Dissolved Oxygen Fluxes and Ecosystem Metabolism in an Eelgrass (Zoster's marina) Meadow Measured with the Novel Eddy Correlation Technique

Hume, Andrew Christer, Department of Environmental Sciences, University of Virginia
Berg, Peter, Department of Environmental Sciences, University of Virginia
McGlathery, Karen, Department of Environmental Sciences, University of Virginia
Wiberg, Patricia, Department of Environmental Sciences, University of Virginia

Community metabolism was measured using the novel in situ eddy correlation technique in a restored eelgrass (Zostera marina) meadow and a nearby bare sediment substrate, located in a coastal bay off the eastern shore of Virginia, USA. Dissolved oxygen (DO) fluxes were measured at 64 Hz (64 times per second) and cumulative fluxes were calculated at 15-min intervals. High variations in these measurements indicate the importance of measuring ecosystem metabolism under natural environmental conditions. Multiple linear regressions of environmental variables show significant relationships between hourly DO fluxes and photosynthetically active radiation (PAR) and significant wave height for both the seagrass-dominated and the bare sediment community. This study is the first to report a significant relationship between DO fluxes and significant wave height over a seagrass-dominated sediment. Mean hourly DO fluxes from multiple eddy correlation deployments were used to calculate community respiration (R), gross primary production (GPP), and net ecosystem metabolism (NEM) during the study period. Rates of seagrass-dominated community R, GPP and NEM were: -120.0 ± 39.2, 143.2 ± 33.2 and 23.2 ± 29.9 mmol O 2 m -2 d -1 , respectively. The nearby bare sediment R, GPP and NEM were: -64.5 ± 28.7, 25.3 ± 15.8 and -39.2 ± 13.1 mmol O 2 m -2 d -1 , respectively. Estimates of C cycling suggest that the bare sediment is a net source of C while the vegetated substrate was a net sink. N assimilation calculations based on the C metabolism indicate an increased assimilation and temporary retention of N in the benthic community as it shifts from bare to algal-dominated and ultimately seagrass-dominated substrate with the successful seagrass restoration efforts. A comparison was made iii between the eddy correlation technique and the conventional open-water technique using a water quality datasonde. Our results indicates that the eddy correlation technique has significant advantages over this, and other, conventional techniques in that it: 1) captures short-term variability in oxygen metabolism that result from environmental variations in light, current, and wave energy; 2) accurately integrates over a large area and thus captures small-scale heterogeneity; 3) is non-invasive and allows for true in situ light and hydrodynamic conditions; and 4) can be used over topographically complex substrates where conventional methods may fail.

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MS (Master of Science)
environment, oxygen, ecosystem
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