Current anthropogenic warming threatens shallow Lake ecosystems on the Tibetan plateau: A palaeolimnological study covering the past 1,600 years in Genggahai Lake

The Tibetan Plateau has similar to 1,200 lakes larger than 1 km(2) with a total area of similar to 46,000 km(2). The annual mean air temperature of the Tibetan Plateau has increased 2.5 degrees C over the past 60 years. Lakes in this region are extremely responsive to climate changes as a result of their low biodiversity and simple food webs. However, it is unclear whether the current anthropogenic warming will benefit or threaten the aquatic ecosystems in this region. We assessed patterns of change associated with climate change in a shallow, freshwater lake (Genggahai Lake) on the NE Tibetan Plateau over the past similar to 1,600 years based on diverse aquatic fossils (macrophytes, molluscs, cladocerans and diatoms), total organic carbon (TOC) and total nitrogen (TN) of a sediment core. The abundances of macrophytes, molluscs and cladocerans, and the concentrations of TOC and TN in the sediments were high during the Mediaeval Warm Period (MWP, similar to 940-1,410 CE) but low during the Dark Ages Cold Period (DACP, similar to 390-940 CE) and the Little Ice Age (LIA, similar to 1,410-1970 CE), suggesting that modest natural warming was associated with the biomass of macrophytes and consumers in the food web. By contrast, low abundance of macrophytes and high abundance of planktonic diatoms were recorded in the sediments during the Current Warm Period (CWP, similar to 1970-2020 CE). Current anthropogenic warming has resulted in significantly higher temperatures than during the MWP, associated with the development of planktonic algae rather than macrophytes. Our findings show that the current anthropogenic warming, coupled with increased atmospheric nitrogen deposition and activated nutrients from thawed permafrost, is associated with phytoplankton dominance in lakes on the Tibetan Plateau, and may lead to significant reductions in ecosystem services provided by the lakes.