稀土矿区河流水体颗粒态稀土浓度遥感定量估算研究

Rare earth elements are the extremely important strategic resources. In recent years, owing to the illegal exploitation of rare earth, particulate rare earth concentration (PREC) of the river waters in mining area have increasing expeditiously, leading to some serious environmental problems. Therefore, pollution monitoring of PREC has to be carried out urgently. Conventionally, PREC in waters is collected from water sampling, and determined through the ICP-MS (Inductively coupled plasma mass spectrometry). However, the traditional method cannot sustain the temporal-spatial details of PREC due to the duration and cost of the shipboard measurement. Based on indoor control experiments and field in situ observations coincident with the satellites in Ganjiang rivers, which are located in the mining area, the objectives of this project are to: (1) investigate the absorption and reflectance spectral characteristics of river waters within particulate rare earth; (2) analyze the influence mechanism of particulate rare earth on the above-water remote sensing reflectance (Rrs) and determine its recognitive spectra of particulate rare earth; (3) explore the relationships between PREC and primary parameters of inherent optical properties (IOPs), such as absorption coefficient and backscattering coefficient in river waters; (4) develop the empirical and semi-analytical remote sensing model to estimate PREC for river waters using in situ hyperspectral data and satellite image data, and (5) broaden the water environmental parameters which can be estimated using remote sensing and furnish technical assistance for surveillance and early warning of PREC.

稀土是极其重要的战略资源，但近年来稀土非法开采和滥采行为日益严重，导致矿区河流水体颗粒态稀土浓度增加使得水环境问题突出，因此开展对河流水体颗粒态稀土浓度监测刻不容缓。常规水体颗粒态稀土浓度监测是从水体取样，带回实验室通过ICP-MS（电感稱合等离子体质谱）进行测定。这种方法耗时耗力，时空尺度上也都是“离散”的信息。本项目以江西赣州市稀土矿区河流为研究对象，拟通过室内控制实验和野外星地同步遥感实验，研究含颗粒态稀土水体的吸收和反射光谱特征，探讨颗粒态稀土对水面遥感反射率的影响机制，确定其遥感识别光谱特征。分析颗粒态稀土浓度变化与水体吸收、后向散射等固有光学特性的响应关系，构建基于实测高光谱数据和卫星影像的颗粒态稀土浓度遥感估算经验和半分析模型，拓展水环境可遥感估算的参数，为颗粒态稀土浓度的遥感监测和预警提供技术支持。

稀土是极其重要的战略资源，赣南等稀土矿区由于开采增加导致水环境问题突出，近年来引起了从国家到地方的高度重视，因此开展对河流水体颗粒态稀土浓度监测对保障稀土矿区及其中下游的生产、生活环境具有迫切的现实意义。本项目通过野外星地同步遥感实验，研究含颗粒态稀土水体的吸收和反射光谱特征，分析颗粒态稀土对水面遥感反射率的影响机制，最终构建基于遥感反射率与高光谱影像的颗粒态稀土浓度遥感估算模型，研究发现：1）赣南稀土矿区河流水体由于流通性较好，因而其光学性质主要由悬浮颗粒物主导，叶绿素a与CDOM浓度较低；2）赣南稀土矿区河流水体中颗粒态稀土浓度值（ug/L）均显著低于国内外报道的河流与湖泊水体（mg/L），相差倍数可达数十倍到千倍量级；3）与此相反，赣南稀土矿区河流水体中溶解态稀土浓度值（ug/L）均显著高于国内外报道的河流与湖泊水体（ng/L），相差倍数亦可达数十倍到千倍量级，表明研究区域受到人为因素（稀土开采）影响较大，具有特殊性；4）赣南稀土矿区颗粒态稀土的浓度值与溶解态稀土浓度值量级相当（ug/L），但关系不稳定且不具有明显的变化规律；5）悬浮颗粒物对颗粒态稀土的吸附作用明显大于对溶解态稀土的吸附作用，颗粒态稀土浓度与悬浮颗粒物浓度呈现极强的相关性（R2=0.941，p<0.001），而溶解态稀土与悬浮颗粒物的相关性则不显著；6）在各颗粒态稀土元素中，La139与Ce140对于悬浮颗粒物表现出很强的吸附能力，Nd146吸附能力较强，Pr141与Lu175吸附能力中等，而其他稀土元素的吸附能力较弱，因此在颗粒态稀土中La139 Ce140、Nd146等3种元素所占比重接近70%；7）水体颗粒态稀土浓度与水体遥感光谱比值具有显著的相关关系。根据这些直接与间接的关系，构建颗粒态稀土浓度的遥感估算模型，为稀土矿区颗粒态稀土浓度的遥感监测和预警提供技术支持，为探讨人类活动、土地利用、气候变化、降雨等多影响因素对于颗粒态稀土时空格局的作用机制奠定基础。