Aquatic crop (Zizania latifolia Stapf–Ipomoea aquatica Forsk) wetlands were constructed to remove nitrogen (N) in drainage from paddy rice fields, with three different storage water depths (namely 4H, 7H and 10H, where H is the routine paddy drainage water depth). Concentrations of ammonium nitrogen (NH₄⁺-N), nitrate nitrogen (NO₃⁻-N) and total nitrogen (TN) during the first two drainage events were reduced within 8–14d of storing by 82.3–92.8%, 84.5–94.3% and 74.9–92.4%, respectively. Generally, the higher N concentration in inlet water, the higher removal efficiency of nitrogen. The removal rate in wetland with 4H water storage was observed higher as compared to those at 7H and 10H. Overall, the aquatic crop wetlands at these storage water depths could intercept more than 93.2% of N output from paddy fields, and the removal efficiency was slightly better in wetland at 4H. For a routine drainage event (about 30–50 mm) occurred following a routine rainfall (about 100 mm at 5–10 years return period) with local water-level management practice in rice field, wetlands with 4H and 7H storage could effectively remove N in drainage by reusing it with aquatic crops. Nevertheless, the larger the proportion (low water depth in wetland for one drainage) of wetland to paddy field, the higher the production efficiency, because the value of aquatic vegetable is much higher than rice. The current results suggested that aquatic crop wetlands constructed in low-lying part within paddy fields could intercept a large amount of N output from paddy field, and with high economic return. Designing wetlands and paddy fields in a proper area ratio is vital important for balancing removal effect of nutrients in paddy drainage and the demand of food security.

中文翻译：

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利用水生作物湿地对稻田排水中氮的吸收和去除

修建水生作物湿地（Zizania latifolia Stapf– Ipomoea aquatica Forsk）湿地以去除稻田排水中的氮（N），其具有三种不同的储水深度（即4H，7H和10H），其中H是常规稻田排水水深）。铵氮浓度（NH ₄ ⁺ -N），硝酸态氮（NO ₃ ^--N）和前两个排水事件中的总氮（TN）在储存的8-14d内分别降低了82.3-92.8％，84.5-94.3％和74.9-92.4％。通常，进水中氮浓度越高，氮的去除效率越高。观察到在蓄水量为4H的湿地中的去除率高于7H和10H。总体而言，在这些存储水深处的水生作物湿地可拦截稻田N的93.2％以上，并且在4H的湿地中去除效率稍好。对于常规降雨（在返还期5-10年内约100毫米）和稻田当地水位管理实践之后发生的常规排水事件（约30–50毫米），湿地4H和7H储存可有效去除氮通过将其与水生作物重复使用来进行排水。不过，湿地与水田的比例（一次排水的湿地水深低）越大，生产效率就越高，因为水生蔬菜的价值远高于水稻。目前的研究结果表明，在稻田低洼地带建设的水生作物湿地可以拦截大量的稻田氮素输出，具有较高的经济效益。以适当的面积比设计湿地和稻田对于平衡稻田排水中养分的去除效果和粮食安全的需求至关重要。目前的研究结果表明，在稻田低洼地带建设的水生作物湿地能够拦截大量的稻田氮素输出，具有较高的经济效益。以适当的面积比设计湿地和稻田对于平衡稻田排水中养分的去除效果和粮食安全的需求至关重要。目前的研究结果表明，在稻田低洼地带建设的水生作物湿地可以拦截大量的稻田氮素输出，具有较高的经济效益。以适当的面积比设计湿地和稻田对于平衡稻田排水中养分的去除效果和粮食安全的需求至关重要。