T. Yoshinari R. L. Smith 2008 <div class="hlFld-Abstract"><div id="abstractBox"><p class="articleBody_abstractText">Little is known about nitric oxide (NO) production or consumption in the subsurface, an environment which may be conducive to NO accumulation. A study conducted in a nitrogen-contaminated aquifer on Cape Cod, Massachusetts assessed the occurrence and turnover of NO within a contaminant plume in which nitrification and denitrification were known to occur. NO (up to 8.6 nM) was detected in restricted vertical zones located within a nitrate (NO₃⁻) gradient and characterized by low dissolved oxygen (&lt;10 μM). NO concentrations correlated best with nitrite (NO₂⁻) (up to 35 μM), but nitrous oxide (N₂O) (up to 1 μM) also was present. Single-well injection tests were used to determine NO production and consumption in situ within these zones. First-order rate constants for NO consumption were similar (0.05−0.08 h⁻¹) at high and low (260 and 10 nM) NO concentrations, suggesting a turnover time at in situ concentrations of 10−20 h. Tracer tests with<span>&nbsp;</span>¹⁵N[NO] demonstrated that oxidation to<span>&nbsp;</span>¹⁵N[NO₂⁻] occurred only during the initial stages, but after 4 h reduction to<span>&nbsp;</span>¹⁵N[N₂O] was the primary reaction product. Added NO₂⁻<span>&nbsp;</span>(31 μM) or NO₃⁻<span>&nbsp;</span>(53 μM) resulted in a linear NO accumulation at 2.4 and 1.0 nM h⁻¹<span>&nbsp;</span>for the first 6 h of in situ tests. These results suggest that NO was primarily produced by denitrification within this aquifer.</p></div></div><div class="hlFld-Fulltext"><br data-mce-bogus="1"></div> application/pdf 10.1021/es801290v en ACS Occurrence and turnover of nitric oxide in a nitrogen-impacted sand and gravel aquifer article