High‐frequency greenhouse gas flux measurement system detects winter storm surge effects on salt marsh

Abstract

The physical controlling factors on coastal plant communities are among the most dynamic of known ecosystems, but climate change alters coastal surface and subsurface hydrologic regimes, which makes rapid measurement of greenhouse gas fluxes critical. Greenhouse gas exchange rates in these terrestrial-aquatic ecosystems are highly variable worldwide with climate, soil type, plant community, and weather. Therefore, increasing data collection and availability should be a priority. Here, we demonstrate and validate physical and analytical modifications to automated soil-flux chamber measurement methods for unattended use in tidally driven wetlands, allowing the high-frequency capture of storm surge and day/night dynamics. Winter CO flux from Sarcocornia perennis marsh to the atmosphere was significantly greater during the day (2.8 mmol m hr ) than the night (2.2 mmol m hr ; p < 0.001), while CH was significantly greater during the night (0.16 μmol m hr ) than the day (-0.13 μmol m hr ; p = 0.04). The magnitude of CO flux during the day and the frequency of CH flux were reduced during a surge (p < 0.001). Surge did not significantly affect N O flux, which without non-detects was normally distributed around -24.2 nmol m hr . Analysis with sustained-flux global potentials and increased storm surge frequency scenarios, 2020 to 2100, suggested that the marsh in winter remains an atmospheric CO source. The modeled results showed an increased flux of CO to the atmosphere, while in soil, the uptake of CH increased and N O uptake decreased. We present analytical routines to correctly capture gas flux curves in dynamic overland flooding conditions and to flag data that are below detection limits or from unobserved chamber-malfunction situations. Storm surge is an important phenomenon globally, but event-driven, episodic factors can be poorly estimated by infrequent sampling. Wider deployment of this system would permit inclusion of surge events in greenhouse gas estimates.

A synthesis of methane emissions from shallow vegetated coastal ecosystems

“…Although several of the reviewed studies include measurements of CH 4 fluxes over several seasons and/or tidal cycles (Adams, Andrews, & Jickells, 2012; Bahlmann et al, 2015; Diefenderfer et al, 2018; Emery & Fulweiler, 2014; Li, Wang, et al, 2018), none of these studies continuously measure CH 4 flux over multiple annual cycles to capture changes driven by climate that may otherwise be missed. Continuous measurements of CH 4 flux over several years, daily and/or several times a season with greater spatial coverage, would help increase the accuracy of CH 4 flux estimates from VCEs as is shown in terrestrial systems (Ueyama et al, 2015).…”

“…The one seagrass study that measured methane flux continuously for a few days reported maximum CH 4 emissions at night indicating that CH 4 oxidation was reduced (Bahlmann et al, 2015). In contrast, maximum mangrove and salt marsh CH 4 emissions can occur during the day (Yang et al, 2018), at night (Diefenderfer et al, 2018), or exhibit no diurnal cycle (Jha et al, 2014; Li, Dai, et al, 2018). Length of measurement period may play a role in these results as studies that measured CH 4 fluxes over an entire year did not find clear diurnal patterns (Jha et al, 2014; Li, Dai, et al, 2018), while studies performed over a few days noted diurnal differences in CH 4 flux (Bahlmann et al, 2015; Diefenderfer et al, 2018; Yang et al, 2018).…”

“…Because of the difficulties of winter sampling, most studies that did measure CH 4 flux during the winter did so infrequently. Diefenderfer, Cullinan, Borde, Gunn, and Thom (2018) measured CH 4 flux continuously in the winter and demonstrated that CH 4 emissions remain low over extended periods of time in winter, but continuous measurements are needed to capture diurnal variability which can switch a system from a CH 4 sink to a source.…”

Representing the function and sensitivity of coastal interfaces in Earth system models

“…Coastal ecosystems are sensitive to rapid and disproportionate hydrological and biogeochemical fluctuations with terrestrial, atmospheric, and oceanic origins including extreme precipitation events 57 , snow/ice melt 10 , accumulation and enhanced dry deposition of atmospheric pollutants 58 , extreme high tides, and storm surges 46,59 . Thus, hot momentsshort time periods with disproportionately high metabolic rates-may play a prominent, but typically ignored role in coastal ecosystem biogeochemical cycling.…”

“…High temporal resolution measurements of different processes are thus needed to couple ecosystem responses (e.g., greenhouse emissions) with the underlying controls to properly represent hot moments in regional models and ESMs. While new technologies are emerging that allow highly resolved organic carbon or gas flux measurements 46,59 , there is a lack of consensus on how to appropriately scale lateral land-water carbon fluxes, or carbon emissions from either the bottom-up or top-down origin 8,65 .…”