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Nitrogen (N) input from residential stormwater runoff causes nutrient enrichment in coastal water which leads to eutrophication. Our objectives were to measure N composition in runoff for residential catchments and compare the composition to different storm event patterns and investigate the processes that might influence N forms composition thus alter the nitrogen (N) cycle in urban waters. Runoff water samples (n=220) were collected during wet season (May to September 2016) from an inlet of stormwater wet pond that has been installed with autosampler. Samples were analysed for various N forms [ammonium (NH3–N), nitrate (NO3–N), dissolved organic nitrogen (DON), and particulate organic nitrogen (PON)]. A total of 22 storm events were captured during the wet season. Total rainfall recorded in 22 events were 37 cm or 38% of total rainfall throughout the study period (91 cm). Duration of rainfall for all collected stormwater events were ranged 10 min to 597 min with rainfall intensity ranged at 0.152 cm/hr to 4.686 cm/hr. Flow weighted mean concentrations of total N (TN) for all collected storm event was 1.2±0.6 mg/L. Total flow of stormwater runoff throughout the 22 storm events was 6.82 million L (32%) of total flow over wet season (21.47 million L) and carried 15.1 kg of TN with DON as the dominant form (47%). Total N was positively correlated with DON throughout the season (R2=0.62, p<0.05) suggesting than TN amounts in the runoff are strongly influence by DON. Runoff volume was positively correlated with rainfall volume (R2=0.97, p<0.05) throughout the 22 storm events. This urban stormwater generated about 1 to 69% of runoff in the watershed. Our results also showed that different storm characteristics will results in different patterns in N composition in the runoff. Finding from this study helps to identify the event that might contribute to high N loadings and provide an information for better stormwater management designs and practices in urban watersheds. |
