Department of Chemistry
University of Otago
PO Box 56, Dunedin
New Zealand
Tel: +64-3-4797908
Fax: +64-3-4797906
email: chemistry@otago.ac.nz
Rudra Dhungana, MSc (2003)
Dr. Barrie Peake 
Rudra Dhungana, MSc (2003) - Thesis Title:
- Nitrogen species in some aquatic environments
- Supervisor:
- Dr. Barrie Peake
- Thesis Abstract:
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The concentrations of dissolved nitrogen species in the surface water of the Water of Leith catchment were measured during the study period of August 2001 to August 2002. There was significant spatial and temporal variation in the levels of dissolved nitrogen species that could be attributed to various catchment characteristics and hydrological regimes. The variation of nitrate concentration among different sampling sites clearly showed that there was an impact of land use on stream water nitrate levels. Higher nitrate concentrations were measured in the streams flowing through some animal (sheep and beef) farming areas whereas lower nitrate concentrations were measured in the streams flowing through forested areas.
Nitrate was the predominant nitrogen species among all the oxidised forms of nitrogen and the levels of nitrite and ammonium were very low as compared to the nitrate levels. The monthly nitrate concentrations measured for a complete one-year period in the Water of Leith catchment showed that there was seasonal variation in nitrate levels in most of the sampling sites although the pattern of variation was different in each site. Nitrate concentrations were higher in the winter season than in the summer season in most of the sites.
The nitrate concentrations measured during several rain events in the present study showed that the concentration always increased well beyond the value that existed before the rainfall. As the stream flow rates during rain events were generally much higher than the base level stream flow-rate and the nitrate concentrations were also considerably higher at such times, the nitrate fluxes were apparently very high during rain events as compared to the base flow. In the present study, the estimated annual nitrate export from the Water of Leith catchment was 3.2 kg/ha/yr which is comparatively lower than the annual nitrate export values reported in other catchments. It is probably due to less intensive farming activities in this catchment and the combined forest and urban area covering a significant portion of the total catchment area.
It is suspected that the higher concentrations of nitrate found in some streams in the present study was probably due to the leaching of animal urine from the pasture area. Therefore, intensification of agriculture through increasing pasture production and livestock population is expected to increase the leaching loss of nitrogen in this catchment.
The concentrations of nitrate in some of the drinking water sources of Kathmandu Valley were found to be much higher than the WHO drinking water standard limit of 10 mg NO3– N/L. Nitrate concentrations exceeding the drinking water standard limit were detected in water from some of the historical stone-taps from Kathmandu City and some of the drinking water wells from the Bhaktapur district of Kathmandu Valley. It is suspected that septic tanks may be the major source of nitrate in these water sources. Microbial nitrification from soil organic matter or nitrogen fertilizers used in farms may be other possible factors contributing to the nitrate build-up over time. However, a more detailed study is necessary to draw any strong conclusion regarding the sources of nitrate in these water sources.
- Life since MSc
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