Do small-scale saltmarsh planting living shoreline projects enhance coastal functionality? A case study in the Northern Gulf of Mexico

Human coastal occupation often leads to the degradation of the structural properties and environmental functions of natural coastlines. . Much research has been done on the cost-effectiveness of various living shorelines designs, however more work is needed for simple, small-scale designs that are typically adopted in waterfront residential or recreational properties. To contribute to this gap, we planted small-scale plots of black needlerush (Juncus roemerianus) in two sites, one in a residential property and another one in a recreational property in the Northern Gulf of Mexico that experienced significant wave energy. Plots were planted at two different densities (50% or 100% initial cover) or left unplanted (controls) and, along with monitoring the evolution of the planted salt marsh, we measured a number of functional metrics including soil slope, abundance of nekton within and in front of the plots, and cover of submerged aquatic vegetation (SAV) in front of the plots monthly over two years. In one of the sites plant cover decreased precipitously, and in the other site we did not observe any significant changes in plant cover over time (i.e. the initial 50% and 100% plantings remained at that level throughout the experiment) despite protecting the planted salt marsh with coir logs. We did not find any changes in soil slope or nekton abundance between planted and control plots. SAV growth was restrained in front of planted plots in relation to control plots, possibly due to deleterious impacts by the coir logs. Overall, the results suggest the protection against wave energy attained in this experiment is insufficient for adequate saltmarsh establishment and growth, thereby encountering decreasing or stationary plant density and no significant differences in soil slope or nekton abundance between planted and non-planted plots. Our results indicate the adoption of small-scale saltmarsh planting to reduce erosion and enhance coastal functionality needs to ensure that wave energy is sufficiently dampened for adequate saltmarsh growth and, concomitantly, the conceived saltmarsh protection mechanism does not negatively impact adjacent SAV.

Towards principles and policy levers for advancing living shorelines

Living shorelines are often better alternatives to stabilize shorelines and reduce dangerous erosion compared to traditional hard armoring practices such as bulkheads and seawalls. Increasing the use of living shorelines will require policy innovation and new approaches to shoreline management, however. Informed by a comparative legal analysis, this article identifies "policy levers" through four categories that demonstrate critical aspects of the human dimension in the estuarine management context that, to greater and lesser extents, promote or inhibit the implementation of living shorelines. Specifically, these categories include: erosion and flood control; neighboring stabilization structures; rebuild policies and sea-level rise projections; and jurisdictional boundaries. The article concludes that the policy levers that are the most optimal baseline choices to advance living shorelines include prohibiting shoreline stabilization in areas where erosion is controlled and bank loss mitigated; eliminating hard armoring as the default erosion and flood control stabilization preference; prohibiting "gap-filling" policies that connect or "align" existing, legal seawalls or armoring; requiring living shorelines in areas where a minimum percentage (10-25%) of the tidal shoreline is already armored; and requiring the replacement of hard armoring with living shorelines when repair is required or certain sea-level rise projections are met. Because modeling frameworks incorporating policy simulations would allow coastal scientists and managers to better visualize how and to what extent policy choices advance or inhibit the adoption of living shorelines, identifying and understanding such policy levers is a critical first step to utilize modeling frameworks to simulate and evaluate how certain legal regimes either promote or inhibit the use of living shorelines for shoreline stabilization in estuarine environments.

Strategies to work towards long-term sustainability and resiliency of nature-based solutions in coastal environments: A review and case studies

The need for sustainable and resilient long-term strategies for coastal restoration and development projects is largely the result of pressures brought by changing climate conditions and growing human populations along coastal boundaries. As anthropogenic impacts along our coasts increase, the demand for sustainable, nature-based solutions (NbS) will grow commensurately. Trusted approaches are needed for successful implementation of NbS, especially in regions hardest hit by environmental changes. Nearshore strategies for new construction and protection of existing coastal infrastructure are shifting rapidly from hardened approaches to more ecologically aligned techniques that work with natural forces and enhance natural habitat. This paper highlights the benefits of living shorelines composed of ecotypic native plants, wave attenuation structures for coastal protection, and managed retreat to restore coastal environments while supporting and maintaining natural habitats. We review several NbS and present two case studies to illustrate the value of incorporating nature-based approaches to vulnerable coastal environments and highlight the importance of maximizing synergies and understanding trade-offs in their long-term use. Integr Environ Assess Manag 2022;18:123-134. © 2021 SETAC.

Identifying social factors that undermine support for nature-based coastal management

Human use and degradation of coastal ecosystems is at an all-time high. Thus, a current challenge for environmental management and research is moving beyond ecological definitions of success and integrating socioeconomic factors. Projects and studies with this aim, however, have focused primarily on monetary valuations of ecosystem functions, overlooking the behaviors and psycho-social motivations of environmental management. Using a nature-based salt marsh restoration project on Martha's Vineyard, Massachusetts, we assess the role of human attitudes and preferences in evaluating social success for ecosystem management. We use structural equation modeling to compare the strengths of social variables in predicting restoration project support, and find public understanding to be a more important predictor than personal values. Our results show that even among stakeholders with strong pro-environmental values, a weak understanding of the management initiative can undermine support. We also find that project support does not necessarily translate to the prioritization of similar management strategies. Instead, when individuals consider overall management priorities, differences arise between particular resource user-groups. This suggests that strong public support for individual initiatives can misconstrue complexities in stakeholder preferences that emerge in more comprehensive management considerations. Future investigations of the psycho-social components of management solutions should address the potentially tiered nature of human preferences, as well as whether public perceptions of management effectiveness act as an additional context-dependency of social viability.

Oyster reef restoration supports increased nekton biomass and potential commercial fishery value

Across the globe, discussions centered on the value of nature drive many conservation and restoration decisions. As a result, justification for management activities increasingly asks for two lines of evidence: (1) biological proof of augmented ecosystem function or service, and (2) monetary valuation of these services. For oyster reefs, which have seen significant global declines and increasing restoration work, the need to provide both biological and monetary evidence of reef services on a local-level has become more critical in a time of declining resources. Here, we quantified species biomass and potential commercial value of nekton collected from restored oyster (Crassostrea virginica) reefs in coastal Louisiana over a 3-year period, providing multiple snapshots of biomass support over time. Overall, and with little change over time, fish and invertebrate biomass is 212% greater at restored oyster reefs than mud-bottom, or 0.12 kg m⁻². The additional biomass of commercial species is equivalent to an increase of local fisheries value by 226%, or $0.09 m⁻². Understanding the ecosystem value of restoration projects, and how they interact with regional management priorities, is critical to inform local decision-making and provide testable predictions. Quantitative estimates of potential commercial fisheries enhancement by oyster reef restoration such as this one can be used directly by local managers to determine the expected return on investment.