Effects of Mercuric Chloride on Carbon Dioxide and Methane Emissions from Water of Tamsui River

Abstract

To investigate carbon dioxide and methane emissions from the river water, mercuric chloride was added to the water for retarding microbial activities during the period from water sampling to laboratory measurement. But the effects of mercuric chloride on emissions of these green house gases from water remain unknown. Therefore, carbon dioxide and methane emissions from water of Tamsui River with different amounts of saturated mercuric chloride solution (69 mg/mL at 20℃) were determined at 25℃ for 6 days. Carbon dioxide and methane emissions decreased with increasing amount of saturated mercuric chloride solution added from 50 to 600 μL (3.45-41.4 mg) in 100 mL water. The gas emissions decreased slightly when the amount of saturated mercuric chloride was higher than 200 μL (13.8 mg). Carbon dioxide and methane emissions decreased linearly with the amount of saturated mercuric chloride supplemented between 0 and 100 μL (0-6.9 mg). The effect of bottle color on the carbon dioxide and methane emissions was studied with colorless and brown-colored bottles. Water in the brown-colored bottles had higher carbon dioxide and methane emissions than in the colorless bottles. The downstream area of Tamsui River had the highest carbon dioxide and methane emissions, followed by the middle-stream area, and the upstream area was the lowest due to the high pollution in the downstream area. Therefore, addition of 100 μL saturated mercuric chloride solution (6.9 mg) in 100 mL of water to retard the microbial activities after sampling in the fields for measurement of greenhouse gases emissions from water is a feasible method.