Assessment of sources and transformation of nitrate in groundwater on the slopes of Mount Meru, Tanzania
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Date
2015-09-21
Journal Title
Journal ISSN
Volume Title
Publisher
Springer
Abstract
The stable isotope compositions of nitrogen-nitrate ( 15 N-NO 3 ) and oxygen-nitrate ( 18 O-NO 3 ), and concentration of nutrients (NO 3 - , NH 4 ? , NO 2 - , PO 43- ) for water samples collected from springs, shallow wells and boreholes during dry and wet seasons were used to inves- tigate sources and biogeochemical transformation of NO 3 - in groundwater along the slopes of Mount Meru. About
80 % of all water sources had nitrate concentration higher than background concentration of 10 mg/l during both seasons, while NH 4 ? and NO 2 - concentrations were very low probably due to nitrification. Concentrations of NO 3 - above 50 mg/l were observed in some water sources. Concentrations of PO 43- in all groundwater sources were very low during the two seasons owing to dilution and adsorption. The d 15 N-NO 3 - for boreholes waters averaged ?11.6 ± 2.1 and ?10.7 ± 2.1 % during dry and wet seasons, respectively. Similarly, the d 18 O-NO 3 - of bore- hole waters for the wet and dry seasons averaged ?5.2 ± 1.3 and ?4.6 ± 1.9 %, respectively. With regard to dug wells, the d 15 N-NO 3 - of well water averaged ?13.3 ± 2.5 and ?12.5 ± 2.3 % during dry and wet seasons, respectively, while the d 18 O-NO 3 - for the wet and dry seasons averaged ?7 ± 2.3 and ?6.4 ± 2.1 %,
respectively. The d 15 N-NO 3 - , for springs averaged ?11.2 ± 2.2 % during dry season and ?11.7 ± 3.5 % during wet season whereas the d 18 O-NO 3 - for the wet and dry seasons averaged ?7.3 ± 3.6 and ?5.9 ± 2.6 %,
respectively. The isotopic data suggested that the source of
NO 3 - in the water sources are dominated by sewage and/or animal manure and to less extent, soil organic N. Few samples collected in close proximity of manure heaps and sanitary facilities had d 15 N values between 16 and 20 %suggesting occurrence of denitrification.
Description
Research articles
Keywords
Groundwater, Nutrients sources, Biogeochemical transformations, Stable isotopes, Meru Tanzania