Hydrological evolution and differential response of the eco-environment recorded in Lake Maozangtianchi, eastern Qilian Mountains, over the past 900 years

The Qilian Mountains (QLMs) serve as an 'eco-security barrier' in western China, substantially impacting downstream ecosystems and water resource utilization. However, the hydrological evolution characteristics of the QLMs during the last millennium remain controversial, and the ecological response to climate change remains poorly understood. Here, we present a pH record based on the brGDGTs (branched glycerol dialkyl glycerol tetraethers) of ¹⁴C-dated sediments from Lake Maozangtianchi and compare it with X-ray fluorescence elemental data and grain size to reconstruct the history of summer monsoon precipitation variability during the last 900 years. The history of eco-environment changes was also reconstructed from the total n-alkane contents. Our results show that, on a centennial timescale, precipitation in the watershed was high during the periods 1100‒1300 CE, and 1750‒2000 CE, while precipitation was low during the period 1400‒1750 CE; there was an abrupt decrease during the MWP (Medieval Warm Period) to LIA (Little Ice Age) transition (1300‒1400 CE). This result, coherent with hydroclimate records from the monsoonal margin of northern China, is likely forced by a combination of El Niño‒Southern Oscillation related to tropical Pacific sea-surface temperature and the meridional shift of the Intertropical Convergence Zone. In addition, there was a coupled relationship between plant biomass in the watershed and monsoon precipitation variation, with higher plant biomass during 1100‒1200 CE, 1750‒1900 CE, and 1950‒2000 CE, and lower values during 1200‒1400 CE and 1900‒1950 CE. In contrast, plant biomass was decoupled with monsoon precipitation during 1400‒1750 CE and exhibited a slightly increase trend. Precipitation is a key climatic factor controlling plant biomass in the QLMs; however, during LIA, nutrients carried by dust and decreased evapotranspiration played important roles in increasing plant biomass. Our research emphasizes the significant moderating effects of exogenic dust on vegetation changes in alpine ecosystems under a context of climatic deterioration.