A Study On The Marine Ecological Effects Of The Coastal Mangrove Wetland In Guangdong Province

Mangrove wetland is a special marine wetland type in tropical and subtropicalcoastal and Estuarine Intertidal area. It’s core is the mangrove communities. It playsan important role in the food supply, the conservation of wild species germplasm, themaintain of population, the protection of the species diversity, the purification ofregional marine environment, the maintain of the ecological balance, carbonsequestration and the regulation of climate. Mangrove wetland is the habitat, breedingfarm and feeding grounds for a biological variety of fishery resources. Over the years,due to population pressure and economic development, mangrove wetland’s qualityand area are shrinking. The recovery of the mangrove wetland has become a hot topicin the world.Guangdong coastal area is an important distribution area of mangrove forests. Inrecent years, with the continuous development of economy, the increase of populationand the severer of human disturbance, Guangdong coastal mangrove wetlandecosystem has become the high vulnerable ecosystem. It is facing the degradation ofecological systems, biological resource depletion, biodiversity decline anddeterioration of the ecological environment and other serious problems. This hasbecome one of the important reasons of recession of fishery resources in Guangdongcoastal area. Systematic study on the Guangdong coastal mangrove’s marineecological effect and to explore the mechanism of inhibition of carbon sinks, ofgreenhouse effect and degradation of pollutants, can provide effectively reference forrepair the degenerated Guangdong coastal mangrove forest ecological system.This research was conducted to study the8major coastal mangrove distributionarea in Guangdong Province, including Huizhou Dayawan mangrove Park, ZhuhaiQi’ao Island Mangrove Nature Reserve, Shenzhen Futian Mangrove NatureReserve,Chenghai Mangrove area, Raoping Fu Ren Cun Mangrove area, ShuidongBay Mangrove area, Jiangmen Guang Bay Mangrove and Lianjiang Gaoqiaomangrove area. The study analyzed11species of mangroves, including10kinds of native species and1kind of introduced species. Native species are Rhizophorastylosa,Aegiceras corniculatum,Acanthus ilicifolius,Bruguieragymnorrhiza,Excoecaria agallocha,Kandelia candel,Heritiera littoralis,Acrostichumaureum,Lumnitzera littorea and Avicennia marina.Sonneratia apetala is theintroduced specie.The main research contents include: the characteristics of plant distribution ofmangrove plants in different area, the growth characteristics of different kinds ofmangrove plants in different area, the distribution characteristics of physical andchemical factors(including carbon, nitrogen, mercury, arsenic, copper, lead, zinc,chromium) of sediments of different mangrove species in different areas, thedistribution characteristics of physical and chemical factors(including carbon,nitrogen, mercury, arsenic, copper, lead, zinc, chromium) of different mangrovespecies in different areas,the analysis of the characteristics of the transfer andenrichment of Physical and chemical factors in the sediments and different mangrovespecies in different areas.Based on the review on the domestic and foreign mangrove’s marine ecologicaleffects and repair technology, the study carry out the survey analysis of mangrove inthe main coastal mangrove distribution area of Guangdong province. The method isthe combination of the field investigation and laboratory analysis. The study can wellknow the marine ecological effect of Guangdong coastal mangrove forests. This mayprovide the reference for the ecological protection of mangrove ecosystem.The main conclusions can be summed up as follows：1.The growth characteristics of mangrove plant:(1)The distribution characteristics of mangrove plants in different regions. Themangrove area of the survey involved is1023.7hm2.Area of all tree species in orderof size:Sonneratia apetala(309.51hm2)＞Aegiceras corniculatum(143.26hm2)＞Bruguiera gymnorrhiza(137.93hm2)＞Acanthus ilicifolius(107.04hm2)＞Kandeliacandel(93.7hm2)＞Excoecaria agallocha(84.93hm2)＞Heritiera littoralis(71hm2)＞Avicennia marina(44hm2)＞Acrostichum aureum(18hm2)＞Rhizophora stylosa(8hm2)＞Lumnitzera littorea(6.4hm2).Area of all regions in order of size:Gaoqiao(445hm2)＞Zhuhai(350hm2)＞Shuidong Bay(107hm2)＞Shenzhen(55.1hm2)＞Raoping(32hm2)＞Guanghai Bay(22hm2)＞Dayawan(7.67hm2)＞Chenghai(5hm2).(2)The growth characteristics of different kinds of mangrove plants in differentarea. Using11kinds of common curve estimation models in SPSS software to fit the height and diameter at breast height or diameter, we can get the correlation equations.The cubic function equation has high correlation(coefficient of determination (R2) islarger, more than0.8).2. Distribution characteristics of carbon and nitrogen in different mangrovespecies in different regions.(1) Carbon. Sediment’s carbon density decreased with the depth increasing. Butdue to the difference of area and species, the vertical change law of sediment’s carbondensity is different. Carbon density of most plant leaves is higher than the roots. Thetotal carbon storage in the order:Zhuhai＞Gaoqiao＞Shenzhen＞Shuidong Bay＞Guanghai Bay＞Raoping＞Dayawan＞Chenghai.(2) Nitrogen. Sediment’s nitrogen density decreased with the depth increasing.But due to the difference of area and species, the vertical change law of sediment’snitrogen density is different. Nitrogen density of most plant leaves is higher than theroots.There is a good correlation between sediment and mangrove plant’s carbon andnitrogen, the correlation coefficients are0.575and0.579.The total nitrogen storage inthe order:Zhuhai＞Gaoqiao＞Shenzhen＞Shuidong Bay＞Raoping＞Guanghai Bay＞Dayawan＞Chenghai.3. Distribution and accumulation of contents of6kinds of heavy metals in thesediments.(1)The density of6heavy metals decreased with increasing depth. The trend hasnothing with mangrove habitats, species and age. Different metal has different trend,in order of obvious: Cu>Zn>Cr>Pb>As>Hg.(2)The average value of Zn, Cu, Pb, Cr,As and Hg in study area were116.59mg/kg,60.14mg/kg,45.86mg/kg,32.09mg/kg,13.9mg/kg,0.1mg/kg respectively.Compared with the background value of China mangrove, the content of Zn, Cu, CrandAs were relatively high.(3)According to the analysis, the most important environmental factorinfluencing the content of Zn, Cu, Cr and As were the using of pesticide and fertilizerand the increasing of oily water of sea and the wastes of living. These factors werecaused buy several reasons: the industrial and mining enterprises are relatively morethan other regions in Guangdong province and in recent years, due to the developmentof fishery, the fish and shrimp pond around the mangrove area.(4)In the plane distribution, the average content of Zn, Cr, Cu and Hg elements inDayawan mangrove wetland were the highest, the average content of Pb, Zn, As and Hg elements in Zhuhai and Guanghai Bay mangrove wetland were the highest, theaverage content of Pb element in Raoping mangrove wetlands was the highest, theaverage contents of Pb and Zn elements in Chenghai mangrove wetland were thehighest and the average content of6kinds of heavy metals in Shenzhen, Gaoqiao andShuidong Bay mangrove wetland were low.(5)Correlation analysis:①There is a good correlation between the6metalelements, especially Zn-Pb, Cr-Zn, Cu-Zn, Zn-Hg and Cr-Hg groups was significant,it explains that these elements have the same source, and the geochemical propertiesis similar, and precipitated or accumulated jointly. As has no significant correlation,probably As with other heavy metal element is not obvious in the earth chemicalbehavior,and As and Cd has different sources with other elements.(6)The enrichment degree of heavy metal elements is asfollows:Cu>Hg>Pb>Zn>As>Cr. Cu and Hg reached serious enrichment, Pb reachedmoderate pollution and Zn and As reached light pollution, so should be close attention;Cr reached poor enrichment, can not meet the normal growth of the crops, someasures should be taken to improve the content of element Cr.4.Distribution and accumulation of the content of6kinds of heavy metalelements in mangrove plants(1)The content of different heavy metal elements in the same specie is different;the content of same kind of heavy metal element in different mangrove plants isdifferent; the content of the same heavy metal element in the same position isdifferent in different mangrove species;the content of same kind of heavy metalelement in different area is different; Contents of different elements of the same areaare also different; the same mangrove plants in different regions are also in differentheavy metal content. Cr, Pb, As and Hg elements are mainly distributed in the rootsand stems. It could be because of the heavy metal elements these has no biologicalactivity, so the plants can absorb a little. But the content of Zn and Cu in11mangroveplants are higher, especially in the stem.(2)Correlation analysis:①Except Hg, the other heavy metal elements have verygood correlation. Especially Zn, Pb, and As have more strong correlation, it showsthat the absorption and transfer ability of these heavy metal elements are similar.②Hg has no significant correlation between most of the other heavy metals.(3)The absorption capacity of Avicennia marina, Bruguiera gymnorrhiza andAegiceras corniculatum are the strongest, Acanthus ilicifolius and Rhizophora stylosa are in general.Avicennia marina has strong absorption capacity of Cr, Cu, Zn, As andHg.Bruguiera gymnorrhiza and Aegiceras corniculatum have strong absorptioncapacity of Cr, Cu, Zn and Hg.(4)11kinds of mangrove plants all showed well transfer ability of the differentheavy metals, but the transport capacity of As is weak. In the future, more mangrovesshould be planted which has well transfer ability ofAs.(5)All the plants have not reached the critical value of hyper accumulator plants.Avicennia marina,Lumnitzera littorea,Excoecaria agallocha and Heritiera littoraliscan be planted as pioneer plants, not only can quickly improve the vegetationcoverage rate of intertidal mangrove wetland, can also enrich a certain amount ofheavy metals.(6)Different heavy metals have different reservation in different areas. The totalreservation of6kinds of heavy metals in Zhuhai and Gaoqiao are far higher than theother areas, this have inseparable relationship with the total area and older.5.The distribution of physical and chemical factors in different sampling areasand blank area.The content of carbon, nitrogen and heavy metal elements in mangrove area arehigher than blank area. The mangrove can increase carbon sequestration, nitrogen sinkcapacity and ability to absorb heavy metals, which are3important aspects of themangrove forest ecosystem’s environment effects.6.Benthic changes.The number of benthic species in mangrove area is much more than blank area.The mangrove can improve the environment for benthic and can increase the benthicspecies. This is an important aspect of the biological effect of mangrove ecosystems.