Collaborative Research: Quantifying Nitrogen Uptake in Bioretention Designed for Semiarid Climates

生物保留是一种低影响的开发管理策略，它采用工程植物群落来减少城市化对雨水径流和污染的影响。该研究扩展了生物保留的评价，并以城市生态系统可以按照基本生态原则进行设计的理论为指导，以可持续地为社会提供必要的服务。本研究的总体目标是提高对工程生态系统如何在城市环境中发挥作用的理解，以便通过最大化流域保护服务和最小化维持工程生态系统所需的资源来优化生物保留设计。这一总体研究目标将通过进行两组实验来实现：(1)一项为期两年的研究，以量化氮(N)在生物保持中的处理随时间的变化；(2)一项同位素标记实验，以描述植物对有机和无机氮处理过程的贡献。三种植物群落类型将使用9个生物保持细胞进行测试：半干旱山地灌木群落，湿地群落和无植物对照。这些实验将检验以下假设：(1)植被覆盖的增加将导致更大的总体氮滞留，即使在多次雨水事件增加每个生物滞留细胞内N残留水平的情况下，(2)在没有植被的细胞中，流出物中无机氮的浓度将大于流入物中无机氮的浓度，(3)在有植被的生物滞留细胞中，出水无机氮的浓度将小于进水无机氮的浓度。该项目将监测三个植物群落的氮处理性能和植物生产力，以模拟每个群落在半干旱气候下如何应对城市雨水的反复淹没。这些研究的结果将结合起来预测干旱和半干旱气候下生物滞留的长期表现。同位素标记研究将通过回收植物组织、土壤材料或花园废水中的标记氮来确定有机和无机氮的处理率和途径。这将决定植物是否能够在湿润事件中快速吸收雨水中的无机氮而不发生转化，以及通过与土壤微生物的复杂相互作用，有机氮将被生物矿化，然后在湿润事件之间被植物缓慢吸收。就更广泛的影响而言，本研究结果将为改善西部干旱和半干旱地区生物保留区的设计和扩大实施提供技术支持。更好地了解不同植物群落在单个风暴事件和时间尺度上是如何处理N的，对于提供设计建议至关重要，这些建议可以确保在广泛实施时的生物保持性能。在干旱和半干旱的西部实施生物保护将使城市化得以实现，同时保护与不断扩大的开发毗邻的脆弱生态系统。本研究项目计划的推广工作包括：(1)为犹他州的地方和州级官员提供两个研讨会，向政策制定者展示生物保留区的功能、经济和环境保护潜力；(2)三个犹他大学学生组织的研讨会，针对雨水专业人员，讨论半干旱气候下生物保留区的设计、植物选择和环境效益；(3)通过网站在全国范围内传播生物滞留研讨会资料；(4)将研究成果整合到现有的城市生态学、水政策和水资源工程研究生和本科生课程中。

1133524 PI PomeroyBioretention is a low impact development management strategy that employs engineered plant communities to reduce the impact of urbanization on stormwater runoff volumes and pollution. The proposed research expands the evaluation of bioretention and is guided by the theory that urban ecosystems can be engineered following basic ecological principles to sustainably perform a necessary service to society. The overarching goal of this research is to improve the understanding of how engineered ecosystems function in urban settings in order to optimize bioretention design by maximizing the service of watershed protection and minimizing the resources necessary to sustain the engineered ecosystem. This overarching research goal will be achieved by conducting two sets of experiments: (1) a two-year study to quantify nitrogen (N) treatment in bioretention over time and (2) an isotopic labeling experiment to describe plant contributions to the treatment processes for organic and inorganic N. Three plant community types will be tested using nine bioretention cells: a semi-arid upland shrub community, a wetland community, and a control with no plants. These experiments will test the following hypotheses: (1) the addition of vegetation cover will result in a greater overall retention of N, even under conditions where multiple stormwater events increase the residual level of N within each bioretention cell, (2) in cells without vegetation, the concentration of inorganic N in the effluent will be greater than the concentration of inorganic N in the influent, (3) in bioretention cells with vegetation, the concentration of inorganic N in the effluent will be less that the concentration of inorganic N in the influent. The PI will monitor the nitrogen treatment performance and plant productivity of the three plant communities to model how each community responds to repeated inundations of urban stormwater in a semi-arid climate. The results of these studies will be combined to predict long-term performance of bioretention in arid and semi-arid climates. The isotopic labeling studies will identify treatment rates and pathways of organic and inorganic N by recovering the labeled N in the plant tissue, soil materials or garden effluent. This will determine if plants can take up inorganic nitrogen from stormwater sources rapidly without transformation during wetting events, and that through complex interactions with soil microbes, organic nitrogen will be biologically mineralized then slowly taken up by plants between wetting events. In terms of the broader impacts, the findings of this research will provide technical support to improve design and expand the implementation of bioretention in the arid and semi-arid west. Better knowledge of how different plant communities process N on the scale of individual storm events and over time is critical to providing design recommendations that ensure bioretention performance when implemented broadly. Implementation of bioretention in the arid and semi-arid west will allow urbanization to occur while protecting fragile ecosystems adjacent to expanding developments. Planned outreach efforts under this research project include (1) two workshops provided for local- and state-level officials within Utah, demonstrating the functionality, economics, and environmental protection potential of bioretention to policy makers, (2) three University of Utah student-organized workshops targeted to stormwater professionals to address design, plant selection, and environmental benefits of bioretention in semi-arid climates, (3) national dissemination of bioretention workshop materials via a website, and (4) integration of the research findings into the curriculum of existing urban ecology, water policy, and water resources engineering graduate and undergraduate courses.