闽北建溪流域表层沉积物营养元素分布特征及生态风险评价

Distribution and ecological risk assessment of nutrient elements in surface sediments of Jianxi Watershed in northern Fujian

为了解闽江上游流域沉积物环境的现状,本文研究闽北建溪流域表层沉积物中营养元素的分布特征及生态风险,描述了表层沉积物中有机碳(TOC)、总氮(TN)和总磷(TP)的含量分布,运用单因子指数法进行生态风险评价,并分析碳、氮、磷的比例,阐述其相关关系及其环境意义.结果表明,沉积物中TOC、TN和TP的含量均值分别为3.05%、1858.05 mg·kg^(-1)和624.68 mg·kg^(-1),对多数底栖生物处于安全范围; TOC的单因子污染指数范围为2.0—5.8,TN污染指数范围为2.3—4.4,TP指数范围则为0.4—1.7,具有潜在的生态风险;沉积物营养元素比值中TOC/TN均值为16.9,TOC/TP均值为53.7,TN/TP均值为3.2,表明建溪流域沉积物营养元素受内、外源共同输入影响,且以外源作用为主导,其中林地营养物质输出是沉积物营养累积的主要原因之一.总体而言,建溪流域沉积物TN的生态风险较高且主要受流域面源排放影响,TOC与TP的生态风险较低.因此,应着重加强流域氮素面源污染调查并对重点污染源加以严控,减轻流域总氮的生态风险.

This study investigated the distribution and ecological risk of nutrient elements in the surface sediments of Jianxi watershed in northern Fujian in order to clarify the sediment environmental status of the upperstream of Minjiang River. The contents of organic carbon（ TOC）,total nitrogen（ TN） and total phosphorus（ TP） in the surface sediments were considered,and the single factor pollution index was employed in the risk assessment of sediment environment. The interrelations of carbon,nitrogen,and phosphorus in sediments and their environmental significance were also discussed. The results showed that the average concentrations of TOC,TN and TP in the sediments were 3.05 %,1858.05 mg·kg（-1） and 624.68 mg·kg（-1）,respectively,which are considered as harmless for most of aquatic organism. There were some potential ecological risks for benthonicorganism with 2.0—5.8 of TOC,2. 3—4. 4 of TN and 0. 4— 1. 7 of TP using the ranges of single factor pollution index. In addition,the average values of elemental ratios（ TOC/TN was 16.9,TOC/TP was 53. 7 and TN/TP was 3. 2） indicated that nutrient elements in the sediments of Jianxi watershed were affected by the exogenous and endogenous inputs. The output of nutrients from forestland was a mian reason for the accumulation of nutrients in the river sediments. Overall,TN in the sediments of Jianxi watershed showed the highest ecological risk for aquatic organism and was mainly affected by non-point sources in the watershed,but TOC and TP in the sediments only exhibited slight risks. Therefore,it is urgent to implement the investigation of the nitrogen pollution sources and strictly control these pollution sources so as to reduce the ecological risk of nitrogen in Jianxi watershed.