Abstract
Multiple stable states are established in coastal tidal wetlands (marshes, mangroves, deltas, seagrasses) by ecological, hydrological, and geomorphological feedbacks. Catastrophic shifts between states can be induced by gradual environmental change or by disturbance events. These feedbacks and outcomes are key to the sustainability and resilience of vegetated coastlines, especially as modulated by human activity, sea level rise, and climate change. Whereas multiple stable state theory has been invoked to model salt marsh responses to sediment supply and sea level change, there has been comparatively little empirical verification of the theory for salt marshes or other coastal wetlands. Especially lacking is long-term evidence documenting if or how stable states are established and maintained at ecosystem scales. Laboratory and field-plot studies are informative, but of necessarily limited spatial and temporal scope. For the purposes of long-term, coastal-scale monitoring, remote sensing is the best viable option. This review summarizes the above topics and highlights the emerging promise and challenges of using remote sensing-based analyses to validate coastal wetland dynamic state theories. This significant opportunity is further framed by a proposed list of scientific advances needed to more thoroughly develop the field.
Highlights
We use the term environmental conditions to indicate the set of extrinsic parameters that influence the system dynamics but are not in turn affected by the state of the system
Whether a system can be said to conform to multiple stable state theory depends on its dynamic response to small perturbations in environmental conditions
To inform large scale and long term adaptive coastal management and restoration, high-resolution, ecosystem-scale observation over extended spatial and temporal scales is a critical need. Such data can be highly useful in empirically testing hypothesized alternative stable states in coastal wetlands
Summary
Coastal wetlands are found from the tropics to the arctic, fringing the shorelines of all continents except Antarctica. It is thought that intact coastal wetlands may serve as critical components of global adaptive management to climate change and perturbed biogeochemical cycles, with real economic value [24] Among their services in this capacity, coastal wetlands may be ideal buffers against sea level rise and increased coastal storm intensity [7,25,26,27], sinks for coastal nutrient pollution [19,21], and enormous potential sinks for the greenhouse gas carbon dioxide (CO2) due to their leading rates of primary production and carbon burial [2,28,29,30] and the low methane (CH4) emissions of saline systems [31,32,33]. These initiatives will document the current extent of coastal wetland environments, they lack a thorough temporal perspective, which prevents accurate description of the evolution of such highly dynamic systems
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