Suburban shallow lake primary producer structure and productivity reshaped by climate warming and anthropogenic disturbance: Century-scale sedimentary and socio-environmental multi-proxy evidence

Shallow lakes are increasingly vulnerable to regime shifts under intensified anthropogenic and climatic pressures, often expressed as transitions in primary producer communities from submerged macrophyte to phytoplankton dominance. However, the long-term trajectories and underlying drivers of such shifts—especially changes in community structure and productivity—remain insufficiently explored in suburban shallow lakes. Using multi-ecological proxy sedimentary records, including plant macrofossils, diatoms, and biogenic silica, this study reconstructs century-scale changes in primary producer structure and productivity in Shitang Lake, a suburban shallow lake in eastern China. Change-point detection using the sequential t-test and the ordinary least squares cumulative sum test identified two abrupt shifts since 1900: the first, around the 1960 s, marked by enhanced submerged macrophyte growth and increased diatom diversity; the second, marking a regime shift by the 1990 s, characterized by macrophyte collapse and the rise of eutrophic planktonic diatoms. Spearman correlation and hierarchical clustering revealed strong biotic-envir-socioeconomic associations. Redundancy and variance partitioning analyses suggested potential drivers, including watershed disturbance (erosion and reduced hydrological connectivity), nutrient enrichment from agriculture, aquaculture, and urban sources, and climate warming. Nutrient-driven bottom-up forces were the dominant driver, whereas aquaculture-related top-down pressures acted as secondary reinforcing factors. This study provides empirical evidence of long-term regime dynamics, showing how catchment and climatic stressors drive lake nutrient accumulation and ecological degradation, ultimately leading to a macrophyte-to-phytoplankton regime shift. The findings emphasize the need for integrated water and catchment management to restore ecological stability and sustain aquatic health, providing insights for safeguarding lake ecosystems in rapidly developing regions worldwide.