Seasonal ecosystem metabolism across shallow benthic habitats measured by aquatic eddy covariance

Abstract

Shallow benthic habitats are hotspots for carbon cycling and energy flow, but metabolism (primary production and respiration) dynamics and habitat‐specific differences remain poorly understood. We investigated daily, seasonal, and annual metabolism in six key benthic habitats in the Baltic Sea using ~ 2900 h of in situ aquatic eddy covariance oxygen flux measurements. Rocky substrates had the highest metabolism rates. Habitat‐specific annual primary production per m2 was in the order Fucus vesiculosus canopy > Mytilus trossulus reef > Zostera marina canopy > mixed macrophytes canopy > sands, whereas respiration was in the order M. trossulus > F. vesiculosus > Z. marina > mixed macrophytes > sands > aphotic sediments. Winter metabolism contributed 22–31% of annual rates. Spatial upscaling revealed that benthic habitats drive > 90% of ecosystem metabolism in waters ≤5 m depth, highlighting their central role in carbon and nutrient cycling in shallow waters.

High Net Primary Production of Mediterranean Seagrass (Posidonia oceanica) Meadows Determined With Aquatic Eddy Covariance

“…Gross primary production in P. oceanica meadows was less than that of these other meadows, but due to the low respiration of P. oceanica, their NEM was greater. More recent studies include summer eddy covariance measurements of Z. marina metabolism in the Baltic Sea (Attard et al, 2019), and Z. noltii in the Black Sea (Lee et al, 2017). The proportion of GPP to R was higher for Z. marina in the Baltic Sea than in Virginia coastal bays, but overall NEM was small, one-fourth or less that of P. oceanica (Figure 7).…”

“…Fluxes are measured at high frequency (e.g., 5 Hz), allowing the user to quantify the diel photosynthetic response to light, among other variables. The technique has been used to quantify metabolism of Zostera marina, Thalassia testudinum, and Zostera noltii (Rheuban et al, 2014a,b;Long et al, 2015b;Lee et al, 2017;Attard et al, 2019;Berg et al, 2019). Among the discoveries is that over an annual cycle, Zostera marina meadows are heterotrophic or negligibly autotrophic (Rheuban et al, 2014a;Attard et al, 2019) although by particle-trapping they may still act as a net carbon sink (Greiner et al, 2013).…”

Technical note: Estimating light-use efficiency of benthic habitats using underwater O<sub>2</sub> eddy covariance

“…Eddy covariance thus overcomes many of the limitations of traditional methods (e.g. chamber incubations) and enables primary production rates to be measured within a wide range of benthic habitats (Chipman et al, 2016;Hume et al, 2011;Long et al, 2013;Volaric et al, 2018;Attard et al, 2019b). Additionally, the EC method can resolve very small benthic fluxes down to ~1 mmol O2 m -2 d -1 or less (Berg et al, 2009;Donis et al, 2016), which allows reliable measurements of primary 5 production to be made in low-activity benthic settings, such as in high-latitude environments in winter and in deep phototrophic communities Attard et al, 2016).…”

“…To our knowledge there is one study using chamber incubations that employs the LUE approach to investigate benthic primary production in lakes (Godwin et al, 2014), and this remains unexplored within underwater EC studies. Since the EC method can produce hourly and daily GPP measurements across many different habitat types (Attard et al, 2019b), applying the LUE approach could provide a useful measure of the efficiency with which solar energy is converted to 5 GPP on the spatial scale of whole habitats. A key requirement for computing the LUE is to have reliable estimates of GPP.…”

The Fight to Capture Light: Functional Diversity Is Related to Aquatic Plant Community Productivity Likely by Enhancing Light Capture

“…Aquatic plant meadows of the northern Baltic Sea are temperate communities with typical seasonal patterns of pronounced summer growth (Boström et al, 2004;Attard et al, 2019). The brackish seawater conditions allow for marine, brackish and limnic species to coincide within the same meadow (Kautsky, 1988), therefore meadows can be highly diverse communities with a variety of different plant traits (Kautsky, 1988;Norkko, 2016, 2019;Angove et al, 2018).…”