Wet season nitrogen export from a residential stormwater pond.

Jariani Jani,Mary G Lusk,Yun-Ya Yang,Gurpal S Toor,Julian Aherne

doi:10.1371/journal.pone.0230908

Abstract

Stormwater runoff is recognized as a cause of water quality degradation because it may carry nitrogen (N) and other pollutants to aquatic ecosystems. Stormwater ponds are a stormwater control measure often used to manage stormwater runoff by holding a permanent pool of water, which reduces the peak flow, magnitude of runoff volume, and concentrations of nutrients and pollutants. We instrumented the outlet of a stormwater pond in an urban residential neighbourhood in Florida, United States to (1) investigate the concentration and composition of N forms during the summer rainy season (May to September 2016), and (2) determine the bioavailability of organic N in the stormwater pond with a bioassay experiment. A total of 144 outflow water samples over 13 storm events were collected at the outlet of the stormwater pond that collects runoff from the residential catchment. Samples were analysed for various inorganic N [ammonium (NH4–N), nitrate (NO3–N)], and organic N forms [dissolved organic nitrogen (DON), and particulate organic nitrogen (PON)]. Flow-weighted mean concentration of total N (TN) in pond outflow for all collected storm events was 1.3±1.42 mg L-1, with DON as the dominant form (78%), followed by PON and NO3–N (each at 8%), and NH4–N (6%). In the bioassay experiment, organic N (DON+PON) was significantly decreased by 25–28% after 5 days of incubation, suggesting that a portion of the DON carried from the pond outflow to receiving water bodies may be bioavailable. These results suggest that efforts to mitigate stormwater N outflows from urban ponds should incorporate both inorganic and organic N in management plans.

Highlights

Stormwater runoff is recognized as an important source of nitrogen (N) in receiving water bodies, especially in urban landscapes with higher impervious surface area [1, 2]
In contrast to organic N, NOx–N concentrations increased by 35–39% and NH4–N concentrations increased by 9–39% (Fig 3)
Our study is the first of which we are aware that includes inspection of both dissolved organic nitrogen (DON) and particulate organic nitrogen (PON) biodegradability within an urban stormwater pond, and that a third to a half of these ON forms were bioavailable in our study indicates that ON can be dynamic in urban aquatic systems

Summary

Introduction

Stormwater runoff is recognized as an important source of nitrogen (N) in receiving water bodies, especially in urban landscapes with higher impervious surface area [1, 2]. The volume and flow velocity of stormwater runoff is generally higher on impervious surfaces than in natural areas. This increased water volume and velocity can change both the flow and quality of receiving streams, necessitating stormwater management practices that collect and mitigate stormwater flows [3,4,5]. Under the US Clean Water Act, states are required to monitor water.

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