【作者】 张莹莹；

【导师】 张经；

【作者基本信息】 华东师范大学 ， 自然地理学， 2007， 博士

【摘要】 陆—海交汇处河口混合区具有多方面的功能。河口中盐度、悬浮泥沙浓度等因素的时空变化频繁，并通过吸附及解吸等过程在一定程度上控制着营养元素在颗粒固相和液相之间的相态分配。当进入河口与近海的陆源生物要素的赋存形式、数量与季节发生改变时会导致相应生态系统的结构和功能产生变化。中国河流普遍具有水浅、多沙和径流量大的显著特征，因此，研究中国河口区元素固—液相态变化过程具有区域特殊性意义。而长江河口区是研究陆—海相互作用的重要场所，可作为研究生物地球化学过程的天然实验室。本论文即针对取自长江口的样品，系统地研究了pH，悬浮颗粒物浓度、盐度、温度、体系中营养盐的总量和溶氧等重要环境因素对营养元素固—液相态变化的影响。基于现场调查和实验室中的模拟，认识如下：1．长江淡水端元中营养盐（溶解无机氮和无机磷）呈指数增长，与此相反，同期活性硅酸盐的浓度呈指数降低了一半左右。随着长江中氮和磷浓度持续增大而硅浓度持续降低，其结果是长江水中营养盐组成（即N：Si：P比值）发生了巨大变化。虽然N：P比值波动较大，但其总趋势是逐渐增大，1965—1975年长江水中N：P比值约为60，而到了1985年后N：P比值陡升至125，且随后基本围绕此值上下波动。与此同期，Si：N比值则从20世纪60年代的15以上呈指数降低至现在接近于1。2．随着长江水中营养盐的巨大变化，长江口中营养盐的浓度和比例也发生了显著改变。虽然长江口无机磷浓度年平均值变化不大，但长江口无机氮浓度年平均值从20世纪60年代到21世纪初增大了1倍；而同期活性硅酸盐浓度年平均值则降低为以前的1／3。至于长江口营养盐比值，其长期变化趋势与长江水中营养盐比值的变化相似，但变化幅度略小。长江口N：P比值60年代约为20，接近于Redfield比值（即N：P=16），2002年已增大到35，约为Redfield比值的2倍；Si：N比值从远大于Redfield比值（即Si：N=1）的3.9降低至2002年略小于Redfield比值的0.8，表明Si将有可能成为长江口生态系统中的限制因子。3．营养盐的分布特点是从口门向外海逐渐递减。长江冲淡水终年存在向长江口东北部输送营养盐的趋势。夏季，高营养盐水舌向东北方向延伸，与冲淡水分布趋势相似；冬季，径流量减少，冲淡水沿岸南下，高营养盐水舌也随之向东南延伸，同时高浓度营养盐的分布范围也向河口方向退缩。4．模拟实验研究显示：磷酸盐吸附量随悬浮颗粒物浓度的变化而变化，尽管水体中颗粒物浓度升高后，单位质量颗粒物上磷酸盐的吸附量降低，但是绝对吸附量仍然增加，也就是说，当水体中悬浮颗粒物浓度较高，悬浮颗粒物对磷酸盐处于吸附状态时，水相中磷酸盐浓度随悬浮物浓度的升高呈降低趋势。随着磷酸盐浓度的增加，体系中SPM对磷酸盐的吸附百分率逐渐降低。无机磷固一液分配程度随着盐度的增加，逐渐增强。SPM对磷酸盐的吸附为吸热反应。SPM对无机P的吸附随溶液中有机质的增加而增大，随溶液中DO含量的增加而增大。且磷酸盐在长江口水体固一液相之间的分配过程不可逆。5．在实验的pH范围内，悬浮颗粒物对NH₄⁺-N的吸附百分率E（％）随着体系pH值的增加而增大，呈“S”形曲线。水体pH、悬浮颗粒物浓度和溶氧的增大总是促进着NH₄⁺-N吸附百分率的增加，而盐度、温度和体系中NH₄⁺-N量的增大则使吸附百分率规律性地减小。盐水解吸实验和相同条件下的吸附实验表明，NH₄⁺-N在长江口水体固—液相之间的分配过程是不可逆的。温度的实验表明，悬浮颗粒物对NH₄⁺-N的吸附可能是一个放热反应过程。6．悬浮颗粒物中SiP₃^2-的解吸量随盐度的升高而增加；悬浮颗粒物对NO₃^-最大解吸量出现在S=15附近。在极值以前，解吸量随盐度增大而增大；在极值以后则相反。悬浮颗粒物中NO₃^-的解吸在pH实验的范围内（5—9）基本保持不变；而悬浮颗粒物中SiO₃^2-的解吸则随着pH值的增大逐渐增加，趋势与盐度对其解吸影响一致。体系DO的变化对颗粒物中SiO₃^2-的解吸基本没有影响，随着体系DO的升高，悬浮颗粒物中NO₃^-的解吸量有增大的趋势。7．本文基于模拟实验研究的模式分析以及对长江口几种营养盐的历史观测资料都表明，溶解态SiO₃^2-与NO₃^-现出显见的混合保守性，PO₄^3-在底层呈现出混合保守性，在表层低盐度表现为一定的溶出，NH₄⁺-N在表层低盐度下呈现出溶出，高盐度表现为溶入行为，在底层的低盐度表现为部分的保守行为，高盐度区域也表现为溶入行为。通过比较模式分析结果与现场观测资料，可以认为，综合考虑悬浮泥沙浓度、盐度和水体pH等其他环境因子协同变化对营养盐溶解态浓度在长江口混合区——特别是在盐度小于20的高浊度区——模拟实验的结果更能反映出现场的真实情况。更多还原

【Abstract】 Estuarine mixing zone between the land and the ocean has multiple functions.Water properties like the concentration of suspended particle matter, Salinity,temperature, DOC, DO and pH in the estuary vary in time and space, and alter thenutrients partitioning between solid phase and solution via adsorption and desorption.Seaward nutrient fluxes change considerably in the estuary and it is important tounderstand the effects of estuarine processes on the phase transformation of nutrientin order that the flux of dissolved phase can be properly made.Chinese estuaries are shallow with abundant water and high concentration ofsuspended sediments, and of particularly interested in studying particulate-solutiontransformation. The Chanjiang Estuary serves as an important land-ocean interactionregion and can be taken as a natural laboratory for studying estuarine biogeochemicalprocesses. In this study, effects of salinity, pH, temperature, dissolved oxygen, organicmatter and SPM on the solid-liquid phase partitioning for nutrients (PO₄^3-, NH₄⁺,SiO₃^2-, NO₃^-) were examined with the samples from Changjing Estuary.Based on the data obtained from in-situ observation and laboratory simulation,some of the results can be summarized below.1. The concentration of suspended particle matter in the Chanjiang Estuary variesconsiderably. Within the maximum turbidity zone, concentration of suspended particlematter reaches up to m ore than 5×10³ mg L^-1. The pH range within the Changjiangestuary is limited to 7.7-8.3.2. Simulation results show that adsorption edges for phosphate adsorption on toSPM under different conditions illustrate the upended sigmoid curve characteristic oftransition phosphate. Changes in pH for the samples have a significant effect on thesolid-liquid partition of phosphate. The adsorption percentage of the phosphate wasincreased with pH-specifically increasing the pH of the water samples inducedpartitioning of phosphate to solid phases. The percentage of the adsorption andpartitioning coefficients for phosphate in the Changjiang Estuary deceasedsignificantly with higher concentrations of phosphate.3. For phosphorus, desorption was higher in seawater than that in fresh water. Asharp increase in percent desorption with an increase in salinity was obviouslyobserved in low salinity（S＜15） water. The amount of phosphorus released increased with an increase pH was previously observed for phosphorus in mixtures. All theprocesses discussed here play a major role in the retention of phosphate in particlesand ultimately in estuaries. Based on the sorption K_d values presented here, we wouldexpect that phosphate would be trapped in the estuarine environment as the metals aremostly associated with the particulate phase in estuaries. The model developed here isin accordance with the observed distribution patterns of phosphate in the ChangjiangEstuary.4. The adsorption edges for NH₄-N adsorption to SPM under different conditionsillustrate the sigmoid curve characteristic of transition NH₄-N. Changes in pH for thesamples from the Changjiang Estuary have a significant effect on the solid-liquidpartition of NH₄-N. The adsorption percentage of the NH₄-N in the experiments wasincreased with pH of the water samples induced partitioning of NH₄-N to solidphases.5. The adsorption percentage of the NH₄-N in the experiments was increasedwith the increasing of SPM, DO of the water samples, while the adsorptionpercentage of the NH₄-N in the experiments was decreased with the increasing ofsalinity, temperature and the concentration of NH₄-N in the samples.6. The desorption percentage of the SiO₃^2- in the experiments was increasedsalinity. When S=15, there was a maximum in the desorption percentage of the NO₃^-.The desorption percentage of the NO₃^- in the experiments was increased when S＜15,while S＞15, the desorption percentage of the NO₃^- in the experiments was decreased.The desorption percentage of the SiO₃^2- in the experiments was increased pH, also.While the desorption percentage of the NO₃^- would be constant with the change of thepH. Dissolved oxygen would not affect the desorption percentage of the SiO₃^2- OffSPM, and the desorption percentage of the NO₃^- was increased with DO7. The Changjiang estuary is known to contribute significantly to theeutrophication that has caused drastic changes to the ecosystem of the East China Sea.However, evidence for historical changes in nutrient concentrations and compositionand the consequent effects on the ecosystem in the coastal water is sparse. Somelong-term data for nutrient concentrations and Si: N: P ratios in the freshwater and theestuary and the long-term response of the ecosystem structure in the estuary. Thesedata reveal increases in the dissolved inorganic nitrogen and phosphate concentrationsin the Changjiang freshwater by a factor of five from the1950s to the end of the 2000sand a reduction in dissolved silicate by two thirds over the same period. Concomitantly, an increase in DIN concentration and a reduction in silicateconcentration both by a factor of two were observed in the surface water of theChangjiang estuary.更多还原