Remediation of crude oil-contaminated coastal marsh soil: Integrated effect of biochar, rhamnolipid biosurfactant and nitrogen application.

Decontamination of oil spills from coastal wetland soils requires a delicate approach. A microcosm study was carried out to investigate the impact of integrated application of biochar, rhamnolipid (RL) biosurfactant and nitrogen (N) on petroleum hydrocarbon remediation in a Louisiana coastal saline marsh and their impact on soil microbial community. The soil was artificially contaminated with crude oil and subjected to treatments of different combinations of sugarcane residue biochar, RL, and coated urea. Total petroleum hydrocarbons (TPH) in the contaminated soil were analyzed periodically using gas chromatograph and associated soil bacterial community was studied using 16 s rRNA sequencing technologies. Results showed that integrated application of biochar + RL, biochar + N, and biochar + N+RL reduced 32.3%, 73.2%, 80.9% of TPH, respectively, and exhibited synergic interaction with higher efficiency than application individually. Combined treatments showed distinct functions that biochar increased the sorption of aromatic compounds, while RL and N enhanced the degradation of heavy and light aliphatic compounds. All remediation treatments caused reduction of soil bacterial diversity while RL and N shifted the microbial community to higher abundances of Proteobacteria and Bacteroidetes, respectively. Overall, the findings of this study demonstrate the positivity of applying integrated biochar, biosurfactant, and N treatment in oil remediation in wetland soils.

Exploring anaerobic CO2 production response to elevated nitrate levels in Gulf of Mexico coastal wetlands: Phenomena and relationships.

Recent studies have shown the effect of nitrate (NO3-) on carbon gas emissions from wetland soils that contradict thermodynamic predictions. In this study, CO2 production in three Mississippi River deltaic plain wetland soils (forest swamp, freshwater and saline marshes) with the presence of different NO3- levels (0.2, 2.0, and 3.2 mM) was evaluated in an anaerobic microcosm. Molecular composition of dissolved organic matter (DOM) of these soils was investigated using pyrolysis-GC/MS, and soil microbial community was characterized based on phosphorus lipid fatty acid (PLFA) method to elucidate the underlying mechanisms. Addition of NO3- promoted CO2 production in swamp forest soil, but inhibited CO2 emission from marsh soils. Pyrolysis-GC/MS analysis showed that swamp soil contained more polysaccharides, whereas both marsh soils had high abundance of phenolic compounds. Total PLFAs of forest swamp soil were 34% and 66% higher than freshwater and saline marsh soils, respectively. The PLFA profiles indicated different microbial distribution along a salinity gradient with the forest swamp having a higher proportion of fungi and NO3- reducers but lower sulfate (SO42-) reducers than marsh soils. Overall, the study indicated that the inherent differences in soil DOM and microbial community led to the contrasting response in soil CO2 respiration between forest swamp and marsh ecosystems to NO3- loading. These differences should be considered in determining the fate of nitrate entering Louisiana coastal wetlands from river diversions and other sources and their management.

Effect of biochar amendment on sorption-desorption and dissipation of 17α­ethinylestradiol in sandy loam and clay soils.

Animal manure application in agricultural land has caused the release of steroid estrogens in the soil environment and further movement to aquatic systems. The objective of this study was to investigate the effects of biochar addition on sorption-desorption and dissipation behaviors of 17α­ethinylestradiol (EE2) in two different textured soils. A Commerce sandy loam and a Shakey clay were selected and subjected to sterilization. Soil samples with and without sterilization were reacted with a series of EE2 solutions of different concentrations for sorption followed by desorption and quantification using HPLC-MS/MS. Long-term dissipation of EE2 in the same soils was also evaluated over a 30-d incubation. Biochar amendment increased the maximum EE2 sorption capacity but decreased its water desorption in both sandy loam and clay soils. On other hand, biochar addition increased the Koc in the clay soil which had low EE2 sorption efficiency but decreased Koc in the sandy loam which had high EE2 sorption efficiency. Biochar did significantly increase both desorbable and non-extractable fractions of EE2, while it reduced the bioavailability of EE2 to microbial degradation. The dissipation of EE2 in non-sterilized soils fit to the first-order kinetic model, whereas it was better described by zero-order kinetic for sterilized soil. Biochar increased the half-life of EE2 dissipation in non-sterilized Commerce sandy loam soil by 48% (from 3.63 to 5.37 d) and in non-sterilized Sharkey clay soil by 67% (from 2.28 to 3.81 d). Overall, this study demonstrated positive impacts of biochar on the retention of estrogen hormones in soils.

Biochar produced from mineral salt-impregnated chicken manure: Fertility properties and potential for carbon sequestration.

In this study, nutrient properties and carbon sequestration potential of biochars derived from chicken manure (CM) impregnated with mineral salts (calcium chloride, magnesium chloride, ferric chloride) were evaluated. Pretreatment with mineral salts reduced phosphorus (P) availability via the formation of insoluble metal phosphate minerals. Less carbon was lost during the pyrolysis of pretreated CM, and the produced biochars (BCCa, BCMg, and BCFe) were more stable (i.e., reduced C loss during chemical oxidation and less CO2 release during incubation) than pristine biochars. Spectroscopic evidence indicated that enhanced biochar stability via metal salt pretreatment before pyrolysis was related to increased aromatization and enhanced physical protection due to the metal-oxygen interaction, together with the formation of metal mineral phases on biochar surfaces. Moreover, ferric chloride was the optimal additive, as it significantly decreased biochar P leachability and increased carbon sequestration potential.

Fundamental and molecular composition characteristics of biochars produced from sugarcane and rice crop residues and by-products.

Biochar conversion of sugarcane and rice harvest residues provides an alternative for managing these crop residues that are traditionally burned in open field. Sugarcane leaves, bagasse, rice straw and husk were converted to biochar at four pyrolysis temperatures (PTs) of 450 °C, 550 °C, 650 °C, and 750 °C and evaluated for various elemental, molecular and surface properties. The carbon content of biochars was highest for those produced at 650-750 °C. Biochars produced at 550 °C showed the characteristics of biochar that are commonly interpreted as being stable in soil, with low H/C and O/C ratios and pyrolysis fingerprints dominated by aromatic and polyaromatic hydrocarbons. At 550 °C, all biochars also exhibited maximum CEC values with sugarcane leaves biochar (SLB) > sugarcane bagasse biochar (SBB) > rice straw biochar (RSB) > rice husk biochar (RHB). The pore size distribution of biochars was dominated by pores of 20 nm and high PT increased both smaller and larger than 50 nm pores. Water holding capacity of biochars increased with PT but the magnitude of the increase was limited by feedstock types, likely related to the hydrophobicity of biochars as evident by molecular composition, besides pore volume properties of biochars. Py-GC/MS analysis revealed a clear destruction of lignin with decarboxylation and demethoxylation at 450 °C and dehydroxylation at above 550 °C. Overall, biochar molecular compositions became similar as PT increased, and the biochars produced at 550 °C demonstrated characteristics that have potential benefit as soil amendment for improving both C sequestration and nutrient dynamics.

Application effects of coated urea and urease and nitrification inhibitors on ammonia and greenhouse gas emissions from a subtropical cotton field of the Mississippi delta region.

Nitrogen (N) fertilization affects both ammonia (NH3) and greenhouse gas (GHG) emissions that have implications in air quality and global warming potential. Different cropping systems practice varying N fertilizations. The aim of this study was to investigate the effects of applications of polymer-coated urea and urea treated with N process inhibitors: NBPT [N-(n-butyl)thiophosphoric triamide], urease inhibitor, and DCD [Dicyandiamide], nitrification inhibitor, on NH3 and GHG emissions from a cotton production system in the Mississippi delta region. A two-year field experiment consisting of five treatments including the Check (unfertilized), urea, polymer-coated urea (ESN), urea+NBPT, and urea+DCD was conducted over 2013 and 2014 in a Cancienne loam (Fine-silty, mixed, superactive, nonacid, hyperthermic Fluvaquentic Epiaquepts). Ammonia and GHG samples were collected using active and passive chamber methods, respectively, and characterized. The results showed that the N loss to the atmosphere following urea-N application was dominated by a significantly higher emission of N2O-N than NH3-N and the most N2O-N and NH3-N emissions were during the first 30-50 days. Among different N treatments compared to regular urea, NBPT was the most effective in reducing NH3-N volatilization (by 58-63%), whereas DCD the most significant in mitigating N2O-N emissions (by 75%). Polymer-coated urea (ESN) and NBPT also significantly reduced N2O-N losses (both by 52%) over urea. The emission factors (EFs) for urea, ESN, urea-NBPT, urea+DCD were 1.9%, 1.0%, 0.2%, 0.8% for NH3-N, and 8.3%, 3.4%, 3.9%, 1.0% for N2O-N, respectively. There were no significant effects of different N treatments on CO2-C and CH4-C fluxes. Overall both of these N stabilizers and polymer-coated urea could be used as a mitigation strategy for reducing N2O emission while urease inhibitor NBPT for reducing NH3 emission in the subtropical cotton production system of the Mississippi delta region.

Fresh and weathered crude oil effects on potential denitrification rates of coastal marsh soil.

On April 20, 2010, the Deepwater Horizon oil platform experienced an explosion which triggered the largest marine oil spill in US history, resulting in the release of ∼795 million L of crude oil into the Gulf of Mexico. Once oil reached the surface, changes in overall chemical composition occurred due to volatilization of the smaller carbon chain compounds as the oil was transported onshore by winds and currents. In this study, the toxic effects of both fresh and weathered crude oil on denitrification rates of coastal marsh soil were determined using soil samples collected from an unimpacted coastal marsh site proximal to areas that were oiled in Barataria Bay, LA. The 1:10 ratio of crude oil:field moist soil fully coated the soil surface mimicking a heavy oiling scenario. Potential denitrification rates at the 1:10 ratio, for weathered crude oil, were 46 ± 18.4% of the control immediately after exposure and 62 ± 8.0% of the control following a two week incubation period, suggesting some adaptation of the denitrifying microbial consortium over time. Denitrification rates of soil exposed to fresh crude oil were 51.5 ± 5.3% of the control after immediate exposure and significantly lower at 10.9 ± 1.1% after a 2 week exposure period. Results suggest that fresh crude oil has the potential to more severely impact the important marsh soil process of denitrification following longer term exposure. Future studies should focus on longer-term denitrification as well as changes in the microbial consortia in response to oil exposure.

Effect of redox potential and pH status on degradation and adsorption behavior of tylosin in dairy lagoon sediment suspension.

Veterinary antibiotics are the most heavily used pharmaceuticals in intensive animal farming operation. Their presence in the environment through application of manure and lagoon water as fertilizer in agricultural fields has generated a growing concern in recent years due to potential threat to the ecosystem and the risk they pose to human and animal health. Among the antibiotics, tylosin, a macrolide class of antibiotics, has been widely used for disease prevention and growth promotion in swine, cattle/dairy, and poultry production. To understand degradation and sorption behavior of tylosin A, a laboratory microcosm incubation study was conducted on dairy lagoon sediments suspension under different pH (5.5, 7.0, 8.5) and redox potentials (Eh at -100 mV, 0 mV, +250 mV, +350 mV). Sorption and degradation of tylosin was strongly influenced by sediment pH and redox conditions. Under acidic (pH 5.5) and reduced (Eh -100 mV) condition, tylosin persisted in the solution phase of dairy lagoon sediment suspension much longer with resident time of 77 d. Under oxidized (Eh +350 mV) condition, microbial degradation was much greater causing 68-75% of tylosin loss from the solution at pH 5.5 and 32-75% at pH 7.0 during the 20 d incubation. At pH 8.5, abiotic transformation of tylosin A into unknown degradates rather than sediment adsorption and microbial degradation was the major mechanism controlling tylosin disappearance from the solution regardless of the status of redox potentials. Overall, the results suggested that under reduced condition with low pH, tylosin will be persisted in the lagoon effluents and residue of tylosin may enter agricultural fields through the application of lagoon slurry as fertilizer.

Characterization of labile organic carbon in coastal wetland soils of the Mississippi River deltaic plain: relationships to carbon functionalities.

Adequate characterization of labile organic carbon (LOC) is essential to the understanding of C cycling in soil. There has been very little evaluation about the nature of LOC characterizations in coastal wetlands, where soils are constantly influenced by different redox fluctuations and salt water intrusions. In this study, we characterized and compared LOC fractions in coastal wetland soils of the Mississippi River deltaic plain using four different methods including 1) aerobically mineralizable C (AMC), 2) cold water extractable C (CWEC), 3) hot water extractable C (HWEC), and 4) salt extractable C (SEC), as well as acid hydrolysable C (AHC) which includes both labile and slowly degradable organic C. Molecular organic C functional groups of these wetland soils were characterized by (13)C solid-state nuclear magnetic resonance (NMR). The LOC and AHC increased with soil organic C (SOC) regardless of wetland soil type. The LOC estimates by four different methods were positively and significantly linearly related to each other (R(2)=0.62-0.84) and with AHC (R(2)=0.47-0.71). The various LOC fractions accounted for ≤4.3% of SOC whereas AHC fraction represented 16-49% of SOC. AMC was influenced positively by O/N-alkyl and carboxyl C but negatively by alkyl C, whereas CWEC and SEC fractions were influenced only positively by carboxyl C but negatively by alkyl C in SOC. On the other hand, HWEC fraction was found to be only influenced positively by carbonyl C, and AHC positively by O/N-alkyl and alkyl C but negatively by aromatic C groups in SOC. Overall these relations suggested different contributions of various molecular organic C moieties to LOC in these wetlands from those often found for upland soils. The presence of more than 50% non-acid hydrolysable C suggested the dominance of relatively stable SOC pool that would be sequestered in these Mississippi River deltaic plain coastal wetland soils. The results have important implications to the understanding of the liability and refractory character of SOC in these wetlands as recent studies suggest marsh SOC to be an important C source in fueling hypoxia in the northern Gulf of Mexico.

Effect of biochar amendment on tylosin adsorption-desorption and transport in two different soils.

The role of biochar as a soil amendment on the adsorption-desorption and transport of tylosin, a macrolide class of veterinary antibiotic, is little known. In this study, batch and column experiments were conducted to investigate the adsorption kinetics and transport of tylosin in forest and agricultural corn field soils amended with hardwood and softwood biochars. Tylosin adsorption was rapid at initial stages, followed by slow and continued adsorption. Amounts of adsorption increased as the biochar amendment rate increased from 1 to 10%. For soils with the hardwood biochar, tylosin adsorption was 10 to 18% higher than that when using the softwood biochar. Adsorption kinetics was well described by Elovich equation ( ≥ 0.921). As the percent of biochar was increased, the rates of initial reactions were generally increased, as indicated by increasing α value at low initial tylosin concentration, whereas the rates during extended reaction times were generally increased, as indicated by decreasing ß value at high initial tylosin concentration. A considerably higher amount of tylosin remained after desorption in the corn field soil than in the forest soil regardless of the rate of biochar amendment, which was attributed to the high pH and silt content of the former. The breakthrough curves of tylosin showed that the two soils with biochar amendment had much greater retardation than those of soils without biochar. The CXTFIT model for the miscible displacement column study described well the peak arrival time as well as the maximum concentration of tylosin breakthrough curves but showed some underestimation at advanced stages of tylosin leaching, especially in the corn field soil. Overall, the results indicate that biochar amendments enhance the retention and reduce the transport of tylosin in soils.

Carbon gas production under different electron acceptors in a freshwater marsh soil.

Dynamics of carbon (C) gas emission from wetlands influence global C cycling. In many freshwater systems such as Louisiana freshwater marsh, soil contents of NO3(-) and SO4(2-) have increased due to nutrient loading and saltwater intrusion. This could affect C mineralization and the emission of the major greenhouse gases carbon dioxide (CO2) and methane (CH4). In this investigation, a laboratory microcosm study was carried out to elucidate the effects of NO(3)(-) and SO4(2-) on CO2 and CH4 production from a freshwater marsh soil located in the Barataria Basin of Louisiana coast, which has been subjected to the Mississippi River diversion and seawater intrusion. Composite soil samples were collected from top 50 cm marsh profile, treated with different levels of NO3(-) (0, 3.2 and 5mM) or SO4(2-) (0, 2, and 5mM) concentrations, and incubated for 214d under anaerobic conditions. The results showed that the presence of NO3(-) (especially at 3.2mM) significantly decreased CO2 productions whereas SO4(2-) did not. On the other hand, both NO(3)(-) and SO4(2-) treatments decreased CH4 production but the NO3(-) almost completely inhibited CH4 production (>99%) whereas the SO4(2-) treatments reduced CH4 production by 78-90%. The overall C mineralization rate constant under the NO3(-) presence was also low. In addition, the results revealed that a large proportion (95%) of anaerobic carbon mineralization in the untreated freshwater soil was unexplained by the reduction of any of the measured major electron acceptors.

Denitrification potential and its relation to organic carbon quality in three coastal wetland soils.

Capacity of a wetland to remove nitrate through denitrification is controlled by its physico-chemical and biological characteristics. Understanding these characteristics will help better to guide beneficial use of wetlands in processing nitrate. This study was conducted to determine the relationship between soil organic carbon (SOC) quality and denitrification rate in Louisiana coastal wetlands. Composite soil samples of different depths were collected from three different wetlands along a salinity gradient, namely, bottomland forest swamp (FS), freshwater marsh (FM), and saline marsh (SM) located in the Barataria Basin estuary. Potential denitrification rate (PDR) was measured by acetylene inhibition method and distribution of carbon (C) moieties in organic C was determined by 13C solid-state NMR. Of the three wetlands, the FM soil profile exhibited the highest PDR on both unit weight and unit volume basis as compared to FS and SM. The FM also tended to yield higher amount of N2O as compared to the FS and SM especially at earlier stages of denitrification, suggesting incomplete reduction of NO3(-) at FM and potential for emission of N2O. Saline marsh soil profile had the lowest PDR on the unit volume basis. Increasing incubation concentration from 2 to 10 mg NO3(-)-N L(-1) increased PDR by 2 to 6 fold with the highest increase in the top horizons of FS and SM soils. Regression analysis showed that across these three wetland systems, organic C has significant effect in regulating PDR. Of the compositional C moieties, polysaccharides positively influenced denitrification rate whereas phenolics (likely phenolic adehydes and ketonics) negatively affected denitrification rate in these wetland soils. These results could have significant implication in integrated assessment and management of wetlands for treating nutrient-rich biosolids and wastewaters, non-point source agricultural runoff, and nitrate found in the diverted Mississippi River water used for coastal restoration.