Tidal Marsh Restoration Research Articles

Suspended-sediment Flux in the San Francisco Estuary; Part II: the Impact of the 2013–2016 California Drought and Controls on Sediment Flux

Recent modeling has demonstrated that sediment supply is one of the primary environmental variables that will determine the sustainability of San Francisco Estuary tidal marshes over the next century as sea level rises. Therefore, understanding the environmental controls on sediment flux within the San Francisco Estuary is crucial for optimal planning and management of tidal marsh restoration. Herein, we present suspended-sediment flux estimates from water year (WY) 2009–2016 from the San Francisco Estuary to investigate the environmental controls and impact of the record 2013–2016 California drought. During the recent drought, sediment flux into Lower South Bay, the southernmost subembayment of the San Francisco Estuary, increased by 345% from 114 kt/year from WY 2009 to 2011 to 508 kt/year from WY 2014 to 2016, while local tributary sediment flux declined from 209 to 51 kt/year. Total annual sediment flux from WY 2009 to 2011 and 2014 to 2016 can be predicted by total annual freshwater inflow from the Sacramento-San Joaquin Delta (R2 = 0.83, p < 0.01), the primary source of freshwater input into the San Francisco Estuary. The volume of freshwater inflow from the Sacramento-San Joaquin Delta is hypothesized to affect shoal-to-channel density gradients that affect sediment flux from broad, typically more saline and turbid shoals, to the main tidal-channel seaward of Lower South Bay. During the drought, freshwater inflow from the Sacramento-San Joaquin Delta decreased, and replacement of typically more saline shoal water was reduced. As a result, landward-increasing cross-channel density gradients enhanced shoal-to-channel advective flux that increased sediment available for tidal dispersion and drove an increase in net-landward sediment flux into Lower South Bay.

Identifying Hydro-Geomorphological Conditions for State Shifts from Bare Tidal Flats to Vegetated Tidal Marshes

High-lying vegetated marshes and low-lying bare mudflats have been suggested to be two stable states in intertidal ecosystems. Being able to identify the conditions enabling the shifts between these two stable states is of great importance for ecosystem management in general and the restoration of tidal marsh ecosystems in particular. However, the number of studies investigating the conditions for state shifts from bare mudflats to vegetated marshes remains relatively low. We developed a GIS approach to identify the locations of expected shifts from bare intertidal flats to vegetated marshes along a large estuary (Western Scheldt estuary, SW Netherlands), by analyzing the interactions between spatial patterns of vegetation biomass, elevation, tidal currents, and wind waves. We analyzed false-color aerial images for locating marshes, LIDAR-based digital elevation models, and spatial model simulations of tidal currents and wind waves at the whole estuary scale (~326 km²). Our results demonstrate that: (1) Bimodality in vegetation biomass and intertidal elevation co-occur; (2) the tidal currents and wind waves change abruptly at the transitions between the low-elevation bare state and high-elevation vegetated state. These findings suggest that biogeomorphic feedback between vegetation growth, currents, waves, and sediment dynamics causes the state shifts from bare mudflats to vegetated marshes. Our findings are translated into a GIS approach (logistic regression) to identify the locations of shifts from bare to vegetated states during the studied period based on spatial patterns of elevation, current, and wave orbital velocities. This GIS approach can provide a scientific basis for the management and restoration of tidal marshes.

Tidal Marsh Restoration at Poplar Island I: Transformation of Estuarine Sediments into Marsh Soils

Dredged materials from navigation channel maintenance represent a potentially valuable resource for wetland creation and restoration. In the northern Chesapeake Bay, fine-grained sediments from Baltimore Harbor approach channels are transported by barge southward for creation of wetlands on the site of an eroded island. High concentrations of ammonium, soluble reactive phosphorus, dissolved iron, and iron sulfide minerals in channel deposits are altered by the transport and drying of these materials prior to wetland development. The oxidation of iron sulfide minerals results in low pH, with the initiation of tidal inundation removing sulfuric acid from near-surface soil horizons and moderating the soil pH. Despite the loss of ammonium during dewatering and soil processing, the resultant soils retained high concentrations of dissolved and adsorbed ammonium. Iron-associated inorganic phosphorus represented a large pool of potentially labile phosphorus and along with the high ammonium, resulted in high nutrient concentrations for plant growth. Combined with results on plant growth presented elsewhere, these data suggest that fine-grained dredged materials from non-contaminated environments are well suited for the creation of tidal wetlands after placement and seasoning 1–2 years.

Tidal Marsh Restoration at Poplar Island: II. Elevation Trends, Vegetation Development, and Carbon Dynamics

In natural tidal marshes, nutrient fertilization stimulates complex responses, bringing into question the suitability of nutrient-rich dredged material as a substrate for tidal marsh restoration. We examined vegetation and elevation trends in the constructed tidal marshes at Poplar Island, Maryland where fine-grained dredged material (high nutrient) and locally dredged sand (low nutrient) were used as substrates. Macrophyte production was higher and root:shoot ratios lower in dredged material marshes. Measured vertical accretion was similar in dredged material (7.4 ± 0.6 mm y−1) and sand (6.4 ± 0.9 mm y−1) marshes, and is keeping pace with local sea-level rise. A detailed carbon budget was developed for one dredged material marsh to examine carbon dynamics under high nutrient availability. High annual macrophyte production combined with small exports via tidal exchange and methane emissions resulted in an annual carbon burial of 206 g C m−2 y−1, and calculated vertical accretion of 6.5 mm y−1 from organic matter. This is attributed to the contribution of organic matter from aboveground biomass due to protection from perimeter dikes constructed to contain dredged material during placement, reducing marsh exposure and organic matter export. With appropriate design and management, fine-grained, high-nutrient dredged material makes a suitable substrate for tidal marsh restoration.

A national approach to greenhouse gas abatement through blue carbon management

There is increasing interest in protecting, restoring and creating ‘blue carbon’ ecosystems (BCE; mangroves, tidal marshes and seagrasses) to sequester atmospheric CO2-C and thereby contribute to climate change mitigation. While a growing number of countries aspire to report greenhouse gas emission and carbon sequestration changes from these ecosystems under voluntary international reporting requirements, few countries have domestic policy frameworks that specifically support the quantification and financing of carbon emission abatement through BCE management.Australia, as home to approximately 5–11% of global blue carbon stocks, has a substantial interest in the development of blue carbon policy. Here we assess the potential inclusion of blue carbon within Australia's Emissions Reduction Fund, emphasizing issues and approaches that have global relevance. We used a participatory workshop of scientific experts and carbon industry stakeholders to identify blue carbon management actions that would meet the requirements of the Fund. In total, twelve actions were assessed for their greenhouse gas emission abatement potential and the ability to measure abatement reliably, using a combination of available data and qualitative and quantitative methods, including expert knowledge.We identify and discuss the five most relevant and promising activities, encompassing the protection, restoration and creation of mangroves, tidal marshes and seagrasses. On a per area basis, mean abatement intensity of organic carbon (Corg) was highest for the (re)introduction of tidal flow resulting in establishment of mangrove (13–15 Mg Corg ha−1 yr−1) and tidal marsh (6–8 Mg Corg ha−1 yr−1), followed by land use planning for sea-level rise for the creation of new mangrove habitat (8 Mg Corg ha−1 yr−1). The avoided disturbance of existing mangroves, tidal marshes and seagrasses has the twofold benefit of avoiding remineralisation of existing stocks, plus the future annual abatement associated with the net sequestration of atmospheric CO2-C as Corg with the continued functioning of these BCE. Our approach offers a template that uses best available information to identify options for carbon abatement through management of coastal landscapes, and details current knowledge gaps and important technical aspects that need to be considered for implementation in carbon crediting schemes.

Social Factors Key to Landscape-Scale Coastal Restoration: Lessons Learned from Three U.S. Case Studies.

In the United States, extensive investments have been made to restore the ecological function and services of coastal marine habitats. Despite a growing body of science supporting coastal restoration, few studies have addressed the suite of societally enabling conditions that helped facilitate successful restoration and recovery efforts that occurred at meaningful ecological (i.e., ecosystem) scales, and where restoration efforts were sustained for longer (i.e., several years to decades) periods. Here, we examined three case studies involving large-scale and long-term restoration efforts including the seagrass restoration effort in Tampa Bay, Florida, the oyster restoration effort in the Chesapeake Bay in Maryland and Virginia, and the tidal marsh restoration effort in San Francisco Bay, California. The ecological systems and the specifics of the ecological restoration were not the focus of our study. Rather, we focused on the underlying social and political contexts of each case study and found common themes of the factors of restoration which appear to be important for maintaining support for large-scale restoration efforts. Four critical elements for sustaining public and/or political support for large-scale restoration include: (1) resources should be invested in building public support prior to significant investments into ecological restoration; (2) building political support provides a level of significance to the recovery planning efforts and creates motivation to set and achieve meaningful recovery goals; (3) recovery plans need to be science-based with clear, measurable goals that resonate with the public; and (4) the accountability of progress toward reaching goals needs to be communicated frequently and in a way that the general public comprehends. These conclusions may help other communities move away from repetitive, single, and seemingly unconnected restoration projects towards more large-scale, bigger impact, and coordinated restoration efforts.

Mapping salt marsh soil properties using imaging spectroscopy

Tidal salt marshes sequester and store blue carbon at both short and long time scales. Marsh soils shape and maintain the ecosystem by supporting complex biogeochemical reactions, deposition of sediment, and accumulation of organic matter. In this study, we examined the potential of imaging spectroscopy techniques to indirectly quantify and map tidal marsh soil properties at a National Estuarine Research Reserve in Georgia, USA. A framework was developed to combine modern digital image processing techniques for marsh soil mapping, including object-based image analysis (OBIA), machine learning modeling, and ensemble analysis. We also evaluated the efficacy of airborne hyperspectral sensors in estimating marsh soil properties compared to spaceborne multispectral sensors, WorldView-2 and QuickBird. The pros and cons of object-based modeling and mapping were assessed and compared with traditional pixel-based mapping methods. The results showed that the designed framework was effective in quantifying and mapping three marsh soil properties using the composite reflectance from salt marsh environment: soil salinity, soil water content, and soil organic matter content. Multispectral sensors were successful in quantifying soil salinity and soil water content but failed to model soil organic matter. The study also demonstrated the value of minimum noise fraction transformation and ensemble analysis techniques for marsh soil mapping. The results suggest that imaging spectroscopy based modeling is a promising tool to quantify and map marsh soil properties at a local scale, and is a potential alternative to traditional soil data acquisition to support carbon cycle research and the conservation and restoration of tidal marshes.

Applying tidal landform scaling to habitat restoration planning, design, and monitoring

Tidal channels are structurally and functionally prominent features in tidal marshes, so their restoration is central to marsh restoration. Prominent design questions in tidal marsh restoration include: How many tidal channels can a restoration site support, and thus, how many dike breaches should be made to restore tidal inundation and tidal channels? How much total channel surface area will be supported by a restored marsh, and thus, how many fish, shrimp, or other organisms can be supported by restored channel habitat? These basic design questions can be addressed by landscape allometry, which describes the proportional relative rates of change in a system between two entities of particular interest—in the case of marsh restoration, between the amount of marsh area to be restored and a wide variety of measures of tidal channel network geometry. This paper briefly reviews the development of landscape allometry, insights that it provides into landforms and related ecological patterns, and its utility and application to marsh restoration planning, design and monitoring. Its practical application is illustrated in a conceptual restoration design that is the basis for a current restoration project.

Change in fish functional diversity and assembly rules in the course of tidal marsh restoration.

Functional trait theory provides a mechanistic framework to understand change in community composition and community assembly through time and space. Despite this, trait-based approaches have seldom been used in ecological restoration. Succession theory predicts that habitat complexity and resource availability will increase with restoration time, leading to increased functional dissimilarity among coexisting species. However, in the case of tidal marsh restoration, it is not clear whether reestablishing the harsh abiotic conditions typical of estuaries will initiate successional trajectories. We investigated monotonic changes in the functional structure of fish communities and shifts in assembly mechanisms, with tidal restoration time. A five-level gradient of ‘intertidal habitat naturalness’ was constructed from a set of artificialized (dyked), restored (with different ages) and natural intertidal sites, and used as a surrogate for restoration progress. The fish ecophases were described using ten functional traits related to food acquisition and swimming ability. The trends in six functional dimensions (identity, richness, evenness, dispersion, originality and specialization) were investigated along the naturalness gradient. Consistenly with succession theory, functional specialization, dispersion and, less markedly, richness increased with intertidal naturalness meaning that restored and natural intertidal habitats supplied fish with specific foraging and dwelling conditions absent from dyked marshes. Community assembly patterns varied with respect to traits and differed at both ends of the naturalness gradient. Dyked marshes were more affected by trait convergence possibly due to limiting resources. Environmental filtering was detected all along the naturalness gradient although the traits affected varied depending on the naturalness level of habitats. Environmental filtering tended to decrease in restored and natural intertidal habitats. Increased naturalness restored the attractivity of benthic habitats as feeding or settling grounds, promoted shelter-seeking vs. free-swimming strategists and favoured ecophases with carnivorous diets, feeding on microinvertebrates and benthic low-mobility macroinvertebrates. Approaches based on functional trait diversity have the potential to question and refine the theoretical frame of ecological restoration and to assist managers in their efforts to restore tidal wetlands.

Rhizosphere Microbial Communities of Spartina alterniflora and Juncus roemerianus From Restored and Natural Tidal Marshes on Deer Island, Mississippi.

The U. S. Gulf of Mexico is experiencing a dramatic increase in tidal marsh restoration actions, which involves planting coastal areas with smooth cordgrass (Spartina alterniflora) and black needlerush (Juncus roemerianus) for erosion control and to provide habitat for fish and wildlife. It can take decades for sedimentary cycles in restored marshes to approach reference conditions, and the contribution of the sediment microbial communities to these processes is poorly elucidated. In this study, we addressed this gap by comparing rhizosphere microbiomes of S. alterniflora and J. roemerianus from two restored marshes and a natural reference marsh located at Deer Island, MS. Our results revealed that plants from the restored and reference areas supported similar microbial diversity indicating the rapid colonization of planted grasses with indigenous soil microbiota. Although close in composition, the microbial communities from the three studied sites differed significantly in the relative abundance of specific taxa. The observed differences are likely driven by the host plant identity and properties of sediment material used for the creation of restored marshes. Some of the differentially distributed groups of bacteria include taxa involved in the cycling of carbon, nitrogen, and sulfur, and may influence the succession of vegetation at the restored sites to climax condition. We also demonstrated that plants from the restored and reference sites vary in the frequency of culturable rhizobacteria that exhibit traits commonly associated with the promotion of plant growth and suppression of phytopathogenic fungi. Our findings will contribute to the establishment of benchmarks for the assessment of the outcome of coastal restoration projects in the Gulf of Mexico and better define factors that affect the long-term resiliency of tidal marshes and their vulnerability to climate change.

Tidal Marsh Restoration Design Affects Feedbacks Between Inundation and Elevation Change

Tidal marsh (re)creation on formerly embanked land is increasingly executed along estuaries and coasts in Europe and the USA, either by restoring complete or by reduced tidal exchange. Ecosystem functioning and services are largely affected by the hydro-geomorphologic development of these areas. For natural marshes, the latter is known to be steered by feedbacks between tidal inundation and sediment accretion, allowing marshes to reach and maintain an equilibrium elevation relative to the mean sea level. However, for marsh restoration sites, these feedbacks may be disturbed depending on the restoration design. This was investigated by comparing the inundation-elevation change feedbacks in a natural versus restoration site with reduced tidal exchange in the Scheldt estuary (Belgium). This study analyzes long-term (9 years) datasets on elevation change and tidal inundation properties to disentangle the different mechanisms behind this elevation-inundation feedback. Moreover, subsequent changes in sediment properties that may affect this feedback were explored. In the restoration area with reduced tidal exchange, we found a different elevation-inundation feedback than on natural marshes, which is a positive feedback on initially high sites (i.e., sediment accretion leads to increasing inundation, hence causing accelerating sediment accretion rates) and a gradual silting up of the whole area. Furthermore, there is evidence for the presence of a relict consolidated sediment layer. Consequently, shallow subsidence is less likely to occur. Although short-term ecological development of the tidal marsh was not impeded, long-term habitat development may be affected by the differences in hydro-geomorphological interactions. An increase of inundation frequency on the initially high sites may cause inhibition of habitat succession or even reversed succession. Over time, the climax state of the restoration area may be different compared to natural marshes. Moreover, sediment-related ecosystem services, such as nutrient and carbon burial, may be positively influenced because of continuing sedimentation, although flood water storage potential will decrease with increasing elevation. Depending on the restoration goals, ecosystem trajectories and delivery of ecosystem services can be controlled by adaptive management of the tidal volume entering the restoration area.

Vegetation Development in a Tidal Marsh Restoration Project during a Historic Drought: A Remote Sensing Approach

Tidal wetland restoration efforts can be challenging to monitor in the field due to unstable local conditions and poor site access. However, understanding how restored systems evolve over time is essential for future management of their ecological benefits, many of which are related to vegetation dynamics. Physical attributes such as elevation and distance to channel play crucial roles in governing vegetation expansion in developing tidal wetlands. However, in Mediterranean ecosystems, drought years, wet years and their resulting influence on salinity levels may also play a crucial role in determining the trajectory of restoration projects, but the influence of weather variability on restoration outcomes is not well understood. Here, we use object-based image analysis (OBIA) and change analysis of the high-resolution IKONOS and WorldView-2 satellite imagery to explore whether mean annual rates of change from mudflat to vegetation are lower during drought years with higher salinity (2011-2015) compared to years with lower salinity (2009-2011) at a developing restoration site in California’s San Francisco Bay. We found that vegetation increased at a mean rate of 1979 m2/year during California’s historic drought, 10.4 times slower than the rate of 20580 m2/year between 2009 and 2011 when the state was not in drought. Vegetation was significantly concentrated in areas in closer to channel edges, where salinity stress is ameliorated, and the magnitude of the effect increased in the 2015 image. In our image analysis, we found that different distributions of water, mud and algae between years led to different segmentation settings for each set of images, highlighting the need for more robust and reproducible OBIA strategies in complex wetlands. Our results demonstrate that adaptive monitoring efforts in variable climates should take into account the influence of weather on tidal wetland ecosystems, and that high-resolution remote sensing can be an effective means of assessing these dynamics.

Short-Term Response of a Coastal Wetland Fish Assemblage to Tidal Regime Restoration in Oregon

Abstract Bandon Marsh National Wildlife Refuge, Oregon, completed construction of a large-scale tidal marsh restoration project on the Ni-les'tun Unit within the Coquille River estuary in 2011. To understand the initial effects of restoration construction and establish a baseline for long-term monitoring, we documented the assemblage of fish species 3 y before and 2 y after restoration construction. The overall fish assemblage in the Ni-les'tun Unit was substantially different after restoration construction, with an increased abundance, frequency, and richness of estuarine and diadromous fish species. Threespine Stickleback Gasterosteus aculeatus and species of Sculpin (family Cottidae) dominated the Ni-les'tun Unit and control area in both relative abundance and capture frequency throughout this study. Among salmonids, Coastal Cutthroat Trout Oncorhynchus clarkii and Coho Salmon Oncorhynchus kisutch had the highest frequency of occurrence and relative abundance both before and after restoration construction. Fish occupied newly constructed channels within 2 y. Species found in new channels included freshwater species (e.g., juvenile salmonids), introduced species (e.g., Mosquitofish Gambusia affinis), and estuarine species (e.g., Sculpin, Threespine Stickleback, and Shiner Perch Cymatogaster aggregata). Changes were likely due to improved access and changing habitat created by the reintroduced tidal regime. We recommend long-term monitoring to assess the trajectory of the biological response to the restoration over time.

Tidal marsh restoration stimulates the growth of winter shorebird populations in a temperate estuary

AbstractThe regional responses of winter shorebird populations in the nearly 3,000 ha estuary of Tomales Bay, California, to the restoration of 223 ha of historic tidal wetlands were evaluated for 27 years: 19 years prior to tidal reintroduction and 8 years after tidal reintroduction. We used interrupted time series analyses to measure the spatial extent of the restoration effect and to model the magnitude and length of time associated with the gradual, restoration‐induced growth of winter shorebird populations in the bay. Expanded, regional benefits of the restoration were revealed by consistent patterns of winter shorebird population growth. Eight years after tidal reintroduction, overall shorebird abundances in southern Tomales Bay nearly tripled in response to the restoration. Substantial winter population growth by most species in southern Tomales Bay was evident within 3 years after tidal reintroduction, and maximum responses to the restoration were estimated to be predominantly achieved within 8 years. In contrast to strong effects of tidal marsh restoration on winter shorebird populations in southern Tomales Bay, no significant overall responses were exhibited by shorebirds in the northern portion of the bay, although marginal evidence of expanded effects on a few species in northern Tomales Bay were suggested. The results illustrate the importance of accounting for restoration effects beyond the spatial and temporal boundaries of the restored habitat, to consider both the potentially expanded benefits and the spatial limits of those benefits to regional wildlife populations.

Comparing Automated Classification and Digitization Approaches to Detect Change in Eelgrass Bed Extent During Restoration of a Large River Delta

Abstract Native eelgrass (Zostera marina) is an important contributor to ecosystem services that supplies cover for juvenile fish, supports a variety of invertebrate prey resources for fish and waterbirds, provides substrate for herring roe consumed by numerous fish and birds, helps stabilize sediment, and sequesters organic carbon. Seagrasses are in decline globally, and monitoring changes in their growth and extent is increasingly valuable to determine impacts from large-scale estuarine restoration and inform blue carbon mapping initiatives. Thus, we examined the efficacy of two remote sensing mapping methods with high-resolution (0.5 m pixel size) color near infrared imagery with ground validation to assess change following major tidal marsh restoration. Automated classification of false color aerial imagery and digitized polygons documented a slight decline in eelgrass area directly after restoration followed by an increase two years later. Classification of sparse and low to medium density eelgrass w...

Responses to salinity of Spartina hybrids formed in San Francisco Bay, California (S. alterniflora × foliosa and S. densiflora × foliosa )

San Francisco Bay (SFB), which supports large populations of the California native cordgrass Spartina foliosa, has been the recipient of introductions of S. alterniflora and S. densiflora. Hybrids have arisen between the native and these exotic species. Sterile F1 S. densiflora × foliosa hybrids have formed numerous times in a number of marshes, while introgressing S. alterniflora × foliosa hybrids are fully fertile and invaded widely in SFB, especially onto naturally-open low tidal flats by inundation-tolerant hybrids. Sarcocornia pacifica, pickleweed, dominates the mid-to-upper marsh zones where the hypersaline conditions that occur during the summer drought, characteristic of this climate, exclude S. foliosa. Here we report on two glasshouse experiments investigating the salinity tolerance of hybrid Spartina. Some hybrids of both origins grew well and flowered at high salinity levels while the parental species grew little and did not flower. Our results imply that mid-zone marshes are also vulnerable to invasion by salinity-tolerant Spartina hybrids. Herbicide control implemented over the last 10 years targeting both the exotic species and their hybrids have reduced their extent. However, efforts in monitoring and management of exotic Spartina and its hybrids must continue as vast areas of tidal marsh restoration are underway and planned in SFB; colonization by Spartina hybrids tolerant to inundation and/or salinity will greatly alter restoration trajectories. These concerns are all the more vital given projections of climate change and its effects on salinity and sea level rise in SFB salt marshes.

A review of 15 years of Spartina management in the San Francisco Estuary

Regional, ecosystem-level conservation projects with significant vegetation management components require planning, coordination, and responsive management strategies to minimize negative impacts and maximize ecological benefits over time. The California State Coastal Conservancy’s Invasive Spartina Project (ISP) offers an example of a complex, ecosystem-scale weed eradication effort guided by regional conservation goals. We review the management framework developed by the ISP, describe decision thresholds used for site-specific management transitions over the project’s 15 years, and present strategies being used to address major challenges to project completion. These strategies include developing genetics and weed mapping approaches to aid with identification of hybrids between the introduced Spartina alterniflora and the native Spartina foliosa. The ISP also developed a tidal marsh restoration project to enhance habitat for an endangered bird, the California Ridgway’s rail (Rallus obsoletus obsoletus), that uses tall, dense forms of hybrid Spartina as high tide refugia and nesting substrate. By 2014, the ISP had installed over 300,000 native plants and recorded a greater than 96 % estuary-wide reduction in hybrid Spartina (from 323 ha to 12 net ha) despite treatment restrictions imposed at 11 sites since 2011 to protect the rail. Approximately 80 % of the remaining hybrid Spartina occurs in areas currently restricted from treatment, delaying project completion. The successes and setbacks of the ISP illustrate the complexities of achieving ecosystem-level conservation goals dependent on large-scale vegetation management.

Parallel scaling of tidal channel length and surface area with marsh area for 1st through Kth-ranked channels and their tributaries: Application for tidal marsh restoration

Scaling relationships in landforms are a signature of locally stable, self-organized critical states, which in tidal marshes result from the interaction of hydrodynamics, sediment dynamics, and biota. Empirical scaling relationships for tidal channel planform were developed for reference tidal marshes in four of the largest river deltas in Puget Sound to explore the potential underlying generative process of the observed patterns and to provide design guidance for restoration of estuarine rearing habitat for juvenile salmon. The length, surface area, and drainage basin area of the largest, 2nd-largest, 3rd-largest, etc., up to 15th-largest tidal channels that drain a marsh island, as well as the lengths of the largest through 5th-largest tributaries to the largest and 2nd-largest channels scaled with marsh area. Additionally, regression of the scaling relationship y-intercepts against channel rank for each delta showed that the rate of channel size decrease from one rank to the next was well fit by a power function, with R2 values approaching 1. These relationships reveal predictable structure in many aspects of tidal channel planforms and allow engineers to design channel excavation in considerable detail. A simulation model of channel formation through recursive marsh island conglomeration in river deltas reproduced the scaling behavior of the empirically observed marsh channels, thereby linking observed patterns to the underlying generative process. Previous allometric modeling has provided predictions of the number of tidal channels a marsh restoration site should have; this study provides a method to predict the size distribution of those channels so that engineers, planners, and restoration scientists can better plan, design, and monitor marsh restoration.

Ecosystem service delivery in restoration projects: the effect of ecological succession on the benefits of tidal marsh restoration

Long-term assessment of ecosystem restoration projects is complex because of ecological processes such as succession, particularly in highly dynamic ecosystems such as estuaries. Restoration of intertidal flats and marshes on formerly embanked land, often called managed coastal realignment (MR), became popular in estuarine management. In our study, biophysical and monetary data were collected to calculate the value of 15 (sub)ecosystem services (ES) delivered by a large tidal marsh restoration project in the Schelde estuary in Belgium and the Netherlands. We hypothesized that ES delivery changes over time due to ecological succession and hence the long-term benefits are subject to this phenomenon and need to be taken into consideration. A marsh sediment accretion model (MARSED) was used to simulate potential marsh succession scenarios. In this way, the temporal evolution of ES delivery caused by ecological succession could be evaluated. Our study shows that benefits during successional marsh stages could actually be higher than for marshes in equilibrium. This finding does not suggest that ecosystems in transition always have a higher value than systems in equilibrium, but emphasizes the need to consider long-term ecological dynamics, such as succession, in a benefit assessment for restoration projects.

Endangered species management and ecosystem restoration: finding the common ground

Casazza, M. L., C. T. Overton, T.-V. D. Bui, J. M. Hull, J. D. Albertson, V. K. Bloom, S. Bobzien, J. McBroom, M. Latta, P. Olofson, T. M. Rohmer, S. Schwarzbach, D. R. Strong, E. Grijalva, J. K. Wood, S. M. Skalos, and J. Takekawa. 2016. Endangered species management and ecosystem restoration: finding the common ground. Ecology and Society 21(1):19.http://dx.doi.org/10.5751/ES-08134-210119