Patrick J. Gearing

Isotopic variability of organic carbon in a phytoplankton-based, temperate estuary

An isotopic survey was made of organic carbon in phytoplankton, sediments, Zooplankton, larval fish, and benthic fauna from Narragansett Bay and the Marine Ecosystems Research Laboratory, Rhode Island; the results quantify the extent of variability in a phytoplankton-based ecosystem and elucidate some of its causes. Carbon from primary producers (phytoplankton) varied with taxon and size, ranging from −20.3 ± 0.6%. (mean ± 1 s.d.) for diatoms (primarily Skeletonema costatum) to −22.2 ± 0.6%. for nanoplankton (primarily microflagellates and non-motile ultraplankton). Planktonic isotope ratios varied little with either water temperature (0 to 20°C) or degree of preservation (up to 2-year aerobic diagenesis in sea water). Isotopically, sediments from East and West Passages of the bay were homogeneous with location and depth, with a mean (−21.8 ± 0.6%.) similar to a mixture of carbon from diatoms and nanoplankton. Providence River sediments reflected terrigenous and anthropogenic carbon (sewage) in their isotopic ratios (−24.2 ± 0.7%.). Ratios of macrozooplankton (> 150 μm) were statistically separable from those of concurrently collected phytoplankton, being, on average, 0.5 to 0.6%. more positive. Secondary consumers in the water column (shrimp and larval fish) were 2.4%. heavier than diatoms. Thirty-four taxa of benthic fauna had relatively positive isotope ratios (−18.1 ± 1.5%.) which may indicate preferential use of carbon originally from diatoms rather than nanoplankton. The wide range of benthic ratios (−22.7 to −14.9%.) resulted from both intraspecific variability (mean range = 3%.) and the variety of trophic positions occupied. Some of the intraspecific variability could be related to size. Among species, the isotope ratios increased from meiofauna (−19.5 ± 0.4%.) to macrofaunal non-carnivores (−18.6 ± 1.3%.) and carnivores (−16.6 ± 0.8%.).

Hydrocarbons in 60 northeast Gulf of Mexico shelf sediments: a preliminary survey

Hydrocarbon results from gas chromatography of 60 recent sediment and 10 benthic algae samples delineate two distinct shelf environments in the northeastern Gulf of Mexico. Sediments off Florida (shell hashes and sands) have moderate amounts of lipids/total sediment (average 113ppm ± 80%) but low hydrocarbon levels (average 3.06 ppm ± 41%). Aliphatic hydrocarbons are dominated by a series of branched or cyclic, unsaturated C25 isomers. The major n-alkane is n-C17. The n-alkane and isoprenoid patterns are consistent with a marine hydrocarbon source. Sediments closer to the Mississippi River (silts and clays) contain large amounts of lipids (average 232 ppm ± 53%) and hydrocarbons (average 11.7 ppm ± 55%) to total sediment. Aliphatic hydrocarbons are mainly odd carbon number high molecular weight n-alkanes, indicating a terrigenous hydrocarbon source. Isoprenoids are present in greater abundance than in sediments off Florida (n-C17/ pristane and n-C18/phytane ratios ~2to 3). Relatively large amounts of n-C16, together with an even distribution of n-alkanes in the range C14–C20 and a substantial unresolved envelope all point to a fossil fuel input to the Mississippi samples. Samples off the Alabama coast show intermediate characteristics.

THE RATES OF TRANSPORT AND FATES OF PETROLEUM HYDROCARBONS IN A CONTROLLED MARINE ECOSYSTEM, AND A NOTE ON ANALYTICAL VARIABILITY

ABSTRACT In order to predict the chemical behavior of oil spilled in a marine environment, it is necessary to quantify the rates of the different transport mechanisms operating on the oil. At the M...

C25 and C30 biogenic alkenes in a sediment core from the upper anoxic basin of the Pettaquamscutt River (Rhode Island, U.S.A.)

Abstract Concentration profiles of five C 25 and C 30 biogenic alkenes in a sediment core collected from the upper anoxic basin of the Pettaquamscutt River have been determined. The five alkenes were identified usin gas chromatography/mass spectrometry as three isomeric C 25 dienes, a C 25 triene and a bicyclic C 30 diene. All five compounds exhibit subsurface concentration maxima, thought to result from either preservation of a past increase in alkene production or a current bacterial in situ production at depth. Similarities exist in the concentrations of two alkenes common to this core and a core from upper Narragansett Bay, despite significant differences in the origin and content of sedimentary organic matter (as inferred from organic carbon and δ 13 C measurements) at each location. These observations support the proposed bacterial in situ synthesis of alkenes. Other alkenes, whose concentration in sediments had been previously correlated with the incidence of marine organic matter, were not detected in the upper basin sediments. Their absence is consistent with the range of organic carbon δ 13 C values measured, which indicate that the component originating from marine sources is small. A comparison of organic carbon and δ 13 C values in this core with those previously reported from a core collected in an adjoining basin indicate that the sedimentary regimes at the two sites differ despite their close proximity and similar hydrography.

Behaviour of no. 2 fuel oil in the water column of controlled ecosystems

Abstract Four experiments were carried out to determine the effect of different temperatures, light levels and biological activities on the residence times of petroleum hydrocarbons. No. 2 fuel oil was added as a seawater dispersion to give an initial concentration of 150 to 300 μg/litre in the water columns of large, outdoor marine microcosms. Hydrocarbons in water samples fractionated on passage through glass fibre filters (0·3 μm pore size) according to the solubilities, so that 80–90 % of the aromatics entered the filtrate while all of the saturates were trapped by the filter. The removal of oil compounds from the water columns was exponential, with rates which appeared to be determined chiefly by the temperature. The half life of total hydrocarbons varied from more than 10 days in March to ∼30 h in July and September. Volatilisation was hypothesised to be an important removal mechanism for the 40–60% of the saturates which were not sedimented with suspended particulate matter. In warm water, the residence times of normal alkanes were increased up to 50 % by poisoning the water column, but no similar increase was noted for the bulk of the F 1 hydrocarbons. Aromatic (F 2 ) hydrocarbons appeared to be removed slowly volatilisation from cold water ( t 1 2 > 200 h ) and rapidly by biodegradation from warm water ( t 1 2 ).

Hydrocarbons in benthic algae from the eastern Gulf of Mexico

Thirty-six samples of benthic algae were collected from the continental shelf along the eastern Gulf of Mexico. The algae contain 82.8±143 ppm aliphatic hydrocarbons by dry weight and 11.8±22.7 ppm aromatic and polyolefinic hydrocarbons. The aliphatic constituents of red algae are composed almost entirely of n-C17 (70 to 95% of aliphatic weight); green algae have varying amounts of n-alkanes in the range of n-C15 to n-C19, with homologous series of odd carbon number n-alkenes. Phytadienes occur as high as 740 ppm dry weight in the green algae and do not appear to be related to time or place of collection or to presence of any petroleum pollutants. The single brown algal species contains predominantly n-C15. About 30% of the samples have hydrocarbons resembling degraded petroleum residues, but no petroleum pollution of recent origin was detected in any specimen.

Transport of no. 2 fuel oil between water column, surface microlayer and atmosphere in controlled ecosystems

Abstract No. 2 fuel oil hydrocarbons put into the bulk water columns of controlled estuarine ecosystems were found to accumulate in the surface microlayer at the air-water interface. The alkane hydrocarbons were disproportionately enriched in the microlayer compared with the aromatic hydrocarbons. A comparison of hydrocarbon boiling point distributions between bulk water, microlayer and air samples indicated that the oil hydrocarbons underwent extensive weathering by evaporation upon reaching the air-water interface. No evidence was found of increased biodegradation in the microlayer compared with that in the underlying water. A fraction of the high molecular weight alkanes, the least water soluble and least volatile constituents of the oil, appeared to be coated out from the microlayer onto the inner walls of the ecosystems.