Sediment hardening changes the physicochemical characteristics and microbial diversity of sediment and has potential effects on submerged macrophytes

The intensification of climate change and increases in dam construction have altered the inherent hydrological rhythms of river-connected lakes and led to the formation of a new feature of lake sediment known as sediment hardening. However, changes in sediment characteristics caused by sediment hardening and their potential effects on submerged macrophytes remain unclear.

A field investigative study and mesocosm experimental study were performed in Dongting Lake to provide evidence on how variations in sediment hardening affect the physical, chemical, and microbial properties of sediments and subsequently impact the health of submerged macrophytes.

Sediment hardening mainly changes the characteristics of the 0–20 cm sediment layer by increasing the proportion of macroaggregates, decreasing the bulk density (BD) and pH, and increasing the contents of sediment total nitrogen (TN), total phosphorus (TP), and organic carbon (SOC). Sediment type (hardened and unhardened) and depth (0–5, 10–15, and 20–25 cm) significantly influenced the richness indices of bacteria and fungi, with sediment type having the greatest effect on the fungal community composition and sediment depth having the greatest effect on the bacterial community composition. The combination of high water depth and sediment hardening resulted in shorter root systems in submerged macrophytes that are not conducive to growth.

Our study is the first to establish a link between sediment hardening and the growth and development of submerged macrophytes. Moreover, it highlights the potential role of sediment hardening and water level interactions in regulating the development and growth of submerged macrophytes in river-connected lakes.