periphyton, sawgrass (Cladium jamaicense), and soil during early phases of freshwater wetland restoration—water year (WY) 2016 (1 May, 2015 to 30 April, 2016) to WY 2019—in Everglades National Park (ENP, Homestead, FL, U.S.A.). Wetland hydroperiod increased by 87 days, following restoration actions and rainfall events that increased median stage in the upstream source canal. Concentrations of TP were highest and most variable at sites closest (<1 km) to canal inputs and upstream wetland sources of legacy P. Surface water TOC:TP and TN:TP ratios were highest in wetlands >1 km downstream of the canal in wet season 2015 with spatial variability reflecting disturbances including droughts, fires, and freeze events. The TP concentrations of flocculent soil surface particles, periphyton, sawgrass, and consolidated soil declined, and TC:TP and TN:TP ratios increased (except soil) logarithmically with downstream distance from the canal. We measured abrupt increases in periphyton (wet season 2018) and sawgrass TP (wet season 2015 and 2018) at sites <1 km from the canal, likely reflecting legacy TP loading. Our results suggest restoration efforts that increase freshwater inflow and hydroperiod will likely change patterns of nutrient concentrations among water and organic matter compartments of wetlands as a function of nutrient legacies.

Water accessibility assessment of freshwater wetlands in the Yellow River Delta National Nature Reserve, China

Water accessibility assessment (WAA) is very important to the ecological restoration of freshwater wetlands and water resources management due to an intensive human disturbance. This paper develops a quantitative methodology for WAA in the Yellow River Delta National Nature Reserve (YRDNNR), from which an assessment of water accessibility is made on the freshwater wetlands. The assessment uses a Water accessibility index (WAI) model by employing GIS network analysis and spatial statistical analysis. Five indicators for the model cover both natural and anthropogenic factors, including distance from freshwater resources, average elevation, road density, ditch density, and number of culverts at the grid scale. The values of the WAI model are between 0.26 and 0.82. The WAI has a significant and positive spatial autocorrelation. There are totally 12 freshwater marsh patches exist in the YRDNNR. The highest WAI value in the freshwater marsh patch occurs near the estuary area of the Yellow River, while the lowest WAI value lies farthest from the Yellow River. There are two freshwater restored wetlands that have lower WAI values, from which a scientific restoration strategy is presented to remove the paddy field, roads and other facilities between two wetlands and the Yellow River Course. The results of the WAI model have been validated by matching the ratio of water body area within patches and consulting with local administrators, which indicates a satisfied WAI assessment effectiveness. The proposed WAI can help administrators to guide wetland ecological restoration and to plan for freshwater resources management.

Designing topographic heterogeneity for tidal wetland restoration

Topographic heterogeneity affects abiotic and biotic components of vegetated ecosystems and has the potential to provide functions and services such as promoting floral and faunal biodiversity. Yet, few studies have documented the design, implementation, and outcomes of mound-type features in estuarine and tidal freshwater wetland restoration projects. Here we report data from a synoptic survey of soil temperature and moisture on mounds at tidal wetland restoration sites in the Pacific Northwest, together with the results of a literature review, and the insights of regional restoration practitioners regarding ecological and practical considerations for mound construction. Few papers reviewed addressed conditions for plant establishment on mounds, such as soil moisture, which is important in climates with annual dry seasons, like the Pacific Northwest. We report 2015 data on soil moisture and temperature for the tops, sides, and toes of 15 mounds constructed between 2001 and 2013 of fill dirt, or dirt and logs, at 5 tidal wetland restoration sites. Two of the restoration projects studied are located in the lower Columbia River and estuary, one is in the Puget Sound, and two are in outer Pacific coastal estuaries in Oregon. The heights of mounds ranged from 0.5 m to 1.5 m above the marsh plain, and the area of individual mounds ranged from 21 m2 to 5185 m2, while most published information treated somewhat smaller topographic features (termed mounds, hummocks, tussocks, ridges, levees, fans, or terraces). Differences in the minimum and maximum values of moisture between the toe and the top of mound in summer ranged from 2.9% to 40%. Statistical analysis strongly suggested stratification of soil moisture by elevation. Analysis of soil temperature was less conclusive, but temperature appeared to be positively correlated with elevation. Soil moisture relative to mound aspect (cardinal direction) was significant in some cases, but inconsistent between mounds. We also report our observations from a third recent restoration project on the tidal Columbia River, and observations made by other practitioners who have designed and installed mounds from San Francisco Bay to northern Puget Sound. Our findings will support design of wetland restoration sites where topographic heterogeneity is an objective.

A Unique Combination of Aerodynamic and Surface Properties Contribute to Surface Cooling in Restored Wetlands of the Sacramento‐San Joaquin Delta, California

AbstractLand use change and management affect climate by altering both the biogeochemical and biophysical interactions between the land and atmosphere. Whereas climate policy often emphasizes the biogeochemical impact of land use change, biophysical impacts, including changes in reflectance, energy partitioning among sensible and latent heat exchange, and surface roughness, can attenuate or enhance biogeochemical effects at local to regional scales. This study analyzes 3 years (2015–2017) of turbulent flux and meteorological data across three contrasting wetland restoration sites and one agricultural site, colocated in the Sacramento‐San Joaquin Delta, California, USA, to understand if the biophysical impacts of freshwater wetland restoration can be expected to attenuate or enhance the potential biogeochemical benefits. We show that despite absorbing more net radiation, restored wetlands have the potential to cool daytime surface temperature by up to 5.1 °C, as compared to a dominant drained agricultural land use. Wetland canopy structure largely determines the magnitude of surface temperature cooling, with wetlands that contain areas of open water leading to enhanced nighttime latent heat flux and reduced diurnal temperate range. Daytime surface cooling could be important in ameliorating physiological stress associated with hotter and drier conditions and could also promote boundary layer feedbacks at the local to regional scale. With a renewed focus on the mitigation and adaptation potential of natural and working lands, we must better understand the role of biophysical changes, especially in novel land use transitions like wetland restoration.

Wetland restoration and hydrologic reconnection result in enhanced watershed nitrogen retention and removal

Restoration of freshwater wetlands presents a potential water quality benefit via removal of nutrients, but complex and unresolved changes in nutrient cycling can occur following restoration. In this study, we evaluated N removal and release in a deltaic wetland under scenarios of hydrologic reconnection and sediment dredging, and we modeled potential downstream impacts of these restoration activities in a Bayesian framework. Denitrification, N2O production, and anammox were measured via the isotope pairing technique in intact sediment cores. Anammox was not detected. Denitrification rates in the control scenario (78.2–87.2 μmol N m−2 h−1) were significantly higher than those under hydrologic reconnection and dredging scenarios (14.7–56.0 μmol N m−2 h−1). N2O production rates were typical of wetland environments. Denitrification and N2O production were stimulated shortly following simulated dredging, indicating a short-term response to sediment disturbance. Under hydrologic reconnection, NH4 + availability was decreased, inhibiting coupled nitrification-denitrification. Despite a decrease in denitrification activity, the wetland has the capacity to remove up to 10% of stream NO3 − following hydrologic reconnection. Restoration is predicted to fully mitigate NH4 + delivery to a downstream eutrophic lake, yet permanent N removal may be reduced due to the decoupling of nitrification and denitrification.

The Introduction of Woody Plants for Freshwater Wetland Restoration Alters the Archaeal Community Structure in Soil

AbstractDue to the severe degradation of wetland ecosystems in China, great efforts, such as the reconstruction of forested wetlands, have been devoted to restore the damaged and degraded wetlands to support species diversity and ecosystem services. However, less attention has been given to the diversity and ecological significance of prokaryotes of the domain Archaea compared with prokaryotes of the domain Bacteria during the reconstruction of forested wetlands. Here, the effects of introduced woody plants (Taxodium distichum and Alnus trabeculosa) on the archaeal community in a freshwater wetland in the Yangtze estuary were investigated. The results showed that Thaumarchaeota obviously predominated at three studied sites in the freshwater wetland, the relative abundance of which decreased with increasing depth, ranging from 93.9% (0–10 cm) to 1.9% (30–40 cm) in mudflats, from 100% (0–10 cm) to 64.8% (30–40 cm) in T. distichum sediment and from 100% (0–10 cm) to 66.7% (40–50 cm) in A. trabeculosa sediment. The abundances of the archaeal amoA gene in woody plant sediments, ranging from 3.27 × 107 to 2.45 × 108 copies g−1 dry soil, were significantly higher than those in bare mudflat, ranging from 9.23 × 106 to 1.35 × 107 copies g−1 dry soil. The archaeal community, which was significantly affected by pH, microbial carbon and SO42− contents according to a canonical correspondence analysis, was significantly altered by plants and soil depth (p < 0.05). These results indicated that the introduction of woody plants stimulates the proliferation of Thaumarchaeota, especially ammonia‐oxidizing archaea, which could be important contributors to the N cycle in forested wetland ecosystems. Copyright © 2017 John Wiley & Sons, Ltd.

When ecological ‘conversion’ behaves like restoration and when it does not

When ecological ‘conversion’ behaves like restoration and when it does not

Interactions between soil physicochemistry and belowground biomass production in a freshwater tidal marsh

The success of tidal freshwater wetland restoration is typically gauged by the re-establishment of characteristics found in reference marshes. Although plant species composition may resemble reference marshes within a few years after the initiation of restoration, return of soil physicochemical properties may take much longer. We investigated soil characteristics in a post-levee breach freshwater tidal marsh restoration site (Liberty Island, California), and the impacts of soil compaction on the survival and growth of emergent macrophytes. In a field study, we examined soil physicochemical properties throughout 50-cm deep soil cores collected from locations at Liberty Island that differed in location and stage of vegetation colonization. In a controlled mesocosm study, we subjected three species that are commonly implemented in restoration plantings (Schoenoplectus acutus, S. californicus, and Typha latifolia) to two levels of soil compaction (control and high soil bulk density) to determine the influence of soil compaction on soil physicochemical properties and macrophyte response. Belowground biomass increased and soil bulk density decreased with time since vegetation colonization. The controlled study showed that both Schoenoplectus species exhibited greater survival than T. latifolia. The species explored are capable of ameliorating compacted soil conditions over time; this ability can facilitate the re-establishment of wetland structure and function at restoration sites.

Diversity Pattern of Macrobenthos Associated with Different Stages of Wetland Restoration in the Yellow River Delta

Because wetland restoration projects are becoming more common and are expensive, it is important to evaluate their success. Evaluation studies common use measurements of soils, vegetation, hydrology and wildlife to evaluate the success of wetland restoration. In contrast, the diversity of macrobenthos and their relationships with environmental factors are often neglected. To better understand the success of wetland restoration, we examined the abundance and diversity of macrobenthos in different stages of a freshwater wetland restoration project in the Yellow River Delta in China, with reference to environmental factors that might explain macrobenthic patterns. Macrobenthic species richness and density were greater in the oldest restoration area versus the younger and no-treatment areas. Macrobenthic biomass, however, was greatest in the no-treatment area. The oldest restoration area had deeper water levels, lower salinities, softer and wetter soils, and higher soil organic, nitrogen and carbon contents, and these variables largely distinguished the macrobenthic samples in a CCA analysis. A combination of landscape position and recovery time (time since the restoration was implemented) likely explains the abiotic differences among restoration areas. We recommend an adaptive management strategy, guided by long-term monitoring and experiments, to improve the success of this and other wetland restoration projects.

Climate Change Adaptation: Putting Principles into Practice

Carrying out wildlife conservation in a changing climate requires planning on long timescales at both a site and network level, while also having the flexibility to adapt actions at sites over short timescales in response to changing conditions and new information. The Royal Society for the Protection of Birds (RSPB), a land-owning wildlife conservation charity in the UK, achieves this on its nature reserves through its system of management planning. This involves setting network-wide objectives which inform the 25-year vision and 5-year conservation objectives for each site. Progress toward achieving each site's conservation objectives is reviewed annually, to identify any adjustments which might be needed to the site's management. The conservation objectives and 25-year vision of each site are reviewed every 5 years.Significant predicted [corrected] long-term impacts of climate change most frequently identified at RSPB reserves are: loss of intertidal habitat through coastal squeeze, loss of low-lying islands due to higher sea levels and coastal erosion, loss of coastal freshwater and brackish wetlands due to increased coastal flooding, and changes in the hydrology of wetlands. The main types of adaptation measures in place on RSPB reserves to address climate change-related impacts are: re-creation of intertidal habitat, re-creation and restoration of freshwater wetlands away from vulnerable coastal areas, blocking artificial drainage on peatlands, and addressing pressures on freshwater supply for lowland wet grasslands in eastern and southeastern England. Developing partnerships between organizations has been crucial in delivering large-scale adaptation projects.

Use of seasonal freshwater wetlands by fishes in a temperate river floodplain

This study examined the use of freshwater wetland restoration and enhancement projects (i.e. non‐estuarine wetlands subject to seasonal drying) by fish populations. To quantify fish use of freshwater emergent wetlands and assess the effect of wetland enhancement (i.e. addition of water control structures), two enhanced and two unenhanced emergent wetlands were compared, as well as two oxbow habitats within the Chehalis River floodplain. Eighteen fish species were captured using fyke nets and emigrant traps from January to the beginning of June, with the most abundant being three‐spined stickleback Gasterosteus aculeatus and Olympic mudminnow Novumbra hubbsi. Coho salmon Oncorhynchus kisutch was the dominant salmonid at all sites. Enhanced wetlands, with their extended hydroperiods, had significantly higher abundances of yearling coho salmon than unenhanced wetlands. Both enhanced and unenhanced emergent wetlands yielded higher abundances of non‐game native fishes than oxbow habitats. Oxbow habitats, however, were dominated by coho salmon. Fish survival in the wetland habitats was dependent on emigration to the river before dissolved oxygen concentrations decreased and wetlands became isolated and stranding occurred. This study suggests that wetland enhancement projects with an outlet to the river channel appear to provide fishes with important temporary habitats if they have the opportunity to leave the wetland as dissolved oxygen levels deteriorate.

Re-establishing freshwater wetlands in Denmark

A national programme for the restoration of freshwater wetlands in Denmark was initiated in 1998. The purpose was to reduce nitrogen load to down-stream recipients and to enhance nature values in restored areas. In August 2005, 3060 ha of land was restored and 3769 ha of land approved for restoration. A monitoring programme for surveying the effects of the restoration of the wetlands has been set up. The programme includes basic data on land use and surveys of environmental effects and natural values. Basic data on land use in restored wetlands has shown that areas were dominated by agriculture (42%) and meadow-land (39%) prior to the re-establishment. Areas possessing plant communities with a high conservation value had a very restricted extension prior to project implementations and only accounted for 1.2% of the total area. Wetlands approved for restoration and wetlands already restored have been grouped in different types according to their hydrological regime. Shallow lakes cover 2985 ha, while a variety of different wetland projects ranging from areas irrigated with drainage water to restored river valleys including remeandered rivers cover 3844 ha. The mean nitrogen removal for all projects was estimated to 259 kg N ha −1 year −1, while results from the monitoring programme have shown that wetlands remove between 39 and 372 kg N ha −1 year −1.

Freshwater wetland restoration of an abandoned sand mine: Seed bank recruitment dynamics and plant colonization

We examined plant recruitment from two soil seed banks used in the freshwater wetland restoration of an abandoned sand mine in South Brunswick, New Jersey. One seed bank was already present at the mine prior to restoration; the other was imported from a nearby wetland to be destroyed by road development. We also investigated the effects of pH and water regime on recruitment in a greenhouse study and assessed plant recruitment at the restoration site during the first growing season. Multivariate analysis of recruitment in greenhouse communities revealed differential responses of the two seed banks to pH and water regime treatments. In the wetland soil, species richness and plant density responded favorably to inundation and increased pH treatments. In the mine soil, species richness and density were greatest with non-inundated and unadjusted pH conditions. The imported seed bank was characterized by greater species richness (n=21) than the mine seed bank (n=14). Mean recruit density was also greater in the wetland soil (263.6 individuals/m2) than the mine soil (60.1 individuals/m2). Recruits unique to the imported wetland seed bank included a significant proportion of obligate wetland species (52.4%). More species were censused in the field study (82) compared to the greenhouse study (24), with 23.2% of species present in both studies. A lower proportion of obligate wetland species (24.0%) was present in the field. The imported wetland seed bank was the major contributor to species richness and plant density, indicating that the use of imported soils as an amendment may enhance success of wetland restoration projects.

Multiobjective Approaches in Freshwater Wetland Restoration and Design

ABSTRACT Water quality problems in receiving waters in the Los Angeles area, and recent federal, state, and local environmental ordinances oblige large developments in California to cleanse urban stormwater runoff on-site before releasing it into storm drains, natural streams, or into the ocean. As a requirement for a land development permit, a channellpond system was engineered to provide three independent functions: flood control for existing and proposed developments, urban stormwater runoff treatment, and freshwater habitat for fish and wildlife. These functions are achieved by designing the channel as a riparian corridor with a freshwater wetlandpond at the downstream end. This article presents an overview of the current regulations, a description of Best Management Practices (BMPs), and the example design of the riparian corridorlfreshwater wetland system emphasizing hydraulic analysis and design, biotic design, environmental function and effectiveness, management, operation, monitoring and maintenance, and project permit requirements.

Wetland creation and restoration: the status of the science

In the last decade, interest has increased in coastal and freshwater wetland restoration and creation at all levels of government, in the scientific community, and in the private sector. US Environmental Protection Agency personnel agreed that there was a pressing need to determine how well created and restored wetlands compensate for losses permitted under Section 404 of the Clean Water Act. An effort was made to capture information not published elsewhere and incorporate it with published literature to produce a unique resource. The status report is the first major publication resulting from research initiated on wetland creation and restoration. Conceived as a mechanism for identifying the adequacy of the available information, this status report will help set priorities for the research program and provide Agency personnel with an analytical framework for making Section 404 permit decisions based on the status of the science of wetland creation and restoration. The report is composed of two volumes. The first volume is a series of regional reviews, summarizing wetland creation and restoration experiences in broadly-defined wetland regions, the second volume is a series of theme papers, covering a wide range of topics of general application to wetland creation and restoration. One report ismore » processed separately for inclusion in the appropriate data bases.« less