EGU2020-8207
https://doi.org/10.5194/egusphere-egu2020-8207
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

224Ra/228Th disequilibrium in sediments of Lake Taihu: Implications of nitrogen fluxes across the sediment–water interface

Xiaoyan shi1,2, Xin luo1,2, Jimmy.Jiu jiao1,2, Jing huang2, Meiqing lu1,2, and Wenzhao liang1,2
Xiaoyan shi et al.
  • 1University of HongKong, Faculty of Science, Department of Earth Science, Hong Kong (earthsci@hku.hk)
  • 2Earth and Environment Research Institute, Zhejiang Institution of Research and Innovation, The University of Hong Kong, Hangzhou, China (hkuziri@hku.hk)

Radium-224 /Thorium-228 (224Ra/228Th) disequilibrium in sediments is an advanced proxy of benthic processes and has been gradually used to quantify the fluxes and solute transfer across the sediment–water interface (SWI). This study makes the first attempt to explore the nitrogen fluxes across the SWI of Lake Taihu, the third largest and highly eutrophic freshwater lake in eastern China, based on the plumbing of 224Ra/228Th disequilibrium in the lake sediments. The microscopic sediment cores (0-20 cm) were collected in different parts of the lake, and exchangeable 224Ra and 228Th in bulk sediments were measured. Dissolved inorganic nitrogen (DIN) in pore water and overlying lake water were also analyzed. Deficits of 224Ra compared to its parent isotopes 228Th were observed in the lake sediments, suggesting the influences of mixing processes. The deficits were relatively significant in the western and northern parts, which are consistent with the relative high-eutrophicated areas of the lake. One-dimensional (1D) radium-thorium diagenetic model in the sediment was used to estimate the benthic fluxes based on the 224Ra deficits. Results show that the benthic fluxes of 224Ra varied from -0.428 to 1.170 dpm cm-2 d-1, and the bio-irrigation and molecular diffusion are considered to be the major factors. Specifically, in the severely eutrophicated area of the lake, the bio-irrigation predominates in benthic fluxes, reaching up to 97.1% of the deficit of 224Ra. The DIN benthic fluxes were also quantified, leading to a flux estimation of 3.41 mol m-2 d-1, which exceeds riverine input (2.63 mol m-2 d-1) and the loading derived from lacustrine groundwater discharge (0.02~0.03 mol m-2 d-1). This study reveals that sediment processes could be the vital factors for the lake nutrient loadings, and highly contribute to the lake eutrophication. This study is constructive for the water remediation and ecosystem restoration in Lake Taihu and other large eutrophic lakes elsewhere.

How to cite: shi, X., luo, X., jiao, J. J., huang, J., lu, M., and liang, W.: 224Ra/228Th disequilibrium in sediments of Lake Taihu: Implications of nitrogen fluxes across the sediment–water interface, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8207, https://doi.org/10.5194/egusphere-egu2020-8207, 2020

Display materials

Display file