【作者】 李华；

【导师】 杨世伦；

【作者基本信息】 华东师范大学 ， 自然地理学， 2009， 博士

【摘要】 潮间带盐沼是重要的湿地生态系统之一,它具有维持生物多样性、为近海鱼类提供饵料和繁育场所的功能,还可以过滤污染物、消能护岸,对海岸带的资源和环境具有重要影响。随着人类对盐沼生态系统重要性的认识,盐沼正成为多学科研究的热点。潮间带盐沼植物对海岸沉积动力过程具有重要影响。它能消能促淤,抵御滩面侵蚀,在海平面加速上升的背景下,这种促淤作用显得尤其重要。同时,它减弱到达岸边的水体能量,保护沿岸的工程设施,或降低沿岸工程设施的建造成本。潮间带盐沼植物的这种重要物理过程和工程效应使之成为河口海岸研究的重要组成部分。本文依托国家自然科学基金项目“潮间带大型植物对沉积动力过程影响的研究”（批准号:44011770）和973中-荷合作项目“河口海岸区域物理与生态过程之间的相互作用”（批准号:2004CB720505）,选择了长江口崇明东滩盐沼和九段沙盐沼为研究对象,设置典型观测段面,使用先进观测仪器获得了波浪、流速、及悬沙浓度等实测数据,并采沉积物样和植物样,在实验室内进行粒度分析及植物黏附泥沙量的测定。在此基础上,着重分析了盐沼植物的削减水动力、黏附悬浮细颗粒泥沙,改变滩面沉积物特性和冲淤稳定性的作用。主要结果和结论如下:1、盐沼植物对水动力的影响。在崇明东滩,波高和流速的降低率（单位滩面高程或距离上波高或潮流流速减小的百分比）在海三棱藨草（Scirpus mariqueter）-互花米草（S.mariqueter）盐沼中比在光滩上可高达一个数量级。互花米草盐沼内波高降低率为7.40%/cm,海三棱藨草盐沼内波高降低率为2.60%/cm,光滩上波高降低率为0.53%/cm。盐沼中平均潮流流速降低率为0.97%/m,最大潮流流速降低率为0.89%/m;光滩上平均潮流流速降低率为0.07%/m,最大潮流流速降低率为0.08%/m.分析认为,盐沼的消浪缓流作用与植物的生态特征有关。植物越高、越密、植被带越宽,其消浪缓流效果越好;盐沼植物是否被淹没,其消浪缓流效果不同。没有被淹没的盐沼植物能更有效地发挥其消浪缓流作用。由此可知,植株矮小易被淹没的海三棱藨草盐沼的消浪缓流作用弱于植株高大不易被淹没的互花米草和芦苇（Phragmites communis）盐沼。2、盐沼植物对水体悬沙浓度的影响.在崇明东滩观测段面上,距盐沼前缘25 m处的悬沙浓度通常都高于距盐沼前缘50 m处的悬沙浓度。在一个潮周期过程中,距盐沼前缘25m处的平均悬沙浓度为2.44 kg/m³,最大悬沙浓度为4.59 kg/m³;距盐沼前缘50 m处的平均悬沙浓度为1.82 kg/m³,最大悬沙浓度为3.35 kg/m³。由此可见,在盐沼中靠近泥沙来源的地方（光滩或潮沟）,水体的悬沙浓度较高,随着向陆距离的增加,悬沙浓度逐渐减小。分析认为,盐沼植物影响悬沙浓度的机制归因于植物对水体能量降低引起的悬沙落淤、滩面沉积物再悬浮减弱以及植物对悬沙的黏附。3、盐沼植物对悬浮细颗粒泥沙的黏附作用。在2005～2007年的植物生长季节,对崇明东滩和九段沙盐沼的植物样进行了黏附泥沙量的测定,结果表明:植物黏附泥沙量的变化范围为18.0～559.0 g/m²,单位面积上,平均黏附在互花米草、芦苇和海三棱藨草上的泥沙量分别为220.6±172.7g/m²,64.9±38.1g/m²和45.2±31.7 g/m²。分析认为,盐沼植物黏附悬浮细颗粒泥沙的多少主要与植物性质、悬沙浓度和滩面高程等有关。植物黏附的泥沙量与植物的生物量呈正相关:y=30.544e^0.0004x（r=0.72,n=16,p＜0.001）;植物茎、叶分叉处和籽、花黏附的泥沙量多于植物的茎干、叶面黏附的泥沙量。水体的悬沙浓度越大,黏附的泥沙量越多。植物群落所处的滩面高程越低,潮水淹没的机会越多,植物黏附的泥沙量越大。不同盐沼植物黏附的泥沙量差异显著,同是盐沼外缘取样的互花米草（369 g/m²）的黏附能力强于海三棱藨草（44.8g/m²）,同是盐沼内缘取样的互花米草（77.3 g/m²）的黏附能力强于芦苇（38.7 g/m²）,但单位生物量的盐沼植物黏附的泥沙量是海三棱藨草（150.5±134.8 g/kg）最高,芦苇（28.8±22.8 g/kg）最低,互花米草（57.5±32.9 g/kg）位于二者之间。盐沼植物生长位置距光滩或潮沟远近不同,其黏附作用不同,在盐沼外缘,单位滩地面积上植物黏附泥沙量以1-3%/m的速度从盐沼外边缘光滩或潮沟向内陆减小。盐沼植物黏附作用的位置差异归因于不同位置悬浮泥沙浓度和滩面高程的差异。植物黏附的泥沙量在垂向上从上到下急剧增大。从基部到顶端,植物黏附的泥沙量从10-15 g/m²减小到＜2 g/m²,靠近滩面部分植物黏附的泥沙量占植物黏附总量的30%以上。盐沼植物黏附泥沙从植物基部向顶端减少的趋势是生物量、悬沙浓度和淹没状况共同影响的结果。盐沼植物黏附的泥沙量季节差异明显。以崇明东滩的海三棱藨草黏附的泥沙量为例,秋初（2007年9月）是春末（2007年5月）的6倍,冬季该植物消失,其黏附泥沙的功能也消失。盐沼植物黏附泥沙量的季节差异,除了潮况及悬沙浓度的影响外,主要与植物的生态特征有关.在崇明东滩,互花米草通过黏附机制对沉积速率的贡献率＞10%。海三棱藨草通过黏附机制对沉积速率的贡献率＜10%.芦苇通过黏附机制对沉积速率的贡献率可能＞10%或＜10%。4、盐沼植物对滩面冲淤过程的影响。盐沼滩面的日平均冲淤速率变化明显小于光滩滩面。如2006年9月15～23日期间,对崇明东滩一个横跨盐沼-光滩的段面观测表明:盐沼日冲淤速率变化范围为-1～3 mm/d,平均日冲淤速率变化范围为-0.2～1.2 mm/d;而光滩日冲淤速率变化范围为-2～5 mm/d,平均日冲淤速率变化范围为-1～2.3 mm/d。海三棱藨草盐沼对滩面的季节性冲淤过程影响明显.如在崇明东滩海三棱藨草盐沼的现场观测发现,植被覆盖季节,滩面持续淤积,一个生长季节滩面累计淤积可超过20cm.在冬季,海三棱藨草衰亡,盐沼变成光滩,滩面停止淤积或遭受侵蚀。分析认为,盐沼植物对滩面冲淤过程的改变归因于盐沼植物对水动力的削弱、茎叶对悬浮细颗粒泥沙的黏附以及植物根系对滩面沉积物的固结作用。5、盐沼植物对滩面沉积物粒径的影响。崇明东滩北、中、南三个盐沼段面沉积物的平均粒径与盐沼段面上的平均植物指数（植物高度与盖度的乘积）呈显著的负相关关系:y=30.951e^-5E-05x（r=0.9999,n=3,p＜0.01）,说明植物越高、越密集,滩面沉积物就越细。盐沼植物（以海三棱藨草为例）消失的冬季（沉积物平均粒径为30.1±7.8μm）,滩面沉积物粒径比植被覆盖的夏季（沉积物平均粒径为16.4±3.8μm）增大约1倍.分析认为,盐沼植物对沉积物粒径的细化作用归因于植物对水动力的衰减和直接黏附。植物摩擦导致水动力衰减,促进细粒悬浮泥沙落淤,同时还抑制滩面侵蚀。植物对细颗粒泥沙的黏附作用也最终增加了细颗粒悬浮泥沙在滩面上的落淤。更多还原

【Abstract】 Tidal salt marsh is one of the important ecosystems of wetlands.It provides important ecosystem functions such as nursing habitats for fish and crustaceans,resting and feeding areas for migratory birds.It also supports biodiversity,filters contaminants,dissipates water energy,and offers intrinsic values such as aesthetics and education.Tidal salt marsh plays a significant role in resource and environment of coastal zone.With people’s acquaintance on its importance,salt marsh ecosystem has become a hot topic of multi-disciplinary research.Tidal salt marsh vegetation affects the hydrodynamics and sedimentation process greatly.It can attenuate hydrodynamic and accelerate accretion as well as resist erosion of bed.In the context of the growing speed of the global sea level rise,this accretion effect seems more important than ever for tidal marsh survival.Besides the above benefits,the vegetation can also protect the engineering of the coastal zone by attenuating the water energy.All of these physical processes and engineering effects make tidal salt marsh vegetation one important study project.This study was funded by the National Science Foundation（44011770） and the Ministry of Science and Technology of China（2004CB720505）.In this study,two exposed tidal wetlands,the Eastern Chongrning and the Jiuduansha,at the seaward side of the Yangtze River delta were selected as the study regions.Using advanced equipments,we observed the data of wave,flow speed and SSC（Suspended Sediment Concentration）.Then,in the laboratory,sampled sediments were used to make grain-size analyzing,and sampled vegetations were used to measure the amount of sediments adhered by plants.Based on the subsequential results,we laid special stress on analyzing the attenuation of hydrodynamics,the trapping effect,the sediment grain size and stability of bed due to vegetations.The following conclusions are obtained:1.Influence of Salt marsh vegetations on hydrodynamics.Attenuation of wave energy and flow speed in S.alterniflora-S,mariqueter salt marsh was one order higher than that in tidal flat in magnitude.The average decrease rate of flow speed was 0.97%/m,and the highest decrease rate was 0.89%/m in salt marsh.In tidal flat,the average decrease rate and the highest decrease rate were 0.070%/m and 0.078%/m respectively.Decrease rate of wave height per unit bed level was 0.53%/cm in tidal flat,while that in S.mariqueter salt marsh was 2.60%/cm,and that in S. alterniflora salt marsh was 7.40%/cm.After analyzing,we found that the attenuation effect of vegetations on hydrodynamics was related with ecological parameters of plants.The higher, denser,and wider the plant was,the greater the attenuation effect on hydrodynamics was.The attenuation effect when the plant was submerged is different from that when the plant was not submerged.When not submerged,the plant can effectively attenuate the wave and flow.Therefore, we can know that the attenuation effect of S.mariqueter salt marsh on hydrodynamics was smaller than that of S.alterniflora salt marsh because the height of the former is smaller than the latter.2.Influence of Salt marsh vegetations on SSC.The SSC at Site 30 m away from the outer marsh edge was typically higher than that at Site 50 m away from the outer marsh edge at the trance in the Eastern Chongming.The tide-averaged SSC at Site 30 m away from the outer marsh edge was 2.44 kg/m³,and that at Site 50 m away from the outer marsh edge was 1.82 kg/m³.The maximum SSCs at the two sites were 4.59 kg/m³ and 3.35 kg/m³ respectively.Thus,we can draw the conclusion that the SSC of water close to sediment source（tidal fiat and creek） was higher. With the increase of the distance away from the landward,the SSC of water decreased.As a result of our analyzing,the mechanism of plant’s influence on SSC dues to the settlement of the suspended particulate,the decrease of the resuspend power,caused by the decrease of the wave energy,and the trapping effect of plants on the sediments.3.Trapping effect of salt tidal marsh vegetation on suspended sediment.We measured weight of sediment trapped by vegetations sample in the Eastern Chongming and the Jiuduansha salt marsh.The results indicate:The dry weight of sediment adhering to plants ranged from 18.0 to 559.0 g/m².On average,the amount of sediment adhering to S.alterniflora,P.australis and S. mariqueter was 220.6±172.7,64.9±38.1,and 31.6±10.0 g/m²,respectively.After analyzing, we find that the amount of sediment adhering to marsh plants per unit of land area depends onthe plant properties,the SSC and the bed level.The general positive relationship between the amount of sediment and plant biomass:y=30.544e^0.0004x（r=0.72,n=16,p＜0.001）.The amount of sediment adhering to the stems and leaves per unit land area was less than that of adhering to the branching and flower/fruit structures.The SSC of water is higher,the amount of sediment adhering to marsh plants is bigger.The lower the bed level,the higher the frequency and duration of tidal submergence,and the more the sediment adhere to plant.The effect of each type plant is different.At the same position,the amount of sediment adhering to S.alterniflora（77.3 g/m²） was typically more than to P.australis（38.7 g/m²）,and at the same position,the amount of sediment adhering to S.alterniflora（369 g/m²） was typically more than to S.mariqueter（44.8 g/m²）. However,also on average,the amount of sediment adhering per plant biomass was highest for S. mariqueter（92.1±35.3 g/kg）,lowest for P.australis（28.8±22.8 g/kg）,and in between for S. alterniflora（57.5±32.9 g/kg）.For the same species,plants closer to a creek of the lower marsh edge tend to trap more sediment.The amount of sediment trapped by vegetation per unit land area in the low marsh margin decreased at a rate of 1-3%/m with distance from the outer marsh edge bordering the mudflat or from the tidal creak where the SSC was higher.The difference of amount trapping by plant in different position attribute to different SSC and bed level.The dry weight of sediment adhering to plants drastically decreased from 10-15 to＜2 g/m² upward from their base to their tip.The amount of particulate trapped by near-bed 51-0 cm section of the plants is over one third in total.The downward increasing trend in sediment adhering to the plants reflects the combined effect of plant biomass,SSC and inundation condition.The amount of particulate adhering to S.mariqueter in the initial stage of autumn（September） was six than that in the end stage of spring（May）.The plants were wither away in winter,and the effect was disappearing.In the Eastern Chongming,we estimate that the contribution of S.mariqueter to the total deposition rate is＜10%and the contribution of P.australis to the total deposition rate may be either＞10% or＜10%.4.Influence of Salt marsh vegetations on A&E（accretion and erosion） process of bed.The daily average A&E rate of salt marsh was obviously less than that in tidal flat.For example,from 15 to 23 September 2006,the observation on a trance across salt marsh-tidal flat in the Eastern Chongming indicated that:The daily A&E rate in salt marsh varied from-1 to 3 mm/d,and the daily average A&E rate in salt marsh varied from-0.2 to 1.2 mm/d.However,the two A&E rates in tidal flat are-2～5 mm/d and-1～2.3 mm/d respectively.S.mariqueter can obviously affect the seasonal change of A&E of bed.For example,through our observations in Eastern Chongming, we found that the bed continuously accreted in season when S.mariqueter plants and the bed level can promote 20 cm in a growing season.In winter when the plants were withered away,the salt marsh becomes tidal flat,and the bed did not promote or be eroded.It can be concluded that the mechanism of plant’s influence on A&E of bed attributes to attenuation of hydrodynamics caused by plants,trapping effect of plant and concretion of root.5.Influence of salt marsh vegetation on grain size of bed sediment.There was obviously negative relation between vegetation index（The product of mean height and coverage of plants） and mean size of surface sediment of north,middle and south salt marsh trances in the Eastern Chongming.The regression relationship was y=30.951e ^-5E-05x（r=0.9999,n=3,p＜0.01）,which indicated that the higher and denser the plant was,the freer the sediment was.Taking S. mariqueter for example,the grain size（average grain size was 30.1±7.8μm） in winter when the salt marsh vegetations die away was two times larger than that in summer（average grain size was 16.4±3.8μm） when the bed was covered by plants.After analyzing,we found that the fining effect of the plants was also attributes to the attenuation of hydrodynamics and their trapping effect.The friction of vegetations induced attenuation of hydrodynamics,and enhanced the settling of fine grain.Meanwhile,the cover of plant prevented the erosion.The trapping effect of plant enhanced the deposition of fine grain to bed finally.更多还原