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11 - Understanding Marsh Dynamics
- from Part II - Marsh Dynamics
- Edited by Duncan M. FitzGerald, Boston University, Zoe J. Hughes, Boston University
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- Book:
- Salt Marshes
- Published online:
- 19 June 2021
- Print publication:
- 22 April 2021, pp 278-299
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Summary
Salt marshes have received considerable scientific attention in recent years due to a combination of factors. Salt marshes host important ecosystems and store large quantities of carbon in their soils (Fagherazzi et al. 2004; Mudd et al. 2009). Currently salt marshes are endangered by accelerated sea-level rise triggered by global warming (Kirwan et al. 2010). A sharp reduction in sediment supply caused by the damming of rivers is also jeopardizing marsh survival along many coasts (Weston 2014). As a result, there is a need to determine the fate of marshlands in different settings in order to inform government and local communities and implement protection strategies. To this end, numerical models are playing an increasingly important role, because they can easily provide future scenarios of marsh conditions under different forcings. However, the evolution of salt marshes as a function of sea-level rise and sediment supply is relatively complex, because of feedbacks among hydrodynamics, sediment transport, and vegetation (Fagherazzi et al. 2012). As a result, marshes are continuously adjusting to a changing environment, in ways often difficult to predict. This intrinsic complexity has generated a flurry of numerical models, each emphasizing a different aspect of salt marsh evolution. It is thus becoming more and more accepted by the scientific community that a comprehensive model of salt marsh evolution is not feasible, given the number and variety of physical and biological processes at play. A detailed approach, based on the description of all possible processes acting at different spatial and temporal scales, has been slowly replaced by a more practical approach, in which separate models are built to address key important processes or to capture specific dynamics.
12 - Salt Marsh Ecosystems: Tidal Flow, Vegetation, and Carbon Dynamics
- from Part IV - Coupling Fluvial and Aeolian Geomorphology, Hydrology/Hydraulics, and Ecosystems
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- By Simon M. Mudd, University of Edinburgh, Sergio Fagherazzi, Boston University
- Edited by Edward A. Johnson, University of Calgary, Yvonne E. Martin, University of Calgary
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- Book:
- A Biogeoscience Approach to Ecosystems
- Published online:
- 27 October 2016
- Print publication:
- 13 October 2016, pp 407-434
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Summary
Introduction
Salt marshes are coastal wetlands located in the intertidal zone that are populated by halophytic vegetation. Although they occupy a relatively small percentage of the Earth's surface, they have been the focus of intense ecological and geomorphological research for several decades due to their importance in filtering pollutants, buffering against coastal storms, serving as nurseries for commercial fisheries, and storing carbon (Barbier et al., 2011). These ecosystems were among the first to be studied in an ecogeomorphic context due to the clear feedbacks between plant populations and landscape formation (e.g., Redfield 1972).
Salt marsh ecosystems are found on all continents except for Antarctica in mid to high latitude locations (Figure 12.1), giving way to mangrove swamps in subtropical and tropical climates. Radiocarbon dating of basal peats suggests that salt marsh ecosystems became widespread sometime between 4000 and 6000 years ago (Allen, 2000). Prior to this, sea level rise associated with post-glacial melt water and ocean expansion was too rapid for marsh establishment. Rates of eustatic sea level rise have increased over the twentieth and into the twenty-first century (Church and White, 2011), and there are now growing concerns that accelerating rates of sea level rise, combined with a decrease of sediment availability due to river damming could threaten marsh ecosystems. The threat of marsh loss has focused research into the balance between plant growth, hydrodynamics, and sedimentation in salt marsh ecosystems.
In this chapter we will examine the close coupling between plant vitality, hydrodynamics on marsh surfaces, and sedimentation. These components of the ecogeomorphic system on salt marshes form a continuous loop: marsh plants respond to edaphic factors such as salinity and depth in the tidal frame, and these are controlled by the hydrodynamics of tidally induced floods and sediment deposition rates. Plants interact with flows through drag, and can affect sedimentation rates through trapping. We begin by examining the factors that control plant productivity on coastal marshes.