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Marine Ecology Progress Series

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MEPS 601:15-32 (2018)  -  DOI:

Ecosystem metabolism of benthic and pelagic zones of a shallow productive estuary: spatio-temporal variability

Peter A. Staehr1,*, Eero Asmala1,2, Jacob Carstensen1, Dorte Krause-Jensen3, Heather Reader4,5

1Department of Bioscience, Aarhus University, Frederiksborgvej, 399, 4000 Roskilde, Denmark
2Tvärminne Zoological Station, University of Helsinki, J. A. Palménin tie 260, 10900 Hanko, Finland
3Department of Bioscience, Aarhus University, Vejlsøvej 25, 8600 Silkeborg, Denmark
4National Institute for Aquatic Resources, Technical University of Denmark, Building 202, Kemitorvet, 2800 Kgs. Lyngby, Denmark
5Department of Chemistry, Memorial University of Newfoundland, St John’s, Newfoundland A1B 3X7, Canada
*Corresponding author:

ABSTRACT: Long-term deterioration of water quality is known to reduce the importance of benthic ecosystem metabolism in shallow coastal ecosystems, but drivers of spatial and short-term variability in ecosystem metabolism are poorly understood. We addressed this knowledge gap through detailed seasonal measurements of ecosystem metabolism across depth gradients from shallow (2 to 3 m) eelgrass-dominated to deeper (4 to 5 m) muddy regions of a shallow, productive estuary. Combined measurements of gross primary production (GPP), respiration (R) and, by difference, net ecosystem production (NEP) by the open-water diel oxygen technique and in situ chamber incubations showed high importance of shallow eelgrass habitats for metabolism at the system scale. Seasonal variations in GPP, R and NEP increased with light availability and temperature with highest NEP in all habitats during the warm and sunny mid-summer. The shallow eelgrass-dominated and neighboring habitats were seasonally net autotrophic (NEP = 0.54 and 0.31 mg O2 m-2 d-1, respectively), compared to net heterotrophy (NEP = -0.26 mg O2 m-2 d-1) at the deeper muddy site. Detailed studies along depth gradients further confirmed the role of eelgrass as a key driver of spatial differences in ecosystem metabolism across the estuary. Strong northerly winds (>8 m s-1) caused short-term (<24 h) periods of similar oxygen dynamics and similar apparent productivity in shallow and deeper waters, indicative of efficient lateral mixing, while calm periods (<4 m s-1) enabled formation of ‘pockets’, i.e. water masses with limited connectivity, which exacerbated the metabolic differences between shallow and deep sites.

KEY WORDS: Intra-estuarine heterogeneity · Benthic habitat · Pelagic habitat · Temporal variability · Eelgrass

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Cite this article as: Staehr PA, Asmala E, Carstensen J, Krause-Jensen D, Reader H (2018) Ecosystem metabolism of benthic and pelagic zones of a shallow productive estuary: spatio-temporal variability. Mar Ecol Prog Ser 601:15-32.

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