【作者】 邵学新；

【导师】 梁新强；

【作者基本信息】 浙江大学 ， 环境工程， 2014， 博士

【摘要】 磷(P)是生态系统中必须的营养元素,也是导致水体富营养化关键因子之一。由磷污染引发的湖泊、河口和近海水体富营养化是当今世界面临的重大环境问题。湿地被誉为“地球之肾”,滨岸潮滩湿地是重要的湿地类型之一,位于海陆交错地带,具有较强的过滤和沉降外来污染物的能力。潮滩湿地是全球磷的主要源、汇和转换器之一,在全球磷循环过程中扮演着十分重要的角色,其对水体磷素的截留能力日益受到关注。但是,有关潮滩湿地系统磷素截留作用中生物因子的驱动过程和机制依然缺乏研究。本论文以我国杭州湾南岸典型潮滩湿地为研究区,通过野外定位观测和室内模拟实验,研究典型潮滩植物对磷素的吸收、植物枯落物分解及其磷素释放、沉积物磷素形态分布及其季节动态,分析沉积物物理化学因子与磷形态分布及转化的关系,探讨植物影响下沉积物微生物和酶活性变化对磷素形态及其转化的作用。研究结果主要包括：1、获取了潮滩湿地植物生物量、P含量动态及枯落物分解与磷素释放特征。3种优势植物芦苇(Phragmites australis)、互花米草(Spartina alterniflora)和海三棱蔗草(Scirpus mariqueter)地上生物量呈典型的单峰值曲线,P含量随植物生长而逐渐降低。地下生物量及根系P含量变化相对不明显。植物P储量与植物生物量显著正相关,表现为互花米草>芦苇>海三棱蔗草。从净化功能上考虑,7月可认为是本研究区域三种植物的最佳收割时间。分解袋法模拟实验表明,枯落物分解具有明显的阶段性,初期(0-15d)损失最快。地下根系分解速率表现为：海三棱蔗草>芦苇>互花米草,地上部分则相反。植物不同部位分解95%所需时间在1.2～8.3年之间。植物分解速率与C/N比相关性不显著,而受C/P比影响较大。环境因子中的大气温度对分解也有影响。2、明确了沿岸潮间带和离岸沙洲两种类型潮滩湿地沉积物中磷形态分布特征及其影响因素。沉积物中各形态磷含量表现为Exch-P<Fe/Al-P<Org-P<Ca-P。沿岸潮间带沉积物TP和Fe/Al-P含量高于离岸沙洲,表明其受人为活动下外源污染物输入的影响。相关分析和PCA分析显示,沉积物颗粒组成是影响磷形态含量和分布的重要因素,而不同植物可以促进Ca-P向活性态磷转化,并通过生物量生产和营养物质循环过程促进沉积物Org-P.的累积。沉积物生物有效态磷(BAP)主要包括Exch-P、Fe/Al-P和Org-P,总含量为32.9～134.2mg·kg-1,约占沉积物TP含量的5.78～21.3%,释放风险较低。3、分析了植物对杭州湾潮滩沉积物-水界面磷素吸附特征的影响。磷酸盐吸附动力学实验表明,沉积物磷的吸附与释放过程包括快速吸附(0-1h)、慢速吸附(1-16h)和平衡(16～72h)三个阶段,植被类型的差异没有明显影响这一趋势,取48h为等温吸附实验的平衡时间。利用改进的Langmuir模型拟合等温吸附过程表明,研究区最大吸附容量(Qmax)在154.5～436.3mg·kg-1间,相比周边区域较高,生长植物的沉积物Qmax明显高于裸滩沉积物。沉积物本底吸附态磷(NAP)较少,分布趋势与Qmax值相似。四种植被类型沉积物间吸附解吸平衡浓度(EPC0)差异较小,且EPCo值低于潮汐水体中PO43--P浓度,说明沉积物主要扮演“汇”的角色。研究区沉积物Qmax口NAP受OM、颗粒组成和TIP含量影响,其中Qmax还受EC影响。说明植物可以通过影响沉积物的物理化学参数,进而影响PO43--P的吸附过程。但研究区EPCo与沉积物理化性质不存在显著相关性。这可能与研究区受潮汐的影响,水体化学环境因子变化剧烈有关。4、探讨了植物及其影响下的沉积物生物化学性质与磷形态分异的关系。春秋两个季节的调查表明,碱性磷酸酶活性表现为夏季高于春季,植物生长下沉积物高于裸滩沉积物,说明其具有显著的空间和时间分布特征。沉积物碱性磷酸酶活性与Fe/Al-P含量显著正相关,与Ca-P含量显著负相关,说明碱性磷酸酶影响着沉积物中磷形态转化。利用Biolog生态板对沉积物微生物群落的功能多样性分析表明,随着植被的演替,沉积物微生物群落功能多样性增加。不同植被类型沉积物微生物群落代谢过程的主要区别在于对糖类及其衍生物和氨基酸及其衍生物等碳源利用的不同。微生物总PLFAs表现为：互花米草>芦苇>海三棱蔗草>裸滩,说明植物生长下沉积物中微生物数量比裸滩要高。沉积物细菌PLFAs与碱性磷酸酶活性显著相关,但不同类型微生物群落生物量与沉积物磷形态含量没有显著的相关关系,需要进一步关注磷素循环的关键功能菌群研究。5、分析了磷储量在杭州湾潮滩湿地沉积物-植物系统的分配,并评估了杭州湾潮滩湿地磷的截留效应。系统中98%以上的磷分布在沉积物系统中,而植物系统的储量占的百分比很小。根据植物的净初级生产力,湿地植物通过吸收磷素对水体的净化系数为6.04～24.0t·(m-2yr-1)。根据颗粒沉积速率,湿地沉积物对磷的截留效应为25.4～31.5g·(m-2y-1)。且沉积物的截留作用远高于植物。总体上,潮滩湿地沉积物-植物系统具有较高的磷素截留效应,保护滨岸湿地对减轻水体富营养化具有重要作用。更多还原

【Abstract】 Eutrophication of surface water body is a worldwide concern. Phosphorus (P) is one of the key nutrients that can cause algal blooms and other water quality problems in lakes, rivers and estuaries. Wetlands are called the "Kidney of the Earth". Coastal wetland is one type of wetlands composed of a complex and assemblage of swamps, marshes, mudflats and etc. As a transitional zone between terrestrial and marine ecosystems, salt marshes are one of the most biologically productive habitats that drive P cycles. The important ecosystem functions particularly nutrient recycling of coastal wetlands has attracted great attention. However, the driving processes and mechanisms of biological factor in P retention of the tidal flat coastal wetland system are still lack of extensive research. In this thesis, the South Bank of Hangzhou Bay, a typical tidal wetland was taken as the study area. By field investigation and litterbag field experiment, the P retention by marsh plants and sediments were evaluated. Plant litter decomposition and release of P from sediment were studied by litterbag field experiment. We investigated typical intertidal plants on P absorption by batch incubation experiments. The influences of sediment properties and macrophytes on phosphorous speciation in the intertidal marsh were investigated. We also analyze the relationship between sediment microbial biomass, enzyme activity and P forms distribution and transformation. The followings were the main results.(1) The plant biomass, concentration and pools of P were measured seasonally in three marsh species Phragmites australis, Spartina alterniflora and Scirpus mariqueter. Results showed that plant aboveground biomass displayed a unimodal curve with nutrient concentration generally decreased from spring to winter. The belowground biomass was relatively low during the rapid growth period with nutrient concentration tended to decrease and then increase during this period. Plant total P (TP) pools showed significant seasonal variations and were significantly correlated to plant biomass. The pools among plant species were under S. mariqueter<P. australis<S. alterniflora. Considering the purification capacity of P, July would be the best harvest time of the study area for three plants. Wetlands litter decomposition affects wetlands nutrient cycling. There are distinctive stages of the plant litter decomposition in litterbag simulation experiments. The loss rate is faster during0-15d than that of later days. The loss rate in root decomposition of three plants are under S. mariqueter> P. australis> S. alterniflora, while the trend is opposite for that of aboveground tissues. The time needed for95%of dry mass decomposition in the plant tissues is between 1.2-8.3a. Pearson’s correlation coefficient shows that there is no significant correlation between the litter decomposition rate and C/N ratio. However, the litter C/P ratio effects greatly on plant decomposition rate. Environmental factors in the atmospheric temperature also have an impact on the decomposition rate of leaves.(2) The influences of sediment properties and plant community types on P speciation in sediments under four plant community types in the tidal flat and offshore sandbar were investigated. The rank order of P species in sediment based on concentration was exchangeable P (Exch-P)<Fe/Al bound P (Fe/Al-P)<organic P (Org-P)<Ca bound P (Ca-P). Sediment TP and Fe/Al-P concentrations were lower in offshore sandbar than that of tidal flat, reflecting effects of anthropogenic contamination in the latter. Sediment particle size distribution strongly affected P speciation, as indicated by significant correlation between them. TP and Org-P concentrations in vegetated sediments were higher than that of bare mudflat. Additionally, there was significant negative correlation between Ca-P and Org-P, and Fe/Al-P, indicating the presence of plant may result in P speciation by converting Ca-P to soluble and active P, and higher Org-P. Overall, sediment particle size distribution is the most fundamental physical property that affects P speciation, and plant community types are important factors that influence Org-P concentration. The bioavailable P in sediments generally included Exch-P, Fe/Al-P and part of Org-P in study area varied from32.9-134.2mg/kg, with measured sedimentary P ranging from5.78～21.3%.(3) Phosphate adsorption kinetics and isotherms on sediment under different plant community types in Hangzhou Bay wetland were studied, and the influence of the sediment physicochemical properties on P sorption characteristics were analyzed. The results showed that there were three stages during sediment adsorption process with rapid adsorption (0-1h), slow adsorption (1～16h) and balance (16～72h). The trend was not affected significantly by different plants. Indexes fitted from improved Langmuir model showed that sediment Qmax is between154.5～436.3mg·kg-1, and is significantly higher in sediment with plant growth than that of bare mudflat. The Qmaxis also higher than the results of adjacent areas. Sediment NAP is between1.84～4.78mg·kg-1, indicating a low native adsorbed exchangeable P. NAP trends between different types of sediments are similar to that of Qmax values. Sediments EPC0under different plant community types are lower than soluble reactive P concentration in the overlying water. So the sediment acts as the P "sink" from tidal water. The variation of EPCo between different sediments is minor. Correlation analysis showed that the sediment Qmax and NAP in Hangzhou Bay wetland were affected by organic matter, particle composition and total inorganic P concentration, and Qmax is also affected by the electrical conductivity value. However, there are no significant correlations between sediments EPCo and physicochemical properties. In conclusion of that, plants can affect the physical and chemical parameters of sediments, thus affecting the adsorption kinetics and isotherms of P.(4) The influences of sediment biochemical properties and plant community types on P speciation in sediments were investigated. Surveys carried out in spring and autumn showed that alkaline phosphatase activity (APA) varied among seasons and plant community types. There were significant positive correlation between APA and Fe/Al-P concentrations, and significant native correlation between APA and Ca-P. This indicates that APA affects the transformation of P forms in sediments. Sediment microbial community functional diversity analysis using Biolog Eco-plate showed that the sediment microbial carbon metabolic function diversity increased with the succession of plant community. Analysis of PCA showed that carbon sources of sugars and amino acids and their derivatives indicate strong differentiation for the microbial communities under different plant community types. Microbial total PLFAs were under S. alterniflora> P. australis> S. mariqueter> bare mudflut. The plant growth increased the microbial biomass than that of bare mudflut. There was significant positive correlation between bacteria PLFAs and APA, while no significant positive correlation between different types of microbial biomass and different P species. As a result, further attention on key functional bacteria in P cycling was needed.(5) The distribution patter of P pools in the sediments and plants were analyzed. Phosphours retention capacity during the process of plants uptake and sedimentation in the marshes were calculated. More than98%of the P pools distributed in sediment while only little percent in plant system. The water purification coefficient (WPC) of P by plant assimilation was6.04～24.0t·(m-2yr-1). According to the sedimentation rate, retention of P in sediments were25.4～31.5g·(m-2yr-1). Sediment has a higher retention capacity than that of plants. Overall, these results suggest that higher annual plant biomass and nutrient assimilation contribute to greater nutrient retention capacity and accumulation in sediments, thereby enabling reduced eutrophication in the transitional waters.更多还原