洞庭湖大气氮湿沉降的时空变异

为研究洞庭湖大气氮素湿沉降的时空变化规律,于2016年1—12月对洞庭湖不同生态区的4个监测点的湿沉降进行了为期1年的观测.结果表明:采桑湖(CSH)、断港头(DGT)、蒋家嘴(JJZ)3个监测点的全年大气氮湿沉降量分别为49.9、38.7和90.9 kg·hm~(-2),其中NO_3~--N沉降量分别占30.3%、25.8%和33.1%,NH_4~+-N沉降量分别占32.9%、41.7%和51.1%,DON沉降量分别占36.8%、32.5%和15.9%;沅江(YJ)监测点7—12月的大气氮湿沉降量为19.0 kg·hm~(-2),NO_3~--N、NH_4~+-N和DON分别占62.2%、25.1%和12.7%,除YJ监测点外,其他各监测点NH_4~+-N沉降量高于NO_3~--N沉降量.湿沉降量与降雨量呈正相关,而湿沉降浓度与降雨量呈负相关;在CSH、DGT和JJZ监测点,湿沉降量均在春季最高,分别占全年总沉降量的54.4%、60.2%和49.7%,JJZ监测点在各个季节的总氮沉降量均高于CSH和JJZ监测点.

Spatio-temporal variability of bulk nitrogen deposition in the Dongting Lake region

To quantify the flux and spatio-temporal variation of bulk nitrogen (N) deposition in Dongting Lake, monitoring was conducted at four sites in different ecological regions in East, West and South Dongting Lakes in 2016. The results showed that the total nitrogen (TN) depositions were 49.9, 38.7, 90.9 and 19.0 kg·hm^-2 at Caisanghu (CSH), Duangangtou (DGT), Jiangjiazui (JJZ) and Yuanjiang (YJ), respectively. N deposition and rainfall were positively correlated, while N concentrations and rainfall were negatively correlated. N deposition was higher in spring and summer, when precipitation accounted for 71.6%, 78.7% and 73.2% of total annual precipitation in CSH, DGT and JJZ, respectively. Seasonal variation was not conducted at YJ site since data were available only from July to December. Nitrate nitrogen (NO₃^--N) depositions were 15.1, 10.0, 30.2 and 11.8 kg·hm^-2 at CSH, DGT, JJZ and YJ, respectively, contributing to 25.8%~62.2% of the TN deposition. Ammonium nitrogen (NH₄⁺-N) depositions were 16.4, 16.2, 46.4 and 4.76 kg·hm^-2 at CSH, DGT, JJZ and YJ, respectively, contributing to 25.1%~51.1% of the TN deposition.Dissolved organic nitrogen (DON) depositions were 18.4, 12.6, 14.4 and 2.4 kg·hm^-2 at CSH, DGT, JJZ and YJ, respectively, contributing to 12.7%~36.8% of the TN deposition. In general, N deposition at Dongting Lake regions was mainly in the form of NH₄⁺-N except at YJ, and DON made a 13%~37% contribution, which could not be ignored in the quantification.