Differential Response of Greenhouse Gas Evasion to Storms in Forested and Wetland Streams

Abstract

Greenhouse gas evasion from inland waters is a globally significant yet highly uncertain flux, especially in regard to effects of wetlands and hydrologic variability. We sampled five first‐order and two second‐order streams with variable wetland influence during storm events for dissolved CO2, CH4, and N2O. We also calculated gas evasion rates. In first‐order streams, pCO2 and pN2O were significantly higher in the stream with the most wetland influence (mean ± 1 std: 3,965 ± 1,504 and 1.18 ± 0.37 μatm, respectively) than the forested stream (2,927 ± 439 and 0.47 ± 0.08 μatm, respectively). In second‐order streams, pCO2, pCH4, and pN2O were higher in the 14% wetland stream (3,274 ± 825, 501 ± 207, and 1.37 ± 0.43 μatm, respectively) than in the 2% wetland stream (1,858 ± 423, 137 ± 53, and 0.37 ± 0.08 μatm, respectively). In first‐order streams, pCO2 in streams with wetland influence increased during rain events, while pCO2 in streams with little to no wetland influence decreased or remained constant. Generally, pCH4 and pN2O followed the same trend, except in one stream with intermediate wetland influence. Gas transfer velocity increased in all streams during storm events. However, the forested streams had higher gas transfer velocities than the wetland streams due to steeper topography. CO2, CH4, and N2O evasion peaked in one of the intermediate wetland streams at high flow (maximum: 66 g C·m−2·day−1, 177 mg C·m−2·day−1, and 9.7 mg N·m−2·day−1, respectively). These findings suggest that gases are shunted downstream in flatter, wetland streams, while gases are evaded closer to their source in steeper, forested streams.

Floods increase carbon dioxide and methane fluxes in agricultural streams

“…However, here, increases in gas exchange did not lower dissolved gas concentrations, as both CO 2 and CH 4 concentrations were higher during floods compared to baseflow days. A similar response was reported for headwater streams draining wetland‐rich catchments (Aho & Raymond, 2019), and concurrent positive relationships between discharge (Q) and both CO 2 concentrations and fluxes were reported for almost half of c . 10,000 stream and river sites distributed across the continental U.S.A. by Liu and Raymond (2018).…”

Highest rates of gross primary productivity maintained despite CO2 depletion in a temperate river network

“…Grab samples for pCO 2 , DIC, and δ 13 C-DIC were collected hourly during daylight, while sondes measured dissolved O 2 , pH, and temperature hourly. For pCO 2 , duplicate samples were collected with headspace equilibration and analyzed on an SRI Model 8610C Gas Chromatograph with FID; this method is detailed in a previous study (Aho and Raymond 2019). For DIC, duplicate water samples were filtered to 0.22 μm, stored in baked (450 C for 5 h) borosilicate glass vials with PolyCone-lined phenolic caps after flushing and subsequently refrigerated until analysis on a Shimadzu TOC-VCSH.…”

Integrating Discharge‐Concentration Dynamics Across Carbon Forms in a Boreal Landscape

“…C‐Q analyses have been widely applied to understand DOC export, and in most cases have revealed either chemostatic patterns or transport limitation (e.g., Creed et al., 2015; Zarnetske et al., 2018). Application of this approach to CO 2 and CH 4 has revealed a broader set of responses (Aho & Raymond, 2019; Dinsmore et al., 2013; Horgby et al., 2019), with both transport and supply limitation reported for gases when considered across large scales (Liu & Raymond, 2018). Here, we extend this approach to consider how unique C‐Q relationships for different carbon forms, depending on catchment type and seasonal timing of flow, govern the overall composition of carbon supplied to boreal streams.…”