When plant-mediated water flows increase biogeochemical efficiency in an aridland urban treatment wetland, and pleasantly surprise the engineers

Wastewater treatment wetlands provide nutrient removal ecosystem services.  However, in hot, arid climates, these wetlands evapotranspire large volumes of water, concentrating solutes and potentially complicating these services. At a treatment wetland in Phoenix AZ, in addition to the combined high transpiration and N retention rates, we also observe a >50% loss of marsh water volume on hot, dry summer days. Thus, plant transpiration is driving a lateral “tide” that replaces the water and nutrients overlying the vegetated marsh roughly every two days, making this wetland more effective at nutrient removal than it might be in a more mesic climate.