长江中游航道整治工程区沉积物及有机质变化

Sediment and Organic Matter Dynamics in Channel Project Areas of the Middle Yangtze River

为了探究长江中游航道整治水下工程区不同恢复阶段沉积物粒度和有机质含量特征与变化规律,2017年3月、6月、9月分别对长江中游6个恢复时间分别为2、3、4、5、10、15年的航道整治工程区进行了沉积物采集,室内利用Master size 2000型激光粒度仪进行分析,并采用MMFr矩值法公式计算粒度特征,灼烧法测量沉积物有机质含量,分析沉积物粒度和有机质含量随恢复时间的变化情况,以及粒度特征参数和有机质含量之间的关系。结果表明,长江中游护岸水下工程区沉积物组成主要以砂为主,粘土、粉砂和砂的平均含量分别是(7.34±4.58)%、(24.26±1.00)%和(68.39±14.06)%。表层沉积物的粒径2.43~6.79φ,平均值是3.95φ,中值粒径2.41~6.05φ,平均值为3.65φ,整体上粒径偏小。工程恢复越久,小颗粒组分占比越高,平均粒径越大;有机质含量随工程恢复时间的增长而增高,河流的涨枯期对有机质含量的影响不显著;表层沉积物中粘土和粉砂总含量、平均粒径、中值粒径与有机质含量关系极显著。本研究结果既符合河流纵向沉积物粒度分布规律,也反映了时间尺度对沉积物粒度组成和有机质含量的影响。

Discharge from Three Gorges Reservoir has caused bank collapse in the middle reaches of Yangtze River.To fortify banks,hydraulic structures have been constructed to decrease flow and promote deposition of clay and sand.In this study,we analyzed the grain size and organic content of sediments in channel regulation areas of the middle Yangtze River at different stages.The objectives were to explore the dynamics of changing particle size and organic matter content after construction of hydraulic structure and the relationship between organic matter content and particle size.The study provides basic data for habitat remediation by construction of channel regulation projects.In March,June and September of 2017,sediments were collected in areas with hydraulic structures in place for periods of 2,3,4,5,10 and 15 years.The Master Size 2000 instrument and MMFr formula were used to characterize grain size of sediment samples and the combustion method was used to determine organic content.Results show that sand was the main component in sediments.The average proportions of clay,silt and sand for the sediments were,respectively,(7.34±4.58)%,(24.26±1.00)%and(68.39±14.06)%.The particle size range of surface sediments was 2.43-6.79φ(average,3.95φ)and median particle diameter range of 2.41-6.05φ(average,3.65φ).The particles were generally small.The proportion of organic matter in the sediment ranged from 1.06%to 4.82%[average,(3.06±1.30)%].Organic matter content varied with season:(2.75±1.05)%in March,(3.65±1.01)%in June and(2.80±1.46)%in September.The longer the recovery project operated,the higher the proportion of small particles accounted for and the larger the average particle size was.The proportion of organic matter increased with time,but no distinct relationship was found between organic matter content and wet/dry periods.The total content of clay and silt,average particle size and median particle size of sediments all correlated significantly with organic matter content.The results of this study are consistent with the normal distribution pattern of sediment grain size and reflect the influence of time on grain size composition and organic matter content in river sediments.