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: In this article, the authors evaluate the success of coastal tidal marsh restoration by the extent of geographical similarity between the vegetation of the restored marsh and the pre-impounded marsh using a geographical information system (GIS).
Abstract: Adequately evaluating the success of coastal tidal marsh restoration has lagged behind the actual practice of restoring tidally restricted salt marshes. A Spartina-dominated valley marsh at Barn Island Wildlife Management Area, Stonington, Connecticut, was tidally restricted in 1946 and consequently converted mostly to Typha angustifolia. With the re-introduction of tidal flooding in 1978, much of the marsh has reverted to Spartina alterniflora. Using a geographical information system (GIS), this study measures restoration success by the extent of geographical similarity between the vegetation of the restored marsh and the pre-impounded marsh. Based on geographical comparisons among different hydrologic states, pre-impounded (1946), impounded (1976), and restored (1988) tidal marsh restoration is a convergent process. Although salt marsh species currently dominate the restored system, the magnitude of actual agreement between the pre-impounded vegetation and that of the restored marsh is only moderate. Further restoration of the salt marsh vegetation may be limited by continued tidal restriction, marsh surface subsidence, and reduced accretion rates. General trends of recovery are identified using a gradient approach and the geographic pattern’ of vegetation change. In the strictest sense, if restoration refers only to vegetation types that geographically replicate preexisting types, then only 28% of the marsh has been restored. Restoration in a broader sense, however, representing the original salt marsh vegetation regardless of spatial position, amounts to 63% restored. Unrestored marsh, dominated by Typha angustifolia and Phragmites australis, remains at 37%. By emphasizing trends during vegetation recovery, this evaluation technique aims to understand the restoration process, direct future research goals, and ultimately aid in future restoration projects.
37 citations
TL;DR: Cluster and nodal analyses identified four broad assemblages based on habitat: 1) an open marsh assemblage, 2) a creek assemblaging, 3) a eurytopic assembLage, and 4) an impoundment assemblAGE.
Abstract: Forty-eight core and grab samples were taken from two impoundments and an adjacent tidal creek and salt marsh during each of six sampling periods (January, June and November 1983; and January, April and July 1984). Habitats sampled within the impoundments included the perimeter ditch and shallow vegeted areas dominated byRuppia maritima, Spartina alterniflora, andScirpus robustus. The adjacent tidal creek bottom and low marsh ofS. alterniflora were sampled for comparison with the impoundment sites. Major differences in faunal composition and density of macrobenthic invertebrates were observed between habitats in this study. Macrobenthic density was highest (475 individuals 0.05 m−2) at the impoundment site dominated byScripus robustus, where oligochaetes were abundant. The open marsh site had a density of 254 individuals 0.05 m−2. Among unvegetated sites, density for all sampling periods was higher in Chainey Creek than in the perimeter ditches of the impoundments. The total number of taxa was highest for the open marsh and tidal creek sites. The impoundments contained vegetated sites which were inhabited by fewer species than nonimpounded sites, while the perimeter ditch sites were comparatively depauperate. Cluster and nodal analyses identified four broad assemblages based on habitat: 1) an open marsh assemblage, 2) a creek assemblage, 3) a eurytopic assemblage, and 4) an impoundment assemblage. The separation of faunal assemblages by sampling site rather than sampling period suggests that physical differences between habitats were important factors determining distribution patterns.
33 citations
Additional excerpts
...…Niering 1993; St. Omer 1994; Brockmeyer et al. * Tele: 360/466-7282; fax: 360/466-4047; e-mail: ghood@ skagitcoop.org 1997), benthic invertebrates (Wenner and Beatty 1988; Peck et al. 1994; Brockmeyer et al. 1997), and nekton—especially fish (Brockmeyer et al. 1997; Raposa and Roman 2001; Swamy…...
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TL;DR: The results obtained in this study and those of other restoring marshes at Barn Island indicate the full recovery of certain animal populations following the reintroduction of tidal flow to impounded marshes may require up to two or more decades.
Abstract: During the last two decades, the State of Connecticut has restored tidal flow to many impounded salt marshes. One of the first of these and the one most extensively studied is Impoundment One in the Barn Island Wildlife Management Area in Stonington, Connecticut. In 1990, twelve years after the re-establishment of tidal flooding, the density of the marsh snail Melampus bidentatus, the numerically dominant macroinvertebrate of the high marsh, in Impoundment One was about half that in reference marshes below the breached impoundment dike. By 1999 the densities of Melampus above and below the dike were not significantly different, but the shell-free biomass was greater above the dike as a result of the somewhat larger number and size of the snails there. Twenty-one years after the renewal of tidal flooding, three marsh macroinvertebrates (the amphipods Orchestia grillus and Uhlorchestia spartinophila and the mussel Geukensia demissa) were significantly less abundant in the previously impounded marsh than in the reference marshes, whereas another amphipod (Gammarus palustris) was more abundant above the breached dike where conditions appeared to be somewhat wetter. In 1991 the fish assemblage in a mosquito-control ditch in Impoundment One was similar to that in a ditch below the breached dike; however, the common mummichog Fundulus heteroclitus appeared to be less abundant in the restoring marsh. By 1999 the number of mummichogs caught in ditches was significantly greater in Impoundment One than in the reference marsh, but the numbers of mummichogs trapped along the tidal creek were comparable above and below the dike. The results obtained in this study and those of other restoring marshes at Barn Island indicate the full recovery of certain animal populations following the reintroduction of tidal flow to impounded marshes may require up to two or more decades. Furthermore, not only do different species recover at different rates on a single marsh, but the time required for the recovery of a particular species may vary widely from marsh to marsh, often independently of other species.
31 citations
TL;DR: In this article, the authors present an analysis of impacts in a small estuary which has been subjected to both diking and ditching,primarily for mosquito control, and the major impacts stem from katteklei formation.
Abstract: Insect control programmes sometimes include environmental modification techniques such as diking and drainage. The impacts of such techniques are not often known or assessed. As a telling example having wide implications, we present an analysis of impacts in a small estuary which has been subjected to both diking and ditching—primarily for mosquito control.The major impacts stem from katteklei formation. Desiccated salt-marsh sediments produce acidified leachates which result from oxidation of pyrites. Lowered pH and high (acid-mobilized) aluminium concentrations both surpass levels that are known to be toxic to aquatic fauna. Fish and invertebrate communities in the basin are impoverished, and important commercial species such as American Eels and Alewives are heavily decimated. The acid-tolerant mosquito Aedes cantator thrives, however. Thus a natural system of substantial economic and aesthetic value has been inadvertently devastated through application of unnecessarily harsh as well as, in this case, ineffective mosquito control methods. Their use should be re-evaluated for similar impacts wherever such application has been carried out or is being contemplated.
25 citations
TL;DR: The distribution of the American oyster is dependent upon the morphological development of tidal streams as mentioned in this paper, and dense populations are most often found associated with large meanders, where the differential current velocities associated with meander formation result in areas of scour and areas of deposition, which are detrimental to survival of oysters.
Abstract: The distribution of the American oyster is dependent upon the morphological development of tidal streams. Dense populations are most often found associated with large meanders. The differential current velocities associated with meander formation result in areas of scour, which are beneficial to development of oyster beds; and areas of deposition, which are detrimental to survival of oysters.
23 citations
"Indirect Environmental Effects of D..." refers background in this paper
...…the ecological role of tidal channel sinuosity are rare, dense populations of oysters (Crassostrea virginica) are associated with meander cut banks (Keck et al. 1973), while meander deposition bars are areas where small fish forage on abundant benthic prey and avoid predators (McIvor and Odum…...
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...Although studies of the ecological role of tidal channel sinuosity are rare, dense populations of oysters (Crassostrea virginica) are associated with meander cut banks (Keck et al. 1973), while meander deposition bars are areas where small fish forage on abundant benthic prey and avoid predators (McIvor and Odum 1988)....
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