Salt Marsh Restoration for the Provision of Multiple Ecosystem Services

Restoration of salt marsh is urgent, as these ecosystems provide natural coastal protection from sea-level rise impacts, contribute towards climate change mitigation, and provide multiple ecosystem services including supporting livelihoods. This study identified potential restoration sites for intervention where agricultural and degraded land could be returned to salt marsh at a national scale in South African estuaries. Overall, successful restoration of salt marsh in some estuaries will require addressing additional pressures such as freshwater inflow reduction and deterioration of water quality. Here, we present, a socio-ecological systems framework for salt marsh restoration that links salt marsh state and the well-being of people to guide meaningful and implementable management and restoration interventions. The framework is applied to a case study at the Swartkops Estuary where the primary restoration intervention intends to route stormwater run-off to abandoned salt works to re-create aquatic habitat for waterbirds, enhance carbon storage, and provide nutrient filtration. As the framework is generalized, while still allowing for site-specific pressures to be captured, there is potential for it to be applied at the national scale, with the largest degraded salt marsh areas set as priorities for such an initiative. It is estimated that ~1970 ha of salt marsh can be restored in this way, and this represents a 14% increase in the habitat cover for the country. Innovative approaches to restoring and improving condition are necessary for conserving salt marshes and the benefits they provide to society.

Hitchhiking Halophytes in Wrack and Sediment-Laden Ice Blocks Contribute To Tidal Marsh Development in The Upper Bay of Fundy.

Salt marshes are a type of coastal wetland that are affected by dynamic coastal processes. Ice blocks and wrack (mats of plant debris) regularly float onto northern marshes and become stranded, affecting vegetation and soil accretion. There is little research regarding the capacity of ice and wrack to transport viable plant propagules onto marshes where they can colonize, which may be particularly important at barren new salt marsh restoration sites. Contributions of sediment by ice may also be important at restoration sites to raise the marsh platform to elevations appropriate for plant colonization. We collected ice (n = 27) and wrack (n = 18) samples at marshes in the Bay of Fundy, ran germination trials with the contents, and measured the quantity of sediment in the ice. We found viable propagules from halophytic and non-halophytic species in wrack, and viable propagules of Sporobolus pumilus in ice. Additionally, we found sediment densities between 0.01 and 4.75 g·cm−3 in ice blocks that translated to 26.61 – 21,483.59 kg of total sediment per block, representing a large source of sediment. We found that the number of germinating propagules could not be predicted by wrack size, and that pH, sediment density, sediment weight in ice blocks were variable across the marsh surface, while ice salinity was negatively correlated with elevation and distance from creek. Our results indicate that ice and wrack represent a potential source for vegetation colonization at salt marsh sites and highlights their contributions to facilitating vegetation colonization through building marsh soils.

Rapid formation of iron sulfides alters soil morphology and chemistry following simulated marsh restoration

Many marshes show signs of degradation due to fragmentation, lack of sediment inputs, and erosion which may be exacerbated by sea level rise and increasing storm frequency/intensity. As a result, resource managers seek to restore marshes via introduction of sediment to increase elevation and stabilize the marsh platform. Recent field observations suggest the rapid formation of iron sulfide (FeS) materials following restoration in several marshes. To investigate, a laboratory microcosm study evaluated the formation of FeS following simulated restoration activities under continually inundated, simulated drought, and simulated tidal conditions. Results indicate that FeS horizon development initiated within 16 days, expanding to encompass > 30% of the soil profile after 120 days under continuously inundated and simulated tidal conditions. Continuously inundated conditions supported higher FeS content compared to other treatments. Dissolved and total Fe and S measurements suggest the movement and diffusion of chemical constituents from native marsh soil upwards into the overlying sediments, driving FeS precipitation. The study highlights the need to consider biogeochemical factors resulting in FeS formation during salt marsh restoration activities. Additional field research is required to link laboratory studies, which may represent a worst-case scenario, with in-situ conditions.

Vegetative Community Diversity Assessment of a Beneficial Use Salt Marsh Restoration

Restoration of lost marsh platforms can include de-novo construction using dredged sediments. Two restoration projects constructed with beneficial use material in 2004 and 2015 were planted with native vegetation in the anticipation they would function similarly to adjacent Juncus roemerianus (Black needlerush) dominated salt marshes. Planted J. roemerianus, however, failed to establish and exists sparsely in the restored marsh. To better understand potential sources of failure, this study assessed vascular plant diversity in Spring and Fall of 2017 through 2019 and demonstrated establishment of both planted and naturally recruited vegetation. The two constructed sites were found to have higher species richness and plant diversity (Shannon-Wiener H’, and Simpson’s D) than the natural reference marsh, in part due to the higher elevations of the two constructed sites. The plant diversity metrics indicated the two beneficial use restorations did not meet the species composition of the reference marsh. Further monitoring should be conducted to observe the species development over the long term with considerations given to the potential future marsh change.

Monitoring the Evolution of a Tidal Salt Marsh Restoration Site with an RTK-enabled UAV

<p>Since 1900 AD, 64-71% of the world’s natural wetlands have been lost due to anthropogenic influences. Wetland restoration projects, such as managed realignment and tidal salt marsh restoration, act to combat these losses, but are also being used as a form of nature-based adaptation to the effects of climate change, including sea level rise. New advances in Unmanned Aerial Vehicle (UAV) technology offer a unique opportunity to quantify the restoring landscape at resolutions and accuracies previously unachievable. This presentation will focus on the use of hyperspatial datasets collected with a Real-Time Kinematic (RTK) GNSS enabled UAV at a managed realignment site in the Bay of Fundy, Canada, to monitor and quantify the geomorphic evolution of the site, including the development of a semi-automated method for mapping embryonic creek networks. Analyzed datasets were collected seasonally over the course of 1 year following the reintroduction of tidal flow, and range in resolution from 2.0 - 3.5 cm. Preliminary results show significant spatial variation in channel evolution patterns, related to the presence and absence of antecedent landscape features. A greater understanding of restoration site evolution, and the effects of the antecedent landscape on that evolution, will allow for a more informed design and implementation of future restoration projects to encourage site resilience and sustainability in terms of climate change adaptation.</p>

Top-down and sideways: Herbivory and cross-ecosystem connectivity shape restoration success at the salt marsh-upland ecotone

Wetland restoration provides remarkable opportunities to understand vegetation dynamics and to inform success of future projects through rigorous restoration experiments. Salt marsh restoration typically focuses on physical factors such as sediment dynamics and elevation. Despite many demonstrations of strong top-down effects on salt marshes, the potential for consumers to affect salt marsh restoration projects has rarely been quantified. Recently, major restoration projects at the Elkhorn Slough National Estuarine Research Reserve in central California, USA provided an opportunity to examine how herbivory influences restoration success. We quantified the strength of consumer effects by comparing caged to uncaged plantings, and compared effects among plant species and sites. We used camera traps to detect which herbivores were most common and how their abundance varied spatially. Beyond characterizing consumer effects, we also tested management strategies for reducing negative effects of herbivory at the restoration sites, including caging, mowing, and acoustic playbacks of predator sounds. We found extremely strong consumer effects at sites with extensive stands of exotic forbs upland of the high marsh; uncaged restoration plants suffered heavy herbivory and high mortality, while most caged plants survived. Brush rabbits (Sylvilagus bachmani) were by far the most frequent consumers of these high marsh plants. Our work thus provides the first evidence of mammal consumers affecting salt marsh restoration success. Mowing of tall exotic forb cover adjacent to the marsh at one restoration site greatly reduced consumption, and nearly all monitored plantings survived at a second restoration site where construction had temporarily eliminated upland cover. Playbacks of predator sounds did not significantly affect restoration plantings, but restoration efforts in marsh communities vulnerable to terrestrial herbivory may benefit from concurrent restoration of predator communities in the upland habitats surrounding the marsh. A landscape approach is thus critical for recognizing linkages between terrestrial and marine vegetation.

Inoculating rhizome-propagated Sporobolus pumilus with a native mycorrhizal fungus increases salt marsh plant growth and survival

Salt marshes are ecosystems of significant ecological importance for coastal stability and fundamental roles in marine ecosystems. Salt marshes are declining due to anthropogenic and natural causes including sea level rise. Coastal restoration efforts have increased worldwide, but many fail in long-term coastal stability. We used a naturally occurring arbuscular mycorrhizal fungus (AMF) to test whether survival and early growth of the salt marsh grass Sporobolus pumilus (formerly Spartina patens) improved under simulated salt marsh conditions. Using a tidal mesocosm bench, we grew inoculated plants with varying AMF treatments under simulated tidal regimes to determine if AMF could aid in establishment of healthy Sporobolus communities. Rhizome-derived S. pumilus had greater survival and grew faster than seed-derived plants. Plants inoculated with propagated AMF consistently outperformed both sterile and native sediment controls in terms of plant survival and growth. Use of rhizome-derived Sporobolus inoculated with propagated Funneliformis geosporum showed the most promise in producing successful plant populations for salt marsh restoration. This may be due to plant life stage and improved plant nutrient status, allowing rhizome-derived plants to grow more quickly than seed-derived plants. Using these plants in future large-scale restoration may increase re-establishment of salt marsh ecosystems.