Tidal Wetland Restoration Research Articles

Identifying priority ecosystem services in tidal wetland restoration.

Classification systems can be an important tool for identifying and quantifying the importance of relationships, assessing spatial patterns in a standardized way, and forecasting alternative decision scenarios to characterize the potential benefits (e.g., ecosystem services) from ecosystem restoration that improve human health and well-being. We present a top-down approach that systematically leverages ecosystem services classification systems to identify potential services relevant for ecosystem restoration decisions. We demonstrate this approach using the U.S. Environmental Protection Agency's National Ecosystem Service Classification System Plus (NESCS Plus) to identify those ecosystem services that are relevant to restoration of tidal wetlands. We selected tidal wetland management documents from federal agencies, state agencies, wetland conservation organizations, and land stewards across three regions of the continental United States (northern Gulf of Mexico, Mid-Atlantic, and Pacific Northwest) to examine regional and organizational differences in identified potential benefits of tidal wetland restoration activities and the potential user groups who may benefit. We used an automated document analysis to quantify the frequencies at which different wetland types were mentioned in the management documents along with their associated beneficiary groups and the ecological end products (EEPs) those beneficiaries care about, as defined by NESCS Plus. Results showed that a top combination across all three regions, all four organizations, and all four tidal wetland types was the EEP naturalness paired with the beneficiary people who care (existence). Overall, the Mid-Atlantic region and the land steward organizations mentioned ecosystem services more than the others, and EEPs were mentioned in combination with tidal wetlands as a high-level, more general category than the other more specific tidal wetland types. Certain regional and organizations differences were statistically significant. Those results may be useful in identifying ecosystem services-related goals for tidal wetland restoration. This approach for identifying and comparing ecosystem service priorities is broadly transferrable to other ecosystems or decision-making contexts.

Winter harvesting reduces methane emissions and enhances blue carbon potential in coastal phragmites wetlands

Enhancing the ability of coastal blue carbon to accumulate and store carbon and reduce net greenhouse gas emissions is an essential component of a comprehensive approach for tackling climate change. The annual winter harvesting of Phragmites is common worldwide. However, the effects of harvesting on methane (CH4) emissions and its potential as an effective blue carbon management strategy have rarely been reported. In this study, the effects of winter Phragmites harvesting on the CH4 and carbon dioxide (CO2) fluxes and the underlying mechanisms in coastal Phragmites wetlands were investigated by comparing the eddy covariance flux measurements for three coastal wetlands with different harvesting and tidal flow conditions. The results show that harvesting can greatly reduce the CH4 emissions and the radiative forcing of CH4 and CO2 fluxes in coastal Phragmites wetlands, suggesting that winter Phragmites harvesting has great potential as a nature-based strategy to mitigate global warming. The monthly mean CH4 fluxes were predominantly driven by air temperature, gross primary productivity, and latent heat fluxes, which are related to vegetation phenology. Additionally, variations in the salinity and water levels exerted strong regulation effects on CH4 emissions, highlighting the important role of proper tidal flow restoration and resalinization in enhancing blue carbon sequestration potential. Compared with the natural, tidally unrestricted wetlands, the CH4 fluxes in the impounded wetland were less strongly correlated with hydrometeorological variables, implying the increased difficulties of predicting CH4 variations in impounded ecosystem. This study facilitates the improved understanding of carbon exchange in coastal Phragmites wetlands with harvesting or impoundment, and provides new insights into effective blue carbon management strategies beyond tidal wetland restoration for mitigating the effects of climate change.

Connecting stakeholder priorities and desired environmental attributes for wetland restoration using ecosystem services and a heat map analysis for communications.

Framing ecological restoration and monitoring goals from a human benefits perspective (i.e., ecosystem services) can help inform restoration planners, surrounding communities, and relevant stakeholders about the direct benefits they may obtain from a specific restoration project. We used a case study of tidal wetland restoration in the Tillamook River watershed in Oregon, USA, to demonstrate how to identify and integrate community stakeholders/beneficiaries and the environmental attributes they use to inform the design of and enhance environmental benefits from ecological restoration. Using the U.S. Environmental Protection Agency's Final Ecosystem Goods and Services (FEGS) Scoping Tool, we quantify the types of ecosystem services of greatest common value to stakeholders/beneficiaries that lead to desired benefits that contribute to their well-being in the context of planned uses that can be incorporated into the restoration project. This case study identified priority stakeholders, beneficiaries, and environmental attributes of interest to inform restoration goal selection. This novel decision context application of the FEGS Scoping Tool also included an effort focused on how to communicate the connections between stakeholders, and the environmental attributes of greatest interest to them using heat maps.

Wetland geomorphology and tidal hydrodynamics drive fine-scale fish community composition and abundance

Effective restoration of tidal wetlands for fish communities requires clear goals and mechanistic understanding of the ecosystem drivers which affect fish distribution and abundance. We examined fish community responses to abiotic habitat features in two adjacent but dissimilar freshwater tidal wetlands in the Sacramento-San Joaquin Delta, CA, USA, each of which represents a potential restoration configuration. The first wetland was characterized by a broad, intertidal basin with relatively high hydrodynamic exchange with surrounding waterways. The second wetland was characterized by a dendritic network of shallow subtidal channels with relatively low hydrodynamic exchange. Fish community composition significantly differed between the two wetlands, based on permutational analysis of variance. Fish abundance within and among the two wetlands was also highly affected by specific geomorphic and hydrodynamic characteristics: distance from connection with the main external waterway, bed elevation, and water surface elevation. The physical configuration of a restored tidal wetland, in conjunction with the way tides move across the restored landscape, has strong implications for local fishes. Manipulating these elements to create a landscape mosaic of habitat configurations can be an effective tool for targeting desired restoration outcomes, such as specific fish communities or target fish densities.

Mapping methane reduction potential of tidal wetland restoration in the United States

Coastal wetlands can emit excess methane in cases where they are impounded and artificially freshened by structures that impede tidal exchange. We provide a new assessment of coastal methane reduction opportunities for the contiguous United States by combining multiple publicly available map layers, reassessing greenhouse gas emissions datasets, and applying scenarios informed by geospatial information system and by surveys of coastal managers. Independent accuracy assessment indicates that coastal impoundments are under-mapped at the national level by a factor of one-half. Restorations of freshwater-impounded wetlands to brackish or saline conditions have the greatest potential climate benefit of all mapped conversion opportunities, but were rarer than other potential conversion events. At the national scale we estimate potential emissions reduction for coastal wetlands to be 0.91 Teragrams of carbon dioxide equivalents year−1, a more conservative assessment compared to previous estimates. We provide a map of 1,796 parcels with the potential for tidal re-connection.

Evaluating Habitat Suitability and Tidal Wetland Restoration Actions With ECOSTRESS

AbstractAs temperatures rise, it is increasingly important to monitor changes in habitat conditions for aquatic species and mitigate emerging stressors. The ECOsystem Spaceborne Thermal Radiometer Experiment on Space Station (ECOSTRESS) instrument provides temperature products at a spatial and temporal scale not previously available. Here, we utilize ECOSTRESS temperature products to assess fluctuations in thermal habitat suitability for an endangered fish species and we also demonstrate the utility of the data set to assess water surface and bulk temperature changes following completion of two tidal wetland restoration efforts in the San Francisco Estuary and Sacramento–San Joaquin River Delta (Bay Delta). During all hours of the day throughout the 2018–2022 study period, key Delta Smelt habitat areas including Honker Bay, West Suisun Bay, and Mid Suisun Bay had greater than 75% of their areas suitable; there were several instances during which less than 25% of the area was thermally suitable generally coinciding with heatwave events. Overall, midday hours are less frequently suitable than morning and evening hours. Early evidence from ECOSTRESS indicates that there may be a decrease in surface water temperature of up to several degrees in tidal restoration areas, but more data is needed to show statistically significant outcomes. The ECOSTRESS record began in summer of 2018, and a longer record is needed to fully capture temperature changes associated with wetland processes and restoration efforts. Future applications of ECOSTRESS products can the capacity to help further understand ecosystem conditions and how restoration efforts affect water temperature, informing decisions that benefit Delta Smelt and other at‐risk aquatic species.

Multi-temporal high-resolution marsh vegetation mapping using unoccupied aircraft system remote sensing and machine learning

Coastal wetlands are among the most productive ecosystems in the world and provide important ecosystem services related to improved water quality, carbon sequestration, and biodiversity. In many locations, wetlands are threatened by coastal development and rising sea levels, prompting an era of tidal wetland restoration. The creation and restoration of tidal marshes necessitate the need for ecosystem monitoring. While satellite remote sensing is a valuable monitoring tool; the spatial and temporal resolution of imagery often places operational constraints, especially in small or spatially complex environments. Unoccupied aircraft systems (UAS) are an emerging remote sensing platform that collects data with flexible on-demand capabilities at much greater spatial resolution than sensors on aircraft and satellites, and resultant imagery can be readily rendered in three dimensions through Structure from Motion (SfM) photogrammetric processing. In this study, UAS data at 5 cm resolution was collected at an engineered wetland at Poplar Island, located in Chesapeake Bay, MD United States five times throughout 2019 to 2022. The wetland is dominated by two vegetation species: Spartina alterniflora and Spartina patens that were originally planted in 2005 in low and high marsh elevation zones respectively. During each survey, UAS multispectral reflectance, canopy elevation, and texture were derived and used as input into supervised random forest classification models to classify species-specific marsh vegetation. Overall accuracy ranged from 97% to 99%, with texture and canopy elevation variables being the most important across all datasets. Random forest classifications were also applied to down-sampled UAS data which resulted in a decline in classification accuracy as spatial resolution decreased (pixels became larger), indicating the benefit of using ultra-high resolution imagery to accurately and precisely distinguish between wetland vegetation. High resolution vegetation classification maps were compared to the 2005 as-built planting plans, demonstrating significant changes in vegetation and potential instances of marsh migration. The amount of vegetation change in the high marsh zone positively correlated with interannual variations in local sea level, suggesting a feedback between vegetation and tidal inundation. This study demonstrates that UAS remote sensing has great potential to assist in large-scale estimates of vegetation changes and can improve restoration monitoring success.

High sedimentation rates lead to rapid vegetation recovery in tidal brackish wetland restoration

IntroductionTidal wetland restoration in the Bay of Fundy involves restoring tidal hydrology to sites with tidal restrictions. Most have focused on salt marsh sites close to the mouth of estuaries, but there are also many tidally restricted wetlands closer to the freshwater end of tidal rivers. Recovery of salt marsh vegetation has been rapid in past projects, but little is known about sediment and vegetation dynamics post restoration in tidal brackish or freshwater environments.MethodsWe implemented tidal wetland restoration projects on two tidal rivers near the inland limit of saltwater. Hydrological restoration involved breaching (St. Croix) or realigning agricultural dykes (Belcher Street). We monitored hydrology, sediment accretion and vegetation at replicated plots on restoration sites and nearby reference tidal marshes; and conducted habitat mapping and elevation surveys using drones.ResultsAfter re-establishing tidal flow, sediment accretion was very rapid, leading to a deep layer of new sediments. Plant colonization at both sites resulted in a high diversity of halophytes in the first 2 years post restoration, but the St. Croix site transitioned to freshwater wetland species dominating by the fifth year post- restoration. The Belcher St. site has a mix of freshwater and brackish wetland species after the fourth-year post-restoration.DiscussionHigh suspended sediment concentrations at both sites suggest that each site was positioned closed to the estuarine turbidity maximum within its river. Tidal wetland restoration at the head of estuaries may benefit from the large ecological disturbance associated with rapid sediment accretion, providing a productive substrate with little competition from prior vegetation. However ultimate vegetation patterns may take longer to develop as elevation gains alter tidal flooding frequency. Low salinities suggest that the physical disturbance of sediment burying prior vegetation is the main mechanism creating a clean slate for plant recolonization, rather than mortality of terrestrial vegetation due to salt water. The majority of elevation change was due to allochthonous sediment deposition, with belowground processes playing a minor role. The wetlands restored showed substantial net elevation gains in the first years following tidal hydrological restoration, but long-term monitoring is required to track their overall resilience in the face of sea level rise.

Identifying priority areas for tidal wetland restoration by integrating ecosystem services supply and demand mismatches

Governments and non-governmental organizations have widely recognized tidal wetland restoration as a sustainable instrument to lessen the threat of climate change, which is reflected by the expansion of the spatial scale of coastal restoration projects. However, approaches to large-scale spatial planning of tidal wetland restoration remain sparse. Previous studies on site selection for restoration planning have focused on the potential supply of ecosystem services (ES) or restoration feasibility with less emphasis on the mitigation of the status of regional ES supply and demand mismatches. We developed a five-step workflow based on systematic conservation planning to identify priority areas for tidal wetland restoration and applied it to the coastal reclaimed areas of Shanghai, China. With this workflow, we analyzed the changes in spatial distribution and the potential ecosystem services supply and restoration costs of priority areas between the two different scenarios of ES demand ignored and ES demand considered. Results showed that the potential restorable areas only accounted for 31.4% (425.2 km²) of the original reclaimed area because of other land use demands (e.g., permanent basic farmland conservation). We extracted 50% of the potential restorable areas as priority areas based on Aichi Target 15. Compared with the ES demand-ignored scenario, the ES demand scenario resulted in a substantial increase in the priority areas of Baoshan District (~177%) and Pudong New Area (~15%) and a small decrease in Chongming District (~4%). No significant change in the potential ES supply for all priority areas was observed between the two scenarios. However, the total restoration cost of the ES demand scenario is 10% higher than that of the ES demand-ignored scenario. Our study highlights the importance of considering the status of regional ES supply and demand (mis)matches in large-scale spatial planning for tidal wetland restoration.

Tidal and Nontidal Marsh Restoration: A Trade‐Off Between Carbon Sequestration, Methane Emissions, and Soil Accretion

AbstractSupport for coastal wetland restoration projects that consider carbon (C) storage as a climate mitigation benefit is growing as coastal wetlands are sites of substantial C sequestration. However, the climate footprint of wetland restoration remains controversial as wetlands can also be large sources of methane (CH4). We quantify the vertical fluxes of C in restored fresh and oligohaline nontidal wetlands with managed hydrology and a tidal euhaline marsh in California's San Francisco Bay‐Delta. We combine the use of eddy covariance atmospheric flux measurements with 210Pb‐derived soil C accumulation rates to quantify the C sequestration efficiency of restored wetlands and their associated climate mitigation service. Nontidal managed wetlands were the most efficient in burying C on‐site, with soil C accumulation rates as high as their net atmospheric C uptake (−280 ± 90 and −350 ± 150 g C m−2 yr−1). In contrast, the restored tidal wetland exhibited lower C burial rates over decadal timescales (70 ± 19 g C m−2 yr−1) that accounted for ∼13%–23% of its annual C uptake, suggesting that the remaining fraction is exported via lateral hydrologic flux. From an ecosystem radiative balance perspective, the restored tidal wetland showed a > 10 times higher CO2‐sequestration to CH4‐emission ratio than the nontidal managed wetlands. Thus overall, tidal wetland restoration resulted in a negative radiative forcing (cooling) through increased soil C accumulation, while nontidal wetland restoration led to an early positive forcing (warming) through increased CH4 emissions potentially lasting between 2.1 ± 2.0 to 8 ± 4 decades.

Eco-hydrology as a driver for tidal restoration: Observations from a Ramsar wetland in eastern Australia.

Land reclamation projects and the installation of drainage infrastructure has impacted coastal wetlands worldwide. By altering water levels and inundation extent, these activities have changed the viable ecosystems onsite and resulted in the proliferation of freshwater species. As more than 50% of tidal wetlands have been degraded globally over the last 100 years, the importance of this issue is increasingly being recognised and tidal wetland restoration projects are underway worldwide. However, there are currently limited sites where large-scale reintroduction of tidal flushing has been implemented with the explicit aim to foster the growth of a threatened ecosystem. In this study, the tidal restoration of an internationally recognised Ramsar listed wetland in eastern Australia is described to highlight how coastal saltmarsh can be targeted by mimicking inundation depths and hydroperiod across the 410-ha site. Coastal saltmarsh is particularly important to this site as it is part of the east Australasian flyway for migratory birds and the minimum saltmarsh extent, as listed within the Ramsar’s limits of acceptable change, have been breached. To recreate coastal saltmarsh habitat onsite, water level and hydroperiod criteria were established based on similar vegetation patterns within the adjacent estuary. A calibrated 2D hydrodynamic model of the site was then used to test how the preferred inundation criteria could be applied to the largest possible restored wetland area. Once optimised, a synthetic tidal signal was implemented onsite via automated hydraulic controls. The onsite vegetation response over an 8-year period was assessed to highlight the ecosystem response to controlled tidal inundation and denoted substantial saltmarsh expansion during the period. The techniques applied onsite have successfully met the restoration targets and can be applied at similar sites worldwide, offsetting sea level rise impacts to natural inundation hydroperiod.

Tidal restoration of a managed wetland in California favors non‐native fishes

Tidal wetland restoration is commonly used to recover ecosystem functions and services that were lost when wetlands were diked for reclamation or management. Less research has been conducted on the response of invertebrate and fish assemblages to tidal restoration than on plants and physical attributes. Blacklock Marsh, a wetland in Suisun Marsh, USA, was once managed for waterfowl hunting and cattle grazing until its dike was breached, restoring full tidal action. We sampled water quality, zooplankton, macroinvertebrates, and fishes in Blacklock Marsh, and compared these metrics to adjacent naturalistic waterways and to a managed wetland focused on waterfowl. Our goal was to compare food production and community assemblage on a restoring marsh to other types of nearby waterways. Blacklock Marsh had less chlorophyll‐a and dissolved organic carbon than nearby dead‐end sloughs and the managed wetland, less zooplankton biomass than the managed wetland, and lower fish diversity—with a fish assemblage dominated by non‐native species—compared to all other waterways. The most abundant fish species in the restoring site, Mississippi silverside (Menidia audens), is a non‐native fish and known predator of Delta smelt larvae (Hypomesus transpacificus), for which the restoration was targeted. Our research suggests that restoring tidal action to managed wetlands alone may worsen rather than improve conditions for at‐risk and native fishes.

Total ecosystem carbon stocks at the marine-terrestrial interface: Blue carbon of the Pacific Northwest Coast, United States.

The coastal ecosystems of temperate North America provide a variety of ecosystem services including high rates of carbon sequestration. Yet, little data exist for the carbon stocks of major tidal wetland types in the Pacific Northwest, United States. We quantified the total ecosystem carbon stocks (TECS) in seagrass, emergent marshes, and forested tidal wetlands, occurring along increasing elevation and decreasing salinity gradients. The TECS included the total aboveground carbon stocks and the entire soil profile (to as deep as 3m). TECS significantly increased along the elevation and salinity gradients: 217±60MgC/ha for seagrass (low elevation/high salinity), 417±70MgC/ha for low marsh, 551±47MgC/ha for high marsh, and 1,064±38MgC/ha for tidal forest (high elevation/low salinity). Soil carbon stocks accounted for >98% of TECS in the seagrass and marsh communities and 78% in the tidal forest. Soils in the 0-100cm portion of the profile accounted for only 48%-53% of the TECS in seagrasses and marshes and 34% of the TECS in tidal forests. Thus, the commonly applied limit defining TECS to a 100cm depth would greatly underestimate both carbon stocks and potential greenhouse gas emissions from land-use conversion. The large carbon stocks coupled with other ecosystem services suggest value in the conservation and restoration of temperate zone tidal wetlands through climate change mitigation strategies. However, the findings suggest that long-term sea-level rise effects such as tidal inundation and increased porewater salinity will likely decrease ecosystem carbon stocks in the absence of upslope wetland migration buffer zones.

Early Ecosystem Development Varies With Elevation and Pre-Restoration Land Use/Land Cover in a Pacific Northwest Tidal Wetland Restoration Project

Tidal wetland restoration through dike removal can enhance coastal ecosystem services, such as flood attenuation, fish production, and carbon sequestration. However, landscape-level heterogeneity may influence recovery. For a 169-ha restoration project in Tillamook Bay, Oregon, we hypothesized that areas of more intensive pre-restoration land use/land cover (cropping, grazing) would differ more from reference conditions before restoration than less-intensive uses and that initial post-restoration recovery would vary by land-use/land-cover type and wetland elevation. Before the restoration, the project site overall had higher non-native plant cover, lower elevation and groundwater levels, and lower soil pH than reference high marsh, with some differences by land-use/land-cover type. The cropped and grazed areas were strongly dominated by non-native species, such as Phalaris arundinacea, and were 74 and 31 cm lower than reference high marsh. Less intensively managed areas had elevations intermediate to the cropped and grazed areas and a trend towards higher native plant cover. The restoration led to higher dry-season groundwater levels, increased soil salinity to mesohaline conditions, and a 10-fold increase in soil pH at the project site, while reducing total plant cover. The degree of pre- to early post-restoration change for some parameters differed by land-use/land-cover type (total and non-native plant cover) and by wetland elevation (soil salinity, pH, and accretion rate; and total and non-native plant cover). Our results suggest that pre-restoration heterogeneity in elevation and land cover/land use may influence early post-restoration recovery. Restoration planning can incorporate such spatial variability into management targets and interventions for specific outcomes.

Temporal Response of California Black Rails to Tidal Wetland Restoration

Temporal Response of California Black Rails to Tidal Wetland Restoration

Potential greenhouse gas reductions from Natural Climate Solutions in Oregon, USA.

Increasing concentrations of greenhouse gases (GHGs) are causing global climate change and decreasing the stability of the climate system. Long-term solutions to climate change will require reduction in GHG emissions as well as the removal of large quantities of GHGs from the atmosphere. Natural climate solutions (NCS), i.e., changes in land management, ecosystem restoration, and avoided conversion of habitats, have substantial potential to meet global and national greenhouse gas (GHG) reduction targets and contribute to the global drawdown of GHGs. However, the relative role of NCS to contribute to GHG reduction at subnational scales is not well known. We examined the potential for 12 NCS activities on natural and working lands in Oregon, USA to reduce GHG emissions in the context of the state's climate mitigation goals. We evaluated three alternative scenarios wherein NCS implementation increased across the applicable private or public land base, depending on the activity, and estimated the annual GHG reduction in carbon dioxide equivalents (CO2e) attributable to NCS from 2020 to 2050. We found that NCS within Oregon could contribute annual GHG emission reductions of 2.7 to 8.3 MMT CO2e by 2035 and 2.9 to 9.8 MMT CO2e by 2050. Changes in forest-based activities including deferred timber harvest, riparian reforestation, and replanting after wildfires contributed most to potential GHG reductions (76 to 94% of the overall annual reductions), followed by changes to agricultural management through no-till, cover crops, and nitrogen management (3 to 15% of overall annual reductions). GHG reduction benefits are relatively high per unit area for avoided conversion of forests (125-400 MT CO2e ha-1). However, the existing land use policy in Oregon limits the current geographic extent of active conversion of natural lands and thus, avoided conversions results in modest overall potential GHG reduction benefits (i.e., less than 5% of the overall annual reductions). Tidal wetland restoration, which has high per unit area carbon sequestration benefits (8.8 MT CO2e ha-1 yr-1), also has limited possible geographic extent resulting in low potential (< 1%) of state-level GHG reduction contributions. However, co-benefits such as improved habitat and water quality delivered by restoration NCS pathways are substantial. Ultimately, reducing GHG emissions and increasing carbon sequestration to combat climate change will require actions across multiple sectors. We demonstrate that the adoption of alternative land management practices on working lands and avoided conversion and restoration of native habitats can achieve meaningful state-level GHG reductions.

Contesting neoliberal knowledge politics in restoration governance: the restorationist’s dilemma

ABSTRACTThe success of ecological restoration efforts is tightly coupled with the effectiveness of many U.S. environmental policies. Yet scholars have raised questions about the ability of restoration to produce intended results. We use a case study of tidal wetland restoration planning in Oregon to examine how neoliberal environmental governance exercises influence through a set of knowledge politics that produces subpar outcomes. We present three main findings: (1) restoration policies produce a restoration economy based on a conception of wetland as commodity (2) practitioners in this restoration economy exhibit competitive behavior resulting in a piecemeal rather than a landscape approach to restoration; and (3) limited monitoring prevents changes to existing policies. Practitioners offer insight into the challenge of treating wetlands as a commodity and call for more monitoring to challenge the assumptions of hegemonic knowledge practices that reinforce a neoliberal environmental governance regime. The divergent ideas of reflexive practitioners, though not yet manifest as action, show where changes to restoration governance might be possible.

Characterizing macroinvertebrate community composition and abundance in freshwater tidal wetlands of the Sacramento-San Joaquin Delta.

Restored tidal wetlands may provide important food web support for at-risk fish species in the Sacramento-San Joaquin Delta (Delta) of California, including Delta Smelt (Hypomesus transpacificus) and Chinook Salmon (Oncorhynchus tshawytscha). Since many tidal wetland restoration projects are planned or have recently been constructed in the Delta, understanding the diversity and variability of wetland invertebrates that are fish prey items is of increasing importance. During this study, two different invertebrate sampling techniques were tested (leaf packs and sweep nets) in four habitat types within three different wetland areas to evaluate which sampling technique provided the most reliable metric of invertebrate abundance and community composition. Sweep nets provided a better measure of fish food availability than leaf packs and were better able to differentiate between habitat types. Generalized linear models showed submerged and floating vegetation had higher abundance and taxa richness than channel habitats or emergent vegetation. Permutational multivariate analysis of variance showed significantly different communities of invertebrates in different habitat types and in different wetlands, and point-biserial correlation coefficients found a greater number of mobile taxa associated with sweep nets. There were more taxa associated with vegetated habitats than channel habitats, and one area had more taxa associated with it than the other two areas. These results suggest that restoration sites that contain multiple habitat types may enhance fish invertebrate prey diversity and resilience. However, the effect of habitat diversity must be monitored as restoration sites develop to assess actual benefits to at-risk fish species.

A global exploration of tidal wetland creation for nature-based flood risk mitigation in coastal cities

Coastal cities around the world are increasingly exposed to flood risks due to climate change, resulting sea level rise and more intense storm surges as well as due to growing coastal population densities and land subsidence. Nature-based risk mitigation, consisting of conservation or creation of coastal ecosystems that have the natural capacity to adapt to sea level rise and to mitigate storm surges, is increasingly proposed, but real-live implementation is yet limited to specific local cases. Our study presents a global scale analysis of the surface areas available for potential creation or restoration of tidal wetlands (salt marshes and mangrove forests) in front of 135 highly populated, flood-exposed coastal cities, as part of nature-based or hybrid strategies to buffer against coastal flood risks. Our results reveal that 34% (4 600 km2) of the total land area within the influence zone of storm surge propagation between the sea and the cities is potentially available for tidal wetlands creation. Those areas mainly correspond to rural areas with a low population density such as croplands, paddy fields or vegetated areas and to water bodies. The key factors influencing the area potentially available for tidal wetlands creation are the geomorphology and the population density, as 60% (8 300 km2) of the land area below mean high tide in front of the studied cities is urbanized or densely populated. Cities located along deltas or estuaries and in bays and lagoons (e.g. Hamburg, Guayaquil, Tianjin, Portland or San Jose) have generally larger low-lying coastal zones and consequently larger potentially available areas for salt marshes and mangrove forests restoration or creation for coastal flood risks mitigation. Our results contribute to increasing evidence and awareness of the possibilities of nature-based mitigation of coastal flood risks by restoring and creating tidal wetlands in front of flood-exposed coastal cities around the world.

Working with land and sea rangers to tackle tropical wetland restoration and conservation on the north-western islands, Torres Straits, Australia

Importance of community stakeholder participation in coastal freshwater and tidal wetland monitoring and restoration has become increasingly recognised. In Australia, Land and Sea Rangers (LSR) are appointed land and sea custodians from local indigenous communities and under guidance of experts learn a range of scientifically relevant and rigorous sampling techniques to protect and conserve Country. Scientific training to build LSR confidence to tackle restoration and conservation of sensitive and culturally important wetlands is shown here. Between May 2014 and May 2015 three training campaigns were completed where LSR on Boigu and Saibai Islands (the most northern islands in the Torres Straits, Australia), completed water quality and wetland flora/fauna surveys across both islands. Forty wetland fauna species were documented (with a similar wetland assemblage on each ANOSIM P > 0.4) comprising 35 fish species (including the invasive freshwater climbing perch, Anabas testudineus), two crustaceans, a freshwater turtle (Chelodina oblonga) (a relic freshwater species after the last sea level rise approximately 6,000 years ago in the region), and two mangrove snakes (Myron richardsoni and Fordonia leucobalia) (both snake records represent a range extension). This data was presented at community workshops with the purpose to build LSR confidence, and with the community, develop a plan to conserve wetland cultural and environmental values. Five thematic wetland conservation themes were identified which resulted in agreeing to management actions necessary on both islands. Since the inception of this program in 2014, additional LSR restoration and monitoring programs have extended to wetlands on other islands in the Torres Straits. We advocate the need for more remote area wetland monitoring and management programs facilitated through LSR programs.