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: In this paper, a causeway isolating the southern portion of the Sarita River estuary was breached in 2018 to enhance juvenile salmon and tidal water access into the southern part of the estuary.
Abstract: On the west coast of Vancouver Island, Canada, in the Treaty Settlement Lands of the Huu‐ay‐aht First Nation, a causeway isolating the southern portion of the Sarita River estuary was breached in 2018 to enhance juvenile salmon and tidal water access into the southern portion of the estuary. Short‐term goals of breaching were to: (1) enhance juvenile salmon access through the causeway; (2) promote colonization of Chinook and Chum Salmon in pools, while retaining Coho Salmon; (3) monitor the entire estuary fish community, including non‐salmonids, to assess breaching success; and (4) homogenize water chemistry in pool and channel ecosystems currently fragmented by the causeway. Immediately following the breach, both fish community and water chemistry measurements indicate that these goals were achieved. Chinook and Chum Salmon utilization increased inside and outside of the causeway following breaching. Similarly, Chinook and Chum salmon were observed in pool ecosystems, and Coho Salmon were also retained in pools following breaching. Water chemistry was homogenized post‐breach, primarily due to increased saltwater penetration. While continued monitoring is required, short‐term indicators suggest that breaching was effective in increasing connectivity of the Sarita Estuary, allowing access to 1.4 km² of habitat that had previously been inaccessible to juvenile salmon.
6 citations
Cites background from "Indirect Environmental Effects of D..."
...Dikes and causeways fragment estuary habitat, restricting movement of water, nutrients, sediment, animals, and plant propagules (Bray et al. 1982; Roni et al. 2002; Hood 2004; van Proosdij et al. 2009)....
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...However, one of the most obvious forms of human alteration in estuaries are dikes and causeways, built to enhance transportation through estuaries, as well as to convert wetlands/marshlands into habitat more suitable for development or farming (Eertman et al. 2002; Hood 2004)....
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...Removing the barrier, or installing culverts/bridges, can have immediate positive impacts not only upon hydrology and sedimentation within the estuary but also upon plant and animal communities (McAlice & Jaeger 1983; Shreffler et al. 1990; Gray et al. 2002; Hood 2004; Morand & Haralampides 2006)....
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TL;DR: A. insularis is an endangered and endemic goby in the Amami-oshima and Okinawa-jima Islands, southern Japan, and its range is restricted to the lowermost course of a few river basins.
Abstract: The genus Acanthogobius of gobiioid fish has been reported for six species from East Asia, and inhabits estuarine and coastal waters. Within this genus, Acanthogobius insularis is an endangered and endemic goby in the Amami-oshima and Okinawa-jima Islands, southern Japan, and its range is restricted to the lowermost course of a few river basins. Basic knowledge on this species is scarce in spite of its vulnerable conservation status. The purpose of this study was to elucidate the life history of A. insularis. Monthly sampling was conducted at five stations in the Taiho River, Okinawa-jima Island, from November 2014 to November 2015. Monthly standard length (SL) distributions were unimodal except in April during the recruiting period, suggesting that A. insularis is an annual species. Analysis of the gonadosomatic index and histological observations of the ovaries revealed that this species spawns from January to May. The beginning of the spawning season seems to be related to a decline in water temperature in December. Growth rates appeared to be lower from April to December and higher in winter months. From monthly collections, A. insularis was found to move upstream with growth, and gather at spawning grounds during the reproductive season. Acanthogobius insularis might be threatened by increasing water temperature due to climate change, since low water temperatures appear to be important for their reproduction and growth. Moreover, habitat diversity, from tidal flats for recruiting grounds to upstream sites with cobbles for spawning, is needed to complete their life cycle, and should be conserved.
5 citations
Cites background from "Indirect Environmental Effects of D..."
...Hood (2004) and Inui & Koyama (2014) suggested there is a need to take measures to conserve brackish areas, considering the effects of direct anthropogenic activities on habitat loss as well as indirect effects such as habitat changes in the surrounding areas....
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TL;DR: The results from the ecological guild analyses showed distinct ecological roles for freshwater and marine species, and overlapping roles for fish sampled at the fishways, and higher effects of between-site variability but not within seasonal variability at each site were observed.
Abstract: Variabilities of biological communities in lower reaches of urban river systems are highly influenced by artificial constructions, alterations of flow regimes and episodic weather events. Impacts of estuary weirs on fish assemblages are particularly distinct because the weirs are disturbed in linking between freshwater and estuarine fish communities, and migration successes for regional fish fauna. This study conducted fish sampling at the lower reaches of the Nakdong River to assess spatio-temporal variations in fish assemblages, and effects of estuary weir on structuring fish assemblage between freshwater and estuary habitats. In total, 20,386 specimens comprising 78 species and 41 families were collected. The numerical dominant fish species were Tachysurus nitidus (48.8% in total abundance), Hemibarbus labeo (10.7%) and Chanodichthys erythropterus (3.6%) in the freshwater region, and Engraulis japonicus (10.0%), Nuchequula nuchalis (7.7%) and Clupea pallasii (5.2%) in the estuarine site. The fish sampled were primarily small species or the juveniles of larger species at the estuary region, while all life stages of fishes were observed at the freshwater habitats. The diversity patterns of fish assemblages varied greatly according to study site and season, with higher trends at estuarine sites during the warm-rainy season. No significant difference in diversity between freshwater and estuarine sites during the cold-dry season were found. Multivariate analyses of fish assemblage showed spatial and seasonal differences of assemblage structures. Higher effects of between-site variability but not within seasonal variability at each site were observed. Variations in assemblage structures were due to different contributions of dominant species in each habitat. Common freshwater species characterized the fish assemblage in the freshwater region, while marine juveniles were significantly associated with the estuarine habitat. The results from the ecological guild analyses showed distinct ecological roles for freshwater and marine species, and overlapping roles for fish sampled at the fishways. The lower reaches of the Nakdong River are an important ecosystem for both freshwater and marine juveniles. Nakdong River estuarine residents and migrant fishes, however, have been negatively affected by the construction of the weir (gravity dam), due to the obstruction to migration from and to freshwater habitats. Conservation and management policies aimed at minimizing anthropogenic influences on estuary ecosystems should focus on evaluating ecological functions of estuary weirs.
5 citations
TL;DR: In this article, a UAV survey of the Shinsi Tidal Flats was conducted over four years and the results showed that the tidal flats became steepened with net sediment export in the lower intertidal zone, suggesting a reduced sediment supply presumably caused by dike construction.
5 citations
01 Jan 2012
5 citations
References
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Book•
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TL;DR: This book is a blend of erudition, popularization, and exposition, and the illustrations include many superb examples of computer graphics that are works of art in their own right.
Abstract: "...a blend of erudition (fascinating and sometimes obscure historical minutiae abound), popularization (mathematical rigor is relegated to appendices) and exposition (the reader need have little knowledge of the fields involved) ...and the illustrations include many superb examples of computer graphics that are works of art in their own right." Nature
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TL;DR: A blend of erudition (fascinating and sometimes obscure historical minutiae abound), popularization (mathematical rigor is relegated to appendices) and exposition (the reader need have little knowledge of the fields involved) is presented in this article.
Abstract: "...a blend of erudition (fascinating and sometimes obscure historical minutiae abound), popularization (mathematical rigor is relegated to appendices) and exposition (the reader need have little knowledge of the fields involved) ...and the illustrations include many superb examples of computer graphics that are works of art in their own right." Nature
7,560 citations
"Indirect Environmental Effects of D..." refers background in this paper
...Tidal channel allometry follows from a more general fractal theory of landforms (RodriguezIturbe and Rinaldo 1997), and the scaling of perimeter with surface area is a common reflection of landform fractal geometry (Mandelbrot 1983; Sugihara and May 1990)....
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3,626 citations
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TL;DR: Fluvial processes in geomorphology, Fluvial Processes in Geomorphology as discussed by the authors, fluvial processes and geomorphological processes in the field of geology.
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"Indirect Environmental Effects of D..." refers background in this paper
...Greater adjustment in width relative to depth with changing discharge is consistent with hydraulic geometry theory (Leopold et al. 1964)....
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...Because high sinuosity is associated with small channel width relative to depth (Leopold et al. 1964), the observed correlation between changes in sinuosity and in mean channel width suggests that distributary channel widths changed to a greater degree than channel depths....
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...As a final error check, meander bends in tidal channels were examined at scales ranging from 1:1,000 to 1:10,000 to determine whether erosion had occurred in the cut banks of the meanders and sediment deposition at the point bars, in accord with theoretical expectations (Leopold et al. 1964)....
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...Sinuosity was the ratio of sinuous length to straight length (Leopold et al. 1964)....
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