Spatio-temporal variability of dissolved organic nitrogen (DON), carbon (DOC), and nutrients in the Nile River, Egypt
Increases in human activity have resulted in enhanced anthropogenic inputs of nitrogen (N) and carbon (C) into the Nile River. The Damietta Branch of the Nile is subject to inputs from industrial, agricultural, and domestic wastewater. This study investigated the distribution and seasonality of dissolved organic nitrogen (DON), dissolved organic carbon (DOC), and nutrients in the Nile Damietta Branch. Water samples were collected from 24 sites between May 2009 and February 2010. Dissolved organic nitrogen concentrations averaged 251 ± 115 μg/l, with a range of 90.2–671 μg/l, and contributed 40.8 ± 17.7 % to the total dissolved nitrogen (TDN) pool. Relative to autumn and winter, DON was a larger fraction of the TDN pool during spring and summer indicating the influence of bacterioplankton on the nitrogen cycle. Concentrations of DOC ranged from 2.23 to 11.3 mg/l with an average of 5.15 ± 2.36 mg/l, reflecting a high organic matter load from anthropogenic sources within the study area, and were highest during autumn. Higher values of biochemical oxygen demand (BOD), chemical oxygen demand (COD), DON, nitrate, and phosphate occurred downstream of the Damietta Branch and were probably due to anthropogenic inputs to the Nile from the Damietta district. A bacterial incubation experiment indicated that 52.1–95.0 % of DON was utilized by bacteria within 21 days. The decrease in DON concentration was accompanied by an increase in nitrate concentration of 54.8–87.3 %, presumably through DON mineralization. Based on these results, we recommend that water quality assessments consider DON and DOC, as their omission may result in an underestimation of the total organic matter load and impact.
KeywordsNile Damietta Branch Water quality DON DOC Bioavailability
The author would like to thank the Faculty of Science, Damietta University in conduct of the research, co-operation of Dr. Talatt Hegazy, and technician Ramzy Metowaly with sample collection. The author would also like to thank Dr. Abdullah Elithy (Egyptian Environmental Affairs Agency) for analysis of the DOC samples. The author acknowledges the generous support of the International Foundation for Sciences (grant no. W/4509-1) for funding this study. The author thanks Drs. Alan D. Tappin (University of Plymouth, UK) and Banalata Sen (AuthorAID mentor) for their constructive scientific/English language review of this manuscript. The comments of the anonymous reviewers are also gratefully acknowledged.
Compliance with ethical standards
This study was funded by the International Foundation for Sciences (IFS) (grant number W/4509-1).
Conflict of interest
The author declares that he has no conflict of interest.
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