Groundwater Nitrate Removal through Denitrification under Farmland in Yangtze River Delta
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Supported by the National Key Research and Development Program of China (No. 2017YFD0200100), the National Natural Science Foundation of China (No. 41425005), and the Joint Sino-German Research Project (No. GZ1262)

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    Abstract:

    【Objective】The Yangtze River Delta is one of the areas, where the input of nitrogen(N) fertilizer is very high, in China, but it is not quite clear whether nitrate (NO3--N) has accumulated in the soil profile in the region as in the North China Plain.【Method】In the present study, two-year field observation combined with indoor incubation experiments were carried out to investigate distribution of NO3--N and denitri?cation capacity in subsoil and groundwater as affected by arable land systems.【Result】The groundwater NO3--N concentration in 1~4 m depth was varied significantly with type of the cultivation system. In the paddy field, groundwater NO3--N was always low (<1 mg·L-1), and did not vary much with depth. While in the vegetable field and vineyard, the average NO3--N concentration reached 5.6 and 17.5 mg·L-1 in 1 m depth, but the NO3--N concentration dropped sharply with the depth and to a very low concentration (<1 mg·L-1) in 4 m depth which was comparable to that in the paddy field. High groundwater NO3--N were only observed in vegetable field and vineyard during the fertilization period and NO3--N was low in non-fertilization period. The findings indicated that no apparent NO3--N accumulation in the farmland soil profile occurs in the Yangtze River Delta. The indoor incubation experiment using undisturbed soil columns shows that denitrification activity was high through the 0~4 m soil profile. The removal efficiency (RE) of NO3--N by denitrification was estimated by direct determination of N2 and N2O, products of denifrifiction, in groundwater. The RE increased with depth and removed 86%, 93% and 89% of the groundwater NO3--N in 4meter depth in paddy field, vegetable field and vineyard, respectively. 【Conclusion】All the findings in this experiment demonstrated that denitrification can effectively remove groundwater NO3--N, which explains why NO3--N does not accumulate in farmland soil profiles in Yangtze River Delta. Highly dissolved N2 produced by denitrification accumulate in groundwater, and flow into nearby water bodies mainly via groundwater. In the case of vegetable field and vineyard, soil N loss in the form of dissolved gaseous N is nearly equal to that of NO3--N and hence an important fate of soil N, which deserves close attention.

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YAN Xiaoyuan, ZHOU Wei. Groundwater Nitrate Removal through Denitrification under Farmland in Yangtze River Delta[J]. Acta Pedologica Sinica,2019,56(2):350-362.

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History
  • Received:September 04,2018
  • Revised:November 07,2018
  • Adopted:November 15,2018
  • Online: December 21,2018
  • Published: