The δ13Ccellulose of aquatic macrophytes residues in lake sediments: The potential for reconstructing past environments

Abstract

The freshwater lakes in the middle and lower reaches of the Yangtze River (MLYR) have been affected by a multitude of factors, including climate change and human activities, and are currently facing a range of aquatic ecological environment problems. In order to establish restoration goals and paths, it is essential to have a scientific understanding of the historical process and pattern of long-term degradation of the lake ecological environment. This study focused on Shengjin Lake, a representative Yangtze River-connected lake in MLYR. Based on the analysis results of cellulose carbon isotopes (δ13Ccellulose) in modern aquatic macrophytes, the response characteristics of aquatic macrophytes δ13Ccellulose to lake environment evolution were revealed by high-resolution multi-proxy (δ13Ccellulose of plant residues and geochemistry indices) analysis of a sediment core. The study also reconstructed the ecological environment evolution process of Shengjin Lake over the past two hundred years. The primary research findings are as follows: Firstly, the results of the modern process survey demonstrated that the δ13Ccellulose of different modern species exhibited considerable variation. The submerged plants exhibited an enrichment of 13C, while the emergent plants exhibited an enrichment of 12C. Secondly, a comprehensive modern process investigation, coupled with palaeo-limnological records and literature data, led to the conclusion that the large plant residues of sediments were primarily derived from submerged plants. Concurrently, statistical analysis indicated that the content of total organic carbon in lakes was the primary factor influencing the changes in sediment δ13Ccellulose. The composition of δ13Ccellulose may be indicative of changes in lake primary productivity. Finally, the paleo-limnological record revealed that the ecological environment of Shengjin Lake has undergone significant changes over the past two hundred years. In particular, since the 1970 s, the δ13Ccellulose has been significantly enriched by 12C, and the geochemical indexes of elements have shown an increasing trend (p < 0.01). This suggests that the ecological environment of Shengjin Lake is gradually deteriorating as a consequence of human activities such as enclosure aquaculture and the construction of Huangpen Sluice, which have occurred in the context of climate warming and regional wind speed decrease in recent decades. This study presents new indicators and evidence for the reconstruction of the evolutionary process of the nutrient environment of lakes in MLYR. Moreover, it provides a foundation for the protection and restoration of lakes.

Keywords

• Stable carbon isotope
• Lacustrine sediment
• Environmental change
• Shengjin Lake