The highly visible coastal phenomenon of wetland loss in coastal Louisiana (LA) was examined through the prism of carbon accumulation and loss. Carbon storage or sequestration in rapidly subsiding LA ...coastal marsh soils was based on vertical marsh accretion and aerial change data. Marshes sequester significant amount of carbon through vertical accretion however, large amounts of carbon previously sequestration in the soil profile is lost through annual deterioration of these coastal marshes. Hurricanes, such as Katrina and Rita, have triggered instantaneous large carbon losses of sequestered soil carbon through the destruction of large areas of marsh. This analysis shows proposed coastal restoration efforts will not be sufficient to restore carbon losses by storms and marsh deterioration. Further, we have estimated the economic benefit of carbon sequestration for coastal wetland restoration efforts. Results show that LA coastal marshes may not serve as a net sink of carbon. These results may serve as a predictor of the impact of future predictions of increasing global sea level rise on carbon sequestration for other coastal regions.
Fungal and bacterial denitrification rates were determined under a range of redox conditions in sediment from a Louisiana swamp forest used for wastewater treatment. Sediment was incubated in ...microcosms at 6 Eh levels (−200, −100, 0, +100, +250 and +400
mV) ranging from strongly reducing to moderately oxidizing conditions. Denitrification was determined using the substrate-induced respiration (SIR) inhibition and acetylene inhibition methods. Cycloheximide (C
15H
23NO
4) was used as the fungal inhibitor and streptomycin (C
21H
39N
7O
12) as the bacterial inhibitor. At Eh values of +250
mV and +400
mV, denitrification rates by fungi and bacteria were 34.3–35.1% and 1.46–1.59% of total denitrification, respectively, indicating that fungi were responsible for most of the denitrification under aerobic or weakly reducing conditions. On the other hand, at Eh −200
mV, denitrification rates of fungi and bacteria were 17.6% and 64.9% of total denitrification, respectively, indicating that bacteria were responsible for most of the denitrification under strongly reducing conditions. Results show fungal denitrification was dominant under moderately reducing to weakly oxidizing conditions (Eh
>
+250
mV), whereas bacterial denitrification was dominant under strongly reducing condition (Eh
<
−100 mV). At Eh values between −100 to +100 mV, denitrification by fungi and bacteria were 37.9–43.2% and 53.0–51.1% of total denitrification, respectively, indicating that both bacteria and fungi contributed significantly to denitrification under these redox conditions. Because N
2O is an important gaseous denitrification product in sediment, fungal denitrification could be of greater ecological significance under aerobic or moderately reducing conditions contributing to greenhouse gas emission and global warming potential (GWP).
Soil flooding in wetlands is accompanied by changes in soil physical and chemical characteristics. These changes include the lowering of soil redox potential (Eh) leading to increasing demand for ...oxygen within the soil profile as well as production of soil phytotoxins that are by-products of soil reduction and thus, imposing potentially severe stress on plant roots. Various methods are utilized for quantifying plant responses to reducing soil conditions that include measurement of radial oxygen transport, plant enzymatic responses, and assessment of anatomical/morphological changes. However, the chemical properties and reducing nature of soil environment in which plant roots are grown, including oxygen demand, and other associated processes that occur in wetland soils, pose a challenge to evaluation and comparison of plant responses that are reported in the literature. This review emphasizes soil-plant interactions in wetlands, drawing attention to the importance of quantifying the intensity and capacity of soil reduction for proper evaluation of wetland plant responses, particularly at the process and whole-plant levels. Furthermore, while root oxygen-deficiency may partially account for plant stress responses, the importance of soil phytotoxins, produced as by-products of low soil Eh conditions, is discussed and the need for development of methods to allow differentiation of plant responses to reduced or anaerobic soil conditions vs. soil phytotoxins is emphasized.
The influence of sediment redox conditions on solubility of selected metals and nutrients in sediment from a coastal Louisiana freshwater lake (Lake Cataouatche) receiving diverted Mississippi River ...water was quantified. Sediment redox was cycled step wise in 50 mV increments between oxidized (-200 to +500 mV) and reduced (+500 to -200 mV) conditions. Changes in sediment oxidation/reduction status and pH influenced solubility of both metals and nutrients. When redox potential (Eh) was increased from -200 to +500 mV, sediment pH decreased from 7.1 to 5.7. When the sediment Eh decreased from +500 to -200 mV, pH increased from 5.7 to 7.1. The increase in sediment acidity upon oxidation resulted in the release of the Pb, Ca, Mg, Al, and Zn into solution. The solution concentration of these elements was inversely proportional to Eh (P</=0.05). The concentration of Fe, Mn, and P in sediment suspension was strongly governed by changes in oxidation-reduction status of sediment. The oxidation of reduced sediment resulted in a decrease in amount of Fe and Mn in solution, a result of the conversion of soluble ferrous and manganous form to less soluble ferric and manganic form. Following reduction of oxidized sediment, Fe and Mn became more soluble because the ferric iron and manganic manganese form changed to ferrous and manganous form. Phosphorus behavior as influenced by oxidation/reduction status was closely related to Fe and Mn chemistry with an increase in phosphate following iron reduction. This study demonstrated that sediment redox potential is an important parameter affecting metal and nutrient solubility and mobility in Louisiana coastal freshwater lake sediment. Reduction or aeration status of sediment should be considered in predicting the release of these elements into the aquatic environment.
The phosphorus (P) adsorption characteristic of sesame straw biochar prepared with different activation agents and pyrolysis temperatures was evaluated. Between 0.109 and 0.300 mg L⁻¹ in the form of ...inorganic phosphate was released from raw sesame straw biochar in the first 1 h. The release of phosphate was significantly enhanced from 62.6 to 168.2 mg g⁻¹ as the pyrolysis temperature increased. Therefore, sesame straw biochar cannot be used as an adsorbent for P removal without change in the physicochemical characteristics. To increase the P adsorption of biochar in aqueous solution, various activation agents and pyrolysis temperatures were applied. The amount of P adsorbed from aqueous solution by biochar activated using different activation agents appeared in the order ZnCl₂ (9.675 mg g⁻¹) > MgO (8.669 mg g⁻¹) ⋙ 0.1N-HCl > 0.1N-H₂SO₄ > K₂SO₄ ≥ KOH ≥ 0.1N-H₃PO₄, showing ZnCl₂ to be the optimum activation agent. Higher P was adsorbed by the biochar activated using ZnCl₂ under different pyrolysis temperatures in the order 600 °C > 500 °C > 400 °C > 300 °C. Finally, the amount of adsorbed P by activated biochar at different ratios of biochar to ZnCl₂ appeared in the order 1:3 ≒ 1:1 > 3:1. As a result, the optimum ratio of biochar to ZnCl₂ and pyrolysis temperature were found to be 1:1 and 600 °C for P adsorption, respectively. The maximum P adsorption capacity by activated biochar using ZnCl₂ (15,460 mg kg⁻¹) was higher than that of typical biochar, as determined by the Langmuir adsorption isotherm. Therefore, the ZnCl₂ activation of sesame straw biochar was suitable for the preparation of activated biochar for P adsorption.
In this study, one of the largest estuaries in the Gulf Coast of USA was investigated for Cu forms and fractionations. Both the water and sediment samples in subsegments of the Lake Pontchartrain ...basin were collected and Cu forms in dissolved phase and sediment phase were analyzed. The BCR sequential extraction procedure was used to extract Cu in exchangeable, reducible, oxidizable and residual fractions in sediments. The results showed that the residual fraction of Cu was a major contributor in Tangipahoa River and I-10 Bridge sediments, while the residual and oxidizable fractions in the case of oil refinery sediments. Cu partitioning in Lake Pontchartrain basin water showed the decreasing trend of inert > labile > organic in both spring and summer. The release of Cu from the sediments into the water column was greater in summer as compared to spring and vice versa. Lower temperature helps in the adsorption of Cu on the surface of sediments in early spring due to low disturbance and temperature.
•The Cu content in water and sediment in Lake Pontchartrainbas in were investigated.•Cu partitioning in water decreased as inert > labile > organic indifferent seasons.•Sediment acted as a source and sink of Cu influenced by season and temperature.
As one of the major constituents of acid volatile sulfide (AVS) in anoxic sediments, mackinawite (FeS) is known for its ability to scavenge trace metals. The interaction between aqueous Hg(II) (added ...as HgCl
2) and synthetic FeS was studied via batch sorption experiments conducted under anaerobic conditions. Due to the release of H
+ during formation of hydrolyzed Hg(II) species which is more reactive than Hg
2+ in surface adsorption, the equilibrium pH decreased with the increase in Hg(II)/FeS molar ratio. Counteracting the loss of FeS solids at lower pH, the maximum capacity for FeS to remove aqueous Hg(II) was approximately 0.75
mol Hg(II) (mol
FeS)
−1. The comparison of X-ray power diffraction (XRPD) patterns of synthetic FeS sorbent before and after sorption showed that the major products formed from the interaction between FeS and the aqueous Hg(II) were metacinnabar, cinnabar, and mercury iron sulfides. With the addition of FeS at 0.4
g
L
−1 to a 1
mM Hg(II) solution with an initial pH of 5.6, Fe
2+ release was approximately 0.77
mol Fe
2+ per
mol
Hg(II) removed, suggesting that 77% of Hg(II) was removed via precipitation reaction under these conditions, with 23% of Hg(II) removed by adsorption. Aeration does not cause significant release of Hg(II) into the water phase.
Marsh soil accretion processes were examined at 12 locations in fresh and brackish marshes in Louisiana's northern Barataria Basin estuary. Soil accretion rate determined from 137Cs ranged from 0.59 ...to 1.03cmyr−1. Soil structure and accretion were controlled primarily by organic matter accumulation rather than mineral sediment deposition with water and entrapped gases occupying the majority of the soil volume ranging from 92 to 95%. Organic matter accumulation ranged from 328 to 580gm−2yr−1 while mineral accumulation ranged from 78 to 380gm−2yr−1 Such organic-based fresh and brackish marsh soil are more fragile than mineral based marsh soils and are subject to impact by salt water intrusion and hurricane storm surge forces. The Davis Pond diversion is a conduit between the Mississippi River and the coastal marshes of Barataria basin currently reintroducing river water into the basin leading to lower basin salinities This hydrologic management measure should benefit and extend the stability of the studied marsh sites encouraging continued vegetation growth and soil organic matter accumulation. Accrual of organic matter is necessary to prevent drowning of the marsh which is subject to both the global eustatic sea level rise (1–2mmyr−1) and significant local subsidence (~10mmyr−1). This high rate of relative sea level rise can lead to open water/ponding and subsequent erosion of the surrounding marsh due to flooding and salinity stress.
•Vertical accretion was related to the amount of soil organic matter accumulation.•Marsh accretion data for maintenance of upper Barataria Basin marshes.•Mississippi River freshwater reintroduction should enhance marsh stability.
The Deepwater Horizon spill oiled coastal wetland ecosystems along the northern Gulf of Mexico. We present data on probable impacts and recovery of these impacted wetlands. Based on numerous ...greenhouse and field studies conducted primarily in coastal Louisiana, we suggest that marsh vegetation will recover naturally without need for intensive remediation. Oiled marshes may reduce the availability of habitat for mobile fish species, resulting in their translocation to unimpacted areas. Impacts on benthic organisms may result in shifts in microbial community structure, but they will probably recover in lightly oil‐impacted areas. The degradation rate or length of time oil remains in impacted wetlands depends on environmental conditions. Oil‐impacted soils already contain adequate indigenous microorganisms capable of degradation under suitable environmental conditions. Nutrient addition, especially N, may increase the rate of oil biodegradation when sediment nutrient levels are low, but O2 availability appears to be the most important variable controlling oil degradation in marsh soils. Oil impacts on sediment O2 demand and restriction in O2 exchange at the sediment–water interface can alter biogeochemical processes and gaseous exchange (CO2 and CH4) with the atmosphere. Even though there were harmful impacts resulting from the Deepwater Horizon oil spill, prior research has demonstrated that Gulf Coast marshes are resilient and can recover. This view is supported by field observations of new shoots appearing in heavily oiled marshes 1 yr following the spill. Even though this review shows that Gulf Coast marshes have a high natural recovery potential, many ecological processes have not been adequately quantified or identified.
The Caernarvon Diversion directs Mississippi River water into coastal marshes in the Breton Sound Estuary. Elevated nitrogen levels in the Mississippi River water result in nutrient loading to these ...coastal marsh systems and consequently to the coastal ocean. The goal of this study is to determine the potential nitrate removal rates for two different substrates. Bayou sediments represent the low flow conditions, when the water is constrained within the canals with high potential for transport to the coastal ocean. The marsh soil represents the high flow diversion events when flood water inundates up into the marshes. We sought to remove the plant effect by using cores containing bayou sediment and marsh soil, removing all roots and flooding with a water column containing 2mg NO3-NL−1. Water column nitrate and ammonium concentration were monitored over 9d. Net nitrate loss in bayou sediments was 9.5±1.5mg Nm−2d−1 while the nitrate loss was significantly less at 7.2±0.9mg Nm−2d−1 in the marsh soil. A comparison of nitrate reduction rates in vegetated and non-vegetated marsh soils indicated that the rate of denitrification increased tenfold in vegetated soils. This increase could be attributed to the “plant effect”. Our results suggest that operating diversions on the high flow end of the spectrum would promote nitrate delivery over the vegetated marsh rather than flowing only through canals. Flooding of the vegetated marsh maximizes the potential for removal of riverine nitrate and limits delivery of nitrate to the coastal ocean, thereby mitigating expressions of eutrophication including algal blooms and hypoxia.
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