Dramatic changes in the horizontal structure of mangrove forests in the largest delta of the northern Beibu Gulf, China

The horizontal structure of mangrove forests is an important characteristic that reflects a significant signal for coupling between mangroves and external drivers.While the loss and gain of mangroves has received much attention,little information about how the horizontal structure of mangrove forests develops from the seedling stage to maturity has been presented.Here,remote sensing images taken over approximately 15 years,UVA images,nutrient elements,sediments,and Aegiceras corniculatum vegetation parameters of the ecological quadrats along the Nanliu Delta,the largest delta of the northern Beibu Gulf in China,are analyzed to reveal changes in the horizontal structure of mangroves and their associated driving factors.The results show that both discrete structures and agglomerated structures can often be found in A.corniculatum seedlings and saplings.However,the combination of seedlings growing into maturity and new seedlings filling in available gaps causes the discrete structure of A.corniculatum to gradually vanish and the agglomerate structure to become stable.The aggregated structure of seedlings,compared to the discrete structure,can enhance the elevation beneath mangroves by trapping significantly more sediments,providing available spaces and conditions for seedlings to continue growing.Furthermore,by catching fine sediments with enriched nutrients,the survival rate of A.corniculatum seedlings in the agglomerated structure can be much higher than that in the discrete structure.Our results highlight the significance of the agglomeration of A.corniculatum,which can be beneficial to coastal mangrove restoration and management.

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.

基于优势关系的直觉模糊信息系统的属性约简

近几年来出现了许多用粗糙集理论处理信息系统的方法,但是对直觉模糊信息系统还没有做出相关的讨论。本文首先在直觉模糊信息系统与决策信息表中定义了优势关系,然后引入了基于此优势关系的约简与相对约简的概念,并通过辨识矩阵及辨识函数得到求解约简与相对约简的具体方法。

Spatial and Temporal Variation Pattern of Vegetation NPP in Guangxi Based on GIS

In order to study the rules of variations in the net primary productivity( NPP) of vegetation in Guangxi,this paper used MOD17 A3 H data to compare the spatial and temporal pattern of net primary productivity of vegetation in different cities by unary linear regression method and standard deviation analysis method. It obtained following results.( i) The annual average NPP of cities in Guangxi is in the range of 498. 77-803. 97 g C/m^2·a,and the Beihai has the lowest NPP and Wuzhou has the highest NPP.( ii) The region with small vegetation NPP fluctuation in Guangxi is 6 044. 22 km^2,the region with the larger fluctuation is 37 735. 38 km^2,the region with large fluctuation is43 690. 84 km^2,the region with general fluctuation is 73 938. 14 km^2,and the region with small fluctuation is 74 622. 43 km^2,most regions have small fluctuation in vegetation NPP.( iii) Regions with basically stable NPP are largest,followed by regions with slight decline.( iv)There are great differences in the spatial distribution of NPP variations in Guangxi. Regions with slight decline of NPP are mainly distributed in the northeastern Guangxi; regions with slight increase of NPP are mainly distributed in the southern Guangxi,and regions with basically stable NPP are mainly distributed in southeastern Guangxi.

The important role of Turbidity Maximum Zone in sedimentary dynamic of estuarine mangrove swamp

Sedimentation is a key process affecting wetland sustainability and carbon burial flux.In context of sea level rise,climate change and human activities,further understanding about the sedimentary dynamic in wetland is critical in predicting the landscape evolution or the change in carbon burial flux.In this study,based on the field hydrological observation in a mangrove system in the Nanliu River estuary,we found the net flux of suspended sediment to mangrove is 39−72 kg/m in tidal cycles with Turbidity Maximum Zone(TMZ)forming in surface layer and only is 9−18 kg/m in tidal cycles without TMZ.The higher net flux of suspended sediment to mangrove in tidal cycles with TMZ forming in surface layer is attributed to high SSC in rising tide and intense flocculation in mangrove.The significant discrepancy in sedimentation rate in the mangrove patches also can be explained by the probability of TMZ forming in the surface layer of estuary.In future,rapid sea level rising may lead to the change of TMZ pattern in estuary,which will result in non-negligible variation in sedimentation rate in wetlands.According to the present data of sedimentation rate in wetlands,the fragility of wetlands in river estuary may be miscalculated.