RAPID: Collaborative Research: Evaluating ecosystem respiration in urban streams using reactive tracer and dissolved oxygen loggers

Academy Of Natural Sciences Philadelphia, Philadelphia PA

Investigators

Abstract

Investigators will quantify shifts in aerobic respiration below the effluent discharge of a wastewater treatment plant (WWTP) in an urban stream and compare these rates to community respiration rates quantified by diel oxygen methods. The request is for the purpose of testing the use of the tracer resazurin (Raz), which irreversibly transform into resorufin (Rru) in the presence of aerobic bacteria, and whose efficacy has not been verified in urban streams. The working theory is that urban streams are overwhelmed by nutrient additions through WWTP effluent for quite a distance downstream, reducing nutrient retention efficiency for kilometers. The impacts on the functioning of stream ecosystems, including the ability of stream ecosystems to ameliorate anthropogenic nutrient loading are poorly understood. This study will fill a gap in quantifying WWTP impacts on the metabolism of the Wissahickon Creek, located in Montgomery and Philadelphia counties, Pennsylvania. The investigators are two early-career scientists launching a research career. Student volunteers involved in data collection during the stream tracer test will learn about stressors in urban streams and field characterization methods. Investigators obtained preliminary results based on diel oxygen monitoring, indicating that even in this stream where a majority of baseflow is comprised of effluent, respiration can be as high as -13 g O2 m-2 day-1 within five kilometers of effluent discharge. Raz-Rru injections would allow for an independent and reach-specific method of calculating instantaneous aerobic respiration. They propose to conduct two tests at the WWTPs on the Wissahickon Creek with differing effluent nutrient concentrations. The basic research question being addressed is whether the stresses of urban systems (in this case, high nutrient concentrations) inhibit or enhance metabolism, and at what temporal scale. The experiments proposed will provide a better understanding of spatial and temporal variation in metabolism, with the added benefit of evaluating a new method for determining metabolism in urban streams. The urgency of this project is controlled by their extensive probe set up for measuring dissolved oxygen, which will only be deployed in summer and fall 2017.