Berg Peter

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Berg
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Peter
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Article

Sub-tropical seagrass ecosystem metabolism measured by eddy covariance

2015-06-08 , Long, Matthew H. , Berg, Peter , McGlathery, Karen J. , Zieman, Joseph C.

The metabolism of seagrass ecosystems was examined at 4 sites in south Florida, USA, using the eddy covariance technique under in situ conditions. Three sites were located across a phosphorus-driven productivity gradient to examine the combined effects of dynamic variables (irradiance, flow velocity) and state variables (sediment phosphorus and organic content, seagrass biomass) on ecosystem metabolism and trophic status. Gross primary production and respiration rates varied significantly across Florida Bay in the summer of 2012 with the lowest rates (64 and –53 mmol O2 m–2 d–1, respectively) in low-phosphorus sediments in the northeast and the highest (287 and –212 mmol O2 m–2 d–1, respectively) in the southwest where sediment phosphorus, organic matter, and seagrass biomass are higher. Seagrass ecosystems offshore of the Florida Keys had similar large daily production and respiration rates (397 and –17 mmol O2 m–2 d–1, respectively) and were influenced by flow through the permeable offshore sediments. Across all sites, net ecosystem metabolism rates indicated that the seagrass ecosystems were autotrophic in the summertime. Substantial day-to-day variability in metabolic rates was found due to variations in irradiance and flow velocity. At all sites the relationship between photosynthesis and irradiance was linear and did not show any sign of saturation over the entire irradiance range (up to 1400 µmol photons m–2 s–1). This was likely due to the efficient use of light by the large photosynthetic surface area of the seagrass canopy, an effect which can only be examined by in situ measurements that integrate across all autotrophs in the seagrass ecosystem.

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Article

Multiple timescale processes drive ecosystem metabolism in eelgrass (Zostera marina) meadows

2014-07-17 , Rheuban, Jennie E. , Berg, Peter , McGlathery, Karen J.

The oxygen flux between benthic ecosystems and the overlying water column is a measure of metabolic status and a commonly used proxy for carbon cycling. In this study, oxygen flux was measured seasonally using the eddy correlation technique in a restored eelgrass (Zostera marina L.) meadow in the Virginia coastal bays (USA). In 5 intensive field campaigns, we covered seasonal variation in oxygen metabolism and biomass with overlap in late summer to observe interannual variability. The high-resolution measurements allowed identification of the drivers of metabolism at multiple timescales: minute to hourly, daily, and monthly to seasonally. There was a strong correlation between nighttime hourly fluxes and current velocity that varied seasonally with seagrass shoot density and temperature. No similar relationship was observed during the day. A hysteresis effect in oxygen flux throughout the day was observed during October and August that was most likely due to increased respiration (R) in the afternoon. In October, net community production was 90% lower in the afternoon than in the morning at the same irradiance. From this hysteresis, we calculated that daytime R may be up to 2.5-fold larger than nighttime R. The magnitudes of daily gross primary production (GPP) and R were well correlated throughout the year with close to a 1:1 ratio that reflected a tight coupling between GPP and R on daily to seasonal timescales. Our results document the dynamic nature of oxygen fluxes that, when integrated over time, translate into highly variable rates of ecosystem metabolism over daily to seasonal timescales. This variation must be incorporated to accurately determine trophic status.

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Dataset

Current flow and oxygen concentrations recorded by the 2OEC-instrument in the Florida Keys from August 2013 and April 2014

2020-06-30 , Huettel, Markus , Berg, Peter

Velocity and external sensor data recorded by the Nortek Vector ADV logger in the Florida Keys from August 2013 and April 2014. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/812523

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Dataset

Temperature and dissolved oxygen recorded two PME Mindot O2 loggers in the Florida Keys from 11-17 July 2017

2021-04-23 , Huettel, Markus , Berg, Peter

This dataset presents the temperature and oxygen data recorded by the two PME Minidot loggers. The loggers were deployed July 11-17, 2017 in a subtropical inner shelf environment (Salinity: 35-36, temperature: 28-31°C) approximately 9 km south of Long Key in the Florida Keys (24° 43.52'N, 80° 49.85'W). The site was located at 9 ± 1 m water depth near the center of a large flat carbonate platform covered with coral sand. The instruments were installed on the 3OEC instrument at ~35 cm above the sediment-water interface. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/849915

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Article

Seagrass metabolism across a productivity gradient using the eddy covariance, Eulerian control volume, and biomass addition techniques

2015-05-22 , Long, Matthew H. , Berg, Peter , Falter, James L.

The net ecosystem metabolism of the seagrass Thalassia testudinum was studied across a nutrient and productivity gradient in Florida Bay, Florida, using the Eulerian control volume, eddy covariance, and biomass addition techniques. In situ oxygen fluxes were determined by a triangular Eulerian control volume with sides 250 m long and by eddy covariance instrumentation at its center. The biomass addition technique evaluated the aboveground seagrass productivity through the net biomass added. The spatial and temporal resolutions, accuracies, and applicability of each method were compared. The eddy covariance technique better resolved the short-term flux rates and the productivity gradient across the bay, which was consistent with the long-term measurements from the biomass addition technique. The net primary production rates from the biomass addition technique, which were expected to show greater autotrophy due to the exclusion of sediment metabolism and belowground production, were 71, 53, and 30 mmol carbon m−2 d−1 at 3 sites across the bay. The net ecosystem metabolism was 35, 25, and 11 mmol oxygen m−2 d−1 from the eddy covariance technique and 10, −103, and 14 mmol oxygen m−2 d−1 from the Eulerian control volume across the same sites, respectively. The low-flow conditions in the shallow bays allowed for periodic stratification and long residence times within the Eulerian control volume that likely reduced its precision. Overall, the eddy covariance technique had the highest temporal resolution while producing accurate long-term flux rates that surpassed the capabilities of the biomass addition and Eulerian control volume techniques in these shallow coastal bays.

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Article

Eddy correlation measurements of oxygen fluxes in permeable sediments exposed to varying current flow and light

2013-07 , Berg, Peter , Long, Matthew H. , Huettel, Markus , Rheuban, Jennie E. , McGlathery, Karen J. , Howarth, Robert W. , Foreman, Kenneth H. , Giblin, Anne E. , Marino, Roxanne

Based on noninvasive eddy correlation measurements at a marine and a freshwater site, this study documents the control that current flow and light have on sediment–water oxygen fluxes in permeable sediments. The marine sediment was exposed to tidal-driven current and light, and the oxygen flux varied from night to day between −29 and 78 mmol m−2 d−1. A fitting model, assuming a linear increase in oxygen respiration with current flow, and a photosynthesis–irradiance curve for light-controlled production reproduced measured fluxes well (R2 = 0.992) and revealed a 4-fold increase in oxygen uptake when current velocity increased from ∼ 0 to 20 cm s−1. Application of the model to a week-long measured record of current velocity and light showed that net ecosystem metabolism varied substantially among days, between −27 and 31 mmol m−2 d−1, due to variations in light and current flow. This variation is likely typical of many shallow-water systems and highlights the need for long-term flux integrations to determine system metabolism accurately. At the freshwater river site, the sediment–water oxygen flux ranged from −360 to 137 mmol m−2 d−1. A direct comparison during nighttime with concurrent benthic chamber incubations revealed a 4.1 times larger eddy flux than that obtained with chambers. The current velocity during this comparison was 31 cm s−1, and the large discrepancy was likely caused by poor imitation by the chambers of the natural pore-water flushing at this high current velocity. These results emphasize the need for more noninvasive oxygen flux measurements in permeable sediments to accurately assess their role in local and global carbon budgets.

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Dataset

Current flow, pressure, and oxygen concentrations recorded by the 3OEC-instrument in the Florida Keys from 11-17 July 2017

2021-04-23 , Huettel, Markus , Berg, Peter

This dataset presents the velocity and external sensor data recorded by the Nortek Vector ADV logger. The eddy covariance instrument was deployed July 11-17, 2017 in a subtropical inner shelf environment (Salinity: 35-36, temperature: 28-31°C) approximately 9 km south of Long Key in the Florida Keys (24° 43.52'N, 80° 49.85'W). The site was located at 9 ± 1 m water depth near the center of a large flat carbonate platform covered with coral sand. The measuring volume of the ADV was adjusted to be ~35 cm above the sediment-water interface. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/849934

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Dataset

PAR recorded by two Odyssey PAR loggers in the Florida Keys from 11-17 July 2017

2021-04-23 , Huettel, Markus , Berg, Peter

This dataset presents the PAR light data recorded by the two Odyssey PAR loggers. The loggers were deployed July 11-17, 2017 in a subtropical inner shelf environment (Salinity: 35-36, temperature: 28-31°C) approximately 9 km south of Long Key in the Florida Keys (24° 43.52'N, 80° 49.85'W). The site was located at 9 ± 1 m water depth near the center of a large flat carbonate platform covered with coral sand. The instruments were installed on the 3OEC instrument at ~185 cm above the sediment-water interface. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/849979