三峡库区香溪河流域非点源氮磷负荷分布规律研究

三峡水库蓄水后,水动力条件改变,营养盐不断累积,导致库区部分支流库湾水华现象及水体富营养化问题严重.本文以香溪河支流为研究区,以氮磷为研究对象,应用SWAT模型进行不同时空尺度非点源氮磷分布式模拟和分析.结果表明:径流和营养盐负荷受降雨影响并与其呈正相关关系,丰水年总氮(TN)和总磷(TP)负荷分别为3.48×103t和0.40×103t,枯水年分别为2.04×103t和0.23×103t,在4—9月丰水期,TN和TP贡献率分别为84.1%和89.4%;TN和TP负荷强度空间差异较大,差异系数分别为0.34和0.58,TN最大值和最小值分别为29.39 kg·hm-2·a-1和3.86 kg·hm-2·a-1,TP最大值和最小值分别为4.900 kg·hm-2·a-1和0.535 kg·hm-2·a-1;TN以硝氮(NO-3-N)为主,TP以矿物磷(MIN-P)为主,TN与TP的相关系数r为0.9258,TP与MIN-P的相关系数r为0.8596,有机氮(ORG-N)与有机磷(ORG-P)的相关系数r为0.9839,氨氮(NH+4-N)与亚硝氮(NO-2-N)的相关系数r为0.9723;污染控制的重点支流是高岚河流域和古夫流域,尤其是耕地面积比例较大的水月寺,黄粮、榛子、古夫4个乡镇,以及库湾周边的七里溪.

Study on the distribution of non-point nitrogen and phosphorus load from Xiangxi River in the Three Gorges Reservoir

After impoundment of Three Gorges Reservoir, flow velocity dropped dramatically with continually accumulated nutrients, resulting in serious algal blooms and eutrophication in its tributary bays. By using SWAT model, nonpoint source nitrogen and phosphorus loadings under varied spatial-temporal scales were studied in Xiangxi River. The results indicate that nutrient loading positive related to runoff with maximum total nitrogen (TN) and total phosphorous (TP) loadings of 3.48×10³ t and 0.40×10³ t in high flow year, respectively and the minimum of 2.04×10³ t and 0.23×10³ t in low flow year, respectively; TN and TP loadings in high flow season accounted for 84.1% and 89.4% of the whole year. TN and TP showed significant spatial variations with coefficients of 0.34(3.86~29.39 kg·hm^-2·a^-1) and 0.58(0.54~4.90 kg·hm^-2·a^-1), respectively. NO₃^--N and MIN-P are the major form of TN and TP, respectively, The correlation coefficients (r) between TN and TP, TP and MIN-P, ORG-N and ORG-P, NH₄⁺-N and NO₂^--N are 0.9238, 0.8596, 0.9839 and 0.9732, respectively. Pollution control should be focused on its two large sub-watersheds, i.e., Gaolan River and Gufu River, especially the four towns with large proportion of farmlands: Shuiyuesi, Huangliang, Zhenzi and Gufu, as well as Qilixi which is next to Xiangxi River.