长江无机氮的分布变化和迁移

DISTRIBUTION, VARIATION AND REMOVAL PATTERNS OF INORGANIC NITROGEN IN THE CHANGJIANG RIVER

于 1 997年 1 1— 1 2月 (枯水期 )、1 998年 8月和 1 0月 (丰水期 ) ,对长江从金沙江至河口干流和主要支流、湖泊入江口各种形式的无机氮进行调查。结果表明 ,长江枯、丰期 ,干、支流NO3 N平均浓度变化很小 ,NO2 N、NH4 N浓度枯水期显著高于丰水期 ,支流高于干流 ;长江NO3 N、NH4 N和DIN在枯、丰期具有基本相似的迁移过程 ;长江水中无机N的迁移变化主要取决于NO3 N ,NO3 N始终是三态无机N的主要存在形式 ,三态无机N处于较稳定的热力学平衡状态中 ;长江干流无机N与径流量呈正相关表明长江水中无机N主要来自于面源。

Over the past 40 years, inorganic N content increased by several times, waters eutrophication is becoming more and more serious, and red tide is increasing in the Changjiang River estuary area. Compared with other rivers in the would such as Mississippi River and Danube River, the study on N in the Changjiang River is very little. It is necessary to strengthen the study on the Changjiang River N in terms of biogeochemistry and environmental chemistry. In this paper, the distribution and removal patterns of various forms of inorganic N in the Changjiang River water were studied for all the catchment, to provide basic data and a scientific basis for further research in N transport in the Changjiang River and its mouth. Various forms of inorganic N were investigated in the mainstream and the mouths of major tributaries and lakes in the Changjiang River (from the Jinshajiang River to mouth) during November and December, 1997 (dry season ) and in August and October 1998 (flood season ). The lowest concentrations of inorganic N in dry and flood seasons were found in Panzhihua, which were far lower than the average concentrations in the mainstream, because of less pollution in the Jinshajiang River. NO 3-N concentration obviously increased in the upper reaches and had a smaller variation in the middle and lower reaches. Variations in DIN and NO 3-N concentrations were nearly simultaneous. Variations in average NO 3-N concentrations were small in the mainstream and tributaries in the Changjiang River during both dry and flood seasons, and average NO 2-N and NH 4-N concentrations were apparently higher in the dry season than in the flood season, and higher in the tributaries than in the mainstream. The removals and variations of NO 3-N, NH 4-N and DIN in the dry season were respectively similar to the flood seasons in the mainstream and tributaries in the Changjiang River, and the removal of inorganic N in the Changjiang River water was mainly determined by NO 3-N. NO 3-N was the main existence form of inorganic N along the Changjiang River. Small variations of ratios of NO 3-N in DIN and high ratio of NO 3-N show that three forms of inorganic N in the Changjiang River water is in stable thermodynamic equilibrium. In the removal process of inorganic N in the Changjiang River catchment from external sources into the Changjiang River water, NH 4-N and NO 2-N were continually changed into NO 3-N, which mainly took place in the cachtment. The rate of transformation in the flood season was higher than in the dry season, and higher in the mainstream than in the tributaries. There were no relationships between various forms of inorganic N and suspended matter, indicating that inorganic N cannot be adsorbed by suspended matter (except part of NH 4-N). Positive relationships between inorganic N concentrations and runoff were found in the Changjiang River mainstream and they were more obvious in the upper reaches than in the middle and lower reaches, indicating that inorganic N mainly comes from non-point sources, e.g., precipitation and agriculture non-point sources (N loss from fertilizer and soil).