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Through comprehensive systematic surveys of algal accumulation layers along the shores of Dianchi Lake during summer and autumn, coupled with studies on the release flux of endogenous pollutants within the lake, this research aims to clarify the sedimentation characteristics of algae in Dianchi Lake and their contribution to endogenous pollution loads. Based on systematic surveys of 24 lake-wide cross-sections and 96 profile characteristics, it was found that the residual algal biomass in Dianchi Lake sediments gradually decreases from north to south. The storage volume in the eastern outer lake area is significantly higher than that in the western area, and this trend aligns with the spatial distribution heterogeneity of cyanobacterial blooms in Dianchi Lake over the years. The overall distribution pattern across the lake's littoral zone was: Central Outer Lake (577.92ng/g) > Northern Outer Lake (521.32ng/g) > Caohai (276.55ng/g) > Southern Outer Lake (240.05ng/g). The thickness of the algal layer in Dianchi Lake generally ranged between 5and 10cm. The 0~10cm depth zone (representing the fresh algal detritus settling and accumulation area) accounted for approximately 27% of the total thickness, while the 10~15cm depth zone contributed over 25%. No significant differences were observed in surface, middle, and bottom layer chlorophyll a concentrations between Caohai and the northern Outer Lake. This correlates closely with the resuspension of surface floc in Caohai and the year-round wind-wave disturbance causing sediment resuspension in the northern Outer Lake. Preliminary calculations indicate Caohai sediment algal biomass at 3.65g/m2, contributing 26.4t and 2.5t of algal-derived nitrogen and phosphorus, respectively. In the outer lake, the biomass was 6.43g/m2, contributing 46.6t and 4.5t of algal-derived nitrogen and phosphorus from the sediment, respectively. At the sediment-water interface, the average release rate of SRP was 2.45mg/(m2·d), and the average release rate of NH4+-N was 138.21mg/(m2·d), both dominated by release processes. SRP and NH4+-N release rates in the northern and central coastal waters of the outer lake were higher than those in Caohai and the southern outer lake, closely aligning with algal accumulation layer distribution characteristics. This may serve as primary evidence that algal-derived nitrogen and phosphorus in Dianchi Lake profoundly influence sediment nitrogen and phosphorus release. Furthermore, analysis revealed a significant positive correlation between Chla content in Dianchi sediment and SRP/NH4+-N release rates. The risk of endogenous release from Dianchi Lake sediments exhibits spatial variation, being higher in the north and lower in the south. The northern Outer Lake (high algal deposition and strong disturbance) and central Outer Lake (high algal deposition) are high-risk zones for endogenous nitrogen and phosphorus release, characterized by relatively poorer overall water quality. The release of algal-derived nitrogen and phosphorus from buried sediments is one of the primary contributing factors. The southern parts of Caohai and the outer lake currently exhibit lower risks but still require enhanced management and monitoring. As a critical component of endogenous pollution control, managing the enrichment and release risks of algal-derived nitrogen and phosphorus in sediments will be a key focus for future endogenous pollution control in Dianchi Lake.
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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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