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题名: 太湖沉积物-水界面营养盐/重金属的物质通量研究
作者: 狄贞珍1
学位类别: 博士
答辩日期: 2016-11
授予单位: 中国科学院大学
授予地点: 北京
导师: 单保庆 ; 张洪
关键词: 太湖,浅水湖泊,氮,磷,重金属,沉积通量,扩散通量,污染风险 ; Taihu, shallow lake, phosphorus, nitrogen, heavy metal, accumulation fluxes, diffusionfluxes, pollution risk
其他题名: Study on fluxes of nutrients/heavy metals overthe sediment-water interface of the Taihu Lake
学位专业: 环境工程
中文摘要: 太湖是我国典型的大型浅水湖泊,近年来富营养化问题十分突出,富营养化造成藻类 快速繁殖并大量衰亡沉降至湖底,导致沉积物-水界面物质交换频繁,特殊的湖流现象使湖 心区具有明显的沉积作用。以太湖沉积物-上覆水界面为研究对象,于2013 年夏季采集48 个样点的沉积物柱状样(简称“沉积柱”),选取其中13 个沉积柱,采用210Pb 和137Cs 年代 学方法,分析太湖沉积速率的历史变化过程,探讨湖泊富营养化对于有机质沉积物过程的 影响,并研究沉积物氮磷营养盐和典型重金属含量和通量年变化。对48 个采样点,通过一 维孔隙水扩散模型,估算沉积物-水界面的营养盐和重金属的扩散通量,分析内源负荷对上 覆水水质影响;在此基础上,估算由于人为活动导致的营养盐和重金属累积状况,并预测 沉积物中营养盐磷的释放时间,为我国东部富营养化严重的浅水湖泊的沉积物营养盐和重 金属潜在的污染风险提供理论基础。主要研究结论如下: 1)富营养化导致太湖沉积速率增加,20 世纪80 年代是沉积速率突增的拐点。 在全湖范围内,太湖的沉积物沉积速率在1960 年以前稳定在较低水平,然后随年代普 遍递增,在20 世纪80 年代后增加尤为明显。湖心区的沉积物沉积速率从1950 年以前的 0.026~0.188 g cm-2 a-1 递增到1980 前后的0.035~0.278 g cm-2 a-1。在1980 年以后各样点的 沉积速率突增明显,在2000 年后达到0.078~0.486 g cm-2 a-1。太湖竺山湾、梅梁湾、西部 沿岸区、南部沿岸区和东部湖区的沉积物沉积速率的年变化趋势与湖心区的沉积速率年变 化趋势相似。沉积物中总碳含量和沉积速率具有显著正相关关系,总碳含量偏离自然衰减 曲线的时间点与沉积速率突增的时间点一致,表明沉积速率与提供沉积物碳源的水生生物 关系密切,20 世纪80 年代后太湖沉积速率的增加与上覆水中水生生物,尤其是水华藻类 的沉积具有密切关系。 2)太湖湖心区相比于其他湖区的沉积速率较大,导致营养盐和重金属在湖心区沉积作 用明显。 湖心区中部在20 世纪80 年代后的沉积速率增长迅速,在近二十年间的沉积速率达到 全湖区的最大值。近几年间(2009~2012)太湖湖心区磷的年沉积通量为628~3600 t a-1,氮 的年沉积通量为1080~5110 t a-1。沉积速率对湖心区氮磷沉积通量的作用比沉积物中氮磷 含量的作用大。与沉积物中磷和氮含量相比,太湖湖心区的营养盐沉积通量与历史富营养 化指数具有更强的相关性,磷和氮的沉积通量更适合指示历史上营养物质从上覆水向沉积 物输送的变化,并更适合用来反映自20 世纪80 年代早期以来太湖日益加重的富营养程度。 湖心区8 种重金属含量(V、Cr、Ni、Cu、Zn、As、Cd 和Pb)的沉积通量与沉积物沉积 速率显著正相关,呈现随年代递增的变化规律。可见湖心区的沉积速率在太湖中污染物沉 积过程中起到重要作用。 3)太湖沉积物中氨氮、正磷酸盐、重金属离子的內源负荷为正值,呈现从沉积物向上 覆水释放的趋势。 太湖表层沉积物孔隙水中的正磷酸盐和氨氮浓度较高,在北部湖湾区的正磷酸盐浓度 和大部分湖区的氨氮浓度高于现行的《地表水质量标准(GB3838-2002)》中Ⅴ类水质标准 限值(NH3-N > 2.0 mg L-1,TP > 0.4 mg L-1)。北部三个湖湾区的沉积物营养盐(包括正磷 酸盐和氨氮)扩散通量最高,正磷酸盐为2.69~4.60 mg m-2 d-1,氨氮为17.8~45.7 mg m-2 d-1, 而湖岸河口区是沉积物中硝氮内源释放显著的区域。全湖区范围内,沉积物向上覆水释放 正磷酸盐和氨氮的年内源污染负荷分别为64.6 t a-1 和1756 t a-1,使太湖表层水中营养盐水 质恶化,氨氮、总磷和总氮内源污染为上覆水贡献的浓度分别为0.361,0.013 和0.134 mg L-1,使氨氮由未污染水质变为III 类水质,总磷由I 类水质变为II 类水质,总氮由V 类水 质变为劣V 类水质。在太湖沉积物孔隙水中,As 浓度高达0.1mg L-1 以上。在部分湖区Zn 浓度大于0.05mg L-1,Cr 和Pb 浓度大于0.01mg L-1。除了北部湖湾区,Cd、As、Zn 在东 部和湖心区的内源释放风险较大,其最大扩散通量分别超过0.284μg m-2 d-1,108 μg m-2 d- 1,53.3 μg m-2 d-1。As、Zn、Mn 和Fe 在大部分湖区均有释放风险。全湖范围内,所有重金 属均呈现向上覆水释放的总内源负荷量,Cd 最低,为0.24 t a-1,Cu、Zn、Ni、Pb、Cr 分 别为26.44 t a-1,32.8 t a-1,13.7 t a-1,7.94 t a-1,11.4 t a-1,As、Mn 和Fe 最高,分别为38.10 t a-1, 2276 t a-1,3615 t a-1。 4)湖心区的氮磷和重金属在近5 年的沉积通量增加比过去迅速,磷净沉积总量超过西 部沿岸区,东部河口处、北部湖区和湖湾区的磷循环十分活跃。 湖心区在近5 年的氮磷平均沉积通量和自1980 年以来的氮磷沉积总量都较大,仅次 于浒光运河河口的对应值。湖心区的V 和Pb 自1980 年以来的沉积通量最大。湖心区的磷 净沉积总量超过了西部沿岸区,达到34.8 g m-2,对将来的磷释放可能带来巨大影响。与其 他湖区相比,磷在东部河口处和北部湖区的释放总量较大,其最大释放总量分别达到57.0 g m-2 和21.2 g m-2,说明这两个区域的磷释放风险十分突出。东部河口处、北部湖区和湖 湾区的磷最小释放时间为负值或为很小的正值,说明这些区域的磷循环十分活跃,表明这 些区域很容易发生初级生产力增加,并导致富营养化现象频发。
英文摘要: The Taihu Lake (Taihu for short), as a typical large shallow lake, has been suffering from eutrophication for decades. This problem not only results in lots of algae blooms but also makes debris of plankton settle in the bottom of the lake, which facilitates fast exchanges of chemicals at the sediment-water interface. Special currents in the overlying water bring sedimentation of plankton and chemicals in the center of Taihu. Sediment-water interface of Taihu was chose to study with 48 sampling sediment cores in the summer of 2013. Choosing 13 sampling points and using the chronology of 210Pb and 137Cs, the changing mass accumulation rates in the history of 100 years were analyzed, the influences of eutrophication on the sedimentation of organic carbon were studied, and the changing accumulation fluxes of nutrients (phosphorus and nitrogen) and heavy metals were calculated. By the one-dimensional diffusion models in the 48 sampling points, the diffusion fluxes of nutrients and heavy metals at the sediment-water interface were estimated and the internal pollution loads of them were analyzed to explain their influences on the water quality. Based on these theories above, the net accumulation masses of nutrient and heavy metals due to human activities were estimated to predict the releasing time of t pollutants from the sediment of Taihu and to provide theoretical foundation to help evaluate the pollution risk of nutrients and heavy metals and to develop the benchmark of sedimental nutrients and heavy metals of the shallow lakes in China. The main results were as followed: 1) Eutrophication made the mass accumulation rates increase by year and the increasing trend turned to speed up after the 1980s. Over the whole lake, the mass accumulation rates (MARs) stayed at a relatively low level before the 1960s, and had been increasing until recently, with a higher speed after the 1980s. In the Center Lake (CL for short) zone, MARs increased from 0.026 - 0.188 g cm-2 a-1 pre-1950 to 0.035 - 0.278 g cm-2 a-1 in ~1980. After ~1980, MARs in all lake zones surged obviously and kept increasing to 0.078 - 0.486 g cm-2 a-1 after ~2000. The lake zones of Zhushan, Meiliang, West, South and East had the similar trend about the yearly changes of mass accumulation rates to the CL zones. The total carbon contents in sediment had a positively significant relationship to MARs, and the measured values of TC in each lake zone went further from the fitting curves when the MARs sharped up, giving evidence that the MARs had close relationship with the plankton who provided carbon source. That is to say, after the 1980s, the increased MARs in Taihu attributed to the algae blooms of eutrophication. 2) The central zone of Taihu had larger mass accumulation rates than other lake zones, leading to larger accumulation fluxes of nutrients and heavy metals in this zone. The MARs of the CL zone grew quickly after the 1980s, and reached the maximum point of the whole lake. In recent years (2009 - 2012), based on the area of the CL zone, the average accumulation fluxes of phosphorus were 628 - 3600 t a-1, and that of nitrogen were 1080 - 5110 t a-1. The MARs contributed more to the accumulation fluxes of nutrients, rather than the contents of them. What’s more, comparing with the sedimental phosphorus and nitrogen, the MARs of the CL zone had a positive correlation with the eutrophication indexes (EI) with higher coefficients, showing that MARs had a more closely relationship to the transport processes of nutrients from the overlying water to the sediment and had a better reflection of increased eutrophication degree due to human activities after the 1980s. The accumulation fluxes of eight metal elements (V, Cr, Ni, Cu, Zn, As, Cd, Pb) were positively correlated with the MARs in the past 100 years with the same yearly increasing trend, indicating that the MARs of the CL zone of Taihu played an important role in the sedimentation of pollutants. 3) The sediment of Taihu had positive values of pollution loads of orthophosphate and heavy metal icons, presenting a phenomenon of releasing from the sediment to the overlying water. The concentrations of PO43--P and NH4+-N were relatively high in the porewater of the surface sediment of Taihu. The concentrations of PO43--P in the northern bays and the concentrations of NH4+-N in most zones had higher values than the thresholds in the Chinese government document of the Surface Water Quality Standard (GB3838-2002) of 2.0 mg L-1 (NH4+-N) and 0.4 mg L-1(TP). In the three northern bays, the diffusion fluxes of nutrients had the largest values of 2.69 -4.60 mg m-2 d-1 (PO43--P) and 17.8 - 45.7 mg m-2 d-1 (NH4+-N), and NO3--N released from sedimentto overlying water in the estuaries near the lakeshore. Over the whole Taihu, the annual internalpollution loads of PO43--P and NH4+-N in the sediment of Taihu were 64.6 t a-1 and 1756 t a-1,which may lead to threaten the quality of overlying water with increasing levels of 0.361 mg L-1(NH4+-N),0.013 mg L-1 (TN ) and 0.134 mg L-1 (TP) and make NH4+-N change from theunpolluted level to the third pollution level, TP change from the first pollution level to the second one and TN change from the fifth pollution level to the worse fifth one. In the porewater of the surface sediments in Taihu, As had a high concentration more than 0.1mg L-1 in most zones, Zn more than 0.05 mg L-1, Cr and Pb more than 0.01 mg L-1in some zones. Like the northern zones, Cd, As, Zn had relatively large releasing risks in the eastern and the central zones with the maximum diffusion fluxes of over 0.284μg m-2 d-1for Cd, over 108 μg m-2 d-1 for As, and over 53.3μg m-2 d-1 for Zn. As, Zn, Mn and Fe had releasing risks in most zones. Over the whole lake, all of the heavy metals had positive internal pollution loads from the sediment to the overlying water with the lowest values of 0.24 t a-1 for Cd, and then 26.4 t a-1 for Cu, 32.8 t a-1 for Zn, 13.7 t a-1 for Ni, 7.94 t a-1 for Pb, 11.4 t a-1 for Cr, and the highest values of 38.1 t a-1 for As, 2276 t a-1 for Mn,3615 t a-1 for Fe. 4) The average accumulation fluxes of phosphorus, nitrogen and heavy metals increased quickly in recent five years in the CL zone faster than before, with a larger net accumulation mass of phosphorus than the western lake zone, and the eastern estuary, the northern lake zone and the bays had very active processes of phosphorus recycling. The CL zone had relatively larger values of the average accumulation fluxes of phosphorus and nitrogen in recent 5 years and the accumulation mass since 1980 of them, which were lager than other zones except the eastern Huguang Canal estuary. The accumulation mass since 1980 of V and Pb had the highest values in the CL zone. The CL zone had higher net accumulation mass of phosphorus than the western lake zone, with the value of 34.8 g m-2, which may have significant influence on the phosphorus release from the sediment of Taihu in future. The eastern estuaries and the northern zones had larger releasing amounts of phosphorus than other lake zones, with the maximum ones of 57.0 g m-2and 21.2 g m-2, indicating that these zones had larger pollution risks than the other zones. The smallest releasing time of the eastern estuary, the northern lake zone and the bays was below zero or very short below one hundred years, showing very active phosphorus recycling processes in these zones, giving evidence that the primary productivity were likely to grow and lead to eutrophication frequently.
内容类型: 学位论文
URI标识: http://ir.rcees.ac.cn/handle/311016/38614
Appears in Collections:环境水质学国家重点实验室_学位论文

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Recommended Citation:
狄贞珍. 太湖沉积物-水界面营养盐/重金属的物质通量研究[D]. 北京. 中国科学院大学. 2016.
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