Morphological analysis
Sediment samples for morphological diatom analyses were treated and examined using standard methods (Battarbee et al. 2001). Specifically, approximately 0.1 g of dry sediment (freeze dried) for each sample was treated with 30 % hydrogen peroxide (H2O2) and 10 % hydrochloric acid (HCl) for 2-3 hours to remove organic matter and carbonates, respectively. The resulting slurries were then washed repeatedly with distilled water until a neutral pH was reached and strewed onto glass coverslips to dry at room temperature. The dry samples were then fixed onto microscope slides with Naphrax®, a highly refractive mountant. At least 400 valves were identified (range 400-407) and enumerated along transects using a light microscope (Leica DM6B, magnification ×1000) with oil immersion objective. Diatom identification and taxonomy were based primarily on general floras such as Krammer and Lange-Bertalot (1986-1991) and Lange-Bertalot, Hofmann, Werum, Cantonati and Kelly (2017). We also used specific taxonomic publications to aid with the identification of difficult groups of diatoms, such as Mohan et al. (2018) forLindavia biswashanti , and Pavlov, Levkov, Williams and Edlund (2013) for species belonging to the Hippodonta genus. To help further with morphological identification, scanning electron microscope (SEM) photographs were taken using a Zeiss MERLIN instrument at the Institute of Geology and Geophysics, CAS, Beijing.