Ecological and economical significance of homestead forest to the household of the offshore island in Bangladesh

An explanatory survey was conducted to assess the contribution of plant diversity to the ecological and socio-economic condition of the rural household in the offshore island of Bangladesh. Assessment was done by means of multistage random sampling. The homestead sizes of the study area were classified into 3 groups viz, large （〉0.25 ha）, medium （0.05-0.25 ha） and small （〈0.05 ha） based on the result obtained from a preliminary survey, and a total of 45 homesteads, 15 from each group, were selected randomly for the study. The average annual income from homestead＇s plant diversity varied from Tk 5730.00 （US$95.5） to Tk 17500.00 （US$291.67）. The rural people were mainly dependent on their homegarden for woodfuel and nutritional requirement as forest was unavailable in the island. The rural people here also cultivated the plant species as a safety measure from frequent cyclone. Constraints hindering the development of homestead plantation were identified and suggestions were given such as the adequate supply of seedlings of fast growing native species and conservation of endangered species to meet the demand of the household as well as to keep ecological balance.

Evolution of the Late Miocene atoll systems offshore Xisha Islands

Modern atolls have been studied systematically and thoroughly in the South China Sea.However,the knowledge of a paleo-atoll and related sedimentary system is very limited.Here we used the newly acquired high resolution 2D seismic data,and discovered three late Miocene atoll systems in the offshore Xisha Islands for the first time.We named them atoll system A,B,C,respectively.These three atoll systems,all developed on the horsts dominated by normal fault,consist mainly of atoll reefs,patch reefs,fore-reef slope deposits,and lagoons.On the basis of the interpreted sequence stratigraphic framework and the identification of fore-reef slope deposits,we suggested only the atoll system A continued to grow until Quaternary,and both of atoll system B and C had been drowned in Pliocene.In late Miocene,the atoll systems in the study area were most developed,either in magnitude or in maturity,which indicated late Miocene was the most flourishing period of reef builders,and this was in accordance with the drilling result of ODP Leg 184 in the South China Sea.Pliocene was an important reef drowning period in the study area,and both atoll systems B and C were drowned and hemipelagic deposits prevailed gradually.Quaternary was another reef drowning period in the study area,two large atoll reefs grown on the atoll system A were finally drowned,and hemipelagic deposits begun to drape and fill the palaeo-atoll systems.The growth and drowning of atolls are controlled mainly by tectonic subsidence in long term,but global eustatic can impact it in short term also.

Effects of offshore artificial islands on beach stability of sandy shores:case study of Hongtang Bay,Hainan Province

Artificial island-type reclamation often exerts certain impacts on near-shore sandy shoreline resources and coastal ecological landscapes.The relationship between artificial islands and offshore beach evolution has attracted considerable attention in coastal protection and engineering construction.In this study,we consider Hongtang Bay in Hainan Province,China,as the research object.We adopted the Gao-Collins model to investigate the substrate transport trend in this sea area based on the analysis of the measured hydrologic and sediment data.The shore section from Nanshanjiao to Hongtangling(Taling),including the flat and straight shore sections,is dominated by the lateral transport trend of the vertical shore.The near-shore water has a strong lateral sediment transport capacity,while the outer deep-water area exhibits a sediment transport trend consistent with the tidal current movement.Using multi-year topographic data,the shoreline and seabed alterations in Hongtang Bay were analyzed,and the LITLINE beach evolution model was adopted to simulate the effects of three artificial island layouts with different island filling areas,offshore distances,and plan forms on the near-shore shoreline deformation.The results obtained indicate that the artificial island arrangement with a large offshore distance and a small area has relatively substantial advantages,such as minimizing the adverse effects of artificial island implementation on the near-shore beach.