Abstract:

This experiment was conducted to investigate how nutrients change with time. Eighteen 110L capacity glass mesocosm tanks were filled with Gulf of Mexico seawater collected 8 km offshore south of Galveston (TX) that had been pre-treated with a charcoal filter to remove large particles and debris. Plankton (≥63 µm) were collected using a net and transferred into polycarbonate bottles after being pre-filtered (115 um) to remove zooplankton, jellyfish and debris. The tanks were amended with WAF (water accommodated fraction) and the DCEWAF (diluted chemically enhanced water accommodated fraction) to a target concentration of 2 mg/L. Concentrated plankton mass was introduced to each of the tanks immediately prior to starting the experiments. A 12:12 light/dark cycle employed. Treatments included controls (2), WAF (8) and DCEWAF (8). One mesocosm was sacrificed at each sampling point. Controls were sampled on Day 0 and Day 12. For WAF and DCEWAF, sampling was more frequent at the start and less frequent with time, such that sampling was done on 0, 0.5, 2, 3, 6, 8, and 12. Nutrients were determined on an autoanalyzer.

Suggested Citation:

Gopal Bera, Terry Wade, Anthony Knap. 2020. Analytical measurements: Time series of nutrients in MICROX, a mesocosm to quantify microbial oxidation and degradation of oil. Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/n7-bkwz-mj61

Purpose:

To investigate how nutrients change with time.

Data Parameters and Units:

Nutrient data are given in 2 conc. or concentration formats: micromoles/L ((µmol/L) and mg/L with respect to the listed standard. The headers are NO3- is nitrate, N is nitrogen, HPO4= is hydrogen phosphate, P is Phosphorus, HSIO3- is hydrogen silicate, SiO3 refers to silicate, NH4+ is ammonium, NO2- is nitrite. M=Mesocosm, W=Water accommodated fraction, D=Diluted Chemically Enhanced WAF, C=controls, CC=control with Corexit.

Methods:

Eighteen 110L capacity glass mesocosm tanks were filled with Gulf of Mexico seawater collected 8 km offshore south of Galveston (TX) that had been pre-treated with a charcoal filter to remove large particles and debris. The salinity was 34 PSU. Plankton (≥63 µm) were collected using a net and transferred into polycarbonate bottles after being pre-filtered (115 um) to remove zooplankton, jellyfish and debris. The goal was to collect enough surface and bottom particles for detailed particle chemical characterization. To provide enough sample material for detailed particle chemical characterization, ~20L each from the bottom layer and the surface layer was collected. As in earlier mesocosm experiments, the target concentration of 2 mg/L was attempted for the concentration of oil in the WAF (water accommodated fraction) and the DCEWAF (diluted chemically enhanced water accommodated fraction). The WAF of oil was prepared by mixing 25 mL (5 ml per each ~ 5 min over 25 min) of Macondo surrogate oil into six baffled recirculating tanks (Wade et al., 2017) containing ~130 L of seawater, which were mixed vigorously for 4 hrs to create a “high energy” WAF (Knap et al. 1983). The WAF was then introduced into the WAF mesocosm tanks, filled to 104L, and mixed. From these tanks, 3.5 L WAF was removed for hydrocarbon analyses. Corexit was mixed with oil in a ratio of 1:20 to make chemically enhanced water accommodated fraction (CEWAF). Then 25 mL of this mixture (5 ml every 5 min for 25 min) of surrogate oil plus Corexit was added to a baffled recirculating tank containing ~130 L of seawater which was not vigorously mixed for 4 hrs prior to being loaded into the mesocosm tanks. From these CEWAF tanks 5L was removed for other analyses (3.5 L hydrocarbon analyses). Diluted CEWAF (DCEWAF) was prepared by mixing 10.4 L of CEWAF with 93.6 L of the original seawater for a total volume of 104 L. This concentrated plankton mass was introduced to each of the tanks (1.5 L to each tank which contained 104L of treated seawater, total volume of seawater was 105.5L per tank) immediately prior to starting the experiments. Banks of lights were placed behind each of the glass mesocosm tanks and a 12:12 light/dark cycle employed. Treatments included controls (2), WAF (8) and DCEWAF (8). One mesocosm was sacrificed at each sampling point. Controls were sampled on Day 0 and Day 12. For WAF and DCEWAF, sampling was more frequent at the start and less frequent with time, such that sampling was done on 0, 0.5, 2, 3, 6, 8, and 12. Total Nutrient Method: Unfiltered samples were collected in contaminant-free containers. It is important to avoid contamination from NO~3~-, NH~4~+ which otherwise add up to the total nutrient values. In the laboratory, sample containers were agitated to resuspend any settled materials. Then, approximately 30 grams of samples were transferred into 40 mL of borosilicate samples vials followed by addition of 5 mL of persulfate. The samples were capped (Teflon septa) and autoclaved. During the autoclave process, 21 psi and 124 ^o^C temperature were maintained for 30 minutes. Once the autoclave step is done, sample vials weighed again to compare with pre-autoclave values. Then the measurement of total nitrogen and total phosphorous are carried out similar to dissolved nutrient measurement. Dissolved Nutrients: Nutrient samples were analyzed by Astoria Pacifica Auto-Analyzer using method described in Geochemical Environmental Research Group (GERG) ARM-SOP-0702. In summary, 30 mL water samples were collected in triplicates from each treatment and were filtered through a 45 µm Milipore filter. The samples were brought back to GERG and were kept in the freezer until analysis. Five calibration standards were prepared. Before the start of the sample run, a NO~2-, NO~3-, the check was run. A blank, duplicate and continuing calibration verification (CCV) standard were run with each batch of 15 samples. Flow Analyzer Software Package (FASPac 2.3) was used to collect and process data from six digital channels and one analog channel. Dissolved inorganic nitrogen is the sum of the NH~4~, NO~2~ NO^3^ and Urea values. Redfield ratios were calculated for each mesocosm.

Instruments:

An Astoria Pacifica Auto-Analyzer

Provenance and Historical References:

Knap, A. H., Sleeter, T. D., Dodge, R. E., Wyers, S. C., Frith, H. R., & Smith, S. R. (1983). The effects of oil spills and dispersant use on corals. Oil and Petrochemical Pollution, 1(3), 157–169. doi:10.1016/s0143-7127(83)90134-5 Wade, T. L., Morales-McDevitt, M., Bera, G., Shi, D., Sweet, S., Wang, B., … Knap, A. H. (2017). A method for the production of large volumes of WAF and CEWAF for dosing mesocosms to understand marine oil snow formation. Heliyon, 3(10), e00419. doi:10.1016/j.heliyon.2017.e00419

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