Dramatical hydro-sedimentary changes induced by bamboo fences over mangrove tidal flat of the largest delta in Beibu Gulf, southwestern China

Mangrove forest is one of the most important ecological and environmental resources by effectively promoting tidal flat deposition and preventing the coastal region from typhoon.However,there have been mass loss of mangrove forests due to anthropogenic activities.It is an urgent need to explore an effective way for mangrove restoration.Here,three rows of bamboo fences with hydro-sedimentary observation set over Aegiceras corniculatum mangrove tidal flat of the Nanliu Delta,the largest delta of Beibu Gulf,China,were conducted to analyze the hydro-sedimentary variations induced by bamboo fences.Results identified that the mean horizontal velocity Um per burst(20 min)decreased by as much as 71%and 40%in comparison with those without bamboo fences in March and November,respectively,when the tidal current entering the bamboo area during flood.The maximum of mean horizontal flow velocity Um-max at bamboo area was 50%–75%of that without bamboo fences during ebb tide.The suspended sediment concentration of bamboo area suggested a maximum reduction of 57%relative to bare flat during flood,and was 80%lower than bare flat at ebb peak.Moreover,the turbulent kinetic dissipationεat flood tide was significantly higher than that at ebb tide,while the bamboo fences greatly increased the turbulent kinetic dissipationεby 2 to 5 times relative to bare flat,resulting in an increase of the bed elevation by inhibiting the sediment incipient motion and intercepting suspended sediment.The siltation rate at the bamboo area was 140%and 29.3%higher than that at the bare flat and the region covered with A.corniculatum,respectively.These results highlight that bamboo fences can effectively attenuate tidal current and thus promote siltation over mangrove flat,which contribute great benefit to mangrove survival.

Seasonal Distribution of Meiofaunal Assemblages in the Mangrove Tidal Flat of Futian,Shenzhen,China

Meiofauna are fundamental components in mangrove ecosystem which play important roles in the energy flow and mat-ter cycling.In order to reveal the spatio-temporal distribution of meiofaunal assemblages in mangrove habitats,sediment samples were collected in July(summer)and October(autumn)of 2013,January(winter)and April(spring)of 2014 in the mangrove tidal flat of Futian,Shenzhen,China.A total of 14 meiofaunal taxa were identified,including free-living marine nematodes,benthic copepods,polychaetes,oligochaetes,ostracods,isopods,etc.Additionally,there were also undetermined taxa.Results showed that the abun-dance range of meiofauna was(488.35±71.29)-(5136.36±623.38)ind(10 cm)−2.Marine nematodes were the most dominant group,with an average abundance of(1869.56±227.92)ind(10 cm)−2,accounting for 98.35%of the total abundance of meiofauna.The sea-sonal distribution of meiofauna showed that the abundance was the highest in summer,followed by those in spring,winter,and au-tumn.Vertical distribution showed that meiofauna were mainly distributed in the upper sediment layer(0-5 cm),with a proportion of 89.56%.Correlation analysis between meiofauna and environmental factors showed that meiofaunal abundance and biomass had significantly negative correlation with salinity.BIOENV analysis between meiofaunal assemblages and environmental factors show-ed that meiofaunal assemblages were affected by the combined effects of temperature,salinity,sediment median grain size,water content,and chlorophyll a content.

Mangrove swamp expansion controlled by climate since 1988:a case study in the Nanliu River Estuary,Guangxi,Southwest China

In the Nanliu River Estuary of Guangxi, China, the naturally expanding process of a mangrove swamp（primarily consist of Aegiceras corniculatum） over past decades is studied by satellite images. From 1988 to2013, the area of studied mangrove swamp increased significantly from 60 hm2 to 134 hm2. The expanding process is not gradual and the significant expansion only took place in some special periods. To reveal the dynamic of mangrove swamp expansion, the evolution of tidal flat elevation and the climate change in past decades are studied respectively. The hydrodynamic condition and nutrient supply are also analysed. The study results show that the climate factors of typhoon intensity and annual minimum temperature are crucial for controlling mangrove expansion. A large number of mangrove seedlings on bare tidal flats can survive only in special climate optimum periods, which are continuous years of low typhoon intensity and high annual minimum temperature. In past decades, the scarcity of climate optimum periods resulted in a non-gradual process of mangrove expanding and a time lag of 30 years between the elevation reaching the low threshold for mangrove seedling survival and the eventual emergance of the mangrove. Compared with the climate factors,the hydrodynamic condition and nutrient supply are not important factors affecting mangrove expansion. In the future, combined with global warming, the enhanced frequency and energy of landing typhoons will most likely restrain the further expansion of this mangrove swamp.

Coastal geomorphic evolution at the Denglou Cape, the Leizhou Peninsula

The Denglou Cape, southwest of the Leizhou Peninsula, is the most typical tropical coast in the continent of China.The coastal geomorphic development basics of the geology and Quaternary environment change are discussed. Aerial photograph interpretation with fieldwork is applied to draw the outlines of geomorphic types. Based on the investigative data, the exogenic forces and marine organism conditions concerning tropical coast development in the area are expounded, and coastal dynamo-deposition geomorphic bodies are analysed, mainly with sea cliff-abrasion platform,barrier-lagoon system, modern beach, coral reef and mangrove tidal flat, and the general process of coastal evolution at this area, as well as coastline changes since middle Holocene transgression.