Degradation and resilience in Louisiana salt marshes after the BP-Deepwater Horizon oil spill.

More than 2 y have passed since the BP-Deepwater Horizon oil spill in the Gulf of Mexico, yet we still have little understanding of its ecological impacts. Examining effects of this oil spill will generate much-needed insight into how shoreline habitats and the valuable ecological services they provide (e.g., shoreline protection) are affected by and recover from large-scale disturbance. Here we report on not only rapid salt-marsh recovery (high resilience) but also permanent marsh area loss after the BP-Deepwater Horizon oil spill. Field observations, experimental manipulations, and wave-propagation modeling reveal that (i) oil coverage was primarily concentrated on the seaward edge of marshes; (ii) there were thresholds of oil coverage that were associated with severity of salt-marsh damage, with heavy oiling leading to plant mortality; (iii) oil-driven plant death on the edges of these marshes more than doubled rates of shoreline erosion, further driving marsh platform loss that is likely to be permanent; and (iv) after 18 mo, marsh grasses have largely recovered into previously oiled, noneroded areas, and the elevated shoreline retreat rates observed at oiled sites have decreased to levels at reference marsh sites. This paper highlights that heavy oil coverage on the shorelines of Louisiana marshes, already experiencing elevated retreat because of intense human activities, induced a geomorphic feedback that amplified this erosion and thereby set limits to the recovery of otherwise resilient vegetation. It thus warns of the enhanced vulnerability of already degraded marshes to heavy oil coverage and provides a clear example of how multiple human-induced stressors can interact to hasten ecosystem decline.

Rapid degradation of Deepwater Horizon spilled oil by indigenous microbial communities in Louisiana saltmarsh sediments.

The Deepwater Horizon oil spill led to the severe contamination of coastal environments in the Gulf of Mexico. A previous study detailed coastal saltmarsh erosion and recovery in a number of oil-impacted and nonimpacted reference sites in Barataria Bay, Louisiana over the first 18 months after the spill. Concentrations of alkanes and polyaromatic hydrocarbons (PAHs) at oil-impacted sites significantly decreased over this time period. Here, a combination of DNA, lipid, and isotopic approaches confirm that microbial biodegradation was contributing to the observed petroleum mass loss. Natural abundance (14)C analysis of microbial phospholipid fatty acids (PLFA) reveals that petroleum-derived carbon was a primary carbon source for microbial communities at impacted sites several months following oil intrusion when the highest concentrations of oil were present. Also at this time, microbial community analysis suggests that community structure of all three domains has shifted with the intrusion of oil. These results suggest that Gulf of Mexico marsh sediments have considerable biodegradation potential and that natural attenuation is playing a role in impacted sites.

Catechol and humic acid sorption onto a range of laboratory-produced black carbons (biochars).

Although the major influence of black carbon (BC) on soil and sediment organic contaminant sorption is widely accepted, an understanding of the mechanisms and natural variation in pyrogenic carbon interaction with natural organic matter (NOM) is lacking. The sorption of a phenolic NOM monomer (catechol) and humic acids (HA) onto BC was examined using biochars made from oak, pine, and grass at 250, 400, and 650 degrees C. Catechol sorption equilibrium occurred after 14 d and was described by a diffusion kinetic model, while HA required only 1 d and followed pseudo-second-order kinetics. Catechol sorption capacity increased with increasing biochar combustion temperature, from pine < oak < grass and from coarse < fine particle size. At lower catechol concentrations, sorption affinity (Freundlich constant, K(f)) was directly related to micropore surface area (measured via CO(2) sorptometry) indicating the predominance of specific adsorption. In contrast, HA exhibited an order of magnitude less sorption (0.1% versus 1%, by weight) due to its exclusion from micropores. Greater sorption of both catechol and HA occurred on biochars with nanopores, i.e. biochars made at higher temperatures. These findings suggest that addition of BC to soil, via natural fires or biochar amendments, will sequester abundant native OM through sorption.

Polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans and polybrominated diphenyl ethers in sediments and fish species from the Murchison Bay of Lake Victoria, Uganda.

Polychlorinated dibenzo-p-dioxins/furans (PCDD/Fs) and polybrominated diphenyl ethers (PBDEs) were analyzed in sediments and fish from the Murchison Bay of Lake Victoria by high resolution gas chromatography/high resolution mass spectrometry (HRGC/HRMS). Average concentrations of total (Σ) PCDD/Fs and ΣPBDEs in sediments ranged from 68.8 to 479 pg g(-1) dry weight (dw) and 60.8 to 179 pg g(-1) dw, respectively. Contamination levels of sedimentary PCDD/Fs and PBDEs were low to moderate compared to other urbanized regions worldwide. The concentrations in different fish species (Nile perch; Lates niloticus and Nile tilapia; Oreochromis niloticus) were 5.32 to 49.0 pg g(-1) wet weight (ww) for PCDD/Fs and 59.3 to 495 pg g(-1) ww for PBDEs. Higher concentrations of the pollutants were found in L. niloticus than O. niloticus, which could be attributed to species differences in feeding habits and lifestyles. World Health Organization-toxic equivalents (WHO2005-TEQs) for PCDD/Fs ranged from 0.08 to 0.33 pgTEQg(-1) dw and 0.001-0.14 pg TEQg(-1) ww in sediments and fish, respectively. The TEQ values were low compared to the data for fresh water fish reported in literature and within a permissible level of 3.5 pg g(-1) ww recommended by the European Commission. Based on the Commission set value and minimum risk level criteria formulated by the Agency for Toxic Substances and Disease Registry, the fish from the Murchison Bay was fit for human consumption.

Polychlorinated biphenyls in sediments and fish species from the Murchison Bay of Lake Victoria, Uganda.

Polychlorinated biphenyls (PCBs) were determined in sediments and two fish species collected from the Murchison Bay in Lake Victoria, using high resolution gas chromatography coupled to a high resolution mass spectrometer. Total PCB concentrations (Σ18PCBs) varied widely with mean values ranging from 777 to 4325pg g(-1) dry weight (dw) for sediments and 80 to 779pg g(-1) wet weight (ww) for fish. The PCB levels in the sediments were significantly higher at the station closest to Nakivubo channel, presumably due to effluents discharged by the channel, which may contain domestically produced commercial PCB mixtures. For fish, the concentrations in Nile perch (Lates niloticus) were significantly greater than those in Nile tilapia (Oreochromis niloticus) at all study stations, possibly due to dietary differences among species. World Health Organization-toxic equivalents (WHO2005-TEQs) for the dioxin-like PCBs were 0.04-0.64pg g(-1) dw and 0.01-0.39pg g(-1) ww for sediments and fish, respectively. The non-ortho PCBs exhibited the highest contribution to the Σ12TEQs (>75%) compared to the mono-ortho PCBs in both fish species. The TEQs in the present study were lower than many reported worldwide in literature for fish and were within the permissible level recommended by the European Commission, implying that the fish did not pose health hazards related to PCBs to the consumers.

Polychlorinated biphenyls and hexachlorocyclohexanes in sediments and fish species from the Napoleon Gulf of Lake Victoria, Uganda.

Polychlorinated biphenyls (PCBs) and hexachlorocyclohexanes (HCHs) were analyzed in surface sediments (<30 cm depth) and two fish species: Nile perch (Lates niloticus) and Nile tilapia (Oreochromis niloticus). The samples were collected from the Napoleon Gulf on the northern shore of Lake Victoria. The analysis was done using a gas chromatograph (GC) coupled to a high resolution mass spectrometer for PCBs and a GC equipped with an electron capture detector for HCHs. Total (Σ) PCBs in the muscles of fish varied widely with mean values ranging from 41 to 670 pg g(-1) lipid weight (lw). The PCB levels in L. niloticus were significantly greater than those in O. niloticus. The large variability observed in the data was attributed to differences in feeding habits and trophic levels. While O. niloticus is a filter-eating fish species feeding mainly on phytoplankton and zooplankton, L. niloticus have predatory feeding behaviors and prefer a diet of live fish and, therefore, are more prone to bio-accumulate contaminants. The mean PCB concentrations in the sediments varied from 362 to 848 pg g(-1) dry weight. Variations in PCB levels were observed from one study site to another, this was attributed to the nature and particle size of the sediments. HCH isomers were detected in fish at mean concentrations of up to 45,900 pg g(-1) lw. The PCB and HCH concentrations were lower than those from previous studies elsewhere in literature and were below the maximum residue limits set by the European Commission and FAO/WHO Codex Alimentarius Commission, implying that the fish was fit for human consumption.

PCDD/Fs and dioxin-like PCBs in fish species from Lake Victoria, East Africa.

Two commercially important fish species, Nile perch (Lates niloticus) and Nile tilapia (Oreochromis niloticus) belonging to different trophic levels were collected from the Napoleon Gulf and Thurston Bay in Lake Victoria. Polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and dioxin-like polychlorinated biphenyls (dl-PCBs) were extracted from the fish muscles and livers using the (13)C isotope dilution method, followed by multiple column chromatography clean-up. Analysis was achieved by a high resolution gas chromatography coupled with a high resolution mass spectrometer. The concentrations of analytes ranged from 0.07 to 0.59pgg(-1) fresh weight (fw) and 0.3-19.0pgg(-1) in L. niloticus and 0.06-0.18 and 0.2-15.7pgg(-1) in O. niloticus, for ∑PCDD/Fs and ∑dl-PCBs, respectively. Differences in congener concentrations were observed between the two fish species and study sites, and this was attributed to differences in feeding habits and trophic levels. World Health Organization-toxic equivalents (WHO-TEQs) were in the range 0.01-0.16pgTEQg(-1) for the PCDD/Fs and 0.001-0.74pgTEQg(-1) for the dl-PCBs. The TEQ values in the present study were lower compared to those of most fish samples reported in literature and were within permissible levels recommended by the European Union, implying that the fish was fit for human consumption.

PCDD/Fs and dioxin-like PCBs in surface sediments from Lake Victoria, East Africa.

Surface sediments (<60 cm) from the Napoleon Gulf and Thurston Bay on the northern shore of Lake Victoria were analyzed for polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and dioxin-like polychlorinated biphenyls (dl-PCBs). Fifteen PCDD/Fs and eleven dl-PCBs were found in 75.5% of the samples. The maximum concentrations of PCDD/Fs and dl-PCBs were 44.1 and 136 pg g(-1) dry weight (dw), respectively. Octachlorodibenzo-p-dioxin was the predominant PCDD/F congener at the Napoleon Gulf and Thurston Bay area. Regarding the dl-PCBs, a variation in levels was observed between the mono-ortho PCBs and non-ortho PCBs, with the former having higher levels than the latter. The PCDD/F and dl-PCB levels, in the sediments of Napoleon Gulf, which is near urban centers and industrial areas were markedly higher (α ≤ 0.05) than those from the Thurston Bay, which is offshore, suggesting that human activities could be sources of the pollutants to the surrounding water resources. World Health Organization-toxic equivalency quotients (WHO-TEQs) lay in the range of 0.07-5.53 pg g(-1) dw for PCDD/Fs and 0.01-0.23 pg g(-1) dw for dl-PCBs. 23.1% of samples from the Napoleon Gulf had their results above the set WHOPCDD/Fs-TEQ value.

Characterization of adsorption and degradation of diuron in carbonatic and noncarbonatic soils.

The adsorption and degradation of the pesticide diuron in carbonatic and noncarbonatic soils were investigated to better understand the fate and transport of diuron in the environment. Batch adsorption experiments yielded isotherms that were well-described by the linear model. Adsorption coefficients normalized to soil organic carbon content (K(oc)) were lowest for carbonatic soils, averaging 259 +/- 48 (95% CI), 558 +/- 109, 973 +/- 156, and 2090 +/- 1054 for carbonatic soils, Histosols, Oxisols, and Spodosols, respectively. In addition, marl-carbonatic soils had much lower K(oc) values (197 +/- 27) than nonmarl-carbonatic soils. Diuron degradation data fit a first-order reaction kinetics model, yielding half-lives in soils ranging from 40 to 267 days. There was no significant difference between the average diuron degradation rate coefficients of each of the soil groups studied. Given the low adsorption capacity of carbonatic soils, it may be advisable to lower herbicide application rates in agricultural regions with carbonatic soils such as southern Florida to protect aquatic ecosystems and water quality.