Sources and transport of organic carbon from the Dongjiang River to the Humen outlet of the Pearl River, southern China

Transport of organic carbon via rivers to estuary is a significant geochemical proc- ess in the global carbon cycle. This paper presents bulk total organic carbon （TOC） from the Dongjiang catchment to the adjacent Humen outlet, and discusses the applicability of 613C and ratio of carbon to nitrogen （C/N） as indicators for sources of organic matter in the surface sediments. Survey results showed that organic carbon concentration in summer were higher than in the winter. An elevated trend of TOC occurred along the river to the Humen outlet in both surveys, and the highest mean values of dissolved and particular organic carbon （DOC-279 μmol L-1 and POC-163μmol L-1） were observed in the urban deltaic region in summer flood flow. Winter samples had a wide range of b＇13C and C/N （5-3C -24.6%o to -30.0%o, C/N 4-13）, and summer ones varied slightly （8-3C -24.2%o to -27.6%0, C/N 6-18）. As results suggest that POC in the three zones of upstream-delta-outlet dominantly came from riverbank soil, phytoplankton and agricultural C3 plants in winter, whereas main sources were from the riverbank and mangrove soil in summer. Moreover, anthropogenic sewage inputs had 11% and 7% contribution to POC in the deltaic and outlet. Transport accompanied with seasonal freshwater variation, phytoplankton production and degradation, and removal be- havior caused variation of organic carbon concentration. The results also discovered that TOC export bulk in Dongjiang was approximately one quarter of Humen flux in the dry flow, and anthropogenic activity significantly impacted the river export contribution.

珠江虎门河口营养盐的分布特征及其环境影响

基于珠江虎门河口2016年枯季(1月3~10日)水文水质多要素同步观测数据,采用Pearson相关分析和主成分分析等方法研究河口动力及氮磷营养盐的潮周期变化,并探讨虎门河口营养盐的环境影响机制。结果显示,大、小潮观测期间氨氮浓度变化范围为0.59~2.06 mg/l,硝酸盐氮浓度变化范围为1.20~3.54 mg/l,亚硝酸盐氮浓度变化范围为0.14~0.49 mg/l,磷酸盐浓度变化范围为0.025~0.063 mg/l,且垂向平均浓度分别为1.20 mg/l,1.84 mg/l,0.32 mg/l和0.04 mg/l,揭示虎门河口动力驱动下氮磷营养盐的潮周期差异显著。水文要素盐度和含沙量亦随潮汐涨落变化较大,而水温无明显潮周期变化,且各因子对氮磷营养盐的影响机制不同。外海水团对氮营养盐的稀释混合作用强于磷营养盐,而悬浮泥沙对氮营养盐以吸附作用为主,对磷营养盐吸附与解吸附作用共存。研究结果将为珠江口的污染治理及生态修复提供科学依据。

珠江虎门河口夏季悬浮物中重金属分布特征及其风险评价

为研究珠江虎门河口悬浮物中重金属的分布特征及其污染风险,为重金属的污染防控和治理提供科学依据,本文于2017年8月在该海域内布设固定观测点进行27 h连续水文观测,共采集了81个悬浮物样品,在室内测定其Zn、Cu、Ni、Mn、Pb和Cr共6种重金属元素的含量。在此基础上,利用Pearson相关性分析、因子分析和潜在生态风险评价指数等方法,对虎门河口悬浮物中重金属的含量特征、来源和污染风险等进行分析。结果表明:6种重金属元素的平均含量为Mn>Zn>Cu>Cr>Pb>Ni,且其含量变化与悬浮物浓度变化具有显著的正相关性;来源分析表明,Cu、Zn、Mn主要源于北江采矿业和冶金厂排放,Ni、Pb、Cr主要源于虎门河口附近的蓄电池等制造业排放;潜在生态风险指数评价结果表明,虎门河口综合潜在生态风险主要为低风险水平,6种元素中Cu、Pb对生态风险贡献率最大,两者贡献率之和高达80%以上,为主要污染防治元素。