Abstract:
Oxygen consumption rates and environmental variables were measured with field-deployed metabolism core chambers in various sites around the Chandeleur Islands in the Fall and Summer of 2015 and 2016. Each chamber consisted of a 15.24 cm diameter (20.32 cm length) acrylic tube, capped at the top with a custom-built fitting for water stirring and HOBO logger placement. For each chamber deployed, dissolved oxygen and water temperature data were collected from within the chamber. Light meters were deployed in parallel with the chambers to detect ambient light penetration into the water column. From these data, sediment oxygen consumption (mmol O2/m2/day) was calculated. These measurements can be correlated with average temperature, light, time of day, habitat type, site, and sampling season. These data can also be associated with infaunal abundances and characteristics in a related dataset (GRIIDC UDI: R4.x262.000:0010).
Suggested Citation:
Kelly Dorgan. 2017. Sediment oxygen demand in shallow water habitats around the Chandeleur Islands in 2015 and 2016. Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/N7X928QC
Purpose:
Sediment oxygen demand is an aggregate measurement of numerous ecosystem functions, including photosynthesis by seagrasses and benthic microalgae, respiration by a diverse microbial community, respiration by meio- and macro-fauna, and enhanced microbial metabolism due to irrigation by macrofauna. We measured sediment oxygen demand at four sites in the Chandeleur Islands, northern Gulf of Mexico, with varied oil contamination from the DWH using light and dark custom-built metabolism chambers. Data were collected across a range of ambient oxygen concentrations resulting from a strong diurnal oxygen cycle in this shallow environment, and sampling was conducted twice annually over two years (June 2015 – Sept. 2016). Results are being analyzed for dependence on ambient oxygen concentration, sediment PAH at the 4 sites, seasonal and annual differences, and infaunal community biomass. This study aims to assess the impact of oil contamination on sediment ecosystem function in the context of natural daily, seasonal, and annual variability in a dynamic ecosystem.
Data Parameters and Units:
1. Core ID - Description: Unique identifiers for each core sampled. This ID includes sample site (Chandeleur Islands [CI]), station (A, B, C1, C2), Habitat (Unvegetated Sediment [O], Ruppia [Hal], Thalassia [Thal], Marsh [M]), Sampling date (ddmmyy), core type (Metabolism [M]), replicate number (#), Light/Dark distinction (L, D), and whether the submerged vegetation was cut (cut). Each ID corresponds to those in the associated metabolism Feature. 2. Sampling Trip - Description: Summer 2015, Fall 2015, Summer 2016, Fall 2016. 3. Date - Description: Date sample was collected from the field (yyyy-mm-dd). 4. Site - Description: Site codes for each sampling location A, B, C1, and C2. 5. Location Latitude - Description: The latitude for each sampling site. Site A was located at 29.864039. Site B was located at 29.894658. Site C1 was located at 29.92758. Site C2 was located at 29.93338. 6. Location Longitude - Description: The longitude for each site. Site A was located at -88.842443. Site B was located at -88.828155. Site C1 was located at -88.82930. Site C2 was located at -88.82949. 7. Habitat - Description: Describes the dominant habitat type from which the sample was collected as well as indication of whether the above-ground vegetation was clipped. Categories include: Open: Unvegetated, open sediment habitat adjacent to either Ruppia or Thalassia beds; Thalassia: Thalassia sp. seagrass habitat; Ruppia: Ruppia sp. seagrass habitat; Cut Thalassia: Thalassia sp. manually cut at the sediment surface and removed prior to sample collection; Cut Ruppia: Ruppia sp. manually cut at the sediment surface and removed prior to sample collection. 8. Light.Dark - Description: Treatment conditions established for each core that either excluded or permitted ambient light penetration into the chamber. Categories include: Light: Light corresponds with chambers that permitted ambient light to penetrate into the chamber to facilitate photosynthesis; Dark: Dark corresponds with chambers that were constructed to excluded ambient light to minimize the dissolved oxygen contribution from photosynthesis. 9. Core Diameter - Description: The diameter in cm of acrylic tube used for sediment oxygen consumption data collection. All cores used for this data collection were 15.24 cm diameter and 20.32 cm in length. 10. Time - Description: Time of day (hh:mm:ss) that the oxygen probe cap was sealed onto the core base deployed in the field. This time was used in identifying the starting point for the calculation of oxygen consumption for each core replicate. 11. Sediment Oxygen Consumption - Description: The oxygen consumption rate calculated from the slope of the dissolved oxygen as a function of time. Data is displayed as mmol O2/m2/day. 12. Initial Oxygen - Description: A measure of starting total dissolved oxygen (mg/L) for each chamber replicate. 13. Average Temperature - Description: Average temperature (Celsius) collected by each HOBO logger for the duration of each core replicate. Temperature was collected from within each sealed chamber. 14. Light - Description: The average ambient light (lumens/m^2) calculated for the duration of each core replicate. Light loggers were placed adjacent to, not within, each chamber for the Fall and Summer 2016 sampling seasons.
Methods:
Cores with specialized HOBO logger caps (to prevent intrusion of ambient water) were deployed to collect data on respiration and photosynthesis rates of benthic infauna/epifauna and vegetation (total dissolved oxygen, temperature, light) present in a variety of submerged nearshore habitats around the Chandeleur Islands. Total oxygen consumption was calculated based on the rate of change in total dissolved oxygen levels over time. Analyses for these data are ongoing.
Instruments:
Each replicate core consisted of transparent acrylic tubing (15.24 cm diameter, 20.32 cm in height ) fitted with sensors that were deployed in the field. Cores were inserted 15 cm into the sediment in previously-specified habitat types (Open/Unvegetated, Ruppia, Cut Ruppia, Thalassia, Cut Thalassia) located at each sampling site (A, B, C1, C2). For cut vegetation conditions, all above-surface vegetation was clipped and removed prior to inserting the core. Once inserted, the cores were sealed using specialized caps fitted with HOBO loggers and water agitators (used to circulate water within the chamber). A gap of 5 cm of water between the sediment surface and cap was ensured to provide a standardized, contained volume of water and with a fixed initial total dissolved oxygen content. The cores were deployed for at least 30 minutes in the field and run in parallel with light loggers placed adjacent to the core to collect ambient light in the water column. After each core was completed, the core of sediment (up to 15 cm) was removed and sieved (0.5 mm mesh) to collect associated infauna animals. At the end of each sampling day, the HOBO logger data for light and oxygen were offloaded using the HOBOware software. Total dissolved oxygen content (mg/L), temperature (Celsius), and intensity (Lumens/ft2) were exported into spreadsheets. From these data, oxygen consumption rates, average light intensity, and average temperature were calculated for each core.
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