State Key Laboratory of Soil and Sustainable Agriculture, Changshu National Agro-Ecosystem Observation and Research Station, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China; University of Chinese Academy of Sciences, Beijing 100049, China.
State Key Laboratory of Soil and Sustainable Agriculture, Changshu National Agro-Ecosystem Observation and Research Station, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China.
Water Res. 2022 Jul 15;220:118639. doi: 10.1016/j.watres.2022.118639. Epub 2022 May 21.
The effects of land use on riverine NO emissions are not well understood, especially in suburban zones between urban and rural with distinct anthropogenic perturbations. Here, we investigated in situ riverine NO emissions among suburban, urban, and rural sections of a typical agricultural-urban gradient river, the Qinhuai River of Southeastern China from June 2010 to September 2012. Our results showed that suburban agriculture greatly increased riverine N concentration compared to traditional agricultural rivers (TAR). The mean total dissolved nitrogen (TDN) concentration was 8.18 mg N L in the suburban agricultural rivers (SUAR), which was almost the same as that in the urban rivers (UR, of 8.50 mg N L), compared to that in TAR (0.92 mg N L). However, the annual average indirect NO flux from the SUAR was only 27.15 μg NO-N m h, which was slightly higher than that from the TAR (13.14 μg NO-N m h) but much lower than that from the UR (131.10 μg NO-N m h). Moreover, the average NO emission factor (EF, NO-N/DIN-N) in the SUAR (0.0002) was significantly lower than those in the TAR (0.0028) and UR (0.0004). The limited indirect NO fluxes from the SUAR are best explained by the high riverine dissolved organic carbon (DOC) and low dissolved oxygen, which probably reduced the denitrification source NO by favoring complete denitrification to produce N and inhibited the nitrification source NO, respectively. An exponential decrease model incorporating dissolved inorganic nitrogen and DOC could greatly improve our EF predictions in the agricultural-urban gradient river. Given the unprecedented suburban agriculture in the world, more studies in suburban agricultural rivers are needed to further refine the EF and better reveal the mechanisms behind indirect NO emissions as influenced by suburban agriculture.
土地利用对河流硝酸盐排放的影响尚不清楚，特别是在城乡之间具有明显人为干扰的郊区地带。在这里，我们调查了中国东南部典型农业-城市梯度河流秦淮河的郊区、城市和农村河段的原位河流硝酸盐排放。结果表明，与传统农业河流（TAR）相比，郊区农业大大增加了河流中的氮浓度。郊区农业河流（SUAR）的总溶解氮（TDN）平均浓度为 8.18mgNL，与城市河流（UR，8.50mgNL）相当，而 TAR 则为 0.92mgNL。然而，SUAR 的年平均间接 NO 通量仅为 27.15μgNO-Nm h，略高于 TAR（13.14μgNO-Nm h），但远低于 UR（131.10μgNO-Nm h）。此外，SUAR 的平均 NO 排放因子（EF，NO-N/DIN-N）（0.0002）明显低于 TAR（0.0028）和 UR（0.0004）。SUAR 中有限的间接 NO 通量可以通过高河流溶解有机碳（DOC）和低溶解氧来很好地解释，这可能通过促进完全反硝化来减少硝酸盐还原源 NO 产生 N，并分别抑制硝化源 NO。结合溶解无机氮和 DOC 的指数递减模型可以大大提高我们在农业-城市梯度河流中的 EF 预测。鉴于世界上前所未有的郊区农业，需要对郊区农业河流进行更多的研究，以进一步细化 EF，并更好地揭示郊区农业对间接 NO 排放的影响背后的机制。
