Marsh‐atmosphere CO₂ exchange in a New England salt marsh

Abstract

We studied marsh-atmosphere exchange of carbon dioxide in a high marsh dominated salt marsh during the months of May to October in 2012-2014. Tidal inundation at the site occurred only during biweekly spring tides, during which we observed a reduction in fluxes during day and night. We estimated net ecosystem exchange (NEE), gross primary production (GPP), and ecosystem respiration (R eco ) using a modified PLIRTLE model, which requires photosynthetically active radiation, temperature, and normalized difference vegetation index (NDVI) as control variables. NDVI decreased during inundation, when the marsh canopy was submerged. Two-time series of NDVI, including and excluding effects of tidal inundation, allowed us to quantify the flux reduction during inundation. The effect of the flux reduction was small (2-4%) at our site, but is likely higher for marshes at a lower elevation. From May to October, GPP averaged −863 g C m −2 , R eco averaged 591 g C m −2 , and NEE averaged −291 g C m −2 . In 2012, which was an exceptionally warm year, we observed an early start of net carbon uptake but higher respiration than in 2013 and 2014 due to higher-air temperature in August. This resulted in the lowest NEE during the study period (−255.9 ± 6.9 g C m −2 ). The highest seasonal net uptake (−336.5 ± 6.3 g C m −2 ) was observed in 2013, which was linked to higher rainfall and temperature in July. Mean sea level was very similar during all 3 years which allowed us to isolate the importance of climatic factors.

Direct and Indirect Effects of Tides on Ecosystem‐Scale CO2 Exchange in a Brackish Tidal Marsh in Northern California

“…Tides also strongly influenced NEE at shorter timescales; while at the diel scale NEE was dominantly and largely synchronously linked to PAR as expected given the control of light on photosynthesis (Sturtevant et al, ), there was also a significant interaction between NEE and WTD, with nighttime flooding of the marsh during summer spring tides causing an instantaneous decrease in respiration (Figures b, c, and ). This is similar to the findings by Forbrich and Giblin (), Kathilankal et al (), and Moffett et al () who also observed a suppression of CO 2 fluxes during flooding tides. However, since flooding tides at Rush Ranch only occurred at night during growing season spring tides (Figure ), with receding water levels throughout the day (Figure b), we did not observe similar suppression of daytime NEE as reported by these other studies.…”

Ecosystem metabolism in salt marsh tidal creeks and ponds : applying triple oxygen isotopes and other gas tracers to novel environments

“…The net organic matter consumption inferred from the NCP/GPP ratios over the entire time-series is consistent with other findings in this and other salt marsh ponds that at least some ponds are sites of net organic matter consumption (Johnston et al 2003, Spivak et al submitted), as opposed to large sinks of atmospheric CO2 like the grass covered marsh platform (Forbrich and Giblin 2015). It has been hypothesized that one mechanism for pond expansion or collapse of marsh flanks into mudflats is the decomposition of the underlying or surrounding peat layers (Johnston et al 2003; in this system, net heterotrophy greatly exceeds photosynthesis over the study period and pond expansion via this mechanism seems likely.…”

Influence of Tidal Inundation on CO<sub>2</sub> Exchange between Salt Marshes and the Atmosphere

“…Site studies of these authors are dominated by marsh grass species which grow upright, either Spartina alterniflora (Kathilankal et al, 2008) or Spartina foliosa and Distichlis spicata (Forbrich and Giblin, 2015;Moffett et al, 2010). The water table threshold of 0.25 m reported in this study is similar to the value reported by Kathilankal et al (2008) Both Kathilankal et al (2008) and this study have a similar ecosystem and dominated plant species which could lead to similar pattern in the reduction of the CO2 flux exchange when flooding occurs.…”

“…Few previous studies have shown that at a certain water table threshold, a reduction in CO2 exchange between salt marsh and atmosphere was observed (Forbrich and Giblin, 2015;Kathilankal et al, 2008;Moffett et al, 2010).…”

“…We expect sea level rise to be a chronic press driver affecting Spartina alterniflora. 15 Thus, the understanding of how Spartina alterniflora responds to variations in inundation variability is critical to predict the future state of coastal marshes in general. However, the documentation on the exchange of CO2 between salt marsh ecosystem and atmosphere measured by modern eddy-covariance systems are still very limited (Kathilankal et al, 2008).…”