摘要
随着经济发展和城市化进程的逐步推进,浅型湖库存在的水化学污染和富营养化问题日趋严重,其中水体中氮、磷等营养盐的输入和富集是导致湖库水体富营养化,继之浮游植物大量繁殖的根本原因。底泥(沉积物)是富营养化水体营养盐的主要蓄积库,其内源负荷释放导致水体富营养化问题更加突出。而浅型湖库沉积物—水界面处的营养物质的运移是湖库底泥中的内源负荷释放和水体营养物质积聚的重要途径,氮、磷等生源要素的垂向循环研究,是了解沉积物—水界面氮、磷迁移规律及湖库内源性营养物质“源／汇”转换机理的基础,也可为水体富营养化的综合治理提供基础资料和科学依据。
本文通过在典型的富营养化浅型湖库——滇池水域采样(共采集水样500L、底泥样40kg)作为模拟材料,利用PVC试筒和塑料筒作为模拟装置,进行水体中氮、磷沉降和沉积物中氮、磷扩散的室内模拟实验,以及pH值对氮、磷迁移的影响模拟实验,通过综合分析和动力学模拟,获取了对沉积物—水界面中各形态氮、磷迁移转化的规律性认识。主要成果如下：
1、共完成测试样品2292件,其中水体样总氮TN、硝酸盐氮N03--N、亚硝酸盐氮NO2--N、铵态氮NH4+-N、总磷TP及可溶性磷DP浓度值各352件,底泥样TN.TP浓度值各90件。
2、研究区水体中的氮、磷浓度值远超出水体富营养化临界值,且沉积物中的氮、磷营养盐存在明显的“源/汇”转换,并与上覆水体间存在能量与物质交换。
3、沉积物是水体中NH4+-N的蓄积库,富氧条件下,沉积物中的有机氮化物经矿化作用,产生NH4+-N等无机离子扩散进入上覆水体中；NH4+-N由硝化细菌通过硝化作用转化为NO3--N,部分转化为NO2--N,并最终转化为NO3--N；NO3--N是含氮有机物氧化分解的最终产物。在相同的水深条件下,底泥的厚度越大则上覆水中的TP、DP、NO2--N.NH4+-N、浓度越大。酸性条件下,硝化作用被抑制,水体中的氮(N)以NH4+-N的形态存在；磷(P)的浓度则与中性条件接近,不受酸性条件影响；碱性条件下,沉积物P的释放作用以及水体P达到一定浓度时的沉降作用均非常强烈；各形态的N的浓度则与中性条件下的浓度和随时间的变化量接近,受碱性条件影响不大：弱碱环境促进NH4+-N硝化生成NO2--N,NO3--N也亦被反硝化生成NO2--N。
4、利用实验数据中获取氮、磷转化的各种参数(氮的转化速率参数、磷的沉降系数和释放系数),初步建立了只考虑沉积物和水体中P释放沉降垂向过程的水体一维全磷迁移模型,以及一维“三氮”(NH4+-N、NO3--N、NO2--N)迁移转化模型。将模拟实验的数据应用到“三氮”迁移转化模型中,模拟显示三种形态的N迁移转化的趋势与一级化学动力学方程理论计算曲线相一致；将全磷迁移模型运用到滇池中,并利用监测点2003年的监测数据进行对比,结果有较好的吻合度。
5、本次建立的现代沉积物—水界面氮、磷迁移、转化模拟实验的流程、方法技术,以及获取的大量实验数据,可为有关实验研究提供借鉴,建立的动力学模拟模型可用于预测富营养化水体中氮、磷浓度的变化趋势及其迁移转化规律。
With the development of economic and urbanization, hydrochemical pollution and eutrophication of the shallow-type lake and reservoir becomes more and more serious.The import and beneficiation of the nutritive material such as nitrogen and phosphorus, is the fundamental reason of eutrophication and phytoplankton bloom of the water. Modern sedimentary is the main carrier of the nutritive material in the eutrophia water substance, and the releasing of these make the problem of the eutrophication more serious. Modern sedimentary-water interface is one of the most important interfaces in the lake and reservoir, nourishment material transferring between modern sedimentary and waterbody is the important approach of the endogenous capacity release in the substrate sludge and the accumulation of nourishment material in the water.Research of the vertical circulation of biogenic elements like nitrogen andphosphorus,and the diffusion, inversion and migration in vertical circulation of vital factors like nitrogen, phosphorus etc. is the key to understand the migration and transformation laws of nitrogen and phosphorus between modern sedimentary and water and the conversion mechanism of endogenous nutrients in the shallow-type lake and reservoir. And the results can provide a series of primary data and scientific principle for the eutrophication control and comprehensive management of lake and reservoir.
As a case to Dianchi Lake, sampling in the typical eutrophic shallow-type-lake and reservoir(water sample 500 litre, modern sedimentary sample 40 kilogram),using the PVC bucket and the bucket made of plastic as the analog device, indoor simulation experiment—sedimentation experiment of nitrogen, phosphorus in water substance, diffusion experiment of nitrogen, phosphorus in modern sedimentary, pH vable of nitrogen and phosphorus migration. A series of migration and transformation laws about various forms of nitrogen and phosphorus has been provided. Based on the comprehensive studying, the results obtained is listed as follows:
Firstly, tested 2292 simples altogether,the simple of consistency on TN, NO3--N, NO2--N, NH4+-N, TP, DP in water has 352 pieces each and the simple of consistency on TN, TP in modern sedimentary has 90 pieces each.
Secondly, in the study area, concentration of the nitrogen and phosphorus far beyond the critical value of eutrophication. Nitrogen and phosphorus in the modern sedimentary has a clear "source/sink" conversion,and changes energy and matter with the water.
Thirdly, modern sedimentary is the carrier of NH4+-N in water substance.When oxygen is sufficient, organic nitrogen content of modern sedimentary generate NH4+-N and other inorganic ion diffusion into the overlying water, nitrifying bacteria translate the NH4+-N into NOO--N by nitration, part into NO2--N, ultimately translated into NO3-N. Insufficient oxygen in the water substance, inhibiting the occurrence of nitrification, N in the overlying water mainly existed in the form of NH4+-N. When water depth in the same conditions,the greater thickness of substrate sludge is, the greater concentration of NO2--N、H4+-N、TP、DP in overlying water becomes. Under the acidic conditions, nitrification was inhibited, the N in water in the form of NH4+-N, yet P is not affected. In alkaline conditions, the release action of P in modern sedimentary and the deposition of P in the water that reaches a certain concentration are very strong, and all the forms of N are not affected. In alkalescent environment, NH4+-N turns to NO2--N by nitrification,and NO3--N turns to NO2--N by denitrification.
Fourthly, on the basis of obtainning various parameter of nitrogen, phosphorus conversion from the experimental data(including rate parameters of the transformation of nitrogen, sedimentation and release coefficient of phosphorus), the one-dimensional TP models of TP concentration in the different depth of water change over time, and the one-dimensional "3N" (NH4+-N、NO3--N、NO2--N) model of migration and transformation is established. Then, applying the simulation experiment data to the model, the compatibility of the trend of the migration and transformation of "3N" and the theoretical calculation curve of first-order chemical dynamic equation is gained. Using the migaration model of TP to the Dianchi lake, and comparing with the monitoring data of the monitoring points in 2003, it is showed that there be little difference between them.
Lastly, the simulation experimental process of the transformation and migration of nitrogen and phosphorus between modern sedimentary and waterbody, and the detailed methods and techniques established in this thesis can be used to the similar research field. At the same time, a large number of experimental data can also be refered to other related experiments. The dynamics simulation model could be used to forecasting the consistency trends and migration laws of nitrogen and phosphorus in the eutrophia water of Dianchi lake and similar shallow-type lake and reservoir.
引文
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