WAN Nannan1, 2, 3, HU Shujie4, RAN Yong1, 2

（1. State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;
2. CAS Center for Excellence in Deep Earth Science, Guangzhou, 510640, China;
3. University of Chinese Academy of Sciences, Beijing 100049, China;
4. National-Regional Joint Engineering Research Center for Soil Pollution Control and Remediation in South China, Guangdong Key Laboratory of Integrated Agro-environmental Pollution Control and Management, Institute of Eco-environmental and Soil Sciences, Guangdong Academy of Sciences, Guangzhou 510650, China）

Abstract： To determine the effect of organic matter and nutrients on the vertical distribution of natural radionuclides in columnar sediments, this paper takes Dianchi Lake, a freshwater lake in southwest China as an example. The distribution characteristics and influencing factors of natural radionuclides in sediments of Dianchi Lake are described, which illustrated the effect of sedimentary organic matter and nutrients on natural radionuclides in Dianchi Lake. The natural radionuclides, total organic carbon (TOC) and total nitrogen (TN) in the samples were determined by multi-channel energy spectrometer (GX6020) and Vario EL III Elementar analyzer, respectively. The content of total phosphorus (TP) was determined by ammonium molybdate spectrophotometry. Pearson correlation analysis of organic matter, nutrients and natural radionuclides was also carried out. The results are as follows: the CRS dating results of 210Pbex of the sediments show that the age range is from 1955 to 2017. The specific activity ranges of 40K, 232Th, 238U, 226Ra and 210Pbex are as follows: from 185 ± 13.2 Bq/kg to 798 ± 61.0 Bq/kg, from 46.2 ± 0.19 Bq/kg to 101 ± 0.47 Bq/kg, from 54.5 ± 3.99 Bq/kg to 136 ± 10.4 Bq/kg, from 28.5 ± 0.20 Bq/kg to 66.5 ± 0.50 Bq/kg, and from 98.1 ± 4.54 Bq/kg to 312 ± 14.0 Bq/kg. TOC, TN, and TP contents ranged from 7.88 to 60.3 mg/g, from 1.11 to 7.35 mg/g, and from 1.43 to 2.78 mg/g, respectively. The internal loop of Dianchi Lake promotes the release of carbon, nitrogen, and phosphorus in the sediments, and provides nutrients for the growth of aquatic organisms, thus increasing the contribution of aquatic organic matter in the sediments. This study revealed the dilution effect of sedimentary organic matter and nutrients on 40K, 232Th and 226Ra and the cleaning effect of 210Pbex, which provided data support for future research on natural radionuclides by lake sedimentary organic matter and nutrients.

Key words：Dianchi Lake; organic matter; nutrient; natural radionuclide

EARTH AND ENVIRONMENT Vol.51, No.3, Tot No.353, 2023, Page 354