High-frequency logger data

In this study, we utilized high-frequency open-water measurements of oxygen, temperature, salinity and wind speed to investigate temporal and spatial variability in estuarine metabolism at sites with different benthic habitats and at different water depth. This enabled us to characterize the seasonality in GPP, R and NEP and investigate the regulating importance of different external conditions over different time scales. A series of benthic and pelagic oxygen in situ incubation studies furthermore allowed assessing the benthic and pelagic contributions to the ecosystem-integrated rates. Multiple measurements along a depth gradient made it possible to test expectations of larger magnitude and variability of ecosystem metabolism in shallow eelgrass-dominated areas compared to deeper muddy parts of the estuary. These measurements along a depth gradient ultimately enabled us to evaluate the influence of meteorological forcing events for short-term oxygen dynamics. The study was conducted in the southern, inner part of Roskilde Fjord, from April to December in 2015. Two of the sites were located at 2-3 m depth, one representing an eelgrass meadow and another, approximately 100 m to the south, representing a neighboring non-eelgrass habitat. The latter is referred to as the “Bare” site, although the habitat had scattered small stones (5 – 10 cm in diameter) covered by filamentous algae. The third site (“Muddy”) represented the deeper (5 m) habitat characterized by fluffy organic-rich sediment and no benthic vegetation. In addition, for quantifying short-term effects of physical forcing, we conducted a gradient study along a transect perpendicular to the shoreline (from ~100 to 500 m off the shore) starting at 1.8 m and reaching ~5 m depth. Continuous measurements (every 10 min) of dissolved oxygen (DO) and water temperature were made with miniDOT oxygen optode loggers (Precision Measurement Engineering, Vista, CA, USA, in the following termed “oxygen logger”) at the three main sites. The chamber incubations were done in triplicates and at the three types of habitat in April, June and August, corresponding to mean temperatures of 9, 16 and 21°C, respectively. Chambers consisted of gas impermeable transparent plastic bags (19 x 42 cm; diameter x height = 12 L) attached to a hard PVC collar, which was secured firmly into the sediment with metal plugs. Incubations were made over a period of approximately 24 hours with logging of oxygen, temperature and light every 10 minutes by a oxygen logger and a light logger placed at a depth of about 30 cm above the seafloor inside each chamber fixed to a metal stick placed into the sediment.