『Abstract
Nitrification and nitrate reduction were examined in an ephemeral
drainage channel receiving discharge from coalbed natural gas
(CBNG) production wells in the Powder River Basin, Wyoming, CBNG
co-produced water typically contains dissolved inorganic nitrogen
(DIN), primarily as ammonium. In this study, a substantial portion
of discharged ammonium was oxidized within 50 m of downstream
transport, but speciation was markedly influenced by diel fluctuations
in dissolved oxygen (＞300μM). After 300 m of transport, 60％ of
the initial DIN load had been removed. The effect of benthic nitrogen-cycling
processes on stream water chemistry was assessed at 2 locations
within the stream channel using acrylic chambers to conduct short-term
(2-6 h), in-stream incubations. The highest ambient DIN removal
rates (2103 μmol N m-2 h-1) were found at
a location where ammonium concentrations ＞350μM. This occurred
during light incubation when oxygen concentrations were highest.
Nitrification was occurring at the site, however, net accumulation
of nitrate and nitrite accounted for ＜12％ of the ammonium consumed,
indicating that other ammonium-consuming processes were also occurring.
In dark incubations, nitrite and nitrate consumption were dominant
processes, while ammonium was produced rather than consumed. At
a downstream location nitrification was not a factor and changes
in DIN removal rates were controlled by nitrate reduction, diel
fluctuations in oxygen concentration, and availability of electron
donor. This study indicates that short-term adaptation of stream
channel processes can be effective for removing CBNG DIN loads
given sufficient travel distances, but the long-term potential
for nitrogen remobilization and nitrogen saturation remain to
be determined.
Keywords: Coal bed natural gas; Powder River Basin; Nitrification;
Nitrate reduction; Ammonium; In situ rate』
1. Introduction
2. Site description
3. Materials and methods
3.1. Water sample collection
3.2. In situ incubations
3.3. Chemical analyses
4. Results and discussion
4.1. Channel water chemistry
4.2. In situ incubations at the nitrification site
4.3. In situ incubations at the nitrate reduction site
5. Implications and conclusions
Acknowledgements
References