Dynamics and spatial differentiation of dissolved copper load in the Yangtze estuary

Abstract Taking the Yangtze river estuary as the study area and based on the field measured data of the longest sequence from 2004 to 2018, analyzes the Dissolved Copper (DCu) concentration change process of six typical sections in the Yangtze river estuary in the past 15 years, namely, Xuliujing, Shidongkou, Nangang, Beigang, Qinglonggang and Qidonggang. The characteristics of the evolution trend of each section are quantitatively evaluated by the method of restandard range analysis. The spatial differentiation rules of DCu in the Yangtze river estuary at different stages were revealed and the correlation characteristics of each section load were calculated by Pearson coefficient. The results show that :(1) the evolution characteristics of DCu in the section of Xuliujing section are relatively complex, which can be divided into four stages. The average concentration of DCu in 15 years is about 3.52 μg/L, and the highest monthly average concentration is 17.8 μg/L.(2) due to the effect of regional sewage discharge, the load of DCu in the mouth section of the south branch stone is generally higher than that of the Nangang and Beigang sections, but the evolution trend of the three sections is basically similar. The oscillation amplitude of DCu concentration in Qidonggang section is the most significant. In 2007, the annual average value of DCu reached 30.3 μg/L, which is the highest annual average value in the existing measured data.(3) Hurst index of Nangang and Qidonggang reached 0.93 and 1.0 respectively, and the evolution trend of cross section DCu showed a strong persistence. The Hurst index of Qinglonggang section is 0.1515, which indicates that the section DCu has anti-persistence.(4) except Qidonggang, the DCu in the other five monitored sections all show significant positive correlation, among which the DCu concentration in Beigang and Qinglonggang have extremely similar variation rules. The main reason for this strong correlation should be related to the main driving weight factor of DCu load in the two sections. The research results have some reference value for prevention and control of heavy metal pollution in Yangtze estuary.