Cladophora reblooming after half a century: effect of climate change-induced increases in the water level of the largest lake in Tibetan Plateau

Abstract

Massive Cladophora growth was reported half a century ago around Birds Island in Qinghai Lake, and in 2015, Cladophora populations have rebloomed and have formed green “meadows,” with areas up to thousands of hectares. The present study investigated the distribution and biomass of Cladophora in Qinghai Lake and found that two key factors contribute to Cladophora blooming. First, recent climate change, especially increased precipitation, has induced the expansion of the lake’s area, and the submerged grassland around Birds Island has provided a plethora of grass stems on which Cladophora can attach and twine. In addition, the submerged grasslands are covered with less than 1 m of water, which allows enough sunlight to support the growth of Cladophora on available substrates. Second, the submerged grassland may function as a key source of nutrients, especially phosphate. A large number of migratory birds live in these area for very long times, which lead to higher phosphorus content due to the accumulated birds dropping. Thus, the high phosphate level further exacerbates the massive growth. Future studies should investigate the functions of Cladophora in the nutrient cycling of submerged areas, and the improvement of methods for removing Cladophora biomass.