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Methane dynamics in the Willamette River, Oregon
Author(s) -
Anthony Sara E.,
Prahl Fredrick G.,
Peterson Tawnya D.
Publication year - 2012
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.2012.57.5.1517
Subject(s) - hydrology (agriculture) , groundwater recharge , groundwater , aquifer , environmental science , biogeochemistry , rainwater harvesting , streams , streamflow , nitrate , spring (device) , precipitation , methane , geology , oceanography , ecology , geography , meteorology , mechanical engineering , drainage basin , computer network , geotechnical engineering , cartography , engineering , computer science , biology
Weekly monitoring of dissolved methane (CH 4 ) at two sites along an ~ 2‐km stretch of the Willamette River (Oregon) between October 2008 and November 2010 revealed persistent supersaturation (24–170× atmospheric equilibrium). The CH 4 concentration difference (δCH 4 : 0–200 nmol L −1 ) between the two sites varied inversely with river flow, which ranged from 125 m 3 s −1 to 1500 m 3 s −1 over the time series. At the downstream site, an ‘excess’ of ≤ 125% was observed, with groundwater input being the likely CH 4 source. Quasi‐synoptic studies of spatial trends in summer (2010, 2011) revealed steady CH 4 decrease along a 12‐km river stretch downstream of the time‐series sites. The estimated loss due to air–water exchange for this stretch was ~ 9× greater than the perceived net loss, consistent with regionally widespread groundwater input of CH 4 . Bi‐weekly dissolved nutrient measurements indicated that a distinct nitrate (NO 3 − ) source also existed between the upstream and downstream time‐series sites. The excesses of and CH 4 were inversely correlated, with the greatest supply corresponding to periods of high rainfall in winter and highest river flow. Although groundwater input is also the probable source of , seasonal seepage of rainwater‐saturated soils (shallow groundwater recharge) explains the input, while hyporheic exchange with a persistent deep aquifer best explains the CH 4 input. Improved understanding of groundwater input and exchange dynamics in the Willamette River will clarify the influence of human activities on river biogeochemistry and help to better constrain the magnitude of CH 4 and other greenhouse gas fluxes associated with inland waters.