New insights into the role of lake sediments in understanding watershed non-point source phosphorus pollution

Abstract

A deep understanding of the relationship between watershed non-point source (NPS) pollution and lake total phosphorus (TP) accumulation is the basis of watershed–lake environmental management and ecological reconstruction, in which the acquisition of long-term NPS P and lake TP data over corresponding temporal and spatial scales seems to be the key issue. In this study, three typical sub-basins within Hongze Lake were selected as study sites. The sediment TP concentrations were designated as the lake indicator to relate with the NPS P loads, and the role of sediment in representing watershed NPS pollution was quantitatively analyzed. The results showed that, first, a notable fluctuation tendency in NPS P loads, which was largely influenced by policy, was found for all three sub-basins. Second, the deposition rate for three sediment cores was approximately 0.40 cm per year, with 13 cm cores reflecting the period since 1990. Third, the sediment is a faithful recorder of watershed NPS P pollution and lake nutrient enrichment. The correlation coefficient (r) between watershed NPS P loads and lake sediment TP concentrations showed notable differences when each watershed was considered separately. In particular, an ideal relationship was found in Basins 1 and 2, especially in the bottom 7 and 8 cm of the sediment cores, in which r exceeded 0.8. This showed that sediment can be an effective indicator of NPS P pollution during certain periods, such as 1990 – 2002, and diverse roles can be attributed to land-use/cover change and lake resuspension conditions. In addition, the weakest relationship existed in the No. 3 watershed, largely due to higher rainfall amounts compared with other two watersheds. For all the watersheds, lake sediment is a suitable indicator of watershed NPS P pollution over certain temporal and spatial scales.

Keywords:

• Non-point source pollution
• phosphorus
• spatial and temporal tendency
• Hongze Lake Basin

Notes

1 Quality standard for surface water (GB3838-2002). State Bureau of Technical Supervision. China. 1994.

Additional information

Funding

The work was funded by The National Natural Science Foundation of China (Grant No. 41671284) and Key Research Plans of Frontier Sciences, Chinese Academy of Sciences (QYZDB-SSW-DQC038). Data were supported by Scientific Data Sharing Platform for Lake and Watershed, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences.