Tidal Flat Area Research Articles

Soldier crab ( Dotilla myctiroides) distribution, food resources and subsequent role in organic matter fate in Ao Tang Khen, Phuket, Thailand

This study aimed to elucidate Dotilla myctiroides (H. Milne-Edwards) food resources and how the soldier crab influences the organic matter composition on the intertidal flat. A preliminary assessment of D. myctiroides size, sex, and population distribution was conducted to clarify the characteristics of the inhabiting population. Overall, D. myctiroides size and abundance was normal across the tidal flat area. Comparison of different sediment types from the soldier crab habitat (surface sediments, igloos, burrow lining, burrow pellets, feeding pellets, and feces) using the fatty acid (FA) analysis technique revealed D. myctiroides removes organic matter via the significantly lower contributions of polyunsaturated FAs, essential FAs, and dinoflagellates in the feeding pellets. Dotilla myctiroides tissue analysis of the hepatopancreas and hindgut in individuals that had been starved for 24 h confirmed not only the consumption of dinoflagellates, but diatoms and macroalgae as well. In addition, the FA metabolism within the digestive system implied the ability of the soldier crab to synthesize highly unsaturated FAs (HUFAs) such as 20:4 n–6, 20:5 n–3 and 22:6 n–3.

Determination of the freshwater budget of tidal flats from measurements near a tidal inlet

The freshwater budget of a tidal flat area is evaluated from long-term hydrographic time series from an observation pole positioned in a tidal channel in the Hörnum Basin (Germany). For each tidal cycle, the freshwater budget is calculated from the total imported and exported water volumes and the corresponding mean densities. The variability of the budget on a tidal scale is characterised by a period of twice the tidal period, exhibiting a minimum when the tidal flats are dry around daylight hours during the foregoing low tide, and a maximum when low tide occurs at night; enhanced evaporation on the flats at daylight hours is identified as the driving process. On the average over one year, while winter observations are missing, the freshwater budget is negative for the years 2002–2005 and positive only for 2006. The interannual mean is negative and amounts to a freshwater loss of about 2 mm day −1, although the large-scale climate in this region is humid. The results demonstrate that the bulk parametrisations for the latent and sensible heat flux between the ocean and the atmosphere must not be applied for the tidelands.

A review on substances and processes relevant for optical remote sensing of extremely turbid marine areas, with a focus on the Wadden Sea

The interpretation of optical remote sensing data of estuaries and tidal flat areas is hampered by optical complexity and often extreme turbidity. Extremely high concentrations of suspended matter, chlorophyll and dissolved organic matter, local differences, seasonal and tidal variations and resuspension are important factors influencing the optical properties in such areas. This review gives an overview of the processes in estuaries and tidal flat areas and the implications of these for remote sensing in such areas, using the Wadden Sea as a case study area. Results show that remote sensing research in extremely turbid estuaries and tidal areas is possible. However, this requires sensors with a large ground resolution, algorithms tuned for high concentrations of various substances and the local specific optical properties of these substances, a simultaneous detection of water colour and land–water boundaries, a very short time lag between acquisition of remote sensing and in situ data used for validation and sufficient geophysical and ecological knowledge of the area.

Remote sensing of intertidal morphological change in Morecambe Bay, U.K., between 1991 and 2007

Tidal Flats are important examples of extensive areas of natural environment that remain relatively unaffected by man. Monitoring of tidal flats is required for a variety of purposes. Remote sensing has become an established technique for the measurement of topography over tidal flats. A further requirement is to measure topographic changes in order to measure sediment budgets. To date there have been few attempts to make quantitative estimates of morphological change over tidal flat areas. This paper illustrates the use of remote sensing to measure quantitative and qualitative changes in the tidal flats of Morecambe Bay during the relatively long period 1991–2007. An understanding of the patterns of sediment transport within the Bay is of considerable interest for coastal management and defence purposes. Tidal asymmetry is considered to be the dominant cause of morphological change in the Bay, with the higher currents associated with the flood tide being the main agency moulding the channel system. Quantitative changes were measured by comparing a Digital Elevation Model (DEM) of the intertidal zone formed using the waterline technique applied to satellite Synthetic Aperture Radar (SAR) images from 1991–1994, to a second DEM constructed from airborne laser altimetry data acquired in 2005. Qualitative changes were studied using additional SAR images acquired since 2003. A significant movement of sediment from below Mean Sea Level (MSL) to above MSL was detected by comparing the two Digital Elevation Models, though the proportion of this change that could be ascribed to seasonal effects was not clear. Between 1991 and 2004 there was a migration of the Ulverston channel of the river Leven north-east by about 5 km, followed by the development of a straighter channel to the west, leaving the previous channel decoupled from the river. This is thought to be due to independent tidal and fluvial forcing mechanisms acting on the channel. The results demonstrate the effectiveness of remote sensing for measurement of long-term morphological change in tidal flat areas. An alternative use of waterlines as partial bathymetry for assimilation into a morphodynamic model of the coastal zone is also discussed.

Continuity and facies heterogeneities of shallow carbonate ramp cycles (Sinemurian, Lower Jurassic, North-east Spain)

The lateral continuity and facies heterogeneities of metre-scale cycles in a greenhouse Lower Jurassic (Sinemurian) carbonate ramp from the northern Iberian Basin (Spain) was evaluated from extensive field analysis carried out on a well-exposed 12 km long outcrop. Eleven high-frequency continuous cycles and their bounding surfaces are traceable laterally through the entire outcrop. However, three of these cycles are found to split laterally into discontinuous cycles of more limited distribution (up to 3 to 5 km of lateral extent). The continuous and discontinuous cycles have a similar field expression in one-dimensional logs. As a consequence, the number of cycles that can be differentiated is variable along the logged sections (i.e. from 11 to 16). Cycles have variable facies heterogeneities and sedimentary trends depending on the environment of formation: shallowing-upward and symmetrical cycles occur in protected lagoon–tidal flat areas and in the open-marine, high-energy domain. These cycles show significant facies heterogeneities, which were controlled mainly by lateral migration of a mosaic of facies over an irregular topography. Deepening-upward and aggradational cycles are generated in low-energy, sub wave-base, open-marine areas. Facies are laterally homogeneous, reflecting low potential for carbonate accumulation and inability to fill the created accommodation space in this low-relief and relatively deep area. Cycle boundaries are generated by stages of rapid accommodation gain, involving the flooding of the carbonate ramp; they are more likely to originate from regional tectonic pulses (related to the extensional tectonics operating in the northern Iberian Basin) rather than greenhouse low-amplitude eustacy. Discontinuous cycles tend to occur in thickened areas and are interpreted as originating from the infill of wedge-shaped accommodation space resulting from differential subsidence (i.e. local tectonic pulses). In conclusion, where thickness variations occur in extensional settings lateral continuity of cycles should not be expected. In less well-exposed, or in one-dimensional sections and in wells, it would not be possible to distinguish continuous from discontinuous cycles, or to understand such two-dimensional heterogeneities. Identification of unique cycle-forming mechanisms or attempting cyclostratigraphic long-distance correlation of cycles is unrealistic without a detailed analysis of the architecture of cycles in laterally continuous outcrops.

Propagation Characteristics of Ulva sp. and Laver in the Yatsu Tidal Flats in Inner Tokyo Bay

The Yatsu Higata wetland is one of the most significant tidal flat areas remaining in Japan. Although the site was officially recognized as an important wetland for migratory bird species in 1993 when it was registered as the Ramsar Convention, the extraordinary growth of Ulva sp. (sea lettuce) in recent years has severely impacted the ecology of the area and has resulted in the widespread death of benthic organisms such as clams and sandworms. Conversely, the crop of laver has decreased along the periphery of the tidal flat area.. This study examined the underlying causes of the increase and decrease in the crops of Ulva sp. and laver populations in the field, respectively. In addition, numerical simulations were performed to estimate the flow movement of Ulva sp. circulating in the inner Tokyo Bay area.

A Teredolites infested fossil wood from the Lower Eocene sediments of the Vastan Lignite Mine of Gujarat, western India

The Vastan Lignite Mine, situated about 30 km northeast of Surat in Gujarat, preserves a fairly continuous record of near shore lignites interbedded with lagoonal and open marine sediments bearing foraminifera and molluscs. This paper reports a teredo-infested fossil dicotyledonous wood belonging to Family Meliaceae from the carbonaceous shale sequence near the top of the Lower Eocene section. The wood is well preserved and shows resemblance with the extant woods of the genus Aglaia Lour. The presence of wood suggests a fluvial transport from its natural habitat of an inland moist tropical forest to a nearby coastal region. The profuse infestation of the wood by teredos further indicates considerable exposure before burial probably in a near shore lagoon or tidal flat area where it was bored by Teredolites.

SPATIO-TEMPORAL DYNAMICS OF COASTAL WETLAND LANDSCAPE PATTERNS IN YANCHENG, JIANGSU PROVINCE

Using the land-use dynamic degree model,conversion matrix and landscape pattern indexes obtained by the RS and GIS,the authors quantitatively analyzed the dynamic process of the coastal wetland landscape pattern in Yancheng city during the past 15 years(from 1992 to 2007).Some conclusions have been reached:(1) Owing to the development of coastal economic and the increasing requirement for land resources,the area proportion of natural landscape in Yancheng coastal zone decreased by 12.63%,while the proportion of man-made landscape rose continuously.(2) The area of original natural landscape types was reduced by 763.62 km2 totally,the number of patches decreased,the total edge shrank,the shape of the patches tended to become more irregular,the preservation ratio became lower,the massive original natural landscape types were converted to the artificial landscape types,and hence the wildlife's habitat decreased badly.During the same period,the area of Spartina alterniflora was expanded,resulting from the initial introduction of 144.92 km2 by 2007,which occupied a large area of tidal flats between the Sheyang river and the Liangduo river in Yancheng coastal zone.(3) The dominant conversion processes indicate that the human reclamation of coastal wetland was enhanced,and the effect of human activities on the change of local environment was also intensified gradually.The achievements in this study can provide scientific basis for the sustainable utilization of land resources and the protection of coastal wetland resources in Yancheng.

The role of crabs ( Macrophthalmus japonicus) burrows on organic carbon cycle in estuarine tidal flat, Japan

The objective of this study is to elucidate the burrow structure and to clarify the role of burrows in material cycle in the tidal flat. In our work, we focused on the dominant species in muddy tidal flat, crab Macrophthalmus japonicus. Burrow structure of Macrophthalmus japonicus was investigated on a Katsuura river tidal flat in Tokushima prefecture, Japan, using in situ resin casting. Sampling was conducted in August 2006, and a total of 48 burrow casts were obtained. Burrows consisted mainly of J-shaped structures (98%) while the rest belonged to U-shaped structures (2%). The maximum measured burrow volume was 120 cm 3 and wall surface area was 224 cm 2, while maximum burrow length and depth were 23.2 cm and 16.5 cm, respectively. Burrow volume and surface area were strongly correlated with carapace width of M. japonicus. Investigation of the individual number of M. japonicus in 13 quadrats (50 × 50 × 20 cm) was conducted using 2 mm sieve. The number of M. japonicus was 15–31 ind./m 2. Using cohort analysis we estimated that surface area of burrows was 0.07–0.15 m 2/m 2. CO 2 emission rate was measured at the surface sediment during the period from June to December 2008. Results varied from 13.8 ± 2.2 to 49.4 ± 3.2 mg CO 2/m 2/h, and organic carbon decomposition was 3.8 ± 0.6–13.5 ± 0.9 mg C/m 2/h. This leads the increase of organic carbon decomposition by 1.1 times, because of the expansion of the tidal flat surface area by burrowing activity. Organic carbon decomposition in burrow walls therefore contributed to organic matter decomposition in the tidal flat. These results indicated that in situ activities of Macrophthalmus japonicus significantly influence the material cycle and it is important to consider the existence of burrow in order to understand the fluxes of materials and to evaluate the purification function of the tidal flat.

The intertidal zoning of cockles (Cerastoderma edule) in the Wadden Sea, or why cockle fishery disturbed areas of relatively high biodiversity

Recently, Kraan et al. (ICES J Mar Sci 64:1735–1742, 2007) reported that areas in the Wadden Sea selected by mechanical cockle dredgers were of greater zoobenthic diversity than areas that remained undredged. The present paper attempts to explain this observation, focussing on the elevation-related zoning of the macrobenthic fauna on tidal flats. Dense beds of cockles Cerastoderma edule occur in a specific intermediate intertidal-height zone where more species are present (and reach their maximal abundance) than in either lower or higher zones. This coincidence of preferred intertidal zones in many species, including cockles, may cause the higher species richness (and higher total macrozoobenthic biomass) of the fisher-chosen dredging areas as compared to other nearby non-dredged tidal-flat areas.

A hydrographic time series station in the Wadden Sea (southern North Sea)

In the tidal inlet between the East Frisian islands of Langeoog and Spiekeroog, southern North Sea, a time-series station was set up in autumn 2002 as part of the research programme BioGeoChemistry of Tidal Flats run by the University of Oldenburg. The purpose of the station is to provide continuous data on physical, biological and chemical parameters. In addition to instruments recording basic hydrographic and meteorological parameters, the time-series station is equipped with acoustic Doppler profilers for measuring surface waves and current profiles. Compact optical spectrometers are being used for spectral measurements of seawater transmission and for daylight reflectance. Additional sensors were installed for measuring oxygen, nutrients and methane in the seawater. The data shall help to quantify the flux of dissolved and suspended matter between the backbarrier tidal flat and the open sea and to characterise the material transformation in the tidal flat area by biogeochemical processes over the tidal cycle. Due to its novel design, operation of the station is also possible during winter and under extreme weather conditions (gales, storm surges, and sea ice) when data sampling with conventional platforms such as research vessels, buoys, or smaller poles could not be performed in the past. In this way, time series of data are obtained, which include events that are most relevant to the evolution of this coastal area. The performance of the station and its equipment are presented with data covering 6 years of operation. Time series of air and water temperature as well as seawater salinity demonstrate the multiyear dynamics of these parameters in the East Frisian Wadden Sea. Hydrographic data collected under specific meteorological conditions such as gales and storm surges exemplify the all-weather capabilities of the station and its value for studying hydrographic processes in the Wadden Sea.

수산부문 저탄소.녹색성장 패러다임

Two of the most important topics of the 21st century are ensuring harmony between man and his environment and the emerging long-tail economy in which niche markets are becoming increasingly more important. Since the Industrial Revolution in 17th century, human beings have increasingly exploited the world's natural capital, such as the natural environment and its ecosystems. Now the world is facing limits to sustainable economic growth because of limits to this natural capital. Thus, most countries are beginning to adopt a new development paradigm, the so-called"Green Development Paradigm" which pursues environmental conservation in parallel with economic growth. Recently, the Korean government announced an ambitious national policy of Low Carbon & Green Growth for the next six decades. This is an important step that transforms the existing national policy into a new future-oriented one. The fisheries sector in particular has great potential for making a substantial contribution to this national policy initiative. For example, the ocean itself with its sea plants and phytoplankton has an enormous capacity for fixing carbon, and its vast areas of tidal flats have a tremendous potential for cleaning up pollutants from both the sea and the land. Furthermore, the fishing industry has great potential for the development of fuel-saving biodegradable technologies, and a long-tail economy based on digital technologies can do much to promote the production and consumption of green goods and services derived from the oceans and the fisheries. In order for this potential to be realized, the fisheries authority needs to develop a new green-growth strategy that is practical and widely supported by fishing communities and the markets, taking into account the need for greenhouse gas reduction, conservation of the ocean environment and ecosystems, an improved system for seafood safety, the establishment of strengthened MCS (monitoring control surveillance) system, and the development of coastal ecotourism. In addition, fisheries green policies need to be implemented through a well-organized system of government aids, regulations and compensation, and spontaneous (voluntary) orders in fishing communities should be promoted to encourage far more responsible fisheries.

Enhanced ocean carbon storage from anaerobic alkalinity generation in coastal sediments

Abstract. The coastal ocean is a crucial link between land, the open ocean and the atmosphere. The shallowness of the water column permits close interactions between the sedimentary, aquatic and atmospheric compartments, which otherwise are decoupled at long time scales (≅ 1000 yr) in the open oceans. Despite the prominent role of the coastal oceans in absorbing atmospheric CO2 and transferring it into the deep oceans via the continental shelf pump, the underlying mechanisms remain only partly understood. Evaluating observations from the North Sea, a NW European shelf sea, we provide evidence that anaerobic degradation of organic matter, fuelled from land and ocean, generates total alkalinity (AT) and increases the CO2 buffer capacity of seawater. At both the basin wide and annual scales anaerobic AT generation in the North Sea's tidal mud flat area irreversibly facilitates 7–10%, or taking into consideration benthic denitrification in the North Sea, 20–25% of the North Sea's overall CO2 uptake. At the global scale, anaerobic AT generation could be accountable for as much as 60% of the uptake of CO2 in shelf and marginal seas, making this process, the anaerobic pump, a key player in the biological carbon pump. Under future high CO2 conditions oceanic CO2 storage via the anaerobic pump may even gain further relevance because of stimulated ocean productivity.

Deep pore water profiles reflect enhanced microbial activity towards tidal flat margins

Microbial activity in permeable tidal flat margin sediments is enhanced by two main processes. First, organic matter is supplied by rapid sedimentation at prograding tidal flat margins. Second, surface and deep pore water advection lead to a replenishment of the dissolved organic matter and sulfate pools. Increasing microbial activity towards the low water line is reflected in sulfate and methane profiles as well as in total cell numbers, sulfate reduction rates, and remineralization products. The impact of high sedimentation rates on pore water biogeochemistry is confirmed by inverse modeling reproducing the depth profiles obtained by measurements. In central parts of the tidal flats, low sedimentation rates and pore water flow velocities limit microbial activity despite the high availability of electron acceptors for microbial respiration such as sulfate. Therefore, tidal flat margins with high microbial activity are of special importance for budgeting biogeochemical cycling in tidal flat areas.

有明海奥部の干潟・浅海域底泥における窒素・リンの季節変化

The seasonal variations of nitrogen and phosphorus in bottom sediments of tidal flat and shallow water areas in the interior parts of the Ariake Sea were investigated during August, 2007-July, 2008. The supply amount of organic matter to sea bottom and sediment temperature had important effects on the seasonal variations of NH4-N in porewater. NO3-N in porewater was significantly influenced by denitrification and NH4-N in porewater that is substrate of nitrification. The seasonal variations of PO4-P in porewater were strongly dependent on those of redox environments in bottom sediment. The release rates of NH4-N and PO4-P were estimated by the diffusion equation. It was found that bottom sediment was an important supply source of NH4-N and PO4-P during summer-autumn.

Methane in the southern North Sea: Sources, spatial distribution and budgets

Measurements of methane (CH 4) so far have always shown supersaturation in the entire North Sea relative to the atmospheric partial pressure and the distribution of surface CH 4 reveals a distinct increase towards the shore. Since North Sea sediments presumably are an insignificant source for CH 4 the coastal contribution via rivers and tidal flats gains in importance. In this work, CH 4 data from the River Weser, the back barrier tidal flats of Spiekeroog Island (NW Germany), and the German Bight are presented. Results from the River Weser are compared to other rivers draining into the German Bight. Measurements in the tidal flat area of Spiekeroog Island highlight this ecosystem as an additional contributor to the overall CH 4 budget of the southern North Sea. A tidally driven CH 4 pattern is observed for the water column with maximum values during low tide. Tidal flat sediments turn out to be the dominating source because pore waters discharged during low tide are highly enriched in CH 4. In contrast, the freshwater contribution to the tidal flats by small coastal tributaries has almost no impact on water column CH 4 concentrations. The CH 4 level seems to be disturbed irregularly by wind forcing due to elevated degassing and prevention of advective flow when tidal flats remain covered by water. Based on our data, two model calculations were used to estimate the impact of tidal flats on the CH 4 budget in the German Bight. Our results demonstrate that the back barrier tidal flats of the east Frisian Wadden Sea contribute CH 4 in an order of magnitude between the Wash estuary and River Elbe and thus have to be considered in budget calculations.

Biofilms in surface sediments of the ephemeral sand bank island Kachelotplate (southern North Sea)

Phototrophic biofilms of the Kachelotplate were studied to assess their role in sediment stabilization. At most sampling stations the surficial sediment was dominated by diatoms with occasional cyanobacterial unicells and filaments interspersed. Coherent mats of filamentous cyanobacteria were found in protected parts of the upper intertidal zone, while the central dune field and foreshore sediments were only rarely colonized. Photosynthetic activity was indicated by iron hydroxide coatings of sand grains below the biofilms. Temporal changes in the distributional record of biofilm phototrophs suggested disturbances by aeolian processes and strong hydrodynamic events. Heavy storm surges and floods erode the central dune field, and also transported sediments towards East into the more sheltered tidal flat area. This results in changing of topographic reliefs, filling-up of sheltered depressions formerly good for mat development and altering of surface habitats for biofilm growth. Aeolian transport of sediment into the biofilm-stabilized tidal flats occurs more or less permanently throughout the year. The sedimentological importance of surface biofilms is demonstrated by their capability to intervene with erosion and sedimentation processes by trapping and binding sediment particles, and by the production of organic matter which gradually alters internal biogeochemistry. After burial, mat-derived strata represent obstacles to interstitial hydrology and fluxes of elements-enriched porewater. Considering the dynamically exposed transitional state of the Kachelotplate from an ephemeral sand bank island to part of a barrier island, the dynamic shifts of habitats favorable for biofilm growth should carefully be monitored.

Morphological evolution of the Dee Estuary, Eastern Irish Sea, UK: A tidal asymmetry approach

Asymmetry in the tide (unequal ebb and flood duration) is a dominant factor in causing residual sediment transport and morphological changes in estuaries. The evolution of estuarine morphology is a process of dynamic equilibrium in the short-term, while these features are ephemeral in the long-term. In this study we investigate the spatial distribution of tidal distortion and asymmetry in the Dee estuary, UK, by 3-dimensional numerical modelling methods. High resolution LIDAR surveys are used to underpin and explain our numerical modelling results in terms of basin hypsometry and areas of recent erosion and deposition. Harmonic analysis of the numerical modelling results showed that the shallower intertidal areas (sand and mud banks) were the most tidally asymmetric, showing flood dominance. The main navigation channels showed some ebb dominance but the tides here were relatively undistorted. This overall flood dominance is likely to induce net sediment import to the Dee, which explains known historical morphological changes (large scale accretion over the last two centuries) and also recent morphological changes as seen from the LIDAR surveys (which show predominantly net accretion between 2003 and 2006). Hypsometrical analysis suggests the Dee may be approaching equilibrium, and that the flood dominance and sedimentation rate may therefore decrease in the future. In an infilling estuary, an increase in the area and elevation of tidal flats can eventually shift an estuary towards ebb dominance, as shown by previous research and by ‘idealised estuary’ modelling results presented in this study. The large tidal amplitude to hydraulic depth ratio of the Dee, however, suggests that the tidal flats would have to be very extensive indeed for this to occur.

A benthic–pelagic coupled ecosystem model to estimate the hypoxic estuary including tidal flat—Model description and validation of seasonal/daily dynamics

A new ecosystem model – the Ecological Connectivity Hypoxia Model (ECOHYM) – was developed and applied to Tokyo Bay, a hypoxic estuary in Japan. ECOHYM permits study of the dynamics and mechanisms of hypoxia from two perspectives: (1) the whole estuary, composed of temporal-spatial mutual linkage of benthic–pelagic or central bay-tidal flat ecosystems (holistic approach), and (2) each biochemical and physical process, contributing to oxygen production/consumption (elemental approach). ECOHYM evaluates the oxygen–carbon–nitrogen–phosphorus-coupled cycle driven by physical and biochemical processes. The processes mechanically describe the ecosystem network consisting of benthic–pelagic and central bay–tidal flat ecosystem coupling. The model also describes the early diagenetic processes of the benthic ecosystems by setting a micro-scale vertical spatial resolution due to the drastic vertical change of benthic biological metabolism and its high contribution to total oxygen consumption. Model variables were mainly selected based on low trophic level; namely, phytoplankton, zooplankton, detritus, dissolved organic matter, NH 4–N, NO 3–N, PO 4–P, benthic algae, suspension feeders, deposit feeders (benthic faunas), dissolved oxygen (DO) and oxygen demand units (ODU, representing the stoichiometric expression of Mn 2+, Fe 2+ and S 2− oxygen demand). Detritus was divided into fast-labile, slow-labile and refractory parts. Bacterial mineralization processes were divided into oxic, suboxic and anoxic fractions. The model was applied for a time frame of 100 years under seasonal forcing functions to achieve an annual periodical steady state. The model results revealed that the seasonal dynamics were more noticeable than the daily/tidal dynamics in the central bay area. In contrast, the daily/tidal dynamics were determinant in the tidal flat area. Calculated seasonal dynamics in the central bay and daily/tidal dynamics in the tidal flat were in good agreement with the observed data. In particular, the model succeeded in reproducing the following vertical DO profiles during the hypoxic season (summer): (1) high oxygen at the sea-surface and hypoxia at the sea-bottom in the central bay area, (2) the reduced thickness of the benthic oxic layer in the central bay area, and (3) the drastic change of DO micro-profiles between daytime and nighttime of the benthic system in the tidal flat areas. Oxygen fluxes at the sediment–water interface in the model also reproduced the in situ observed values both in the central bay and tidal flat areas.

英虞湾における干潟の歴史的変遷とその底質，底生生物への影響

The total areas of the existing natural and reclaimed tidal flat in Ago Bay were estimated by multispectrum aerial picture analysis. Approximately 70% of the tidal flat and shallow areas have already been lost because of land reclamation and dyke construction. The sediment quality and characteristics of macrobenthos in the natural tidal flats (estuary, in front of and behind the dykes) were investigated in this study. The macrobenthos in the natural tidal flat in front of and behind the dyke was poor in organic matter, because these sediments were relatively oligotrophic in front of the dyke and hypertrophic behind the dyke. Thus it is considered that the reclamation by constructing the dykes was one of the major causes of the deterioration of the benthic ecosystem and decrease in the biological productivity of Ago Bay.