In order to explore the characteristics and influencing factors of nitrogen export at the watershed scale during storm events, this study carried out water quality and quantity monitoring of six typical storm events in the Fengyu River Watershed in the upper subbasin of Erhai Lake in Basin 2022 and 2023. The changes of nitrogen export during rainfall-runoff process and the influence mechanism of rainfall intensity, duration, flow and other factors on nitrogen load were investigated. The results indicated that it was more likely to cause larger rainfall runoff when the antecedent soil moisture was highter in the early stage of rainfall event. A large fluctuation of nitrogen concentration was observed when the rainfall intensity reached heavy rain (level 3), indicating that the loss of nitrogen is affected by the rainfall intensity. The analysis of different stages of rainfall events showed that nitrogen was mainly lost in the late stage of the event, accounting for about 62.25%~78.77% of nitrogen load during the whole event, but the amount of nitrogen loss per unit time was large in the early stage of rainfall. For heavy and extreme events, the proportion of nitrogen loss in the middle period was more than 50% of nitrogen load during the whole event, and the nitrogen loss per unit time was the largest in the middle period of the event. Redundancy analysis of rainfall-runoff process and nitrogen loss factors showed that nitrogen concentration change and load export were mainly positively correlated with Antecedent Precipitation Index (API), followed by average rainfall intensity (RI), maximum 30-minute rainfall (I30) and peak flow (FP). Among them, ammonia nitrogen (NH4+-N) and nitrate nitrogen (NO3--N) were significantly correlated with total discharge (FA), duration of rainfall (RT), and total rainfall (RA). However, dissolved organic nitrogen (DON) has a greater correlation with API and a weaker or negative correlation with other factors.
| 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 |