embayment

湾形成

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2012/08/13 09:04:52」(JST)

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Main articles: Bay and Headland

Looking towards the Beachy Head cliffs and bay

Headlands and bays are two related features of the coastal environment.

Geology and geography

Headlands and bays are often found on the same coastline. A bay is surrounded by land on three sides, whereas a headland is surrounded by water on three sides. Headlands are characterized by high, breaking waves, rocky shores, intense erosion, and steep sea cliffs. Bays generally have less wave (and often wind) activity than the water outside the bay, and typically have sandy beaches. Headlands and bays form on discordant coastlines, where bands of rock of alternating resistance run perpendicular to the coast. Bays form where weak (less resistant) rocks (such as sands and clays) are eroded, leaving bands of stronger (more resistant) rocks (such as chalk, limestone, granite) forming a headland, or peninsula. This difference in the rate of erosion is caused by differential erosion. Refraction of waves occurs on headlands concentrating wave energy on them, so many other landforms, such as caves, natural arches and stacks, form on headlands. Wave energy is directed at right angles to the wave crest and lines drawn at right angles to the wave crest (orthogonals) represent the direction of energy expenditure. Orthogonals converge on headlands and diverge in bays which concentrates wave energy on the headlands and dissipating wave energy in the bays.^[1] In the formation of sea cliffs, wave erosion undercuts the slopes at the shoreline and they retreat landward. This increases the shear stress in the cliff-forming material and accelerates mass movement.^[1] The debris from these landslides collects at the base of the cliff and are also removed by the waves, usually during storms where wave energy is greatest. This debris provides sediment, transported through longshore current for the nearby bay. Joints in the headlands are eroded back to form caves which erode further to form arches. These gaps eventually collapse and leave tall stacks at the ends of the headlands. Eventually these too are eroded by the waves.^[2] Wave refraction disperses wave energy through the bay, and along with the sheltering effect of the headlands this protects bays from storms. This effect means that the waves reaching the shore in a bay are weaker than the waves reaching the headland and the bay is thus a safer place for water activities like surfing or swimming. Through the deposition of sediment within the bay and the erosion of the headlands, coastlines eventually straighten out then start the same process all over again.

Beach stability

Beaches are dynamic geologic features that can fluctuate between advancement and retreat of sediment. The natural agents of fluctuation include waves, tides, currents, and winds. Man-made elements such as the interruption of sediment supply, such as a dam, and withdrawal of fluid can also affect beach stabilization.^[3] A headland bay beach can be classified as being in three different states of sedimentation. Static equilibrium refers to a beach that is stable and does not experience littoral drift or sediment deposition or erosion.^[4] Waves generally diffract around the headland(s) and near the beach when the beach is in a state of static equilibrium. Dynamic equilibrium occurs when the beach sediments are deposited and eroded at approximately equal rates.^[4] Beaches that have dynamic equilibrium are usually near a river that supplies sediment and would otherwise erode away without the river supply. Unstable beaches are usually off the ocean have little land extending into it.

Notes

^ ^a ^b Easterbrook, D. (1999). "Surface Processes and Landforms: Second Edition". Prentice Hall].
^ Link test.
^ Schwartz, M. (2005). "Encyclopedia of Coastal Science" . Springer. ISBN 978-1-4020-1903-6 p399
^ ^a ^b Benedet, L., Klein, A., and Hsu, J. (2004). "Practical Insights and Applications of Empirical Bay Shape Equations". ICCE.

External links

GeoResources - diagrams of headland and bay formation

English Journal

Assessment of sediment quality in Avicennia marina-dominated embayments of Sydney Estuary: The potential use of pneumatophores (aerial roots) as a bio-indicator of trace metal contamination.

Nath B1, Birch G2, Chaudhuri P3.Author information 1School of Geosciences, University of Sydney, Sydney, NSW 2006, Australia. Electronic address: bibhash.nath@sydney.edu.au.2School of Geosciences, University of Sydney, Sydney, NSW 2006, Australia.3School of Geosciences, University of Sydney, Sydney, NSW 2006, Australia; Department of Environmental Science, University of Calcutta, Kolkata 700 019, India.AbstractCurrently, coastal intertidal environments are under stress from increased contaminant loads due to urbanization and other anthropogenic disturbances. Mangrove habitats are abundant in tropical and sub-topical intertidal zones and frequently act as a metal bio-filter in estuarine systems. Mangrove reforestation is often considered as one of the management options to protect estuarine-marine habitats. The main objective of the present investigation was to assess the bio-indicator potential of Avicennia marina by determining heavy metal concentrations in pneumatophore (aerial root) tissues and ambient sediments from Sydney Estuary (Australia). We collected mangrove sediments and pneumatophores in fifteen locations covering five major embayments of the estuary for a detailed biogeochemical investigation. Metal concentrations in sediment were mostly above Australian interim sediment quality guidelines (ISQG)-Low and in few instances above ISQG-High values. Enrichment factors (EFs >6, especially of Cu, Pb and Zn) suggest "very severe" modification of sediment in Sydney Estuary in all but one embayment which was mainly due to rapid changes in land use in connection with urbanization. High bio-concentration factors (BCFs) were observed for Cu and Ni in comparison with other metals (i.e., As, Cd, Co, Cr, Pb and Zn). A strong, positive relationship between metals in sediments and pneumatophores suggests potential use of these tissues as a bio-indicator of estuarine contamination and that metals are entering the biotic environment. The study further highlights a positive role of mangroves in sequestering metals from sediments and the water column and thus protecting estuarine environments from pollution.
The Science of the total environment.Sci Total Environ.2013 Dec 14;472C:1010-1022. doi: 10.1016/j.scitotenv.2013.11.096. [Epub ahead of print]
Currently, coastal intertidal environments are under stress from increased contaminant loads due to urbanization and other anthropogenic disturbances. Mangrove habitats are abundant in tropical and sub-topical intertidal zones and frequently act as a metal bio-filter in estuarine systems. Mangrove r
PMID 24345861

A Quantitative Assessment of the Role of the Parasite Amoebophrya in the Termination of Alexandrium fundyense Blooms within a Small Coastal Embayment.

Velo-Suárez L, Brosnahan ML, Anderson DM, McGillicuddy DJ Jr.Author information Department of Applied Ocean Physics and Engineering, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, United States of America ; Department Dynamiques de l'Environnement Côtier, Institut Français de Recherche pour l'Exploitation de la MER, Plouzané, France.AbstractParasitic dinoflagellates of the genus Amoebophrya infect free-living dinoflagellates, some of which can cause harmful algal blooms (HABs). High prevalence of Amoebophrya spp. has been linked to the decline of some HABs in marine systems. The objective of this study was to evaluate the impact of Amoebophrya spp. on the dynamics of dinoflagellate blooms in Salt Pond (MA, USA), particularly the harmful species Alexandrium fundyense. The abundance of Amoebophrya life stages was estimated 3-7 days per week through the full duration of an annual A. fundyense bloom using fluorescence in situ hybridization coupled with tyramide signal amplification (FISH- TSA). More than 20 potential hosts were recorded including Dinophysis spp., Protoperidinium spp. and Gonyaulax spp., but the only dinoflagellate cells infected by Amoebophrya spp. during the sampling period were A. fundyense. Maximum A. fundyense concentration co-occurred with an increase of infected hosts, followed by a massive release of Amoebophrya dinospores in the water column. On average, Amoebophrya spp. infected and killed ∼30% of the A. fundyense population per day in the end phase of the bloom. The decline of the host A. fundyense population coincided with a dramatic life-cycle transition from vegetative division to sexual fusion. This transition occurred after maximum infected host concentrations and before peak infection percentages were observed, suggesting that most A. fundyense escaped parasite infection through sexual fusion. The results of this work highlight the importance of high frequency sampling of both parasite and host populations to accurately assess the impact of parasites on natural plankton assemblages.
PloS one.PLoS One.2013 Dec 4;8(12):e81150. doi: 10.1371/journal.pone.0081150.
Parasitic dinoflagellates of the genus Amoebophrya infect free-living dinoflagellates, some of which can cause harmful algal blooms (HABs). High prevalence of Amoebophrya spp. has been linked to the decline of some HABs in marine systems. The objective of this study was to evaluate the impact of Amo
PMID 24324668

Predictors of mercury spatial patterns in San Francisco Bay forage fish.

Greenfield BK, Slotton DG, Harrold KH.Author information San Francisco Estuary Institute, Richmond, California, USA; Environmental Health Sciences Division, School of Public Health, University of California, Berkeley, California, USA.AbstractPollution reduction efforts should be targeted toward those sources that result in the highest bioaccumulation. For mercury (Hg) in estuaries and other complex water bodies, carefully designed biosentinel monitoring programs can help identify predictors of bioaccumulation and inform management priorities for source reduction. This study employed a probabilistic forage fish Hg survey with hypothesis testing in San Francisco Bay (California, USA). The goal was to determine what pollution sources, regions, and landscape features were associated with elevated Hg bioaccumulation. Across 99 sites, whole-body Hg concentrations in Mississippi silversides (Menidia audens) and topsmelt (Atherinops affinis) followed a broad spatial gradient, declining with distance from the Guadalupe River (Pearson's r = -0.69 and -0.42, respectively), which drains historic mining areas. Site landscape attributes and local Hg sources had subtle effects, which differed between fish species. Topsmelt Hg increased in embayment sites (i.e., enclosed sites including channels, creek mouths, marinas, and coves) and sites with historic Hg-contaminated sediment, suggesting an influence of legacy industrial and mining contamination. In 2008, Mississippi silverside Hg was reduced at sites draining wastewater-treatment plants. Fish Hg was not related to abundance of surrounding wetland cover but was elevated in some watersheds draining from historic Hg-mining operations. Results indicated both regional and site-specific influences for Hg bioaccumulation in San Francisco Bay, including legacy contamination and proximity to treated wastewater discharge. Environ Toxicol Chem 2013;32:2728-2737. © 2013 SETAC.
Environmental toxicology and chemistry / SETAC.Environ Toxicol Chem.2013 Dec;32(12):2728-37. doi: 10.1002/etc.2335.
Pollution reduction efforts should be targeted toward those sources that result in the highest bioaccumulation. For mercury (Hg) in estuaries and other complex water bodies, carefully designed biosentinel monitoring programs can help identify predictors of bioaccumulation and inform management prior
PMID 23893557

Japanese Journal

調査観測兼清掃船「海輝」「海煌」による八代海の海域環境特性の把握

土木学会論文集B3（海洋開発） 71(2), I_491-I_496, 2015
NAID 130005097518

SEASONAL CHANGES IN BODY SIZE AND OIL SAC VOLUME OF THREE PLANKTONIC COPEPODS, PARACALANUS PARVUS (CLAUS, 1863), PSEUDOCALANUS NEWMANI FROST, 1989 AND OITHONA SIMILIS CLAUS, 1866, IN A TEMPERATE EMBAYMENT: WHAT CONTROLS THEIR SEASONALITY?

Crustaceana 87(3), 364-375, 2014-03
NAID 120005446628

二つの繋がった汽水湖における湖底堆積物からの窒素，リン及びDOCの回帰速度からみた水域の特性評価

陸水学雑誌 76(1), 35-44, 2014
NAID 130005121668

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