Sediment magnetic record of anthropogenic environmental changes in the catchment of a typical submerged macrophyte-dominated lake over the last approximately 168 years.

The trajectories of magnetic parameters in lake sediment cores are frequently used to reconstruct environmental evolution in lake basins. However, this strategy is rarely used in macrophyte-dominated lakes because macrophytes' potential influence on the reliability of this approach is unknown. In this study, magnetic characteristics were systematically investigated in a dated sediment core from Liangzi, a typical submerged macrophyte-dominated shallow lake, to reconstruct the environmental transformation in the catchment of this lake of the past approximately 168 years. The findings indicated that the magnetite elements in all sediments were primarily catchment detrital in origin. Before ca. 1922, sediments had high χ% and detrital hematite levels, indicating a pristine pedogenic process with minimal anthropogenic disturbance in the catchment. The values of magnetic concentration proxies (χ, χ, and saturation isothermal remnant magnetization (SIRM)) decreased significantly in sediments from ca. 1929 to ca. 1995. However, the particle size-dependent proxy (χ/SIRM) increased, indicating a lower input of magnetic materials to the lake and a smaller magnetic particle size. The onset of this transition coincided with the construction of a sluice gate connecting the Yangtze River and the lake, suggesting that the lack of magnetic material influx from the Yangtze River may have resulted in a decrease in the number and size of magnetic particles. Magnetic proxies have not reversed since the 1960s, despite extensive human activity in the lake catchment, including land reclamation and agricultural development, which increased magnetic particle influx and caused an increase in particle size. This unexpected result could be attributed to the concurrent expansion of submerged macrophytes in the lake, which increased magnetic particle deposition, particularly large ones around the lake shoreline, with just a fraction of the smaller magnetic particles being transported to the open lake area. Interestingly, an unusual magnetic proxy, S, recorded an increase in human activity in the lake catchment during this period. The magnetic concentration and particle size proxies have reversed since ca. 1997, when submerged macrophyte productivity decreased significantly and no longer influenced magnetic particle transfer; thus, these proxies could reliably record the intensity of anthropogenic disturbances in the catchment. The results of this study show that luxuriant aquatic macrophytes in lakes can alter the reliability of magnetic proxies to reconstruct environmental changes in lake catchments. However, S proxy appears to be less affected by this effect, and it is particularly recommended for studies on macrophyte-dominated lakes.