A millennial record of lake ecosystem responses to climatic variability in the Yellow River Source Area

Abstract

The Yellow River Source Area (YRSA), a key habitat for protected wild animals and an ecological security barrier in northern China, is crucial for biodiversity and downstream welfare. Climate warming has significantly degraded the YRSA ecological environment. However, owing to a lack of monitoring records, little is known about how freshwater lake ecosystems respond to climatic variability. In this study, we investigated the long-term hydroclimatic changes and diatom community evolution in Gyaring Lake, the second largest lake in the YRSA, by analyzing the total organic carbon (TOC), biogenic silica (BSi), authigenic carbonate δ¹⁸O and fossil diatoms in a sedimentary core (ZLH2) that was radiocarbon-dated (¹⁴C). Our results indicated that the YRSA hydroclimate transformed from warm–dry conditions during the Medieval Warm Period (MWP) to cold–wet during the Little Ice Age (LIA). The ensuing ecological effects include a shift in dominant diatom species from benthic to periphytic taxa, which may reflect an extension and diversification of micro-habitats. Despite the significant linear relationship between diatom biomass and hydroclimate over the past millennium, the response of diatom diversity to climate change appears to be more complex, showing a nonlinear relationship. The divergence in seasonal temperature records and alterations in habitat corresponded with the variations in diatom biomass and diversity, suggesting that the length of the growing season and habitat are crucial for freshwater ecosystem biodiversity in the YRSA. In summary, our research provides biostratigraphical evidence of the impact of climatic variability on lake biota and reveals a nonlinear pattern of freshwater ecosystem responses to climate on the Qinghai–Tibetan Plateau (QTP).