Long-term monitoring and research of the ecology of the Tres Rios constructed treatment wetland, Phoenix, Arizona, USA, ongoing since 2011

# Project Description

In order to better understand the water, nutrient and treatment dynamics of aridland constructed treatment wetlands, we have developed datasets tracking primary productivity (aboveground and belowground), nutrient and water budget dynamics, soils, and aquatic metabolism at the Tres Rios wetlands, operated by the City of Phoenix Water Services Department, since July 2011. The 3-cell Tres Rios Wetlands were completed in 2010 and are associated with the 91st Avenue Wastewater Treatment Plant, the largest in Phoenix. This project is focused on the largest of the three wetlands treatment cells which was the first to be planted and became operational in Summer 2010. The wetland cells are bounded by roads (the "shoreline"), and the system we study is 42 ha in size, approximately half of which is open water and half of which is fringing vegetated marsh. Water depth is relatively consistent across the marsh (approximately 25cm) and effluent inflow to the cell varies seasonally from 95,000 to over 270,000 m3 d-1. Measurements are taken along two gradients representing the two hydraulic pathways of the system: The whole-system, from inflow to outflow, within the vegetated marsh itself.

# Abstract

Constructed treatment wetlands (CTW) provide cost effective and ecosystem-service based solutions to the problem of urban wastewater treatment. They are a particularly attractive option for water reuse in arid cities, where water resources are scarce, and understanding CTW function in these environments is critical to facilitating sustainable water use practices. Although CTW are well established and studied in mesic climates, how they function in and respond to hot, arid climates is comparatively not well understood. Specifically, large atmospheric water losses via evaporation and plant transpiration comprise a much larger component of the whole-system water budget than in mesic climates. Additionally, given the primary role that emergent macrophytes play in nitrogen removal, the effects of plant community composition and primary productivity patterns on system performance in the context of aridland constructed treatment wetlands have not been extensively studied. Our goal is to develop a model of how these "working wetlands" perform in arid climates by developing and comparing nutrient and water budgets. At the Tres Rios constructed treatment wetland in Phoenix, AZ, USA, we measure atmospheric water losses via plant transpiration and open water evaporation as well as inorganic nitrogen fluxes at the whole system and the vegetated marsh scales. Total water losses via evaporative pathways peaked at 300,000 m3 per mo-1 (714 L H2O m-2 mo-1) in the hot summer months and represented more than 70% of the whole-system water budget over a 27 month time period. These evaporative losses are nearly an order or magnitude higher than rates observed in mesic systems. Peaks in above-ground biomass ranged from 1586±179 to 2666±164 gdw m-2, with Typha spp. accounting for up to two-thirds of total biomass. Overall, the vegetated marsh removed almost all of the inorganic N supplied to it, and large transpirative water losses were observed to move large volumes of replacement water into the marsh via a plant-mediated "biological tide." This process providing additional opportunities for soil microbes and emergent macrophytes to process target solutes, and potentially enhancing the treatment efficacy of the aridland Tres Rios constructed treatment wetland relative to more humid and mesic systems.

# 项目概况
为深入理解干旱区人工处理湿地（Constructed Treatment Wetlands, CTW）的水分、营养盐及处理动态，我们自2011年7月起，针对菲尼克斯市水务部门运营的特雷斯里奥斯湿地，构建了涵盖初级生产力（地上与地下部分）、营养盐与水平衡动态、土壤及水生代谢的追踪数据集。该湿地含3个处理单元，于2010年完工，配套接入菲尼克斯规模最大的第91大道污水处理厂。本项目聚焦3个湿地处理单元中体量最大的一个——该单元是首个完成植被种植并于2010年夏季投入运行的单元。湿地单元以道路作为"shoreline"边界，研究系统总面积为42公顷，其中约一半为开阔水域，另一半为边缘植被沼泽。沼泽区域水深相对均一，约为25厘米；该单元的尾水进水流量随季节变化，介于95000至270000立方米/日之间。研究采样沿代表系统两条水力路径的梯度开展：即植被沼泽内部从进水端到出水端的全系统梯度。

# 摘要
人工处理湿地（Constructed Treatment Wetlands, CTW）可为城市污水处理提供兼具成本效益与生态系统服务价值的解决方案，在水资源匮乏的干旱城市中，其作为水回用方案尤为具有吸引力。深入理解此类湿地在干旱环境中的运行机制，对推动可持续用水实践至关重要。尽管人工处理湿地在中生湿润气候下的应用与研究已较为成熟，但针对炎热干旱气候环境的运行机制与响应特征，目前相关认知仍相对匮乏。具体而言，相较于湿润气候区，干旱区湿地通过蒸发与植物蒸腾产生的大气水分损失，在全系统水平衡中占比显著更高。此外，鉴于挺水大型植物在氮去除过程中发挥核心作用，目前针对干旱区人工处理湿地中植物群落组成与初级生产力格局对系统处理性能的影响，仍缺乏广泛深入的研究。本研究旨在通过构建并对比营养盐与水平衡模型，揭示此类"功能性湿地"在干旱气候下的运行表现。在美国亚利桑那州菲尼克斯的特雷斯里奥斯人工处理湿地中，我们于全系统及植被沼泽尺度下，测量了植物蒸腾与开阔水体蒸发导致的大气水分损失，以及无机氮通量。在炎热夏季，蒸发途径导致的总水分损失峰值可达30万立方米/月（714升 水/平方米·月），在27个月的监测周期内，该损失占全系统水平衡的70%以上，其速率较湿润气候系统高出近一个数量级。地上生物量峰值区间为1586±179至2666±164克干重（gram dry weight, gdw）/平方米，其中香蒲属（Typha spp.）植物占总生物量的比例可达三分之二。总体而言，植被沼泽几乎可完全去除输入的无机氮；同时，大量蒸腾水分损失通过植物介导的"生物潮汐"过程为湿地补充了大量水体，该过程为土壤微生物与挺水大型植物提供了更多处理目标溶质的机会，相较湿润气候系统，显著提升了干旱区特雷斯里奥斯人工处理湿地的处理效能。