Nitrogen composition in urban runoff--implications for stormwater management

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 (approximately 80%), with ammonia the least-abundant form (approximately 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 (mu = 48% during baseflows and 49% during storms) than in the international literature (mu = 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.