千岛湖大气氮磷干湿沉降特征及周年入库负荷

大气氮磷沉降是湖库营养盐输入的重要途径，深刻地影响着湖库水体营养盐平衡及生态系统演化进程. 为了解山区大型水库大气氮磷沉降对水体的贡献，于2020年11月—2021年10月在千岛湖街口和淳安县城2个监测站点开展了大气氮磷干湿沉降周年观测，分析千岛湖大气氮磷沉降特征及入库负荷. 结果表明:千岛湖街口监测点大气总氮(TN)、总磷(TP)沉降量分别为1 774.83和34.11 kg/(km2·a)，淳安县城监测点大气TN、TP沉降量分别为1 799.73和34.44 kg/(km2·a). 大气TN沉降以湿沉降为主，街口和淳安县城监测点TN湿沉降分别占总沉降的92%和88%；两个监测点大气TP沉降的组成差异较大，其中街口监测点湿沉降占53%，淳安县城监测点干沉降占60%. 气象条件(降雨)叠加人类活动(施肥等农业活动和旅游等城市活动)能够显著增加大气营养盐沉降量，全年85%的TN沉降和71%的TP沉降集中在降雨期. 观测期间，千岛湖大气TN、TP干湿沉降入湖负荷分别估算为1 041.98和20.04 t/a，分别占千岛湖河道TN、TP输入的9.4%和8.3%. 研究显示，千岛湖大气氮磷沉降量显著低于长三角地区其他水体，但农耕、旅游等人类活动仍造成千岛湖大气营养盐沉降量明显升高. 

Atmospheric Deposition Characteristics and Flux of Nitrogen and Phosphorus in Qiandaohu Reservoir,China

Atmospheric nitrogen and phosphorus deposition is an important source of the nutrient input to lakes and reservoirs, which profoundly affects the nutrient balance and the evolution of aquatic ecosystems. Increased human activities have increased nitrogen and phosphorus loads in the rivers flowing into lakes and reservoirs, and also increased the flux of nitrogen and phosphorus deposition from atmosphere to lakes and reservoirs. In order to understand the contribution of atmospheric nitrogen and phosphorus deposition to the nutrient input of large-scale reservoirs in mountainous areas, annual observations of atmospheric dry and wet deposition were conducted in Jiekou and Chun'an in the upper and middle reaches of Qiandaohu Reservoir from November 2020 to October 2021. The observations revealed the characteristics of the atmospheric nitrogen and phosphorus deposition and its loading in the reservoir. The results showed that the atmospheric deposition of total nitrogen (TN) and total phosphorus (TP) in Jiekou were 1774.83 and 34.11 kg/(km2·a), respectively. In contrast, the atmospheric TN and TP deposition in Chun'an were 1799.73 and 34.44 kg/(km2·a), respectively. Wet deposition accounted for 92% and 88% of atmospheric TN deposition, while dry deposition accounted for 47% and 60% of atmospheric TP deposition in Jiekou and Chun'an, respectively. Meteorological conditions (rainfall) combined with human activities (agricultural activities such as fertilization and urban activities such as tourism) could significantly increase atmospheric nutrient deposition. In Qiandaohu Reservoir, 85% of atmospheric TN deposition and 71% of atmospheric TP deposition were concentrated in the rainfall period. Without regarding to the influence of long-term transformation and weather variation, agricultural activities (e.g., fertilization) during rainfall period contributed 22% of the annual atmospheric TN deposition and 32% of atmospheric TP deposition in Jiekou, where plowland is the main type of land use. Human activities (e.g., tourism) contributed 33% of atmospheric TN deposition in Chun'an, and it received more than 10 million tourists every year. During the observation period, the load fluxes of atmospheric TN and TP deposition into the reservoir with both dry and wet deposition were estimated to be 1 041.98 and 20.04 t/a, accounting for 9.4% and 8.3% of the TN and TP loading from inflow rivers, respectively. It shows that the atmospheric nitrogen and phosphorus deposition in Qiandaohu Reservoir is lower than other water bodies in the Yangtze River Delta region, which can be used as a background value for environmental protection of surrounding waters. However, the critical roles of farming and tourism in increasing the atmospheric nitrogen deposition in Qiandaohu Reservoir should be paid attention.