Does biogeomorphic feedback lead to abrupt shifts between alternative landscape states?: An empirical study on intertidal flats and marshes
TL;DR: In this paper, the authors analyzed historical records of intertidal elevation surveys and aerial pictures from the macrotidal current-dominated Western Scheldt estuary (SW Netherlands) and found that the abrupt nonlinear shift between low-lying bare flats and high-elevation vegetated marshes can be considered as alternative stable landscape states with the occurrence of rapid catastrophic shifts between them.
Abstract: [1] Low-elevation bare intertidal flats and high-lying vegetated marshes are the main components of intertidal areas of estuaries, deltas and coastal embayments. Large-scale transitions between them have been reported worldwide. Because vegetated marshes provide significant services to coastal societies, predicting transitions between vegetated and unvegetated states is of widespread importance. Previous theoretical and modeling work highlighted the potential bistable nature of intertidal elevations, with low-elevation bare flats and high-elevation vegetated marshes being two alternative stable states. However, empirical evidence of this bistable condition is limited. In this study, we tested empirically the hypothesis that bare flats and vegetated marshes can be considered as alternative stable landscape states with the occurrence of rapid catastrophic shifts between them. We analyzed historical records of intertidal elevation surveys and aerial pictures from the macrotidal current-dominated Western Scheldt estuary (SW Netherlands). We found (1) a bimodal distribution of intertidal elevations corresponding to either a completely bare state or a densely vegetated state. (2) The shift from bare to vegetated state is accompanied with a relatively rapid shift in elevation, i.e., the mean accretion rate during the shift is 2 to 8 times larger than during the equilibrium state. (3) A threshold elevation could be identified above which the shift from bare to vegetated state has a high chance to occur. Hence, our results demonstrate the abrupt nonlinear shift between low-lying bare flats and high-elevation vegetated marshes, suggesting that the occurrence of catastrophic shifts between alternative stable states is indeed a potential mechanism in intertidal systems.
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TL;DR: In this paper, the authors argue that coastal marsh vulnerability is often overstated because assessments generally neglect feedback processes known to accelerate soil building with sea level rise, as well as the potential for marshes to migrate inland.
Abstract: In this Perspective it is argued that coastal marsh vulnerability is often overstated because assessments generally neglect feedback processes known to accelerate soil building with sea level rise, as well as the potential for marshes to migrate inland. Coastal marshes are considered to be among the most valuable and vulnerable ecosystems on Earth, where the imminent loss of ecosystem services is a feared consequence of sea level rise. However, we show with a meta-analysis that global measurements of marsh elevation change indicate that marshes are generally building at rates similar to or exceeding historical sea level rise, and that process-based models predict survival under a wide range of future sea level scenarios. We argue that marsh vulnerability tends to be overstated because assessment methods often fail to consider biophysical feedback processes known to accelerate soil building with sea level rise, and the potential for marshes to migrate inland.
490 citations
TL;DR: A review of wave-driven sediment resuspension and transport in estuaries, including generation of bed shear stress by waves, initiation of sediment motion by waves and the ways waves modulate, add to, and interact with sediment transport driven by currents, can be found in this paper.
Abstract: Waves are fundamentally important to the physical and biological functioning of estuaries. Understanding and predicting contaminant transport, development of sedimentary structures, geomorphological response to changes in external forcings such as rising sea level, and response of estuarine ecosystems to contaminant stressors require understanding of the relative roles of wave- and current-driven sediment transport. We review wave-driven sediment resuspension and transport in estuaries, including generation of bed shear stress by waves, initiation of sediment motion by waves, and the ways waves modulate, add to, and interact with sediment transport driven by currents. A key characteristic of the wave-induced force on the seabed is extreme spatial and temporal variations; simple analytical models are revealing of the way such patterns develop. Statistical methods have been widely applied to predict wave resuspension of intertidal-flat bed sediments, and physically based predictors of resuspension developed from open-coast studies appear to also apply to short-period estuarine waves. There is ample experimental evidence to conclude that over the long term, waves erode and tidal currents accrete intertidal flats. Waves indirectly add to the formation of fluid mud by adding to the estuarine pool of fine sediment, and waves may fluidize subtidal seabeds, changing bed erodibility. Models have been used to explore the dynamic balance between sediment transport by waves and by currents and have revealed the key control of waves on estuarine morphology. Estuarine intertidal flats are excellent natural laboratories that offer opportunities for working on a number of fundamental problems in sediment transport.
192 citations
TL;DR: Spartina species of the mid-low intertidal areas are powerful ecological engineers that are highly valued where they are native, but elsewhere, they overgrow native salt marsh and open interTidal mudflats, diminish biota, increase costs of managing wildlife, and interfere with human uses of estuaries.
Abstract: Spartina species of the mid-low intertidal areas are powerful ecological engineers that are highly valued where they are native. Elsewhere, they overgrow native salt marsh and open intertidal mudflats, diminish biota, increase costs of managing wildlife, and interfere with human uses of estuaries. Huge efforts have been mounted to kill some populations of invading Spartina. All large Spartina invasions are by S. densiflora (2n = 7x = 70) or S. alterniflora (2n = 6x = 62) or hybrids between the hexaploid species (2n = 6x). Hybridization is a recurrent theme in Spartina; the allododecaploid S. anglica (2n = 12x = 120) and the hybrid swarm in San Francisco Bay arose through the introductions of S. alterniflora into the range of native Spartina species. The ancient hybrid S. densiflora also hybridized with native Spartina species. Hybridization promotes the evolution of highly invasive populations and hampers control efforts. Whether Spartina, native and not, would protect the shore as sea levels rise depends...
163 citations
TL;DR: The approach to long-term predictions is discussed, the coupling between physical and biological processes are focused on, and the role of anthropic drivers in the evolution of these systems are introduced.
147 citations
Cites background from "Does biogeomorphic feedback lead to..."
...For example, studies have identified the coupling mechanisms leading to morphological alternative stable states and associated these equilibria to a distribution of vertical elevations, low for tidal flats andhigh for vegetated areas (Marani et al., 2013; Wang and Temmerman, 2013)....
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TL;DR: In this article, the authors identify the mechanisms that translate large-scale physical forcing in the system into vegetation change, in particular the initiation of lateral erosion on an expanding marsh, and the control of seedling establishment in front of an eroding marsh cliff.
Abstract: Our study aims to enhance process understanding of the long-term (decadal and longer) cyclic marsh dynamics by identifying the mechanisms that translate large-scale physical forcing in the system into vegetation change, in particular (i) the initiation of lateral erosion on an expanding marsh, and (ii) the control of seedling establishment in front of an eroding marsh-cliff. Short-term sediment dynamics (i.e., seasonal and shorter changes in sediment elevation) at the mudflat causes variation in mudflat elevation over time (δzTF). The resulting difference in elevation between the tidal flat and adjacent marsh (ΔZ) initiates lateral marsh erosion. Marsh erosion rate was found to depend on sediment type and to increase with increasing ΔZ and hydrodynamic exposure. Laboratory and field experiments revealed that seedling establishment was negatively impacted by an increasing δzTF. As the amplitude of δzTF increases towards the channel, expanding marshes become more prone to lateral erosion the further they extend on a tidal flat, and the chance for seedlings to establish increases with the distance that marsh has eroded back towards the land. This process-based understanding, showing the role of sediment dynamics as explanatory factor for marsh cyclicity, is important for protecting and restoring valuable marsh ecosystems. Overall, our experiments emphasize the need for understanding the connections between neighbouring ecosystems such as mudflat and salt marsh.
122 citations
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TL;DR: In this paper, the authors have estimated the current economic value of 17 ecosystem services for 16 biomes, based on published studies and a few original calculations, for the entire biosphere, the value (most of which is outside the market) is estimated to be in the range of US$16-54 trillion (10^(12)) per year, with an average of US $33 trillion per year.
Abstract: The services of ecological systems and the natural capital stocks that produce them are critical to the functioning of the Earth's life-support system. They contribute to human welfare, both directly and indirectly, and therefore represent part of the total economic value of the planet. We have estimated the current economic value of 17 ecosystem services for 16 biomes, based on published studies and a few original calculations. For the entire biosphere, the value (most of which is outside the market) is estimated to be in the range of US$16-54 trillion (10^(12)) per year, with an average of US$33 trillion per year. Because of the nature of the uncertainties, this must be considered a minimum estimate. Global gross national product total is around US$18 trillion per year.
18,139 citations
TL;DR: Recent studies show that a loss of resilience usually paves the way for a switch to an alternative state, which suggests that strategies for sustainable management of such ecosystems should focus on maintaining resilience.
Abstract: All ecosystems are exposed to gradual changes in climate, nutrient loading, habitat fragmentation or biotic exploitation. Nature is usually assumed to respond to gradual change in a smooth way. However, studies on lakes, coral reefs, oceans, forests and arid lands have shown that smooth change can be interrupted by sudden drastic switches to a contrasting state. Although diverse events can trigger such shifts, recent studies show that a loss of resilience usually paves the way for a switch to an alternative state. This suggests that strategies for sustainable management of such ecosystems should focus on maintaining resilience.
6,213 citations
"Does biogeomorphic feedback lead to..." refers background in this paper
...Although ecosystems generally respond smoothly to gradual changes in environmental conditions, sudden shifts may occur when a critical threshold condition is exceeded [Scheffer et al., 2001]....
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...…evidence requires the study of the reverse transition from vegetated to bare state and the further demonstration of the existence of hysteresis, i.e., that the forward and backward shifts between ecosystem states happen at different critical conditions [Scheffer, 2009; Scheffer et al., 2001]....
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...[3] The occurrence of so-called catastrophic shifts between alternative stable ecosystem states has been recognized in ecology as an important mechanism in several ecosystem types [May, 1977; Scheffer, 2009; Scheffer et al., 2001]....
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...…alternative stable states are often irreversible due to hysteresis effects, which mean that the threshold environmental conditions to recover the original state are far more difficult to reach than the threshold conditions that caused the shift [Scheffer and Carpenter, 2003; Scheffer et al., 2001]....
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...…by ecological theory on catastrophic shifts between alternative stable ecosystem states resulting from organism-resource feedbacks [e.g., May, 1977; Scheffer et al., 2001], we may expect that biogeomorphic systems, which are governed by feedbacks between organisms and landforms [Corenblit et al.,…...
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TL;DR: In this paper, the main ecological services across a variety of estuarine and coastal ecosystems (ECEs) including marshes, mangroves, nearshore coral reefs, seagrass beds, and sand beaches and dunes are reviewed.
Abstract: 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.
3,750 citations
"Does biogeomorphic feedback lead to..." refers background in this paper
...The understanding and prediction of such pending shifts is important, since vegetated marshes provide important ecosystem services to coastal and estuarine societies [Barbier et al., 2011]....
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01 May 2011
TL;DR: Hydrodynamic analysis of simulated hurricane storm surges and economic valuation of expected property damages shows that the presence of coastal marshes and their vegetation has a demonstrable effect on reducing storm surge levels, thus generating significant values in terms of protecting property in southeast Louisiana.
Abstract: The Indian Ocean tsunami in 2004 and Hurricanes Katrina and Rita in 2005 have spurred global interest in the role of coastal wetlands and vegetation in reducing storm surge and flood damages. Evidence that coastal wetlands reduce storm surge and attenuate waves is often cited in support of restoring Gulf Coast wetlands to protect coastal communities and property from hurricane damage. Yet interdisciplinary studies combining hydrodynamic and economic analysis to explore this relationship for temperate marshes in the Gulf are lacking. By combining hydrodynamic analysis of simulated hurricane storm surges and economic valuation of expected property damages, we show that the presence of coastal marshes and their vegetation has a demonstrable effect on reducing storm surge levels, thus generating significant values in terms of protecting property in southeast Louisiana. Simulations for four storms along a sea to land transect show that surge levels decline with wetland continuity and vegetation roughness. Regressions confirm that wetland continuity and vegetation along the transect are effective in reducing storm surge levels. A 0.1 increase in wetland continuity per meter reduces property damages for the average affected area analyzed in southeast Louisiana, which includes New Orleans, by $99-$133, and a 0.001 increase in vegetation roughness decreases damages by $24-$43. These reduced damages are equivalent to saving 3 to 5 and 1 to 2 properties per storm for the average area, respectively.
2,672 citations
TL;DR: In this paper, the authors review emerging ways to link theory to observation, and conclude that although, field observations can provide hints of alternative stable states, experiments and models are essential for a good diagnosis.
Abstract: Occasionally, surprisingly large shifts occur in ecosystems. Theory suggests that such shifts can be attributed to alternative stable states. Verifying this diagnosis is important because it implies a radically different view on management options, and on the potential effects of global change on such ecosystems. For instance, it implies that gradual changes in temperature or other factors might have little effect until a threshold is reached at which a large shift occurs that might be difficult to reverse. Strategies to assess whether alternative stable states are present are now converging in fields as disparate as desertification, limnology, oceanography and climatology. Here, we review emerging ways to link theory to observation, and conclude that although, field observations can provide hints of alternative stable states, experiments and models are essential for a good diagnosis.
2,464 citations
"Does biogeomorphic feedback lead to..." refers background in this paper
...Despite such evidence, it is still possible that the system shows a threshold response which is not caused by alternative attractors or bifurcation [Scheffer, 2009; Scheffer and Carpenter, 2003]....
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...…to the occurrence of alternative stable states in ecosystems, resulting from positive feedbacks between organisms and limiting resources [Rietkerk et al., 2004; Scheffer and Carpenter, 2003; Van De 1University of Antwerp, Department of Biology, Ecosystem Management Research Group, Wilrijk, Belgium....
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...The bimodality of ecosystem state variables and threshold behavior are generally used as empirical indicators of the presence of alternative stable states in ecosystems [e.g., Scheffer and Carpenter, 2003; Schröder et al., 2005]....
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...[31] A bimodal distribution is an indicator for the potential existence of alternative attractors in a system [Scheffer and Carpenter, 2003]....
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...…alternative stable states are often irreversible due to hysteresis effects, which mean that the threshold environmental conditions to recover the original state are far more difficult to reach than the threshold conditions that caused the shift [Scheffer and Carpenter, 2003; Scheffer et al., 2001]....
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