陆地人类活动排放的营养物质和重金属污染物进入水体，最终汇聚于河口进入海洋并影响全球海洋生态环境安全。沉积物是河流和海洋水环境的基本要素，对沉积物的分析既有助于探究河口三角洲的冲淤演变，也可以量化河流-河口变化环境下污染物的沿程变化规律及其对环境的影响，同时揭示河口和流域的环境质量与风险。但以上这些研究大都针对河口沉积物本身，很少有研究将河口沉积物的“汇”与河流沉积物的“源”进行耦合研究。因此，在研究河口海岸带中污染物迁移转化机制时，如能考虑上游河流沉积物沿程迁移变化的规律，对于揭示污染物的河流-河口源汇效应具有重要意义。黄河是全球主要的含沙河流，黄河水沙环境的变化加剧了河口的生态风险和敏感性。尽管近年来对黄河口污染物的迁移特征、污染水平和时空分布已有很多研究，但通过分析污染物在河口的沉积通量累积规律，逆向探寻流域泥沙污染物流失与河口三角洲沉积属性之间的定量关系尚少有报道。如何建立河口沉积通量-流域流失通量之间的定量关系，是基于河口环境质量变化反演流域污染物流失负荷响应机制中的关键。

针对上述问题，首先，本研究基于遥感反演、野外采样和历史水文资料相结合的方法探究三角洲面积和入海泥沙的变化趋势及组成特征，解析了入海泥沙特性与河口污染物沉积的关系，揭示了重金属对磷沉积通量的响应特征；其次，通过野外采样和室内实验，系统地分析磷在黄河干流的沿程变化和分布差异特征，探究了磷的吸附规律和形态特征，识别了不同河段磷流失特征差异的主控因素；再次，系统地分析黄河干流沉积物中重金属的沿程变化和分布差异特征，评价了重金属的富集程度和环境风险，明晰了不同形态重金属对污染的影响差异以及磷和重金属的共输移机制，最后，基于上述内容背景，建立了SPARROW模型模拟了磷的输送和衰减动态过程，并在流域尺度上确定了不同磷源的负荷和贡献，识别了污染流失的关键源区，探究了黄河流域上中下游不同土地利用格局对磷负荷及产率的影响。主要结论如下：

(1) 河口区的沉积物主要受河口三角洲陆源输入的控制，粉土是黄河三角洲沉积物的主要类型，也是向海洋输送的主要物质。放射性核素定年分析可知，²¹⁰Pb_ex的比活度-深度曲线呈“混合层-衰减层-平衡层”三段垂直分布。根据CRS模型模拟结果，质量累积速率范围为41.67-1988.46 mg/cm²·yr^-1，平均线性沉积速率为0.61 cm/yr。通过CRS模型计算得出黄河口沉积物39 cm沉积柱代表了2009-2018年的沉积历史。应用线性回归分析揭示了重金属的沉积通量与磷的沉积通量之间的显著正相关关系，As、Cd和Cr与磷回归分析的r²值分别为0.981、0.991和0.639。沉积通量的年代-深度关系虽然显示出沉积通量在年际波动范围上出现了一些变化，但总体上仍然是保持一个上升的趋势，2017年磷的最高沉积通量达到22.68 g/m²·yr^-1。河口磷和重金属的相关性分析表明具有较大比表面积的细颗粒对重金属和磷具有较高的吸附量。RDA和MFA分析表明土壤养分相关金属 (Fe和Mn)与沉积物重要组分 (粉土和TOC)之间的交互作用不强，组内单个组分之间的相互作用相对较强。

(2) 黄河干流中的磷主要以颗粒态结合的形式出现，储存在悬浮颗粒物和表层沉积物中。悬浮颗粒物对磷的截留是减少水体磷的主要驱动力，表层沉积物的磷也可以反映出悬浮颗粒物的沉积趋势。表层沉积物中的总磷主要表现为HCl-P形态 (83.4%)。NaOH–P (2.4%)和OP (14.2%)两种形态占比非常低，平均值分别为14.64 ± 5.90 mg/kg和86.41 ± 24.52 mg/kg。NaOH-P和OP从上游到下游的变化趋势并不明显。HCl-P通常来源于沉积物老化过程中形成的难降解无机磷，不易释放，但是可以持续累积。NaOH-P主要由岩石风化形成产生，与Fe/Al等氢氧化物结合，两种形态均显示出本研究区较低的生物利用度。PCA和RDA分析表明，粉土组分和粒径是驱动黄河干流段沉积物对磷吸附的关键因素，随悬浮颗粒物的沉降是磷沉积的主要机制。除了颗粒大小对磷吸附起主导作用外，区域异质性也导致了悬浮颗粒物的不均匀分布，悬浮颗粒物的截留对溶解态磷的还原起着重要作用，从而驱动了磷的吸附和沉积。

(3) 黄河干流表层沉积物中的重金属As、Cd、Cr、Cu、Pb和Zn的含量分别为8.29 mg/kg、0.15 mg/kg、47.52 mg/kg、11.78 mg/kg、10.65 mg/kg和46.56 mg/kg，平均含量排序为：Cr > Zn > Cu > Pb > As > Cd。与中国土壤背景值 (SBV)比较，Cu、Pb、Zn的含量均低于对应的SBV。对黄河干流表层沉积物中重金属的形态分析表明，重金属主要以残渣态和可氧化态存在，重金属的生物可利用性较低。EF因子和I_geo指数显示Cd的污染水平最高，As污染存在轻微的污染水平。PERI指数表明黄河流域大多数地区被列为中度生态风险，贡献率依然以Cd为主。风险评价编码法可知全流域的重金属生态风险值RAC均在50%以下，未出现极高风险地区。磷和重金属形态之间的相关性表明As的可氧化态和残渣态与HCl-P有显著的相关性 (r = -0.63，p < 0.05；r = 0.64，p < 0.01)。Cd、Cr、Cu的可氧化形态与OP呈显著正相关。RDA分析揭示了Mz对As的形态有最大的正效应和对其他重金属可氧化态和残渣态的负效应。

(4) 黄河流域总磷的模拟负荷为 41.76×10⁴ t/yr，不同地区的磷负荷呈现很强的空间异质性，排序为中游 (736.08 t/yr) > 下游 (549.73 t/yr) > 上游 (470.32 t/yr)。对各污染源解析表明农田是子流域磷负荷的主要来源，建设用地是区分不同负荷水平的重要因素。黄河流域满足Ⅰ、Ⅱ类水质标准的河段长度分别占比18%和40.8%，总共占比约58.8%，主要分布在黄河干流源区和下游。Pearson相关性分析表明建设用地输出的磷负荷是影响水体磷浓度的最显著因素。蒙特卡洛敏感性分析表明磷产率对农田的敏感性最高，达到0.97，远高于其他土地利用类型，并且上游对农田更为敏感 (0.92)。在未来黄河流域磷污染的控制中，除了限制磷肥过量施用等措施以外，还要重点发展绿色生态农业，加强跨区域之间的环境投资与环境保护合作，从而能够在更大范围和空间配置资源和能源，这不仅仅有助于保护黄河流域的水环境和水生态，而且也为其他大流域的管理防治提供参考和借鉴。

Nutrients and heavy metal (HM) pollutants discharged into the water body finally gather in the estuary into the ocean and affect the global marine ecological environment security. Sediment is the fundamental element of the river and ocean environment. The sediment analysis helps explore the erosion and deposition evolution of the estuarine delta and quantify the variation law of pollutants along the river and estuary and their impact. It also reveals the environmental quality and risks of estuaries and watersheds. However, most of the above studies have focused on the estuary sediment itself. Few studies have coupled the "sink" of the estuary sediment with the "source" of the river sediment. Therefore, when studying the mechanism of pollutant migration and transformation in the estuary and coastal zone, it is crucial to reveal the river-estuary source-sink effect of pollutants if the mechanism of migration and variation along the upstream river sediment is feasible. The Yellow River is a major sediment-laden river in the world. Changes in the water and sediment environment of the Yellow River have exacerbated the ecological risks and sensitivity of the estuary. Although there have been many studies on the migration characteristics, pollution levels, and temporal and spatial distribution of pollutants in the Yellow River estuary recently, few studies explore the quantitative relationship between the loss of sediment pollutants in the basin and the sedimentary attributes of the estuary delta by analyzing the accumulation of pollutants in the estuary. Establishing the quantitative relationship between estuary sedimentation flux and basin-derived load is the key to inverting the response mechanism of pollutant loss load in the basin based on changes in estuary environmental quality.

To solve the above issues, firstly, based on the combination of remote sensing, field sampling, and historical hydrological data, this study investigated the variation trend and composition characteristics of the delta area and sediment into the sea, it furthered analyzed the relationship between sediment characteristics into the sea and estuarine pollutant deposition and revealed the response characteristics of HMs to phosphorus (P) deposition flux. Secondly, through in-situ monitoring and indoor experiments, P deposition flux was systematically analyzed. Based on the spatial deposition and distribution pattern of the mainstream of the Yellow River, the adsorption law and morphological characteristics of P were explored, and the main controlling factors of P loss characteristics in different river sections were identified. Thirdly, the spatial deposition and distribution pattern of HMs in the sediments of the mainstream of the Yellow River were systematically analyzed. The enrichment degree and environmental risk of HMs were evaluated to clarify the impact of different forms of HMs on ecological and P pollution. Finally, based on the above content, the SPARROW model was established to simulate the dynamic process of P transport and attenuation at the basin scale, discovering the load and contribution of different P sources. The effects of different land-use patterns on P load and flux in the upper, middle and lower reaches of the Yellow River Basin were explored. The critical source areas of pollution loss were identified. The main conclusions are as follows：

(1) Silt is the main component of the Yellow River Delta sediment and the primary material transported to the sea. The specific activity depth curve of ²¹⁰Pb_ex shows a vertical distribution of the "mixing layer-attenuation layer-equilibrium layer." According to CRS simulation results, the mass accumulation rate ranges from 41.67 to 1988.46 mg/(cm²·yr), and the average linear rate is 0.61 cm/yr. Through CRS model calculation, the 39 cm sediment column of the Yellow River Estuary represents the history of 2009-2018. Linear regression analysis revealed a significant positive correlation between the deposition fluxes of HMs and P. The R² values of As, Cd, Cr, and P were 0.981, 0.991, and 0.639, respectively. Although the age-depth relationship of sediment flux shows some changes in the interannual fluctuation range, it still maintains an upward trend on the whole, with the highest sediment flux reaching 22.68 g/m²·yr^-1 in 2017. Correlation analysis showed that small particles with a larger specific surface area had higher adsorption capacity for HMs and P. RDA and MFA analysis showed that the interaction between soil nutrient-related metals (Fe and Mn) and important sediment components (silt and TOC) was not strong. The interaction between individual components was relatively strong.

(2) Phosphorus in the mainstream of the Yellow River mainly appears in particle form, which is stored in suspended particles and surface sediments. The interception of P by suspended particulate matter is the main driving force to reduce P in the water body, and the P in surface sediment can also reflect the deposition trend of suspended particulate matter. The main form of total P in surface sediments was HCl-P (83.4%). The proportions of NaOH-P (2.4%) and OP (14.2%) were lower, with an average of 14.64 ± 5.90 and 86.41 ± 24.52 mg/kg, respectively. The variation trend of NaOH-P and OP from upstream to downstream is not apparent. HCl-P comes from inorganic P formed in the process of sediment aging, which is difficult to be released but can be accumulated continuously. NaOH-P is mainly formed by rock weathering and combined with Fe / Al hydroxides. Both forms show low bioavailability in this study area. PCA and RDA analysis show that fine sediment and smaller particle size are the key factors driving the P adsorption of sediments in the mainstream of the Yellow River. Sediment deposition is the primary mechanism of P deposition. In addition to the dominant role of particle size in P adsorption, regional heterogeneity also leads to the uneven distribution of suspended particles. The interception of suspended particles plays an essential role in reducing dissolved P, thus driving the adsorption and deposition of P.

(3) The average concentrations of As, Cd, Cr, Cu, Pb and Zn were 8.29 mg/kg, 0.15 mg/kg, 47.52 mg/kg, 11.78 mg/kg, 10.65 mg/kg and 46.56 mg/kg, respectively, with the order of Cr > Zn > Cu > Pb > As > Cd. Compared with the soil background values (SBV) in China, the Cu, Pb, and Zn contents were lower than the corresponding SBV. HMs in the Yellow River show low bioavailability, which are usually present in the lattice of primary minerals and secondary silicate minerals. They are difficult to be released under normal conditions. EF factor and I_geo index showed that the pollution level of Cd was the highest, and that of as was slight. The peri index shows that most areas of the Yellow River Basin are classified as moderate ecological risk, and the contribution rate is still dominated by Cd. According to the risk assessment coding method, the ecological risk values (RAC) of HMs in the whole basin are all below 50%, and there is no extremely high-risk area. The oxidizable and residual states of as were significantly correlated with HCl-P (r = -0.63, P < 0.05; r = 0.64, P < 0.01). The oxidizable forms of Cd, Cr, and Cu were positively correlated with OP. RDA analysis revealed that MZ had the largest positive effect on As species and negatively affected other HMs.

(4) The simulated total P load in the Yellow River Basin was 41.76 × 10⁴ t/yr, and the spatial heterogeneity of P load in different regions was extreme, with the order of middle reaches (736.08 t/yr) > lower reaches (549.73 t/yr) > upper reaches (470.32 t/yr). The analysis of pollution sources shows that farmland is the primary source of P load in the subwatershed, and construction land is an essential factor to distinguish different load levels. In the Yellow River Basin, 18% and 40.8% of the river reach the class I and class II water quality standards, respectively, accounting for about 58.8% of the total, mainly distributed in the source area and the lower reaches of the mainstream of the Yellow River. Pearson correlation analysis showed that P load from construction land was the most significant factor affecting P concentration in water. Monte Carlo sensitivity analysis showed that the sensitivity of P yield to farmland was the highest, reaching 0.97, which was much higher than other land use types, and the upstream was more sensitive to farmland (0.92). Towards sustainable levels of P and pollution control in the future, in addition to limiting the excessive application of P fertilizer and other measures, we should focus on developing a greener ecological agriculture, as well as intensifying cross-regional cooperation in environmental investment and environmental protection. These actions will facilitate the relocation of resources and energy in a more extensive scope and space, which help protect the aquatic environment and ecology of the Yellow River Basin, the development of other large basins and as a guide for pollution management and prevention.