Analysis of spatiotemporal characteristics and influencing factors of nutrient levels in Bosten Lake from 2021 to 2024

As the largest inland freshwater lake in China’s arid zone, Bosten Lake in Xinjiang is the most important recharge water source in the lower reaches of the Tarim River. Bosten Lake’s ecological health is directly related to the sustainable development of the Tarim River Basin. Based on 28 sets of monthly lake and river water quality data in the study area from 2022 to 2023, 63 sets of water samples (including 38 sets of lake water, 10 sets of river water and 15 sets of groundwater) sampled and tested in 2024, and 3 sets of data automatically recorded by the national automatic monitoring system from 2021 to 2024 at a 4h interval, nutritional status indexing, spatial interpolation, and statistical analysis methods were comprehensively used to preliminarily explore the spatiotemporal changes and influencing factors of the eutrophication level of Bosten Lake. The spatiotemporal variations of nutrients (total nitrogen (TN) and total phosphorus (TP)), chlorophyll a (Chl.a), transparency (SD), permanganate index (CODMn), and comprehensive nutritional status index (TLI) in Bosten Lake were systematically analyzed. The results showed the following. First, the TP and TN concentrations in the central area (Zone Ⅳ) were relatively low (mean: TP 0.012 mg·L-1, TN 0.41 mg·L-1); the western pumping station area (Zone Ⅰ) is the core ecotone of lake pollution input-output and artificial regulation. The TP and TN concentrations at the Kaidu River entrance were highest (peak: TP 0.026 mg·L-1, TN 0.59 mg·L-1). The TP and TN concentrations in the Huangshuigou District (Zone Ⅲ) were high (mean: TP 0.016 mg·L-1, TN 0.48 mg·L-1). Second, the annual Chl.a concentration peaked in summer (June-August) due to the increase in water temperature and algae proliferation, but it decreased in autumn (September-November) with water temperature and algae biomass. Third, the TLI showed a fluctuating upward trend. The TLI in Zones Ⅲ and Ⅳ, respectively, increased from 20.8 and 25.8 (poor nutrition) in 2021 to 42.2 and 45.1 (medium nutrition) in 2024, and the TLI in summer and autumn was substantially higher than that in winter and spring. This study reveals the mechanism of eutrophication intensification under the synergistic effect of climate change and human activities, provides theoretical support for the sustainable management and ecological protection of Bosten Lake, as well as offers a reference for studying other similar arid lakes.