4.7 Article

Strong variability in nitrogen (N) removal rates in typical agricultural pond from hilly catchment: Evidence from diel and monthly dissolved N2 measurement

期刊

ENVIRONMENTAL POLLUTION
卷 314, 期 -, 页码 -

出版社

ELSEVIER SCI LTD
DOI: 10.1016/j.envpol.2022.120196

关键词

Lowland pond; Membrane inlet mass spectrometry (MIMS); Denitrification rate; N pollution; Tea hillslopes

资金

  1. Ecological Civilization Project Towards A Beautiful China [XDA23020403]
  2. National Natural Science Foundation [42071143, 41877513]
  3. Science and Technology Planning Project of Yunnan Provincial Department of Science and Technology [202202AE090034]

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This study investigated the dynamics of nitrogen removal rate in a typical agricultural pond. It found significant differences in nitrogen removal rates between day and night, with higher rates at night due to fluctuation in dissolved oxygen levels. On a monthly scale, nitrogen removal rate was generally higher during warmer and rainier months, correlated with nitrogen levels in the pond.
Ponds, depressional submerged landscapes that can store and process nitrogen (N)-enriched runoff from surrounding uplands, are recognized as biogeochemical hotspots for N removal. Despite their strong potential for N removal, information is limited concerning the specifics of their changing nature. Here, we investigated the dynamics of N removal rate in a typical agricultural pond from a hilly catchment, by unraveling the monthly and diel patterns of N-2 concentrations and fluxes. Our observations showed that the N pollution in the pond was severe. Its averaged total N level reached 3.6 mg L-1, of which -72% consisted of NO3-N. Meanwhile, the water samples were supersaturated with N-2, demonstrating N removal occurring in the pond. Further estimates of net N-2 fluxes indicated that N removal rates exhibited obvious day-and-night and monthly differences. On the diel scale, N removal rates exhibited a distinct diurnal cycle, with nocturnal rates around 20% higher than during the day. Such a diel pattern can be mainly explained by the fluctuation in DO levels, showing that at nighttime when photosynthesis is absent, low DO environments are conducive to N removal. On a monthly scale, the monthly rates ranged from 0.02 to 0.49 mmol N-2 m(-2) h(-1) mean: 0.23 mmol N-2 m(-2) h(-1)), with generally higher removal rates in the warmer and concurrently rainy months (June-September). N levels in the pond were the corresponding primary explanatory variables. Assembled data from both monthly and hourly scales provided a more complete picture of the changing nature of N removal in ponds. Future work should carefully consider the effects of altered environmental conditions triggered by hydrological events to better reveal the control mechanisms behind the time-immediate N removal from lowland ponds.

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