Nitrous oxide production and consumption processes in a groundwater contaminated by nitrogen compounds in Kathmandu Valley, Nepal: a study using nitrogen and oxygen isotopes ratio of nitrous oxide and nitrate
Abstract
We investigated production and consumption processes of nitrous oxide by measuring nitrogen and oxygen isotopes ratio of dissolved nitrous oxide and nitrate, dissolved nitrous oxide concentration and other chemicals in the groundwater at Kathmandu Valley, Nepal. We collected the groundwater samples from 36 wells in August and September 2009, and Aug 2010. Well depth ranged from 2.8 to 21 m (median. 6.2 m). We show the data from observation in August and September 2009. DO concentrations in the groundwater were low in many plots and ranged from 0.1 to 4.7 mg/L (median: 0.4 mg/L). DOC concentrations ranged from 0.8 to 7.8 mg/L (median: 2.8 mg/L). These conditions that were anoxic and organic available indicate denitrification could occur in the groundwater body. The nitrate concentrations ranged from 0.0 to 44.7 mgN/L (Median: 2.4 mgN/L) and fractionation of nitrogen and oxygen isotope of nitrate indicated denitrification occurrence in the groundwater. Except for a few sample, nitrous oxide concentrations had a positive correlation with nitrate concentration (r =0.57), and ranged from 0.0 to 172.3 μgN/L (Median: 5.8 μgN/L). The difference between nitrogen isotopes of nitrous oxide and nitrate ranged from -39.1 to 15.3 per mill. These data permit the explanation that nitrous oxide mainly originated from denitrification and more denitrified in the groundwater, because the nitrogen isotopic fractionation from nitrate to nitrous oxide by denitrification is reported as -39 per mill (Toyoda et al., 2005).
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.H53F1123O
- Keywords:
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- 0454 BIOGEOSCIENCES / Isotopic composition and chemistry;
- 0470 BIOGEOSCIENCES / Nutrients and nutrient cycling;
- 0490 BIOGEOSCIENCES / Trace gases;
- 1806 HYDROLOGY / Chemistry of fresh water