CAO Yiru, LI Minjing, MAO Shengjun, LI Yuqiong, ZHU Zichao, TONG Lei, LIU Hui
（China University of Geosciences (Wuhan) Hubei Wuhan 430078）

Abstract: The river water-groundwater interaction zone is called a biological filter, which has the function of intercepting and removing nitrogen and other pollutants. Here, 3 sections and 9 boreholes were set up in the lower reaches of the Han River to collect sediment and groundwater samples and to analyze the distribution characteristics of nitrogen in the interaction zone between river water and groundwater. The results showed that the water level of the river and groundwater in profile 1 was recharged by river water, and profile 2 was opposite to profile 1, but in profile 3 river water and groundwater level was almost the same during the sampling period. The groundwater pH in the interaction zone was generally neutral, and its main water chemical type was HCO3--Ca, , which was in anoxic or anaerobic reducing environment; nitrate-nitrogen was 0.02-0.22 mg/L, and nitrite-nitrogen was less than 0.02 mg/L, which was less than the nitrogen concentration limits of the class I or II groundwater; The ammonia-nitrogen of the well 1-2 located in a farmland was 1.93 mg/L, and it fitted the nitrogen concentration limit of the class V groundwater, while the ammonia-nitrogen of the other 8 wells was 0.01-0.32 mg/L which was less than the nitrogen concentration limit of the Class III groundwater. The pH of the sediments in the interaction zone is neutral to slightly alkaline. The ammonia-nitrogen of the sediments at different depths in the drilling 1-2 was 0.05-2.45 mg/kg, but the ammonia-nitrogen of other drilling sediments was 0.03-0.34 mg/kg. These results indicate that agricultural nitrogen fertilizer was the main cause of high ammonia in the interaction zone, but its influencing zone was relatively limited. In addition, the ammonia nitrogen in the interaction zone mainly exists as exchangeable ammonium-nitrogen, and the dissolved ammonia-nitrogen accounts for much less level.

Key word: lower reaches of the Han River; river-groundwater interaction zone; Groundwater; sediment; nitrogen distribution

EARTH AND ENVIRONMENT Vol.49, No.5, Tot No.343, 2021, Page 463-471