Elsevier

Water Research

Volume 39, Issue 10, May 2005, Pages 1982-1989
Water Research

Nitrogen composition in urban runoff—implications for stormwater management

https://doi.org/10.1016/j.watres.2005.03.022Get rights and content

Abstract

A study was conducted to characterise the composition of nitrogen in urban stormwater in Melbourne, Australia, during baseflows and storm events, and to compare the results with international data. Nitrogen in Melbourne stormwater was predominantly dissolved (∼80%), with ammonia the least-abundant form (∼11%). Concentrations of nitrogen species did not vary significantly between baseflow and storms, although the proportion of nitrogen in particulate form was higher during storm events (p=0.04).

Whilst the composition of nitrogen in Melbourne was broadly consistent with international data, the level of dissolved inorganic nitrogen was higher in Melbourne (μ=48% during baseflows and 49% during storms) than in the international literature (μ=29%). Limitations in the international dataset precluded comparison of total dissolved nitrogen.

The results have implications for stormwater management. Whilst nitrogen species concentrations are variable, they are not strongly related to flow conditions, so treatment systems must be designed to cope with stochastic inflow concentrations at all times. To optimise their performance, stormwater treatments should be designed to improve dissolved nitrogen removal. Further research is needed to improve the ability of treatment systems to achieve this aim.

Introduction

Urban runoff contributes to the eutrophication of receiving waters around the world, and while phosphorus is normally the limiting nutrient in fresh water, nitrogen may also be of concern (Field et al., 1998; Heaney et al., 1999; Lee and Bang, 2000; Novotny and Witte, 1997). Whilst considerable data exist on the concentration of nitrogen in urban runoff (Duncan, 1999), there are less on its composition.

Particulate nitrogen in urban runoff enters receiving waters predominantly in organic form (Harris et al., 1996). However, it cannot be assumed that all organic nitrogen (Org-N) is particulate. Unfortunately, the proportions of Org-N in dissolved or particulate form are rarely quantified in the literature (Seitzinger et al., 2002).

Dissolved inorganic nitrogen (DIN) includes ammonia (NH3), nitrite (NO2), and nitrate (NO3) (Fig. 1). These constituents have the greatest impact on water bodies because they are readily available for uptake by simple organisms (Seitzinger et al., 2002), and may lead to eutrophication, hypoxia, and loss of biodiversity and habitat (Galloway et al., 2003). Nitrate is often the most common soluble species in aquatic systems and urban runoff (Feth, 1966; Galloway et al., 2003; Oms et al., 2000), and is not well retained by soil particles. High nitrate concentrations in receiving waters can indicate general urban impacts, whilst high ammonia concentrations may indicate anaerobic conditions, or organic pollution from sewers (Gibb, 2000). While many data exist for DIN, less are available for dissolved organic nitrogen (DON); yet it may contribute up to half the total nitrogen (TN) load (Cerda et al., 2000).

Many studies have demonstrated the impacts of excessive nitrogen loads on receiving waters. For example, the Chesapeake Bay study showed that increases in reactive nitrogen contributed to increased anoxic and hypoxic waters within the bay (Galloway et al., 2003). Similarly, a study of Melbourne's Port Phillip Bay identified the need to reduce annual nitrogen loads by 1000 tonnes, to reduce the risk of eutrophication (Harris et al., 1996). In Moreton Bay in Queensland, Australia, nitrogen was identified as a key pollutant influencing ecological sustainability (Abal et al., 2001). Given its bioavailability, appropriate management strategies are therefore required to reduce the loads of dissolved nitrogen entering receiving waters.

Current approaches to stormwater management aim to treat stormwater to remove pollutants, often using a “treatment train” approach, whereby coarse material is removed first, followed by finer particulates and finally dissolved components (Kadlec, 1999; Mitsch and Gosselink, 2000; Wong et al., 1999). For example, a stormwater wetland's inlet zone promotes coarse-particulate sedimentation (Urbonas and Stahre, 1990), whilst downstream shallower macrophyte zones facilitate biofilm growth, which remove fine particulates and dissolved pollutants (Brix, 1994; Brock et al., 1994; Hart and Grace, 2000). Similarly, stormwater biofiltration systems typically use a vegetated buffer strip to remove coarse particulates, whilst the filter medium (gravel, sand or soil) promotes biochemical and fine particulate removal (Fletcher et al., 2003).

In designing stormwater treatment systems, however, it is necessary to understand the composition of nitrogen in urban runoff, to maximise the removal of nitrogen forms which are dominant or of most concern to receiving environments. Understanding nitrogen composition in urban runoff will assist in proportioning and prioritising the processes to be facilitated by treatment systems.

Section snippets

Study overview

This study seeks to characterise the composition of nitrogen in urban baseflow and stormflow, with the ultimate aim of improving treatment strategies for nitrogen reduction. The study was undertaken in Melbourne, Australia. To place the results in context, the Melbourne data were compared to a review of international data.

Nitrogen composition

Water samples were collected from 14 monitoring sites in urban catchments (Table 1) ranging in area from 0.8 to 122 ha, and from 35% to 80% impervious cover. Flow-weighted composites were collected during storm events (n=32 events) using Sigma 900 autosamplers, with 24 1 L polyethylene bottles, to derive an event mean concentration. Baseflow samples (n=23) were collected manually with a 10 L polyethylene bucket.

Samples were stored and analysed according to Standard Methods (Greenberg et al., 1999)

Comparisons between Melbourne baseflow and storm events, and international data

In Melbourne, TDN made up the largest proportion of TN (μ=84% during baseflows, 77% during storms), PON thus accounting for 16% and 23% in baseflows and storms, respectively (Fig. 4). Ammonia was consistently the least-abundant constituent. Variability (shown by coefficient of variation, CV; Table 2) was high during both dry and wet weather. There were no significant differences in the concentration of any of the nitrogen species between baseflow and storm event conditions (Table 2). However,

Nitrogen behaviour

Concentrations of most nitrogen species were highly variable, supporting other studies such as Duncan, 2003 and Terstriep et al., 1986. High variability during storm events is a well-known phenomenon caused by variations in aerial deposition and rainfall quality (Duncan, 1995; Zhang et al., 1999), catchment soils (Feth, 1966) and past and present catchment activities (e.g. Mayer et al., 2002).

The observed variability during baseflows has a number of possible causes, including impacts from

Conclusion

The composition of TN in both baseflow and storm events was dominated by TDN (typically around 80% of TN). Examination of international data showed a lower proportion of DIN, with a subsequently higher proportion of Org-N.

The composition of nitrogen prior to entering treatment systems such as constructed wetlands is an important consideration for enhancing current wetland treatment capabilities. Nitrogen concentrations appeared to be highly stochastic, but did not vary significantly between

Acknowledgements

This manuscript benefited from the advice of Marie Keatley, Chris Walsh, Belinda Hatt, and Peter Newall.

References (46)

  • M.A. Brock et al.

    Plants and Processes in Wetlands

    (1994)
  • A. Cerda et al.

    Determination of organic nitrogen

  • W.F. Cowen et al.

    Nitrogen availability in urban runoff

    J. Water Pollut. Control Fed.

    (1976)
  • Duncan, H.P., 1998. Urban stormwater quality improvement in storage. Paper Presented at the HydraStorm 98, Third...
  • H.P. Duncan

    Urban Stormwater Quality: A Statistical Overview

    (1999)
  • Duncan, H.P., 2003. Urban stormwater quality. In: Wong, T.H.F. (Ed.), Australian Runoff Quality. Sydney, Australia:...
  • H.P. Duncan

    Water quality in urban low flows—the Hampton Park experience

    Catchword

    (2004)
  • J.H. Feth

    Nitrogen compounds in natural water—a review

    Water Resour. Res.

    (1966)
  • R. Field et al.

    Urban wet-weather flows

    Water Environ. Res.

    (1998)
  • T.D. Fletcher et al.

    Buffer strips, vegetated swales and bioretention systems

  • Fletcher, T.D., Poelsma, P., Li, Y., Deletic, A.B., 2004. Wet and dry weather performance of constructed stormwater...
  • Fuchs, S., Brombach, H., Weilb, G., 2004. New database on urban runoff pollution. Paper Presented at the Novatech 2004,...
  • Cited by (0)

    View full text