Indirect Environmental Effects of Dikes on Estuarine Tidal Channels: Thinking Outside of the Dike for Habitat Restoration and Monitoring
TL;DR: In this article, the authors analyzed historical photos of the Skagit River delta marshes (Washington, U.S.) and compared changes in estuarine marsh and tidal channel surface area from 1956-2000 in the Wiley Slough area of the South Fork Skagits delta, and from 1937-2000 on the North Fork delta.
Abstract: While the most obvious effects of dike construction and marsh conversion are those affecting the con- verted land (direct or intended effects), less immediately apparent effects also occur seaward of dikes (indirect or unintended effects). I analyzed historical photos of the Skagit River delta marshes (Washington, U.S.) and compared changes in estuarine marsh and tidal channel surface area from 1956-2000 in the Wiley Slough area of the South Fork Skagit delta, and from 1937-2000 in the North Fork delta. Dike construction in the late 1950s caused the loss of 80 ha of estuarine marsh and 6.7 ha of tidal channel landward of the Wiley Slough dikes. A greater amount of tidal channel surface area, 9.6 ha, was lost seaward of the dikes. Similar losses were observed for two smaller North Fork tidal channel systems. Tidal channels far from dikes did not show comparable changes in channel surface area. These results are consistent with hydraulic geometry theory, which predicts that diking reduces tidal flushing in the undiked channel remnants and this results in sedimentation. Dikes may have significant seaward effects on plants and animals associated with tidal channel habitat. Another likely indirect dike effect is decreased sinuosity in a distributary channel of the South Fork Skagit River adjacent to and downstream of the Wiley Slough dikes, compared to distributary channels upstream or distant from the dikes. Loss of floodplain area to diking and marsh conversion prevents flood energy dissipation over the marsh surface. The distributary channel has responded to greater flood energy by increasing mean channel width and decreasing sinuosity. Restoration of diked areas should consider historic habitat loss seaward of dikes, as well as possible benefits to these areas from dike breaching or removal. Habitat restoration by breaching or removal of dikes should be monitored in areas directly affected by dikes, areas indirectly affected, and distinct reference areas.
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TL;DR: It is concluded that the best way to protect salt marshes and the services they provide is through the integrated approach of ecosystem-based management.
Abstract: Salt marshes are among the most abundant, fertile, and accessible coastal habitats on earth, and they provide more ecosystem services to coastal populations than any other environment. Since the Middle Ages, humans have manipulated salt marshes at a grand scale, altering species composition, distribution, and ecosystem function. Here, we review historic and contemporary human activities in marsh ecosystems—exploitation of plant products; conversion to farmland, salt works, and urban land; introduction of non-native species; alteration of coastal hydrology; and metal and nutrient pollution. Unexpectedly, diverse types of impacts can have a similar consequence, turning salt marsh food webs upside down, dramatically increasing top down control. Of the various impacts, invasive species, runaway consumer effects, and sea level rise represent the greatest threats to salt marsh ecosystems. We conclude that the best way to protect salt marshes and the services they provide is through the integrated approach of ecosystem-based management.
770 citations
TL;DR: In this article, the authors developed a remote-sensing method to assess change over ~4000 km of the Yellow Sea coastline and discovered extensive losses of the region's principal coastal ecosystem associated with urban, industrial, and agricultural land reclamations.
Abstract: In the Yellow Sea region of East Asia, tidal wetlands are the frontline ecosystem protecting a coastal population of more than 60 million people from storms and sea-level rise. However, unprecedented coastal development has led to growing concern about the status of these ecosystems. We developed a remote-sensing method to assess change over ~4000 km of the Yellow Sea coastline and discovered extensive losses of the region's principal coastal ecosystem – tidal flats – associated with urban, industrial, and agricultural land reclamations. Our analysis revealed that 28% of tidal flats existing in the 1980s had disappeared by the late 2000s (1.2% annually). Moreover, reference to historical maps suggests that up to 65% of tidal flats were lost over the past five decades. With the region forecast to be a global hotspot of urban expansion, development of the Yellow Sea coastline should pursue a course that minimizes the loss of remaining coastal ecosystems.
369 citations
TL;DR: In this article, the authors explore restoration concepts, examples, and challenges from the Pacific and Gulf coasts and review the concepts of ecosystem trajectories, alternative restoration approaches, and the ideal attributes of functional self-sustaining restoration in the context of realities of restoration planning, design, and implementation.
217 citations
TL;DR: In this article, the authors focus on ecosystem recolonization by the biota and their functioning and separate Type A Ecoengineering, where the physico-chemical structure is modified on the basis that ecological structure and functioning will then follow, and Type B Ecoengineering where the Biota are engineered directly such as through restocking or replanting, where suitable physical conditions, especially hydrography and sedimentology, are created to recover estuarine ecology by natural or human-mediated colonisation of primary producers and consumers.
Abstract: Ecological Engineering (or Ecoengineering) is increasingly used in estuaries to re-create and restore ecosystems degraded by human activities, including reduced water flow or land poldered for agricultural use. Here we focus on ecosystem recolonization by the biota and their functioning and we separate Type A Ecoengineering where the physico-chemical structure is modified on the basis that ecological structure and functioning will then follow, and Type B Ecoengineering where the biota are engineered directly such as through restocking or replanting. Modifying the physical system to create and restore natural processes and habitats relies on successfully applying Ecohydrology, where suitable physical conditions, especially hydrography and sedimentology, are created to recover estuarine ecology by natural or human-mediated colonisation of primary producers and consumers, or habitat creation. This successional process then allows wading birds and fish to reoccupy the rehabilitated areas, thus restoring the natural food web and recreating nursery areas for aquatic biota. We describe Ecohydrology principles applied during Ecoengineering restoration projects in Europe, Australia, Asia, South Africa and North America. These show some successful and sustainable approaches but also others that were less than successful and not sustainable despite the best of intentions (and which may even have harmed the ecology). Some schemes may be ‘good for the ecologists’, as conservationists consider it successful that at least some habitat was created, albeit in the short-term, but arguably did little for the overall ecology of the area in space or time. We indicate the trade-offs between the short- and long-term value of restored and created ecosystems, the success at developing natural structure and functioning in disturbed estuaries, the role of this in estuarine and wetland management, and the costs and benefits of Ecoengineering to the socio-ecological system. These global case studies provide important lessons for both the science and management of estuaries, including that successful estuarine restoration is a complex and often difficult process, and that Ecoengineering with Ecohydrology aims to control and/or simulate natural ecosystem processes.
129 citations
TL;DR: A new SD model is developed and test which simulates the dynamics between the farmers' economic system and their rice agriculture operations, and uniquely, integrates the role of fluvial sediment deposition within their dyke compartment, and is used to explore a range of alternative rice cultivation strategies.
105 citations
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TL;DR: The authors examined the gut contents of mummichogs, Fundulus heteroclitus L., entering and leaving ditches in three marsh regions within the Barn Island Wildlife Management Area in Connecticut: a restored impounded valley marsh, a marsh below the impoundment dike (Headquarters Marsh), and an unimpounded valley Marsh (Davis Marsh).
Abstract: We examined the gut contents of mummichogs, Fundulus heteroclitus L., entering and leaving ditches in three marsh regions within the Barn Island Wildlife Management Area in Connecticut: a restored impounded valley marsh, a marsh below the impoundment dike (Headquarters Marsh), and an unimpounded valley marsh (Davis Marsh). On the Headquarters Marsh and at certain times on the other two marshes, fish entered the ditches on the flooding tide with relatively little food in their guts and left them on the following ebbing tide with considerably more food in their guts. Since the high tides did not flood the surface of the high marsh, it appears that the ditches are important foraging areas. Major components of the gut contents were detritus, algae, amphipods, tanaids, copepods, and insects. During the summer, fish in the restored impounded marsh consumed less food per unit body weight than did fish inhabiting the other marsh regions.
102 citations
TL;DR: In this article, sediment cores were collected from flow-restricted restricted salt marshes along the Connecticut coast of Long Island Sound to assess the impact of tidal flow restriction on marsh sedimentation processes.
Abstract: Many salt marshes in densely populated areas have been subjected to a reduction in tidal flow. In order to assess the impact of tidal flow restriction on marsh sedimentation processes, sediment cores were collected from flow-restricted restricted salt marshes along the Connecticut coast of Long Island Sound. Cores were also collected from unrestricted reference marshes and from a marsh that had been previously restricted but was restored to fuller tidal flushing in the 1970's. High bulk densities and low C and N concentrations were found at depth in the restricted marsh cores, which we attribute to a period of organic matter oxidation, sediment compaction, and marsh surface subsidence upon installation of flow restrictions (between 100 and 200 years before the present, depending on the marsh). Recent sedimentation rates at the restricted marshes (as determined by137Cs and210Pb dating) were positive and averaged 78% (137Cs) and 50% (210Pb) of reference marsh sedimentation rates. The accumulation of inorganic sediment was similar at the restricted and reference marshes, perhaps because of the seasonal operation of the tide gates, while organic sediment accretion (and pore space) was significantly lower in the restricted marshes, perhaps because of higher decomposition rates. Sedimentation rates at the restored marsh were significantly higher than at the reference marshes. This marsh has responded to the higher water levels resulting from restoration by a rapid increase in marsh surface elevation.
96 citations
"Indirect Environmental Effects of D..." refers background in this paper
...…how dikes affect sediment accretion, soil density, soil organic content, and marsh surface subsidence (Thom 1992; Bryant and Chabreck 1998; Anisfeld et al. 1999; Portnoy 1999); biogeochemistry and water chemistry (Soukup and Portnoy 1986; Portnoy 1991; Portnoy and Giblin 1997); the…...
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01 Jan 2002
TL;DR: In this article, the effect of estuarine landscape structure and scale on their effectiveness for protecting and rehabilitating coastal fisheries resources is explored. And the authors argue that basing restoration solely on site-specific criteria may be significantly inhibiting our ability to re-establish estuarial support function for fisheries resources.
Abstract: Juveniles of many Pacific Northwest coastal fishes and particularly anadromous species, utilise coastal marshes as “nursery” habitats, predicating the assumption that restoration of marsh sites will promote increased fish survival and production. However, species such as anadromous salmonids have evolved life history strategies that to various degrees depend upon the structure and scale of the estuarine landscape rather than habitat sites per se. Examples include: 1) migration of juvenile salmon among interconnected wetlands along estuarine gradient, 2) their access to dendritic tidal channels, and 3) extended residence in tidal freshwater sloughs. Unfortunately, estuarine habitat restoration is seldom designed or implemented with landscape structure and scale in mind, ignoring important landscape attributes and processes such as habitat matrix heterogeneity, dendritic tidal channel complexity, allometric relationships of estuarine sloughs, and disturbance frequency and intensity. In this analysis, we draw on several estuarine wetland mitigation and restoration sites in the Pacific Northwest to explore the effect of estuarine landscape structure and scale on their effectiveness for protecting and rehabilitating coastal fisheries resources. We argue that basing restoration solely on site-specific criteria may be significantly inhibiting our ability to re-establish estuarine support function for fisheries resources. To significantly recover the function of juvenile fish migration and survival in coastal ecosystems, future marsh restoration must be conceptualized, designed, constructed and assessed taking into account estuarine landscape structure and scale.
81 citations
TL;DR: In this paper, it is shown that it is highly unlikely that geomorphic steady states exist, because the dependent variables of a geomorphic open system cannot attain a time-independent state where the independent variables do not remain constant.
Abstract: Allometry is the study of the relative rates of change of two variables of a system. In the study of landforms, or the processes acting upon them, the power function Y = a X b is useful for correlating changes in variables. Allometric analysis includes the study of dynamic interrelations during geomorphic history, or the static interrelations at a given time. Such analyses may include aspects of geomorphic open systems that are tending toward a steady state, have attained a steady state, or do not tend toward a steady state. The highly flexible allometric model can be used to demonstrate adjustment between interdependent variables of hillslopes, streams, and depositional environments. It is highly unlikely that geomorphic steady states exist, because the dependent variables of a geomorphic open system cannot attain a time-independent state where the independent variables do not remain constant. Independent variables, such as climate, uplift, base level, erodibility of surficial materials, and impact of man, are changing at rates that are sufficiently rapid as to preclude attainment of steady state, particularly for those landforms that require geologic time spans to approach steady-state configurations. For most studies of processes and landforms, a broad perspective of the interrelations of materials, processes, and landforms can be obtained by using the model of allometric change in which landscape elements and processes are changing at different rates.
78 citations
"Indirect Environmental Effects of D..." refers background in this paper
...A wide variety of landforms have been shown to be allometric or, equivalently, self-affine fractals (Bull 1975; Church and Mark 1980; Ouchi and Matsushita 1992; Rodriguez-Iturbe and Rinaldo 1997)....
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...A wide variety of landforms have been shown to be allometric or, equivalently, self-affine fractals (Bull 1975; Church and Mark 1980; Ouchi and Matsushita 1992; Rodriguez-Iturbe and Rinaldo 1997)....
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TL;DR: In this article, a new absolute order is suggested, derived by raising the bifurcation ratio to successive integer powers equivalent to stream order minus one, which is the stream order of the Yule stochastic process.
Abstract: Rivers are open systems and achieve a steady state or grow allometrically, according to the general equation y = ax b . This equation yields a straight line on double logarithmic paper and reflects a lognormal or Yule stochastic process. Horton9s laws are shown to be statements of these processes, and successive stream orders are seen to be new logarithmic cycles to the base of the bifurcation ratio for a river system. A new absolute order is suggested, derived by raising the bifurcation ratio to successive integer powers equivalent to stream order minus one.
70 citations
"Indirect Environmental Effects of D..." refers background in this paper
...A system is allometric when the relative rate of change of one part of a system (y) is proportional to the relative rate of change of another part of the system (x), or of the whole system, i.e., dy 1 dx 1 5 b y dt x dt where b is a proportionality constant (Woldenberg 1966)....
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