湖南蔡家塘森林小流域氮和硫的输入输出特征

Input-output dynamics of nitrogen and sulfur in Caijiatang forested catchment in Hunan Province

以湖南韶山蔡家塘小流域2001～2003年的监测数据为基础,对森林在酸沉降作用下无机氮（NH＋4,NO-3）和硫输入、输出的月均通量进行了研究.结果表明,总氮的年输入通量为24～28 kg·hm^-2·a^-1,主要以NH＋4形式（占总输入氮的62%～67%）输入该森林生态系统;年氮输出通量为2～3kg·hm^-2·a^-1,主要以NO^-3形式（占总输出N的83%～98%）输出该森林生态系统.韶山森林年无机氮的滞留量达到22～26kg·hm^-2·a^-1,其中NH＋4占到总氮净截留量的68%～72%.硫的截留量为13～21kg·hm^-2·a^-1.高氮沉降导致了一部分氮的输出,但是输出氮仅占到输入氮的8%～9%.有超过90%的氮被生态系统截留.由此可以推断,韶山森林尽管有高氮输入,但是生态系统远没有达到氮饱和状态.

The input - output dynamics of inorganic nitrogen （ NH4^＋ and NO3^- ） and sulfur （ SO4^2-） were investigated under acid rain in Caijiatang （CJT） forested catchment in Hunan Province during the period 2001 -2003. Results show that total N-input flux is estimated to be 24 - 28 kg·hm^-2·a^-1 and the total N-output flux to be 2 - 3 kg·hm^-2·a^-1 between 2001 and 2003, indicating a net N retention of 22 - 26 kg·hm^-2·a^-1 in CJT forested catchment. The input flux of NH4^＋ accounts for 62% -67 % of total N-input flux. The output flux of NO3^- amounts to 83% -98 % of total N-output flux. The net retention of SO4^2- is calculated to be 13 - 21 kg·hm^-2·a^-1. Although the high N deposition flux results in the output of N from CJT catchment, the output part accounts for 8% -9% of the input N, which suggests that the flux of N retained by the forest system is higher than 90 % of the input N. CJT forest is of high N-input, but the forest is far from the nitrogen saturation.