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Outline
Lake Daihai remains ice-covered for approximately one-third of the year, forming a multi-media system comprising ice, water, and sediment. To clarify the migration patterns of nutrients at the ice-water-sediment interfaces, a systematic study was conducted on the spatiotemporal distribution, source-sink characteristics, and driving factors of nitrogen nutrients in the three phases (ice, water, sediment) before the freezing period (October) and during the freezing period (January, February). The results revealed significant spatiotemporal heterogeneity of nitrogen nutrients across the media. Total nitrogen (TN) and ammonium nitrogen (NH4+-N) concentrations increased slightly in the ice layer. The TN concentration in the lower ice layer was higher in February than in January, with the lower ice layer exhibiting higher concentrations compared to other layers. From pre-freezing to late freezing periods, TN and nitrate nitrogen (NO3--N) concentrations continuously increased in the water and sediment. The NO3--N concentration in the water increased by 62.5% between January and February. Spatially, TN and NH4+-N concentrations in the sediment were generally higher in the central area and lower in the eastern part, and overall exceeded those in the under-ice water. During the freezing period, the fractionation coefficients followed the order: NO3--N< TN <NH4+-N. At the ice-water interface, NO3--N dominated TN migration, with a higher flux observed in January than in February. Sediment acted as a "source" for TN and NH4+-N, but as a "sink" for NO3--N. The flux of nitrogen nutrients at the ice-water interface had a greater impact on their concentrations than the sediment-water interface flux. The dynamic changes of nutrients in the water were jointly influenced by the freezing-induced salt rejection effect and endogenous sediment release. Key environmental drivers for the distribution and migration of nitrogen nutrients before and during the freezing period included ice growth rate, dissolved oxygen, salinity, and water temperature.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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