The global decline in estuarine and coastal ecosystems (ECEs) is affecting a number of critical benefits, or ecosystem services. We review the main ecological services across a variety of ECEs, including marshes, mangroves, nearshore coral reefs, seagrass beds, and sand beaches and dunes. Where possible, we indicate estimates of the key economic values arising from these services, and discuss how the natural variability of ECEs impacts their benefits, the synergistic relationships of ECEs across seascapes, and management implications. Although reliable valuation estimates are beginning to emerge for the key services of some ECEs, such as coral reefs, salt marshes, and mangroves, many of the important benefits of seagrass beds and sand dunes and beaches have not been assessed properly. Even for coral reefs, marshes, and mangroves, important ecological services have yet to be valued reliably, such as cross-ecosystem nutrient transfer (coral reefs), erosion control (marshes), and pollution control (mangroves). An important issue for valuing certain ECE services, such as coastal protection and habitat-fishery linkages, is that the ecological functions underlying these services vary spatially and temporally. Allowing for the connectivity between ECE habitats also may have important implications for assessing the ecological functions underlying key ecosystems services, such coastal protection, control of erosion, and habitat-fishery linkages. Finally, we conclude by suggesting an action plan for protecting and/or enhancing the immediate and longer-term values of ECE services. Because the connectivity of ECEs across land-sea gradients also influences the provision of certain ecosystem services, management of the entire seascape will be necessary to preserve such synergistic effects. Other key elements of an action plan include further ecological and economic collaborative research on valuing ECE services, improving institutional and legal frameworks for management, controlling and regulating destructive economic activities, and developing ecological restoration options.

https://esajournals.onlinelibrary.wiley.com/doi/pdf/10.1890/10-1510.1

The value of estuarine and coastal ecosystem services

Changes in climate extremes and their impacts on the natural physical environment: An overview of the IPCC SREX report

The risk of flood disasters is increasing for many coastal societies owing to global and regional changes in climate conditions, sea-level rise, land subsidence and sediment supply. At the same time, in many locations, conventional coastal engineering solutions such as sea walls are increasingly challenged by these changes and their maintenance may become unsustainable. We argue that flood protection by ecosystem creation and restoration can provide a more sustainable, cost-effective and ecologically sound alternative to conventional coastal engineering and that, in suitable locations, it should be implemented globally and on a large scale.

Ecosystem-based coastal defence in the face of global change

For more than a century, coastal wetlands have been recognized for their ability to stabilize shorelines and protect coastal communities. However, this paradigm has recently been called into question by small-scale experimental evidence. Here, we conduct a literature review and a small meta-analysis of wave attenuation data, and we find overwhelming evidence in support of established theory. Our review suggests that mangrove and salt marsh vegetation afford context-dependent protection from erosion, storm surge, and potentially small tsunami waves. In biophysical models, field tests, and natural experiments, the presence of wetlands reduces wave heights, property damage, and human deaths. Meta-analysis of wave attenuation by vegetated and unvegetated wetland sites highlights the critical role of vegetation in attenuating waves. Although we find coastal wetland vegetation to be an effective shoreline buffer, wetlands cannot protect shorelines in all locations or scenarios; indeed large-scale regional erosion, river meandering, and large tsunami waves and storm surges can overwhelm the attenuation effect of vegetation. However, due to a nonlinear relationship between wave attenuation and wetland size, even small wetlands afford substantial protection from waves. Combining man-made structures with wetlands in ways that mimic nature is likely to increase coastal protection. Oyster domes, for example, can be used in combination with natural wetlands to protect shorelines and restore critical fishery habitat. Finally, coastal wetland vegetation modifies shorelines in ways (e.g. peat accretion) that increase shoreline integrity over long timescales and thus provides a lasting coastal adaptation measure that can protect shorelines against accelerated sea level rise and more frequent storm inundation. We conclude that the shoreline protection paradigm still stands, but that gaps remain in our knowledge about the mechanistic and context-dependent aspects of shoreline protection.

The present and future role of coastal wetland vegetation in protecting shorelines: answering recent challenges to the paradigm

Salt marshes protect coastlines against waves. Wave flume experiments show that marsh vegetation causes substantial wave dissipation and prevents erosion of the underlying surface, even during extreme storm surge conditions.

/pdf/wave-attenuation-over-coastal-salt-marshes-under-storm-surge-cenihcxco5.pdf

Wave attenuation over coastal salt marshes under storm surge conditions

In response to the 2004 and 2005 hurricane seasons, surge risk assessment approaches have been re-evaluated to develop more rapid, reliable methods for predicting the risk associated with extreme hurricanes. Here, the development of dimensionless surge response functions relating surge to hurricane meteorological parameters is presented. Such response functions present an opportunity to maximize surge data usage and to improve statistical estimates of surge probability by providing a means for defining continuous probability density functions. A numerical modeling investigation was carried out for the Texas, USA coastline to develop physical scaling laws relating storm surge response with hurricane parameters including storm size, intensity, and track. It will be shown that these scaling laws successfully estimate the surge response at any arbitrary location for any arbitrary storm track within the study region. Such a prediction methodology has the potential to decrease numerical computation requirements by 75% for hurricane risk assessment studies.

A surge response function approach to coastal hazard assessment. Part 2: Quantification of spatial attributes of response functions

https://www3.nd.edu/~coast/reports_papers/2010-OE-ewbdc.pdf

Development of storm surge which led to flooding in St. Bernard Polder during Hurricane Katrina

: The numerical model documented here, RCPWAVE, can be used to solve wave propagation problems over arbitrary bathymetry. The governing equations solved in the model are the mild slope equation for linear, monochromatic waves, and the equation specifying irrotationality of the wave phase function gradient. Finite difference approximations of these equations are solved to predict wave propagation outside the surf zone. Inside the breaker zone, an empirical method is used to predict wave transformation. This method is based on a hydraulic jump representation of the entire surf zone. The model is verified using laboratory and field data. A user's manual section is provided to aid potential users. This documentation describes job control language files, job submission procedures, sample input and output files, and execution costs.

Regional Coastal Processes Numerical Modeling System: Report 1, Rcpwave-a Linear Wave Propagation Model for Engineering Use

Beach profiles and sediment samples were collected on a daily basis along three crossshore transect lines during the DUCK94 nearshore experiment lasting for 18 days in October 1994. Conditions ranged from near calm during the first week of the experiment to full storm conditions during the second and third weeks, with a two day initiation of beach recovery at the end of the experiment. The profiles responded with similar elevation change, with little morphologic variability during the calm period. During the storm, the bar migrated seaward 70 to 100 m, but the foreshore exhibited little change. The bar began to migrate shoreward at initiation of recovery. Sediment grain-size distributions vary in the cross-shore direction, with medium size grains on the upper foreshore, coarse gravel deposits on the lower foreshore and progressively finer sands in the offshore direction. After the storm, the foreshore and bar/trough samples were coarser with little change in the nearshore sediment distributions.

http://frf.usace.army.mil/duck94/sediments/stauble.pdf

Sediment dynamics and profile interactions: duck94

Global warming may result in substantial sea level rise and more intense hurricanes over the next century, leading to more severe coastal flooding. Here, observed climate and sea level trends over the last century (c. 1900s to 2000s) are used to provide insight regarding future coastal inundation trends. The actual impacts of Hurricane Katrina (2005) in New Orleans are compared with the impacts of a similar hypothetical hurricane occurring c. 1900. Estimated regional sea level rise since 1900 of 0.75 m, which contains a dominant land subsidence contribution (0.57 m), serves as a ‘prototype’ for future climate-change induced sea level rise in other regions. Landform conditions c. 1900 were estimated by changing frictional resistance based on expected additional wetlands at lower sea levels. Surge simulations suggest that flood elevations would have been 15 to 60 % lower c. 1900 than the conditions observed in 2005. This drastic change suggests that significantly more flood damage occurred in 2005 than would have occurred if sea level and climate conditions had been like those c. 1900. We further show that, in New Orleans, sea level rise dominates surge-induced flooding changes, not only by increasing mean sea level, but also by leading to decreased wetland area. Together, these effects enable larger surges. Projecting forward, future global sea level changes of the magnitude examined here are expected to lead to increased flooding in coastal regions, even if the storm climate is unchanged. Such flooding increases in densely populated areas would presumably lead to more widespread destruction.

Mary A. Cialone

Papers

A surge response function approach to coastal hazard assessment. Part 2: Quantification of spatial attributes of response functions

Development of storm surge which led to flooding in St. Bernard Polder during Hurricane Katrina

Regional Coastal Processes Numerical Modeling System: Report 1, Rcpwave-a Linear Wave Propagation Model for Engineering Use

Sediment dynamics and profile interactions: duck94

Simulations of Hurricane Katrina (2005) under sea level and climate conditions for 1900