Cecchetti Aidan R, Sytsma Anneliese, Stiegler Angela N, Dawson Todd E, Sedlak David L
Department of Civil & Environmental Engineering, University of California Berkeley Berkeley, CA 94720, United States.
US National Science Foundation Engineering Research Center (ERC) for Re-Inventing the Nation's Urban Water Infrastructure (ReNUWIt), United States.
Water Res X. 2020 Sep 16;9:100070. doi: 10.1016/j.wroa.2020.100070. eCollection 2020 Dec 1.
In nature-based treatment systems, such as constructed wetlands, plant uptake of nutrients can be a significant removal pathway. Current methods for quantifying plant uptake of nitrogen in constructed wetlands, which often involve harvesting biomass and assuming that all nitrogen stored in plants was derived from wastewater, are inappropriate in pilot- and full-scale systems where other sources of nitrogen are available. To improve our understanding of nitrogen cycling in constructed wetlands, we developed a new method to quantify plant uptake of nitrogen by using stable isotopes and a mixing model to distinguish between nitrogen sources. We applied this new method to a pilot-scale horizontal levee system (i.e., a subsurface constructed wetland) over a two-year monitoring period, during which 14% of nitrogen in plants was wastewater-derived on average and the remaining plant nitrogen was obtained from the soil. Analysis of nitrogen isotopes indicated substantial spatial variability in the wetland: 82% of nitrogen in plants within the first 2 m of the slope came from wastewater while less than 12% of plant nitrogen in the remainder of the wetland originated from wastewater. By combining these source contributions with remote-sensing derived total biomass measurements, we calculated that 150 kg N (95% CI = 50 kg N, 330 kg N) was taken up and retained by plants during the two-year monitoring period, which corresponded to approximately 8% of nitrogen removed in the wetland. Nitrogen uptake followed seasonal trends, increased as plants matured, and varied based on design parameters (e.g., plant types), suggesting that design decisions can impact this removal pathway. This new method can help inform efforts to understand nitrogen cycling and optimize the design of nature-based nutrient control systems.
在诸如人工湿地等基于自然的处理系统中，植物对养分的吸收可能是一条重要的去除途径。目前用于量化人工湿地中植物对氮的吸收的方法，通常包括收获生物量并假设植物中储存的所有氮都来自废水，但在有其他氮源的中试规模和全规模系统中并不适用。为了更好地理解人工湿地中的氮循环，我们开发了一种新方法，利用稳定同位素和混合模型来区分氮源，从而量化植物对氮的吸收。我们在一个为期两年的监测期内，将这种新方法应用于一个中试规模的水平堤坝系统（即地下人工湿地），在此期间，植物中平均14%的氮来自废水，其余的植物氮则从土壤中获取。氮同位素分析表明，湿地中存在显著的空间变异性：斜坡前2米内植物中82%的氮来自废水，而湿地其余部分植物氮中来自废水的比例不到12%。通过将这些来源贡献与遥感得出的总生物量测量值相结合，我们计算出在两年的监测期内，植物吸收并留存了150千克氮（95%置信区间 = 50千克氮，330千克氮），这相当于湿地中去除氮的约8%。氮的吸收遵循季节性趋势，随着植物成熟而增加，并因设计参数（如植物类型）而异，这表明设计决策会影响这条去除途径。这种新方法有助于为理解氮循环和优化基于自然的养分控制系统的设计提供信息。
