Publication Date:
2013-06-21
Description:
[1] A 30-day time course laboratory weathering experiment was conducted using rock samples collected from the West Fork of the Gallatin River watershed (WFW) in southwestern Montana, U.S.A. The goal of these experiments was to quantify the amount of labile nitrogen in rock samples collected from the watershed and determine if chemical weathering is a source of dissolved nitrogen in stream water. Several rock samples investigated produced nitrate in significantly higher concentrations than the silica bead control ( p 〈 0.05) and the data were consistent with elevated NO 3 - concentrations measured in associated WFW streams. Isotopic analyses of 15 N-NO 3 in 22 stream water samples from the WFW and 4 rock:water extracts from the laboratory experiments indicated that the isotopic composition of NO 3 was comparable from rocks and streamwater samples in the same watershed and differed strongly from waters downstream of development. We suggest that the NO 3 - measured in WFW streams includes nitrogen derived from mineral dissolution products from soils and rock. The results presented herein further indicate that rock weathering is a source of streamwater N in the West Fork watershed and inform water quality assessment, total maximum daily load (TMDL) development, and the relative influences of natural and anthropocentrically derived N sources across this developing mountain watershed.
Print ISSN:
0148-0227
Topics:
Biology
,
Geosciences
