The content and first flush effect of inorganic nitrogen in different urban runoffs of Wenzhou City

The purpose of this study is to investigate the characteristics of dissolved inorganic nitrogen in storm runoff and the first flush effect in urban areas. Six land use locations, including urban traffic road, parking lot, roof and road in residential lot, lawn and sewer outlet, in two watersheds in the city of Wenzhou were selected for sampling and studied during four storm events. Quality parameters such as ammonium (NH₄⁺-N), nitrate (NO₃^--N), nitrite (NO₂^--N) and physicochemical indexes of storm runoff water were analyzed. The results showed that event mean concentrations (EMC) of NH₄⁺-N, NO₃^--N and NO₂^--N ranged from 0.40 to 5.55, from 0.01 to 4.70 and from 0 to 0.87 mg·L^-1, respectively. The nitrogen concentrations in Jiushanwai watershed were higher than Shanxia watershed, and there was heavy nitrogen pollution at urban traffic road and residential lot. NH₄⁺-N dominated dissolved inorganic nitrogen in most runoffs, with percentages higher than 50%. NH₄⁺-N levels were higher than the fifth grade value of national surface water quality standards in samples from Jiushanwai watershed. The first flush effect of NH₄⁺-N appeared to occur more frequently at sampling locations except for road in residential lot, while the first flush effect of NO₃^--N only appeared at roof of residential lot and sewer outlet occasionally.