RESUMO
Anthropogenic pressures, such as diking, construction of dams, and oil spills negatively impact coastal marshes creating growing pressure to preserve and to restore salt marshes due to their critical role in permanently removing nitrate runoff through denitrification as well as other ecosystem services they provide. This study determined denitrification rates across a typical northern Gulf of Mexico salt marsh landscape that included a natural marsh, a tidal creek, and a 21-year-old restored salt marsh. Denitrification capacity, measured with the isotope pairing technique on a membrane inlet mass spectrometer, was comparable across the sites despite significant differences in above and below ground characteristics. Total extractable ammonium concentrations and sediment carbon content were higher at the natural marsh compared to the restored marsh. Hydrogen sulfide concentrations were highest at the creek compared to the vegetated sites and lowest at the restored marsh. This suggests that marsh restoration projects reestablish nitrogen removal capacity at rates similar to those in natural systems and can help to significantly reduce nitrogen loads to the coastal ocean.
Assuntos
Desnitrificação , Monitoramento Ambiental , Sedimentos Geológicos/química , Poluição por Petróleo , Áreas Alagadas , Alabama , Compostos de Amônio/análise , Carbono/análise , Ecossistema , Golfo do México , Sulfeto de Hidrogênio/análise , Nitrogênio/análiseRESUMO
This study investigated potential nitrogen fixation, net nitrification, and denitrification responses to short-term crude oil exposure that simulated oil exposure in Juncus roemerianus salt marsh sediments previously impacted following the Deepwater Horizon accident. Temperature as well as crude oil amount and type affected the nitrogen cycling rates. Total nitrogen fixation rates increased 44 and 194 % at 30 °C in 4,000 mg kg(-1) tar ball and 10,000 mg kg(-1) moderately weathered crude oil treatments, respectively; however, there was no difference from the controls at 10 and 20 °C. Net nitrification rates showed production at 20 °C and consumption at 10 and 30 °C in all oil treatments and controls. Potential denitrification rates were higher than controls in the 10 and 30 ºC treatments but responded differently to the oil type and amount. The highest rates of potential denitrification (12.7 ± 1.0 nmol N g(-1) wet h(-1)) were observed in the highly weathered 4,000 mg kg(-1) oil treatment at 30 °C, suggesting increased rates of denitrification during the warmer summer months. These results indicate that the impacts on nitrogen cycling from a recurring oil spill could depend on the time of the year as well as the amount and type of oil contaminating the marsh. The study provides evidence for impact on nitrogen cycling in coastal marshes that are vulnerable to repeated hydrocarbon exposure.
Assuntos
Sedimentos Geológicos/química , Ciclo do Nitrogênio/efeitos dos fármacos , Poluição por Petróleo/efeitos adversos , Petróleo/toxicidade , Áreas Alagadas , Clorofila/análise , Clorofila A , Cromatografia , Desnitrificação/efeitos dos fármacos , Golfo do México , História do Século XXI , Magnoliopsida/crescimento & desenvolvimento , Nitrificação/efeitos dos fármacos , Petróleo/análise , Poluição por Petróleo/história , Estações do Ano , TemperaturaRESUMO
The rates of crude oil degradation by the extant microorganisms in intertidal sediments from a northern Gulf of Mexico beach were determined. The enhancement in crude oil degradation by amending the microbial communities with marine organic matter was also examined. Replicate mesocosm treatments consisted of: (i) controls (intertidal sand), (ii) sand contaminated with crude oil, (iii) sand plus organic matter, and (iv) sand plus crude oil and organic matter. Carbon dioxide (CO(2)) production was measured daily for 42 days and the carbon isotopic ratio of CO(2) (δ(13)CO(2)) was used to determine the fraction of CO(2) derived from microbial respiration of crude oil. Bacterial 16S rRNA clone library analyses indicated members of Actinobacteria, Bacteroidetes, and Chloroflexi occurred exclusively in control sediments whereas Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, and Firmicutes occurred in both control and oil contaminated sediments. Members of the hydrocarbon-degrading genera Hydrocarboniphaga, Pseudomonas, and Pseudoxanthomonas were found primarily in oil contaminated treatments. Hydrocarbon mineralization was 76% higher in the crude oil amended with organic matter treatment compared to the rate in the crude oil only treatment indicating that biodegradation of crude oil in the intertidal zone by an extant microbial community is enhanced by input of organic matter.
Assuntos
Sedimentos Geológicos/microbiologia , Hidrocarbonetos/metabolismo , Petróleo/metabolismo , Bactérias/classificação , Bactérias/genética , Bactérias/metabolismo , Biodegradação Ambiental , Dióxido de Carbono/metabolismo , Golfo do México , Filogenia , RNA Bacteriano/genética , RNA Ribossômico 16S/genética , Dióxido de SilícioRESUMO
In the present study, microbial community responses to exposure to unweathered Macondo Well crude oil and conventional diesel in a sandy beach environment were determined. Biodegradation was assessed in mesocosm experiments with differing fuel amounts (2,000 and 4,000 mg/kg) and with or without inorganic nutrient amendment. Carbon dioxide production was measured daily for 42 d. Aerobic alkane, total hydrocarbon, and polycyclic aromatic hydrocarbon (PAH) degraders were enumerated in treated and control mesocosms and changes in their abundances were measured weekly. Hydrocarbon mineralization occurred in all treatments. In the inorganic nutrient-amended treatments, the degradation rates were 2.31 and 2.00 times greater in the 2,000 mg/kg diesel and crude oil treatments, respectively, and 3.52 (diesel) and 4.14 (crude) times higher for the fuel types at the 4,000 mg/kg fuel concentrations compared to unamended treatments. Microbial lag phases were short (<3 d) and alkane and total hydrocarbon degrader numbers increased by five orders of magnitude compared to the uncontaminated treatments within 7 d in most treatments. Hydrocarbon degrader numbers in diesel and in crude oil treatments were similar; however, the PAH degraders were more abundant in the crude oil relative to diesel treatment. These findings indicate that hydrocarbon degradation by extant microbial populations in the northern Gulf of Mexico sandy beach environments can be stimulated and enhanced by inorganic nutrient addition.