府河-白洋淀硝酸盐来源判定及迁移转化规律

近年来白洋淀流域内经济高速发展、人口增加,生活污水排放量增大,严重威胁府河和白洋淀水质,其中硝酸盐浓度过高引发的水体富营养化是河流系统面临的重要难题。以白洋淀和唯一一条常年有水的入淀河流——府河为研究对象,结合水化学、水中氢氧同位素(δ~2H、δ~(18)O)和硝酸盐氮同位素(δ~(15)N)的方法 ,分析2008—2016年水化学特征和水化学类型变化,明确府河-白洋淀淀区硝酸盐污染来源以及沿程迁移转化规律,为其水质富营养化管理提供参考。研究结果表明:府河2008年硝酸盐δ~(15)N值10‰,2014年硝酸盐δ~(15)N值的变化范围是2.07‰~18.49‰,府河硝酸盐主要来自于保定市和沿府河村落的生活污水;但2009年硝酸盐δ~(15)N值的变化范围是-3.7‰~4‰,府河硝酸盐主要来源于工业废水。白洋淀淀区2008年和2014年硝酸盐δ~(15)N值的变化范围分别是5.8‰~11.7‰和3.31‰~12.53‰,2009年δ~(15)N值的变化范围是-3.8‰~0.7‰,说明府河的生活污水和工业废水是白洋淀淀区硝酸盐的主要来源。2008—2014年Cl~-和SO_4~(2-)浓度比例逐渐减小,工业废水和生活污水的排入受到控制;2009年因工业废水的排放NO3-浓度超过50 mg·L~(-1),2014年和2016年NO_3~-浓度未超标;控制硝酸盐浓度变化的主要因素是降水稀释、外源输入及反硝化脱氮作用,当溶解氧(DO)小于2 mg·L~(-1)时,硝酸盐的减少主要受反硝化作用影响。

Sources, migration and transformation of nitrate in Fuhe River and Baiyangdian Lake, China

The increasing urban sewage discharges have severely threatened the quality of surface water. Baiyangdian is the largest freshwater lake in the North China Plain, which plays a critical role in flood control, micro-climate regulation, improvement of eco-logical environment and development of aquaculture and tourism in the region. However, with rapid economic development and population growth in recent years, its' pollutant load has increased rapidly. Also eutrophication of water body caused by high nitrate concentration has created a significant problem. Excessive nitrate in water not only causes eutrophication, but also threatens human health. Therefore, the investigation of the sources of nitrate pollution and transformation in Fuhe River-Baiyangdian Lake area is important in order to provide a reference for the management of eutrophication and water quality. For the period 2008–2016, the variation in hydrochemical type as well as sources of nitrate in Fuhe River and Baiyangdian Lake surface water systems were inves-tigated by the combined use of hydrochemistry with isotopes (δ2H,δ18O andδ15N). The environmental behavior of NO3- along the river was evaluated using Cl- as the standard reference to estimate the dilution and mix of different waters in the study area. 1) If variation in measured NO3- was similar to calculated NO3-, then it implied that dilution and mix effects were the controlling factors for the change in NO3- in the river. 2) If the measured NO3- was smaller than calculated NO3-, it implied that apart from dilution and mix-ing, other processes such as biochemical reactions influenced the change in NO3-. 3) If also measured NO3- was larger than calculated NO3-, it implied that there was excess NO3- entering the river compared with Cl-. The results showed that in September 2008, NO3-δ15N in Fuhe River was higher than 10‰, with a range of 2.07‰–18.49‰ in July 2014. Domestic waste water from nearby villages was the dominant source of nitrate in Fuhe River. However, in June 2009, the range of NO3-δ15N was-3.7‰–4‰ and dis-charge of industrial waste water had a significant impact on nitrate concentration in the river in June 2009. In Baiyangdian Lake, the ranges of NO3-δ15N for September 2008 and July 2014 were 5.8‰–11.7‰ and 3.31‰–12.53‰, respectively. However, the range of NO3-δ15N for June 2009 was-3.8‰–0.7‰. Domestic and industrial waste water in Fuhe River were the main source of nitrate pollu-tion in Baiyangdian Lake. For 2008–2014, the proportion of Cl- and SO42-decreased gradually and the discharge of industrial waste-water and domestic sewage was controlled. In 2009, NO3- concentration in industrial waste water exceeded 50 mg·L-1. Then in 2014 and 2016, NO3- concentration fell below the standard. The spatial variation in nitrate concentration along the river was mainly af-fected by dilution, extra input of sewage and denitrification. In June 2011, the variation in nitrate concentration along the river was mainly affected by extra input of sewage. In June 2009, July 2014 and June 2016, denitrification impacted the decrease in concentra-tion of nitrate in Fuhe River when dissolved oxygen (DO) was less than 2 mg·L-1.