Primary production and eddy correlation measurements of CO₂ exchange over an intertidal estuary

Abstract

[1] Field measurements by eddy correlation indicate an average CO 2 uptake of 1.9 g C m À2 d À1 by the intertidal Wadden Sea estuary in spring 2008. The flux did not show a dependency on the tide and fluxes during high and low tide were comparable. We hypothesize that biological production in the water column and in microbial mats that cover sediments lead to an undersaturation of CO 2 that is strong enough to support the observed fluxes. The total carbon uptake by this intertidal estuary from day of the year 101 -168 is estimated to be À1.7 Tg C. Extrapolation of this flux over three months in spring suggests that the uptake of CO 2 by this estuary over this period is comparable to 24% of the yearly carbon flux over the North Sea and the European estuaries. Citation:

Spatial and temporal CO<sub>2</sub> exchanges measured by Eddy Covariance over a temperate intertidal flat and their relationships to net ecosystem production

“…In spring, the Arcachon flat represented a net sink of CO 2 of −2.4 g C m −2 day −1 , whereas in summer and early autumn, it acted either as a small source or sink of CO 2 , with 0.1 and −0.2-0.5 g C m −2 day −1 , respectively. Such carbon fluxes are similar to or greater than those computed in the other tidal flats in France and in the Netherlands within a range of −1.9-0.2 g C m −2 day −1 (Migné et al, 2004;Spilmont et al, 2006;Zemmelink et al, 2009). They remained low compared to other tidal systems, such as salt or freshwater marshes with flux values from −0.8 to 0.4 g C m −2 day −1 (Houghton and Woodwell, 1980;Rocha and Goulden, 2008) or as European estuaries that degas large quantities of CO 2 to the atmosphere from 1.2 to 9.1 g C m −2 day −1 in average .…”

“…CO 2 fluxes at the airsediment interface at low tide can be assessed by deploying benthic chambers (Migné et al, 2002), but this method suffers from variability of intertidal sediment habitat resulting from patchiness at all timescales and particularly from spatial patchiness (Migné et al, 2004). Micrometeorological measurements, especially the Eddy Covariance technique (EC), show potential, as CO 2 fluxes across heterogeneous intertidal areas can be obtained with the same technique, at high tide and low tide (Houghton and Woodwell, 1980;Kathilankal et al, 2008;Zemmelink et al, 2009). In addition, the EC method is non-invasive and provides direct and continuous measurements of the net carbon dioxide exchange of a whole ecosystem across a spectrum of time scales from hours to years (Baldocchi et al, 1988;Aubinet et al, 2000;Baldocchi, 2003).…”

“…averages; (4) linear de-trending of sonic temperature, H 2 O and CO 2 channels; (5) determining time lag values for H 2 O and CO 2 channels using a cross-correlation procedure; (6) computing mean values, turbulent fluxes and characteristic parameters, e.g. the Monin-Obhukov stability index Z/L; (7) high-frequency corrections via transfer functions based on Kaimal-Moore's co-spectral models (Kaimal et al, 1972;Moore, 1986); and (8) performing a WebbPearman-Leuning correction to account for the effects of fluctuations of temperature and water vapour on measured fluctuations in CO 2 and H 2 O (Webb et al, 1980). In parallel to frequency corrections, a cospectral analysis was carried out for each period to quantify the distribution by frequency of the covariance of the raw measured signals.…”

Net uptake of atmospheric CO 2 by coastal submerged aquatic vegetation

“…The method has also been used to estimate air‐sea CO 2 fluxes in the ocean and coastal seas (McGillis et al ., ; Vesala et al ., ; Kondo & Tsukamoto, ; Zemmelink et al ., ; Huotari et al ., ; Polsenaere et al ., ) and to estimate sediment‐water O 2 fluxes (Berg et al ., ; Kuwae et al ., ). However, several studies have reported that results from the eddy covariance method are inconsistent with results from other methods, such as the bulk formula method (Kondo & Tsukamoto, ; Zemmelink et al ., ). In addition, this method requires sufficient spatial uniformity within the study area.…”

Carbon Dioxide and Methane Dynamics in Estuaries

“…To date, there is no method totally satisfactory to quantify k in estuaries, and this question is still a matter of debate between biogeochemists, ecologists and physicists. Although nonintrusive methods such as tracer or micrometeorological techniques should in theory be preferred, their applications in estuarine systems are difficult and scarce (Clark et al, 1994;Carini et al, 1996;Zappa et al, 2003Zappa et al, , 2007Zemmelink et al, 2009), and most of the k parametrizations published so far were derived from floating chamber measurements (Marino and Howarth, 1993;Kremer et al, 2003aKremer et al, , 2003bBorges et al, 2004aBorges et al, , 2004bGuérin et al, 2007;Abril et al, 2009). Floating chamber experiments indeed offer the advantage of being easy and cheap, and, most importantly, to be short enough (5-20 min when using infrared gas analyzers) to adequately describe the temporal variability of k driven by wind and current in estuaries.…”