Abstract:

This was a multiple mesocosm experiment where seawater that had been collected 8 km offshore south of Galveston (TX) and pre-treated with a charcoal filter to separate large particles were exposed to different treatments such as mixing with the oil slick, and DCEWAF (diluted chemically enhanced water accommodated fraction). Controls were also enacted. Samples for chemical analysis of particles were taken from the surface and bottom of tanks at specific time points. Nutrient samples were analyzed by Astoria Pacifica Auto-Analyzer.

Suggested Citation:

Bera Gopal, Wade Terry. 2020. Analytical measurements of nutrients in a mesocosm, a Long Term Oil and Particle Oxidation Study (LTOPOS). Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/GNK5X0RS

Purpose:

To study time series of nutrients in a mesocosm, LTOPOS, a Long Term Oil and Particle Oxidation.

Data Parameters and Units:

Gerg ID (Geochemical Environmental Research Group ID), nutrient bottle #, nutrient concentration (NO3-, HPO4=, HSIO3-, NH4+, NO2-, Urea, and NO3- + NO2-). These concentrations were reported in both µmol/L and mg/L.

Methods:

Eighteen glass mesocosm tanks with a capacity of 110L were filled with Gulf of Mexico seawater that had been collected 8 km offshore south of Galveston, Texas and pre-treated with a charcoal filter to separate large particles. The measured salinity was 25 PSU. With the use of a net, plankton (≥63 µm) were harvested and passed through a 115-micron filter to remove zooplankton, jellyfish and debris. Plankton was placed in polycarbonate bottles. The phytoplankton concentrate displayed a salinity of 25 PSU. About 20L from the bottom/surface layer were collected in order to collect sufficient particles for chemical analysis. DCEWAF (diluted chemically enhanced water accommodated fraction) was added at the target concentration of 2 mg/L. To make chemically enhanced water accommodated fraction (CEWAF), corexit was mixed with oil in a ratio of 1:20 (Knap et al., 1983). Diluted CEWAF (DCEWAF) was made by combining 10.4 L of CEWAF with 93.6 L of the original seawater for a total volume of 104 L. Immediately prior to starting the experiments plankton mass was introduced to each of the tanks (3L to each tank which contained 104L of treated seawater, the total volume of seawater 105.5L per tank). 42 mL of Macondo surrogate oil was added to the surface of one mesocosm tank of 105L to simulate an oil slick. A 12:12 light/dark cycle employed with the use of banks of lights that were placed behind each of the glass mesocosm tanks. Treatments were 1 oil slick, controls (4), DCEWAF (10). A sampling of surface water column particles (WCP) occurred on days T0, T4, T8, and T16 from control (C) tanks 2, 3, 4 and DCEWAF (D) tank 1, 2, and 3. The bottom particles (BP) were sampled on T0 from the stock waters for the control and from D4 for the DCEWAF. Tank D4 was sampled on T0.5. The BP tank sampled on each specific time point was sacrificed for the sample from then on. So for T1, tank D5 was sampled and sacrificed, then for T2, D6; for T3, D7; for T4, D8; for T8, D9; for T16, both C1 and D10 were sampled. Dissolved Nutrients: Using the method described in Geochemical Environmental Research Group (GERG) ARM-SOP-0702, nutrient samples were analyzed by Astoria Pacifica Auto-Analyzer. 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 NH4, NO2 NO3 and Urea values. Redfield ratios were calculated for each mesocosm. Total Nutrients: Contaminant free containers were used to collect unfiltered samples. Avoiding contamination from NO3-, NH4+ which otherwise add up to the total nutrient values was important. After resuspension of settled materials 30 grams of samples were mixed with 5 mL of persulfate. The samples were autoclaved at 21 psi and 124 ^o^C temperature for 30 minutes. Upon completion of the autoclaving process, sample vials were weighed again to compare with pre-autoclave values. This was followed with measurements of total nitrogen and total phosphorous just like dissolved nutrient measurement.

Instruments:

Astoria Pacifica Auto-Analyzer

Error Analysis:

Five calibration standards were used. NO2-, NO3- check was run before the start of the sample run. With each batch of 15 samples, a blank, duplicate and continuing calibration verification (CCV) standard were run.

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

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