季风边缘区湖泊表层沉积物粒度组分分布特征与影响因素

对内蒙古等地68个湖库共139个表层沉积物样品的粒度组分分布及其影响因子进行研究,探讨湖泊沉积物粒度分布特征及其成因机制和粒度组分的环境指示意义。结果表明：湖泊表层沉积物粒度可分为C1~C6共6个组分（0.4~1.9 μm、2.0~12.0 μm、17.0~58.0 μm、70.0~150.0 μm、170.0~500.0 μm和>600.0 μm）,近湖心样品粒度组分以C1、C2、C3为主,过渡带样品以C3和C4为主,近湖滨样品以C5主导。受入湖河流影响的样点处水动力条件决定了粒度组分的空间分布,波浪作用造成的二次悬移再沉积可能造成了C3组分向湖心迁移并导致近岸C5组分富集。C1及C2组分中径流输入不容忽视,C3组分中风力悬移搬运贡献较大。C4、C5和C6含量可指示样点距河口的相对位置,C3可反映样点距岸相对位置。

Within-lake distributions of grain-size components and environmental implications based on the survey of lake surface sediment of Chinese monsoon marginal area

In this paper, within-lake grain-size components distribution was disclosed and its relationship to the controlling and influencing environmental factors were explored, to present bases for interpretation of core grain-size data. Specifically, 139 lake surface sediments were achieved from 68 lakes and reservoirs in the Inner Mongolia Autonomous Region, Gansu Province and Ningxia Hui Autonomous Region. The grain-size of surface sediments was measured using Microtrac S3500 particle size analyzer, and the grain-size components were fitted and partitioned using lognormal distribution function. Correlation analysis and ordination analysis including detrended component analysis (DCA) and redundancy analysis (RDA) were used to analyze the relationships between grain-size components distribution and influencing factors, including water depth (De), the distance to shoreline (Ds), the distance to river mouth (Dr), the ratio between the distance to shoreline and the lake's radius (Ds/R), and the ratio between the lake's radius and the distance to river mouth (R/Dr). These factors can reflect the re-suspension caused by wave action (De), the transport of shoreline clastic deposit (Ds and Ds/R), the riverine clastic deposition and erosion process (Dr), and the overall influence of riverine clastic deposition under specific hydraulic conditions (R/Dr). Thus, the fitting and partitioning yields six components (i.e., C1: 0.4-1.9, C2: 2.0-12.0, C3: 17.0-58.0, C4: 70.0-150.0, C5: 170.0-500.0 and C6: >600.0 μm). The grain-size components of the samples near lake center mainly contain clay (C1), fine silt (C2) and medium-to-coarse silt (C3). The grain-size components of the samples in the transitional area mainly include medium-to-coarse silt (C3) and fine sand (C4). The grain-size components of samples near the shoreline mainly contain medium-to-coarse sands (C5). The results of scatter plot show that the R/Dr is extremely significant positively correlated with the C4 (n=139, R=0.280), C5 (n=139, R=0.273) and C6 (n=139, R=0.255), and significant negatively correlated with the C2 (n=139, R=0.233), suggesting river transportation and the hydraulic conditions is the major factor influencing the grain-size distribution of lake surface sediment. In addition, the factor of Ds/R shows extremely significant positive correlations with C3 (n=139, R=0.265) and extremely significant negative correlations with C5 component (n=139, R=0.299), suggesting that the relative location of the sample site to shoreline is the secondary influencing factor. Significant correlation was also found between the De and the C1, indicating that the water depth related wave action energy was also a factor influencing the distribution of clay components. The RDA results support those of the scatter plot and further disclose the relationship between the variables and the environment factors. That is, RDA results show that the R/Dr (F=7.20, P=0.0020) and the Ds/R (F=4.96, P=0.0120) are statistically correlated to the spatial distribution of grain-size of lake sediments. C4, C5 and C6 have a small angle with the positive vector of R/Dr, suggesting that the R/Dr is positively correlated with C4, C5 and C6. C3 has a small angle with the positive vector of Ds/R, suggesting the Ds/R is positively correlated with C3. Furthermore, the box plot comparisons of the grain-size component percentages between the lakes with inflow rivers and the lakes without inflow rivers suggest that, the river input and the related resuspension process control or influence the grain-size distribution, resulting in the enrichment of the clay and fine silt in the lake center. So the fractions of the riverine clay and fine silt in the lake surface sediment and associated environmental implications should arouse much attention.