Mangrove forest decline: consequences for livelihoods and environment in South Sulawesi

Mangrove forests in the tropics and subtropics grow in saline sediments in coastal and estuarine environments. Preservation of mangrove forests is important for many reasons, including the prevention of coastal erosion and seawater intrusion; the provision of spawning, nursery, and feeding grounds of diverse marine biota; and for direct use (such as firewood, charcoal, and construction material)—all of which benefit the sustainability of local communities. However, for many mangrove areas of the world, unsustainable resource utilization and the profit orientation of communities have often led to rapid and severe mangrove loss with serious consequences. The mangrove forests of the Takalar District, South Sulawesi, are studied here as a case area that has suffered from degradation and declining spatial extent during recent decades. On the basis of a post-classification comparison of change detection from satellite imagery and a survey of households, we provide an estimate of the mangrove change in the Takalar District during 1979–2011 and the consequences of those changes. Mangrove forest areas were reduced by 66.05 % (3344 hectares) during the 33-year period of analysis, and the biggest annual negative change in dense mangrove forest cover (8.37 %) occurred during the period 2006–2011. The changes were caused mainly by the mangrove clearing and conversion to aquaculture, and consequences have been increasing forest degradation, coastal abrasion, seawater intrusion, a decline in fish capture, a reduction in juvenile shrimp and milkfish, and outbreaks of shrimp disease. On the other hand, the clearing and impoundment of mangrove forests for shrimp and seaweed culture have provided a source of foreign exchange and new opportunities for employment in the study area.     

Coastal vulnerability assessment of the predicted sea level rise in the coastal zone of Krishna–Godavari delta region,Andhra Pradesh,east coast of India

The Krishna–Godavari coastal region in east coast of India has a 525.15-km-long coastline with low-lying tidal mudflats, beaches, mangrove swamp, creek and tidal channels. Recently, the increasing frequency of tropical cyclones in the Bay of Bengal, i.e., Phylin and Hudhud in Andhra Pradesh coast, and the devastating impact of the 2004 tsunami in India increased the significance in assessing the vulnerability of the coastal lands to inundation and flooding, notably in the context of climate change-induced sea level rise. This study aims to estimate a coastal vulnerability index (CVI) for the coastal subregion of Krishna–Godavari delta and to use the calculated index to evaluate the vulnerability of 14 coastal talukas of the Krishna–Godavari delta region. This CVI is calculated by using four geological and three physical parameters characterizing the vulnerability of the study coastal region, including regional slope, coastal elevation, geomorphology, significant wave height, mean tidal range and relative sea level using different conventional and remotely sensed data. Using a composite coastal vulnerability index based on the relative risk rating of those parameters, each of the 14 coastal talukas was classified according to their vulnerability. The CVI results depict that coasts are least and most vulnerable to inundation, flooding and erosion of coastal lands where geological parameters are more efficient to CVI. The paper alerts to decision makers and planners to mitigate the natural disaster and manage the coastal zone and is a primary step toward prioritizing coastal lands for climate change adaptation strategies in the view of increased storminess and projected sea level rise.     

中国海岸湿地环境特点与开发利用

海岸湿地是由低地、滩涂与生物群落组合的海岸环境。中国海岸湿地环境受季风波浪、潮汐与大河影响的河海交互作用为特征,地跨39个纬度带,其面积约占中国湿地总面积的1/5。按成因与表相可分为：河口芦苇、草滩湿地,平原海岸草滩盐沼湿地及在华南隐蔽港湾顶部红树林沼泽湿地3种类型。均具有潮上带、潮间带与潮下带分带特性。海岸湿地是珍贵的新生空间资源,但由于滥伐垦殖、外来生物种属入侵危害、陆源水沙减少及海平面上升招致海岸侵蚀、盐潮入侵与内涝频繁等灾害影响,海岸湿地环境质量下降,面临着解决海岸湿地生态保护与沿海人民生计这一新生矛盾问题。需沿流域进行陆海结合的系统研究与对比总结,找出湿地保护与开发的临界度,全面规划实施。     

Efficiency in heavy metal purge in crustaceans during the ecdysis

Environment, Development and Sustainability - An abundant population of Ucides cordatus swamp crabs is present at Lameirão Ecological Station (Brazil), a tropical ecosystem man-made with...     

The influence of socioeconomic, environmental, and demographic factors on municipality-scale land-cover change in Mexico

Land-cover change is the result of complex multi-scale interactions between socioeconomic, demographic, and environmental factors. Demographic change, in particular, is thought to be a major driver of forest change. Most studies have evaluated these interactions at the regional or the national level, but few studies have evaluated these dynamics across multiple spatial scales within a country. In this study, we evaluated the effect of demographic, environmental, and socioeconomic variables on land-cover change between 2001 and 2010 for all Mexican municipalities (n?=?2,443) as well as by biome (n?=?4). We used a land-cover classification based on 250-m MODIS data to examine the change in cover classes (i.e., woody, mixed woody, and agriculture/herbaceous vegetation). We evaluated the trends of land-cover change and identified the major factors correlated with woody vegetation change in Mexico. At the national scale, the variation in woody vegetation was best explained by environmental variables, particularly precipitation; municipalities where woody cover increased tended to be in areas with low average annual precipitation (i.e., desert and dry forest biomes). Demographic variables did not contribute much to the model at the national scale. Elevation, temperature, and population density explained the change in woody cover when municipalities were grouped by biome (i.e., moist forest, dry forest, coniferous forest, and deserts). Land-cover change at the biome level showed two main trends: (1) the tropical moist biome lost woody vegetation to agriculture and herbaceous vegetation, and (2) the desert biome increased in woody vegetation within more open-canopy shrublands.     

Analyzing coastal wetland change in the Yancheng National Nature Reserve,China

Coastal zones provide habitat cores and corridors that maintain the diversity of entire landscapes, and they can form the cornerstone elements of regional conservation strategies. Natural environmental driving factors and excessive anthropogenic activities play important roles in coastal wetland change. Many studies have used remote sensing images to map and assess coastal wetland change on local or regional scales. This paper aims to provide insight into coastal wetland change in the Yancheng National Nature Reserve (YNNR) using remote sensing technology and landscape metrics analysis. The results reveal that grass flat and reed areas have significantly decreased, whereas agriculture fields, aquaculture ponds and built-up areas have continuously increased from 1988 to 2006. The spatial pattern of the coastal landscape has become fragmented and heterogeneous under great pressure from rapid economic development and population growth. The wetland changes have important impacts on natural habitat of the red-crowned cranes. The results of this study provide basic information that is required for developing measures toward a sustainable management and conservation of the YNNR.     

The Use of Remote Sensing and GIS in the Sustainable Management of Tropical Coastal Ecosystems

The sustainable use and management of important tropical coastal ecosystems (mangrove forests, seagrass beds and coral reefs) cannot be done without understanding the direct and indirect impacts of man. The ecosystem's resilience and recovery capacity following such impacts must be determined. The efficacy of mitigation measures must also be considered. Remote sensing and geographic information systems (GIS) are excellent tools to use in such studies. This paper reviews the state of the art and application of these tools in tropical coastal zones, and illustrates their relevance in sustainable development. It highlights a selected number of remote sensing case-studies on land cover patterns, population structure and dynamics, and stand characteristics from South-East Asia, Africa and South-America, with a particular emphasis on mangroves. It further shows how remote sensing technology and other scientific tools can be integrated in long-term studies, both retrospective and predictive, in order to anticipate degradation and to take mitigating measures at an early stage. The paper also highlights the guidelines for sustainable management that can result from remote sensing and GIS studies, and identifies existent gaps and research priorities.There is a need for more comprehensive approaches that deal with new remote sensing technologies and analysis in a GIS-environment, and that integrate findings collected over longer periods with the aim of prediction. It is also imperative to collect and integrate data from different disciplines. These are essential in the spirit of sustainable development and management, particularly in developing countries, which are often more vulnerable to environmental degradation.     

Community-based natural resources management (CBNRM) in Xinhui, Guangdong Province, China

Using institutional appraisal focused groups (FG) and participatory appraisals with Dillman Total Design Method (TDM), this study examines community interaction with and utilization of wetland resources in Xinhui, Guangdong Province, China. Field results show high commercial activities and corresponding impacts on coastal environment. Other interacting factors identified include: legislation and ecosystem management, stakeholders’ participation, international guidelines criteria, and utilization of mangrove resources in the region. Sensitivity index and community-based natural resources management collaboration comparison percentile showed significant differences between cumulative distributions of respondents (D = 0.2568, P = 0.078). Likert statement of 11 sensitivity optional indexes in EMS of K–S test at 0.05 level of P = 0.078 also show significant differences in interaction between respondent groups and sensitivity factors. This indicates a dysfunction between regional environmental management systems and CBNRM in Xinhui coastal district. Considering the high tourism potential and economic quest of the region, there is the need for coordinated community enlightenment and further studies on the social, ecological and economic value of wetland resources. Readers should send their comments on this paper to: BhaskarNath@aol.com within 3 months of publication of this issue.     

Economic,equitable, and affordable adaptations to protect coastal settlements against storm surge inundation

The distribution of risk of coastal inundation, and the potential benefits of adapting to protect against inundation, vary greatly both within and between coastal communities. This diversity is a result of physical factors, such as the risk of storm surge, sea level rise projections, and the topography of the landscape, as well as socio-economic factors, such as the level of development, and the capacity within the community to adapt. Despite this strong local variation, various communities share common characteristics that constrain or enable different adaptation options in different situations. Understanding these drivers is likely to be important in engaging coastal communities in the discussion around adaptation and may provide new insights into which adaptation options are suitable for each of our at-risk coastal communities. We performed a property-level analysis of 6 suburb-sized case studies distributed along the coast of Queensland, Australia. We assessed the potential economic costs of inundation events now and in the future under sea level rise projections, and the potential avoided costs following adaptation to protect against inundation. We went beyond this to estimate the distribution of risk in each community and compared the potential costs of adaptation with the capacity of the community to pay for their implementation. We used these insights to propose a typology of coastal communities based on their exposure to total inundation risk, the distribution of that risk within the community, and their capacity to adapt.     

厦门海岸带湿地变化的研究

通过“压力-状态-响应”分析模型，对厦门海岸带湿地变化的主要原因（压力）、成分退化和结构改变（状态）以及对厦门海岸带生态系统的主要影响（响应力）之间的作用机制进行了探讨。提出厦门海岸带湿地面临的主要压力来自海岸带围垦造地、近海滩涂养殖和九龙江河口输入；状态变化突出表现在浅海海域面积的减少。红树林的面积减少。近岸泥沙淤积。沉积物类型改变和沉积物污染；主要影响是造成厦门海域水质下降、近海底橙生物类型改变、航道泥沙淤积、水产养殖产量下降和珍稀海洋物种分布和数量改变。     

Heading for the hills: climate-driven community relocations in the Solomon Islands and Alaska provide insight for a 1.5 °C future

Whilst future air temperature thresholds have become the centrepiece of international climate negotiations, even the most ambitious target of 1.5 °C will result in significant sea-level rise and associated impacts on human populations globally. Of additional concern in Arctic regions is declining sea ice and warming permafrost which can increasingly expose coastal areas to erosion particularly through exposure to wave action due to storm activity. Regional variability over the past two decades provides insight into the coastal and human responses to anticipated future rates of sea-level rise under 1.5 °C scenarios. Exceeding 1.5 °C will generate sea-level rise scenarios beyond that currently experienced and substantially increase the proportion of the global population impacted. Despite these dire challenges, there has been limited analysis of how, where and why communities will relocate inland in response. Here, we present case studies of local responses to coastal erosion driven by sea-level rise and warming in remote indigenous communities of the Solomon Islands and Alaska, USA, respectively. In both the Solomon Islands and the USA, there is no national government agency that has the organisational and technical capacity and resources to facilitate a community-wide relocation. In the Solomon Islands, communities have been able to draw on flexible land tenure regimes to rapidly adapt to coastal erosion through relocations. These relocations have led to ad hoc fragmentation of communities into smaller hamlets. Government-supported relocation initiatives in both countries have been less successful in the short term due to limitations of land tenure, lacking relocation governance framework, financial support and complex planning processes. These experiences from the Solomon Islands and USA demonstrate the urgent need to create a relocation governance framework that protects people’s human rights.     

A bibliometric analysis of tropical mangrove forest land use change from 2010 to 2020

Environment, Development and Sustainability - Mangrove land use changes of varied intensities have long been a problem in tropical mangrove forests. This has resulted in various degrees of mangrove...     

Using sustainability science to analyse social–ecological restoration in NE Japan after the great earthquake and tsunami of 2011

In the wake of the catastrophic earthquake and tsunami that devastated part of northeastern Japan in March 2011, proposals for reconstruction and rehabilitation are still subjects of debate. The claim by many climate scientists that large-scale extreme events can be expected in the future, with similar catastrophic effects in coastal areas, suggests the need for long-term planning that aims at building resilience, the ability for socio-ecological systems to withstand and recover quickly from natural disasters, and continue to develop. We hypothesize that ecosystems and socio-economic resilience will provide affected communities with flexible barriers against future disasters and greater protection in the long run than will hard/engineering solutions such as high seawalls aimed at ensuring only physical security. Building social/ecological resilience in the Tohoku region will increase general security and is anticipated also to contribute to an enhanced quality of life now and for generations to come. This paper argues that building resilience in the affected area requires a transformation to sustainable agriculture, forestry and fisheries and we describe how the links between satoyama and satoumi, traditional rural territorial and coastal landscapes in Japan, can contribute to this revitalization and to strengthening the relationship between local residents and the landscape in the affected communities. Decision makers at local, regional and national levels need to take a holistic approach based on sustainability science to understand the inter-relationships between these landscapes and ecosystems to develop a robust rebuilding plan for the affected communities. Moreover, this paper suggests that building resilient communities in Japan that demonstrate the strategic benefits of satoyama and satoumi linkages can be a model for building resilient rural and urban communities throughout the world.     

Vegetation of Northeast China during the late seventeenth to early twentieth century as revealed by historical documents

Historical vegetation antedates current anthropogenic land use. It can therefore be used to reveal land use/cover changes due to human activities. We collected 197 records from Chinese historical documents, including gazettes, government files, private literature, and travel notes, to reveal vegetation status during the late seventeenth century to early twentieth century across Northeast China. The results indicate that woodland and grassland were the dominant landscapes, whereas swamps accounted for a small area. Woodland was composed of needleleaf deciduous forest, broadleaf deciduous forest, and mixed needleleaf and broadleaf forest. Mixed forest occupied the largest area. This forest type covered most of the Greater Khingan Range, Lesser Khingan Range, and Changbai Mountains. Grassland occupied the Songnen Plain, Liao River Plain, and Inner Mongolia Plateau, whereas swamps covered nearly the entire Sanjiang Plain. In addition, the data revealed that most current cropland was converted from grassland in the Northeast Plain, whereas a small area of cropland was converted from woodland and swamp.     

Detecting spatiotemporal change of land use and landscape pattern in a coastal gulf region,southeast of China

Geographic information system (GIS), remote sensing (RS), gradient analysis, and landscape pattern metrics were coupled to quantitatively characterize the spatiotemporal change of land use and landscape pattern over the period 1988–2007 in a coastal gulf region, southeast China. The results obtained show an increase in cropland, buildup land, and aquiculture area and decrease in orchard, woodland, and beach area during 1988–2007. Landscape fragmented processes were strengthened and landscape pattern structure became more complicated in the last two decades in Luoyuan gulf region. The dynamics intensity of landscape pattern is stronger during 2002–2007 than that during 1988–2002. Spatial difference of urban–rural landscape pattern can be detected distinctively in two transects in terms of landscape metrics. Urbanization processes and the policy developed to transfer seawater into buildup land are two driving forces leading to the spatiotemporal change of landscape pattern in Luoyuan gulf region in the last two decades.     

Potentials and impacts of short-rotation coppice plantation with aspen in Eastern Germany under conditions of climate change

Woody biomass generated in short-rotation coppice (SRC) plantations with aspen (Populus tremula L.) has good properties for bioenergy crop production: annual yields are high, labour input per year is low, and it is ecologically valuable because of the multi-year rotation periods. Eastern Germany has a special advantage in producing bioenergy crops: the former “agricultural cooperatives” built up quite large farms with, compared to Western Germany, comparatively large fields. Therefore, a modelling study of the potential and the impacts of aspen SRC plantations in the five eastern federal states of Germany under the recent climate and future climate projections was conducted. The ecophysiological forest growth model 4C was used to simulate the growth of aspen SRC plantations and their impacts on carbon in soils, and groundwater recharge, on selected suitable areas currently under crops but with marginal site conditions for cropping. A clear signal to enhanced growth condition over the whole area can be seen in the simulation of the mean annual woody biomass yield under conditions of climate change, which increased from 7.47 t DW ha⁻¹ a⁻¹ under the recent climate to 9.26 t DW ha⁻¹ a⁻¹ at the end of the considered future period 2034–2055 under climate change. The mean soil carbon sequestration rate was 0.81 t C ha⁻¹ a⁻¹ under the recent climate and could rise up to 0.93 t C ha⁻¹ a⁻¹ under the assumption of climate change. On the other hand, the mean annual percolation rate, used as an indicator of impacts on the regional water budget, will diminish under future climatic conditions. The results suggest that aspen SRC plantations are a suitable contribution to regional CO₂ mitigation and carbon sequestration under possible change of climate, but that negative impacts on the regional water budget are possible.     

Co-evolution of wetland landscapes,flooding, and human settlement in the Mississippi River Delta Plain

River deltas all over the world are sinking beneath sea-level rise, causing significant threats to natural and social systems. This is due to the combined effects of anthropogenic changes to sediment supply and river flow, subsidence, and sea-level rise, posing an immediate threat to the 500–1,000 million residents, many in megacities that live on deltaic coasts. The Mississippi River Deltaic Plain (MRDP) provides examples for many of the functions and feedbacks, regarding how human river management has impacted source-sink processes in coastal deltaic basins, resulting in human settlements more at risk to coastal storms. The survival of human settlement on the MRDP is arguably coupled to a shifting mass balance between a deltaic landscape occupied by either land built by the Mississippi River or water occupied by the Gulf of Mexico. We developed an approach to compare 50 % L:W isopleths (L:W is ratio of land to water) across the Atchafalaya and Terrebonne Basins to test landscape behavior over the last six decades to measure delta instability in coastal deltaic basins as a function of reduced sediment supply from river flooding. The Atchafalaya Basin, with continued sediment delivery, compared to Terrebonne Basin, with reduced river inputs, allow us to test assumptions of how coastal deltaic basins respond to river management over the last 75 years by analyzing landward migration rate of 50 % L:W isopleths between 1932 and 2010. The average landward migration for Terrebonne Basin was nearly 17,000 m (17 km) compared to only 22 m in Atchafalaya Basin over the last 78 years (p < 0.001), resulting in migration rates of 218 m/year (0.22 km/year) and <0.5 m/year, respectively. In addition, freshwater vegetation expanded in Atchafalaya Basin since 1949 compared to migration of intermediate and brackish marshes landward in the Terrebonne Basin. Changes in salt marsh vegetation patterns were very distinct in these two basins with gain of 25 % in the Terrebonne Basin compared to 90 % decrease in the Atchafalaya Basin since 1949. These shifts in vegetation types as L:W ratio decreases with reduced sediment input and increase in salinity also coincide with an increase in wind fetch in Terrebonne Bay. In the upper Terrebonne Bay, where the largest landward migration of the 50 % L:W ratio isopleth occurred, we estimate that the wave power has increased by 50–100 % from 1932 to 2010, as the bathymetric and topographic conditions changed, and increase in maximum storm-surge height also increased owing to the landward migration of the L:W ratio isopleth. We argue that this balance of land relative to water in this delta provides a much clearer understanding of increased flood risk from tropical cyclones rather than just estimates of areal land loss. We describe how coastal deltaic basins of the MRDP can be used as experimental landscapes to provide insights into how varying degrees of sediment delivery to coastal deltaic floodplains change flooding risks of a sinking delta using landward migrations of 50 % L:W isopleths. The nonlinear response of migrating L:W isopleths as wind fetch increases is a critical feedback effect that should influence human river-management decisions in deltaic coast. Changes in land area alone do not capture how corresponding landscape degradation and increased water area can lead to exponential increase in flood risk to human populations in low-lying coastal regions. Reduced land formation in coastal deltaic basins (measured by changes in the land:water ratio) can contribute significantly to increasing flood risks by removing the negative feedback of wetlands on wave and storm-surge that occur during extreme weather events. Increased flood risks will promote population migration as human risks associated with living in a deltaic landscape increase, as land is submerged and coastal inundation threats rise. These system linkages in dynamic deltaic coasts define a balance of river management and human settlement dependent on a certain level of land area within coastal deltaic basins (L).     

Human ecological effects of tropical storms in the coastal area of Ky Anh (Ha Tinh,Vietnam)

Vietnam is prone to tropical storms. Climate change effects contribute to sea level rise, floods, progression of the low water line and coastal erosion. This paper inventories the perception of local people, assesses and values main aspects of the livelihood damage caused by the tropical storms of the period 2008–2013 in three coastal communes of the Ky Anh District of the Ha Tinh Province in Central Vietnam. The communes were selected because the location of their coastal line is perpendicular to the storm itself, which made them prone to damage. The effects of increasingly extreme weather conditions on three communities in an area most affected by storms and floods on the local residents and their responses to these changing environmental conditions are analyzed and assessed. The results of questionnaires completed by randomly selected local inhabitants of these communes show that storms and related hazards such as flood, sea level rise and heavy rain are perceived as the most impacting climate change intensified phenomena on agriculture and aquaculture, livestock, household property and income. Opinions and measured data provided by the commune and district authorities allow estimating the total direct cost of the tropical storm at 1.56 million $US (The used conversion rate VND/$US is 21,730 when the research was conducted in 2014) during the period 2008–2013. The long-term costs of adaptation and social impact measures will be significantly higher. Details of the monetary figures allow identifying the physical and natural capital of the area as being most affected by the storm. Trend and cost analysis show that the total financial support for hazard prevention and management during 2014–2019 is estimated at 1.19 up to 1.32 million $US. Local stakeholders indicate that climate change adaptation should not be limited to technical measures such as strengthening dikes, but also should target planting protection forests and mangroves and land use planning. Financial support for the relocation policy, stakeholder involvement and integrating climate change adaptation in both the socioeconomic development master plan and local land use planning are also of importance.     

Community-based scenario planning: a process for vulnerability analysis and adaptation planning to social–ecological change in coastal communities

The current and projected impacts of climate change make understanding the environmental and social vulnerability of coastal communities and the planning of adaptations important international goals and national policy initiatives. Yet, coastal communities are concurrently experiencing numerous other social, political, economic, demographic and environmental changes or stressors that also need to be considered and planned for simultaneously to maintain social and environmental sustainability. There are a number of methods and processes that have been used to study vulnerability and identify adaptive response strategies. This paper describes the stages, methods and results of a modified community-based scenario planning process that was used for vulnerability analysis and adaptation planning within the context of multiple interacting stressors in two coastal fishing communities in Thailand. The four stages of community-based scenario planning included: (1) identifying the problem and purpose of scenario planning; (2) exploring the system and types of change; (3) generating possible future scenarios; and (4) proposing and prioritizing adaptations. Results revealed local perspectives on social and environmental change, participant visions for their local community and the environment, and potential actions that will help communities to adapt to the changes that are occurring. Community-based scenario planning proved to have significant potential as an anticipatory action research process for incorporating multiple stressors into vulnerability analysis and adaptation planning. This paper reflects on the process and outcomes to provide insights and suggest changes for future applications of community-based scenario planning that will lead to more effective learning, innovation and action in communities and related social–ecological systems.     

Spatial-temporal analysis of wetland landscape pattern under the influence of artificial dykes in the Yellow River delta

The influence of anthropogenic activities,especially artificial dykes,on the coastal wetland landscape is now considered as a serious problem to the coastal ecosystem.It is important and necessary to analyze changes of coastal landscape pattern under the influence of artificial dykes for the protection and management of coastal wetland.Our study aimed to reveal the quantitative characteristics of the coastal wetland landscape and its spatial-temporal dynamics under the influence of artificial dykes in the Yellow River delta(YRD).It was analyzed by the methods of the statistical analysis of landscape structure,five selected landscape indices and the changes of spatial centroids of three typical wetland types,including reed marshes,tidal fiats and aquaculture-salt fields.The results showed that:(1)Reduction of wetland area,especially the degradation of natural wetlands,had been the principal problem since the dykes were constructed in the YRD.The dykes created conditions for the development of artificial wetlands.However,the new born artificial wetlands were still less than the vanished natural wetlands.(2)Compared with the open area,the building of artificial dykes significantly speeded up the changes of landscape patterns and the aggravation of the landscape fragmentation in the closed area.(3)The changes of area-weighted centroids of three typical wetland landscapes were greatly affected by dykes,and the movement of the centroid of the aquaculture-salt field was very sensitive to the dykes constructed in the corresponding period.