Nitrogen and Sediment Capture of a Floating Treatment Wetland on an Urban Stormwater Retention Pond—The Case of the Rain Project

Brendan Mcandrew,Changwoo Ahn,Joanna Spooner

doi:10.3390/su8100972

Abstract

Nitrogen is widely recognized as a chronic urban stormwater pollutant. In the United States, wet retention ponds have become widely used to treat urban runoff for quantity and quality. While wet ponds typically function well for the removal of sediments, nitrogen removal, performance can be inconsistent due to poor design and/or lack of maintenance. Retrofitting ponds to improve their nitrogen capture performance, however, is often expensive. By hydroponically growing macrophytes on wet ponds, floating treatment wetlands (FTW) may provide a cheap, sustainable means of improving nitrogen removal efficiency of aging stormwater ponds. Few studies have been performed on the effectiveness real-world stormwater systems, however. In this study, we investigated the nitrogen and sediment capture performance of a 50 m2 floating treatment wetland deployed for 137 days on a stormwater wet pond located within an urban university campus near Washington, D.C. A total of 2684 g of biomass was produced, 3100 g of sediment captured, and 191 g of nitrogen removed from the pond. Although biomass production was relatively low (53 g/m2), we found that nitrogen uptake by the plants (0.009 g/m2/day) was comparable to contemporary FTW studies.

Highlights

Urban runoff, or stormwater, is increasingly responsible for the transport of sediment, nutrients, and other pollutants into natural waterways [1,2]
Over the past two decades, nitrogen and phosphorus have become recognized as pervasive stormwater pollutants targeted by water quality regulations and implementation of the Environmental Protection Agency’s (EPA) Total Maximum Daily Load (TMDL) program [4]
We investigated the performance of a small floating treatment wetlands (FTW) on an urban stormwater retention pond near Washington, D.C. as part of “The Rain Project”, an interdisciplinary student group research and scholarship project addressing sustainable stormwater management on a university campus [30]

Summary

Introduction

Stormwater, is increasingly responsible for the transport of sediment, nutrients, and other pollutants into natural waterways [1,2]. In the wake of the Clean Water Act’s passage in 1972, urban retention ponds became the most common SCM used to treat urban runoff [7] These ponds are a ubiquitous feature of modern development with some 200–300 ponds in Fairfax County, Virginia alone [8]. Depending on their design, these perennially wet ponds may reduce the risk of flooding downstream and limit stream bank erosion by attenuating the flow of stormwater into receiving waterways [9]. Renovating ponds to meet design criteria that favor nutrient removal can, be expensive (approx. $20,000–$60,000/acre for dredging alone), prompting research into alternative methods for improving nutrient removal in wet ponds [16]

Methods

Results

Conclusion