Biodegradability of trimethylbenzene isomers under the strictly anaerobic conditions in groundwater contaminated by gasoline

Trimethylbenzene (TMB), as a constituent of gasoline, is often expected to be used as a conservative tracer in anaerobic BTEX-contaminated groundwater site to correct for attenuation due to dispersion, dilution and sorption along a flow path. To evaluate the suitability of using TMB as a tracer and to better understand biodegradability of TMB in contaminated groundwater by gasoline under anaerobic conditions, laboratory microcosms were conducted with mixed nitrate/iron/sulfate electron-acceptor amendments, using aquifer materials collected from Canadian Forces Base (CFB), Borden, Ontario, Canada. The results showed that under denitrifying conditions, biodegradation of 1,3,5-TMB, 1,2,4-TMB and 1,2,3-TMB were relatively slow and after 204 days of incubation approximately 27, 24, and 16% of the initial concentrations, respectively, were degraded in the microcosms. Under sulfate-reducing conditions, TMB isomers were recalcitrant. In contrast, significant biodegradation of TMB was observed under iron-reducing conditions. 1,3,5-TMB, 1,2,4-TMB and 1,2,3-TMB were degraded to 44, 47, and 24% of initial concentrations with first-order biodegradation rate constants of 0.003, 0.006 and 0.013 d⁻¹, respectively. This study indicates that TMB biodegradation is insignificant under nitrate and sulfate-reducing conditions but significant under iron-reducing conditions. Therefore, the use of TMB as a tracer for interpreting removal of other biodegradable gasoline constituents such as BTEX requires caution, especially in the presence of iron-reducing conditions.     

生物降解原油地球化学研究新进展

生物降解作用是原油的一种重要的蚀变作用,对原油的物性和经济价值有着负面的影响。全球石油大多遭受过生物降解。生物降解作用对常见生物标志物的影响得以较好的描述,综述了近年来高分子量正构烷烃、三环萜烷、25 降藿烷生物降解的新进展。目前对生物降解作用的细节、发生机理尚不十分清楚,讨论了原油喜氧和厌氧降解机制,认为厌氧作用可能起主导作用,降解速率很慢。温度是控制生物降解作用的重要因素,储层温度大于80℃不会发生生物降解作用。生物降解原油多为混源油,介绍了研究生物降解原油的多期成藏方法。沥青质不易生物降解,其热解产物及钌离子催化氧化产物在生物降解原油对比、油源对比中具有重要的作用;最后指出了今后的发展方向。     

Oxidative Ce3+ sequestration by fungal manganese oxides with an associated Mn(II) oxidase activity

Sequestration of Ce³⁺ by biogenic manganese oxides (BMOs) formed by a Mn(II)-oxidizing fungus, Acremonium strictum strain KR21-2, was examined at pH 6.0. In anaerobic Ce³⁺ solution, newly formed BMOs exhibited stoichiometric Ce³⁺ oxidation, where the molar ratio of Ce³⁺ sequestered (Ce_seq) relative to Mn²⁺ released (Mn_rel) was maintained at approximately two throughout the reaction. A similar Ce³⁺ sequestration trend was observed in anaerobic treatment of BMOs in which the associated Mn(II) oxidase was completely inactivated by heating at 85 °C for 1 h or by adding 50 mM NaN₃. Aerobic Ce³⁺ treatment of newly formed BMO (enzymatically active) resulted in excessive Ce³⁺ sequestration over Mn²⁺ release, yielding Ce_seq/Mn_rel > 200, whereas heated or poisoned BMOs released a significant amount of Mn²⁺ with lower Ce³⁺ sequestration efficiency. Consequently, self-regeneration by the Mn(II) oxidase in newly formed BMO effectively suppressed Mn²⁺ release and enhanced oxidative Ce³⁺ sequestration under aerobic conditions. Repeated treatments of heated or poisoned BMOs under aerobic conditions confirmed that oxidative Ce³⁺ sequestration continued even after most Mn oxide was released from the solid phase, indicating auto-catalytic Ce³⁺ oxidation at the solid phase produced through primary Ce³⁺ oxidation by BMO. From X-ray diffraction analysis, the resultant solid phases formed through Ce³⁺ oxidation by BMO under both aerobic and anaerobic conditions consisted of cerianite with crystal sizes of 5.00–7.23 Å. Such nano-sized CeO₂ (CeO_2,BMO) showed faster auto-catalytic Ce³⁺ oxidation than that on well-crystalized cerianite under aerobic conditions, where the normalized pseudo-first order rate constants for auto-catalytic Ce³⁺ oxidation on CeO_2,BMO was two orders of magnitude higher. Consequently, we concluded that Ce³⁺ contact with BMOs sequesters Ce³⁺ through two oxidation paths: primary Ce³⁺ oxidation by BMOs produces nano-sized crystalline cerianite, and subsequent auto-catalytic Ce³⁺ oxidation efficiently occurs using dissolved oxygen as the oxidizing agent. Pretreatment of newly formed BMOs with La³⁺ solution resulted in decreased rate constants for primary Ce³⁺ oxidation by BMO due to site blocking by La³⁺ sorption. The results presented herein increase our understanding of the role of BMO in oxidative Ce³⁺ sequestration process(es) through enzymatic and abiotic paths in natural environments and provide supporting evidence for the potential application of BMOs towards the recovery of Ce³⁺ from contaminated waters.     

Intrinsic bioremediation of MTBE-contaminated groundwater at a petroleum-hydrocarbon spill site

An oil-refining plant site located in southern Taiwan has been identified as a petroleum-hydrocarbon [mainly methyl tert-butyl ether (MTBE) and benzene, toluene, ethylbenzene, and xylenes (BTEX)] spill site. In this study, groundwater samples collected from the site were analyzed to assess the occurrence of intrinsic MTBE biodegradation. Microcosm experiments were conducted to evaluate the feasibility of biodegrading MTBE by indigenous microorganisms under aerobic, cometabolic, iron reducing, and methanogenic conditions. Results from the field investigation and microbial enumeration indicate that the intrinsic biodegradation of MTBE and BTEX is occurring and causing the decrease in MTBE and BTEX concentrations. Microcosm results show that the indigenous microorganisms were able to biodegrade MTBE under aerobic conditions using MTBE as the sole primary substrate. The detected biodegradation byproduct, tri-butyl alcohol (TBA), can also be biodegraded by the indigenous microorganisms. In addition, microcosms with site groundwater as the medium solution show higher MTBE biodegradation rate. This indicates that the site groundwater might contain some trace minerals or organics, which could enhance the MTBE biodegradation. Results show that the addition of BTEX at low levels could also enhance the MTBE removal. No MTBE removal was detected in iron reducing and methanogenic microcosms. This might be due to the effects of low dissolved oxygen (approximately 0.3 mg/L) within the plume. The low iron reducers and methanogens (<1.8×10³ cell/g of soil) observed in the aquifer also indicate that the iron reduction and methanogenesis are not the dominant biodegradation patterns in the contaminant plume. Results from the microcosm study reveal that preliminary laboratory study is required to determine the appropriate substrates and oxidation-reduction conditions to enhance the biodegradation of MTBE. Results suggest that in situ or on-site aerobic bioremediation using indigenous microorganisms would be a feasible technology to clean up this MTBE-contaminated site.     

Laboratory and field studies of the relative mobility of 239,240Pu and 241Am from lake sediments under oxic and anoxic conditions

Laboratory extraction experiments and field observations were employed to determine the relative mobility of ^239,240pu and ²⁴¹Am from lake sediments under aerobic and anaerobic conditions. Laboratory investigations show that under aerobic conditions ²⁴¹Am is more readily extracted from Lake Michigan sediments than is ^239,240Pu. Under anaerobic conditions, the extractability of plutonium and americium does not increase significantly relative to aerobic conditions. Field studies indicate that neither element is recycled from the sediment to the overlying water column during anaerobic conditions attendant with thermal stratification. The adsorption of these elements onto sediments does not appear to be correlated with extractable iron, manganese, and organic compounds such as humic and fulvic acids.     

Assessment of MTBE biodegradation in contaminated groundwater using C and C analysis: Field and laboratory microcosm studies

Radiolabelled assays and compound-specific stable isotope analysis (CSIA) were used to assess methyl tert-butyl ether (MTBE) biodegradation in an unleaded fuel plume in a UK chalk aquifer, both in the field and in laboratory microcosm experiments. The ¹⁴C-MTBE radiorespirometry studies demonstrated widespread potential for aerobic and anaerobic MTBE biodegradation in the aquifer. However, δ¹³C compositions of MTBE in groundwater samples from the plume showed no significant ¹³C enrichment that would indicate MTBE biodegradation at the field scale. Carbon isotope enrichment during MTBE biodegradation was assessed in the microcosms when dissolved O₂ was not limiting, compared with low in situ concentrations (2 mg/L) in the aquifer, and in the absence of O₂. The microcosm experiments showed ubiquitous potential for aerobic MTBE biodegradation in the aquifer within hundreds of days. Aerobic MTBE biodegradation in the microcosms produced an enrichment of 7‰ in the MTBE δ¹³C composition and an isotope enrichment factor (ε) of −1.53‰ when dissolved O₂ was not limiting. However, for the low dissolved O₂ concentration of up to 2 mg/L that characterizes most of the MTBE plume fringe, aerobic MTBE biodegradation produced an enrichment of 0.5-0.7‰, corresponding to an ε value of −0.22‰ to −0.24‰. No anaerobic MTBE biodegradation occurred under these experimental conditions. These results suggest the existence of a complex MTBE-biodegrading community in the aquifer, which may consist of different aerobic species competing for MTBE and dissolved O₂. Under low O₂ conditions, the lower fractionating species have been shown to govern overall MTBE C-isotope fractionation during biodegradation, confirming the results of previous laboratory experiments mixing pure cultures. This implies that significant aerobic MTBE biodegradation could occur under the low dissolved O₂ concentration that typifies the reactive fringe zone of MTBE plumes, without producing detectable changes in the MTBE δ¹³C composition. This observed insensitivity of C isotope enrichment to MTBE biodegradation could lead to significant underestimation of aerobic MTBE biodegradation at field scale, with an unnecessarily pessimistic performance assessment for natural attenuation. Site-specific C isotope enrichment factors are, therefore, required to reliably quantify MTBE biodegradation, which may limit CSIA as a tool for the in situ assessment of MTBE biodegradation in groundwater using only C isotopes.     

含沙水体污染物生物降解反应动力学研究

以含多组分的生活污水为模拟污染物,通过实验方法对含沙水体中污染物生物降解规律进行了研究,得出了污染物生物降解速率常数与含沙量的关系式。研究结果表明:(1)低浓度污染物在含沙水体中的生物降解过程符合一级反应动力学过程;(2)对同一粒径组泥沙而言,含沙量越大,污染物生物降解速度越快。即泥沙的存在促进了污染物的降解;(3)污染物生物降解速率常数随着含沙量的增大而增大,两者存在非线性的函数关系。含沙量增大到一定值时,降解速率常数趋于最大值。     

Isotopic fractionation associated with biosynthesis of fatty acids by a marine bacterium under oxic and anoxic conditions

Shewanella putrefaciens (Strain MR-4), a gram negative facultative marine bacterium, was grown to stationary phase under both aerobic and anaerobic conditions using lactate as the sole carbon source. Aerobically-produced cells were slightly enriched in ¹³C (+1.5‰) relative to the lactate carbon source, whereas those from anaerobic growth were depleted in ¹³C (−2.2‰). The distribution of fatty acids produced under aerobic conditions was similar to that resulting from anaerobic growth, being dominated by C_16:1 ω7 and C_16:0 fatty acids with a lesser amount of the C_18:1 ω7 component. Low concentrations of saturated even numbered normal fatty acids in the C₁₄ to C₁₈ range, and iso-C_15:0 were synthesized under both conditions. Fatty acids from anaerobic cultures (average δ¹³C=−37.8‰) were considerably depleted in ¹³C relative to their aerobically-synthesized counterparts (−28.8‰). The distinct differences in isotopic composition of both whole cells and individual fatty acid components result from differences in assimilation pathways. Under aerobic conditions, the primary route of assimilation involves the pyruvate dehydrogenase enzyme complex which produces acetyl-CoA, the precursor to lipid synthesis. In contrast, under anaerobic conditions formate, and not acetate, is the central intermediate in carbon assimilation with the precursors to fatty acid synthesis being produced via the serine pathway. Anaerobically-produced bacterial fatty acids were depleted by up to 12‰ relative to the carbon source. Therefore, detection of isotopically depleted fatty acids in sediments may be falsely attributed to a terrestrial origin, when in fact they are the result of bacterial resynthesis.     

吲哚类杂环芳香族有机物在好氧和厌氧条件下的微生物降解途径

用红树林的底泥通过富集培养得到在好氧或厌氧条件下能完全矿化吲哚的细菌，并对降解过程及中间代谢产物进行了鉴定。此研究中，吲哚化合物是培养液中的唯一碳和能量来源，而厌氧条件包括有产甲烷和硫酸盐还原。结果表明，不论在哪种条件下，吲哚噪降解过程分二步敖基化反应，分别发生在2和3位上，形成氧化吲哚和靛红。同时，1、2或3位上的甲基替代使1—甲基吲哚，2—甲基吲哚和3—甲基吲哚的降解受到严重抑制。显然，杂环类芳香族化合物的代谢有其共同点，同时不同替代会完全改变有机物的可降解程度。     

Changes in the sorption capacity of Coastal Plain sediments due to redox alteration of mineral surfaces

Chemical characteristics of grain coatings in a Coastal Plain sandy aquifer on the Eastern Shore of Virginia were investigated where sediments have been exposed to distinct groundwater redox conditions. Dissolved O₂ was 5.0 to 10.6 mg L⁻¹ in the regionally extensive aerobic groundwater, whereas in a narrow leachate plume it was only <0.001 to 0.9 mg L⁻¹. The amount of dissolved Fe in the aerobic groundwater was only 0.005 to 0.01 mg L⁻¹, but it was 12 to 47 mg L⁻¹ in the anaerobic zone. The amount of extractable Fe was an order of magnitude higher for the aerobic sediments than for the anaerobic sediments indicating that reductive dissolution removed the oxide coatings. The capacity for anion sorption on the sediment surfaces, as indicated by the sorption of ³⁵SO₄^2-, was an order of magnitude higher in the aerobic vs. anaerobic sediments. The presence of anaerobic groundwater did not significantly alter the amount of extractable Al oxides on the surface of the sediments, and those coatings helped to maintain a high surface area. The removal of the Fe oxides from the grain surfaces under anaerobic conditions was solely responsible for the significant reduction of SO₄ sorption observed. This loss of capacity for anion sorption could lead to more extensive transport of negatively charged constituents such as some contaminant chemicals or bacteria that may be of concern in groundwater.     

Recognising biodegradation in gas/oil accumulations through the δC compositions of gas components

A large suite of natural gases (93) from the North West Shelf and Gippsland and Otway Basins in Australia have been characterised chemically and isotopically resulting in the elucidation of two types of gases. About 26% of these gases have anomalous stable carbon isotope compositions in the C₁–C₄ hydrocarbons and CO₂ components, and are interpreted to have a secondary biogenic history. The characteristics include unusually large isotopic separations between successive n-alkane homologues (up to +29‰ PDB) and isotopically heavy CO₂ (up to +19.5‰ PDB). Irrespective of geographic location, these anomalous gases are from the shallower accumulations (600–1700 m) where temperatures are lower than 75°C. The secondary biogenic gases are readily distinguishable from thermogenic gases (74% of this sample suite), which should assist in the appraisal of hydrocarbons during exploration where hydrocarbon accumulations are under 2000 m. While dissolution effects may have contributed to the high ¹³C enrichment of the CO₂ component in the secondary biogenic gases, the primary signature of this CO₂ is attributed to biochemical fractionation associated with anaerobic degradation and methanogenesis. Correlation between biodegraded oils and biodegraded “dry” gas supports the concept that gas is formed from the bacterial destruction of oil, resulting in “secondary biogenic gas”. Furthermore, the prominence of methanogenic CO₂ in these types of accumulations along with some isotopically-depleted methane provides evidence that the processes of methanogenesis and oil biodegradation are linked. It is further proposed that biodegradation of oil proceeds via a complex anaerobic coupling that is integral to and supports methanogenesis.     

Biodegradation of crude oil and mineral deposition in a shallow Gulf Coast salt dome

Crude oil biodegradation and related mineral deposition are taking place at the present time in the shallow caprock and overlaying Heterostegina limestone of the Damon Mound Salt Dome, Brazoria County, Texas. Scanning electron microscopy shows calcite, pyrite, and some elemental sulfur in intimate association with microbes, biodegraded crude oil, and gypsum. Similar processes, involving aerobic and anaerobic microbial activity, are suggested to explain the massive deposition of secondary minerals which occurred at Damon Mound in the geologic past.     

Laboratory chalcopyrite oxidation by Acidithiobacillus ferrooxidans: Oxygen and sulfur isotope fractionation

Laboratory experiments were conducted to simulate chalcopyrite oxidation under anaerobic and aerobic conditions in the absence or presence of the bacterium Acidithiobacillus ferrooxidans. Experiments were carried out with 3 different oxygen isotope values of water (δ¹⁸O_H2O) so that approach to equilibrium or steady-state isotope fractionation for different starting conditions could be evaluated. The contribution of dissolved O₂ and water-derived oxygen to dissolved sulfate formed by chalcopyrite oxidation was unambiguously resolved during the aerobic experiments. Aerobic oxidation of chalcopyrite showed 93 ± 1% incorporation of water oxygen into the resulting sulfate during the biological experiments. Anaerobic experiments showed similar percentages of water oxygen incorporation into sulfate, but were more variable. The experiments also allowed determination of sulfate–water oxygen isotope fractionation, ε¹⁸O_SO4–H2O, of ~ 3.8‰ for the anaerobic experiments. Aerobic oxidation produced apparent ε_SO4–H2O values (6.4‰) higher than the anaerobic experiments, possibly due to additional incorporation of dissolved O₂ into sulfate. δ³⁴S_SO4 values are ~ 4‰ lower than the parent sulfide mineral during anaerobic oxidation of chalcopyrite, with no significant difference between abiotic and biological processes. For the aerobic experiments, a small depletion in δ³⁴S_SO4 of ~? 1.5 ± 0.2‰ was observed for the biological experiments. Fewer solids precipitated during oxidation under aerobic conditions than under anaerobic conditions, which may account for the observed differences in sulfur isotope fractionation under these contrasting conditions.     

Evidence of microbially mediated arsenic mobilization from sediments of the Aquia aquifer, Maryland, USA

Sediments from the Aquia aquifer in coastal Maryland were collected as part of a larger study of As in the Aquia groundwater flow system where As concentration are reported to reach levels as high as 1072 nmol kg⁻¹, (i.e., ∼80 μg/L). To test whether As release is microbially mediated by reductive dissolution of Fe(III) oxides/oxyhydroxides within the aquifer sediments, the Aquia aquifer sediment samples were employed in a series of microcosm experiments. The microcosm experiments consisted of sterilized serum bottles prepared with aquifer sediments and sterilized (i.e., autoclaved), artificial groundwater using four experimental conditions and one control condition. The four experimental conditions included the following scenarios: (1) aerobic; (2) anaerobic; (3) anaerobic + acetate; and (4) anaerobic + acetate + AQDS (anthraquinone-2,6-disulfonic acid). AQDS acts as an electron shuttle. The control condition contained sterilized aquifer sediments kept under anaerobic conditions with an addition of AQDS. Over the course of the 27 day microcosm experiments, dissolved As in the unamended (aerobic and anaerobic) microcosms remained constant at around ∼28 nmol kg⁻¹ (2 μg/L). With the addition of acetate, the amount of As released to the solution approximately doubled reaching ∼51 nmol kg⁻¹ (3.8 μg/L). For microcosm experiments amended with acetate and AQDS, the dissolved As concentrations exceeded 75 nmol kg⁻¹ (5.6 μg/L). The As concentrations in the acetate and acetate + AQDS amended microcosms are of similar orders of magnitude to As concentrations in groundwaters from the aquifer sediment sampling site (127-170 nmol kg⁻¹). Arsenic concentrations in the sterilized control experiments were generally less than 15 nmol kg⁻¹ (1.1 μg/L), which is interpreted to be the amount of As released from Aquia aquifer sediments owing to abiotic, surface exchange processes. Iron concentrations released to solution in each of the microcosm experiments were higher and more variable than the As concentrations, but generally exhibited similar trends to the As concentrations. Specifically, the acetate and acetate + AQDS amended microcosm typically exhibited the highest Fe concentrations (up to 1725 and 6566 nmol kg⁻¹, respectively). The increase in both As and Fe in the artificial groundwater solutions in these amended microcosm experiments strongly suggests that microbes within the Aquia aquifer sediments mobilize As from the sediment substrate to the groundwaters via Fe(III) reduction.     

Effect of geochemical conditions on fate of organic compounds in groundwater

In situ microcosms were successfully used to study the degradation of a range of organic compounds in two pristine aquifers, one aerobic (Vejen) and one anaerobic (Villa Farm). Degradation and sorption behavior in the laboratory column microcosms packed with Villa Farm sediment was very similar to that in the in situ microcosms. However, when the columns were packed with quartz and equilibrated with aerated Villa Farm groundwater, behavior mirrored that at Vejen, indicating that oxygen rather than sediment or groundwater composition was the critical parameter. The aromatic and polyaromatic compounds (benzene, toluene,o-xylene, naphthalene) degraded under aerobic conditions only. The organochlorine compounds (trichloroethylene, tetrachloroethylene, 1,1,1-trichloroethane, 1,4-dichlorobenzene and 1,2-dichlorobenzene) showed little or no sign of degradation either aerobically or anaerobically. Interpretation of the data was complicated by strong sorption to the Villa Farm sediment but tetrachloromethane, nitrobenzene, ando-nitrophenol appeared to degrade under anaerobic conditions only. Phenol degraded rapidly under both sets of conditions.     

The chemistry of suspended particulate material in a highly contaminated embayment of Port Jackson (Australia) under quiescent,high-wind and heavy-rainfall conditions

This study investigated physico-chemical characteristics of the water column and chemistry of suspended particulate material (SPM) under quiescent, high-wind and high-wind/heavy-rainfall conditions in Homebush Bay, a highly contaminated embayment of Port Jackson (Australia) to distinguish source and possible adverse effects to benthic and pelagic animals. Mean concentrations in surficial sediment were <1, 14, 181, 141, 37, 290 and 685 μg g⁻¹ for Cd, Co, Cr, Cu, Ni, Pb and Zn, respectively. Sediment chemistry indicated these metals had multiple sources, i.e. the estuary, stormwater and industry. Mean total suspended solids (TSS) were 7, 17 and 20 mg L⁻¹ during quiescent, high-rainfall and heavy rainfall/high wind conditions, respectively, whereas SPM Cd, Co, Cr, Cu, Ni, Pb and Zn concentrations varied between 13–25, 166–259, 127–198, 38–82, 236–305 and 605–865 μg g⁻¹, respectively under these conditions. TSS and total water metal concentrations were lowest during quiescent conditions. High TSS and metal loads in surface water characterised high-rainfall events. Wind-induced resuspension contributed the greatest mass of SPM and metals to the water column. Benthic animals may be adversely affected by Pb and Zn in sediment. Total water Cu and Zn concentrations may pose a risk to filter-feeding animals in the water column due to resuspension of contaminated sediment.     

Decolourisations and biodegradations of model azo dye solutions using a sequence batch reactor,followed by ultrafiltration

The main objective of this study was to investigate the efficiency of biological treatment of azo dye-containing wastewater with a sequencing batch reactor system, followed by ultrafiltration. The performance of the system was quantified by measuring the chemical oxygen demand and azo dye concentration. The biodegradation was carried out under combined alternating anaerobic and aerobic conditions with Nylosan Yellow E2RL SGR as a model azo dye contaminant. The bioprocess revealed a maximal reduction in chemical oxygen demand and dye removal efficiency of 91 and 85%, respectively. After ultrafiltration of effluent from the biological treatment, the efficiency increased to 94% for chemical oxygen demand and to 97% for the azo dye decolourisation. Samples of activated sludge from the bioprocess were collected for microbial characterisation. Bacteria and fungi were isolated and identified by 16S rRNA gene and ITS1-5.8S rDNA-ITS2 sequence analysis, respectively. Serratia marcescens and Klebsiella oxytoca were the most common bacteria with the highest number present during the aerobic and anaerobic phases of the bioprocess. In addition, a high number of Elizabethkingia miricola, Morganella morganii, Comamonas testosteroni, Trichosporon sp. and Galactomyces sp. were detected. Taken together, our results demonstrated that the sequencing batch reactor system combined with ultrafiltration is an efficient technique for treatment of wastewater containing azo dye. Moreover, the ultrafiltration effectively removes the microbiota from the final effluent resulting in stable product water.     

Suspended particulate matter and dynamics of the Mfolozi estuary,Kwazulu-Natal: Implications for environmental management

 The Mfolozi Estuary on the KwaZulu-Natal coast of South Africa is the most turbid estuary in Natal due to poor catchment management, leading to large quantities of suspended particulate matter (SPM) entering the estuary from the Mfolozi River. This paper quantities some of the solute and sediment dynamics in the Mfolozi Estuary where the main documented environmental concern is the periodic input of SPM from the Mfolozi Estuary to the St. Lucia system, causing reduction of light penetration and endangering biological productivity in this important nature reserve. Synoptic water level results have allowed reach mean bed shear stresses and velocities to be calculated for an observed neap tidal cycle. Results indicate that ebb velocities dominate the sediment transport processes in the estuary when fluvial input in the Mfolozi River is of the order of 15–20 m³ s^–1. Observed and predicted flood tide velocities are too low (<0.35 m s^–1) to suspend and transport significant amounts of SPM. Observed results indicate that although the SPM load entering the estuary is dominantly from the Mfolozi River, the Msunduzi River flow plays a major role in the composition of the estuary's salinity and velocity fields. It is calculated that the Mfolozi Estuary would fill with sediment in 1.3 years if it was cut off from the sea. The major fluvial flood events help maintain the estuary by periodically pushing sediment seawards (spit progrades seawards 5 m yr^–1) and scouring and maintaining the main flow channel in the estuary. During low fluvial flow conditions, tidal flow velocities will become the dominant control on sediment transport in the estuary. Interchange of SPM between the St. Lucia and Mfolozi estuaries under present conditions is complicated by the strong transverse velocity shear between the two systems at their combined mouth. This is creating a salinity-maintained axial convergence front that suppresses mixing of solutes and SPM between the systems for up to 10 h of the tidal cycle during observed conditions. Received: 22 May 1995 · Accepted: 31 July 1995     

The effect of organic matter and oxygen on the degradation of bacterial membrane lipids in marine sediments

The biodegradation of purified radiolabelled membrane lipids from a methanogenic bacterium and a pseudomonad were investigated in mangrove, beach and high marsh marine sediments under aerobic and anaerobic conditions. The effect of organic matter on the amount and rate of degradation was also examined by supplementing beach sediments with humic acids. In aerobic sediments, CO₂ was the major product of lipid degradation while under anaerobic conditions both CO₂ and CH₄ were major end products and the overall rates were reduced (up to 40%) relative to aerobic conditions. Total bacterial numbers increased during all incubations with the largest increases occurring in anaerobic sediments supplemented with humic acids. No lipid degradation occurred in aerobic or anaerobic sediments treated with formaldehyde or autoclaving. In low organic beach sediments, the ester-linked phospholipid of the pseudomonad was degraded much more rapidly than the diphytanyl glycerol diether of the methanogen with 69% of the phospholipid degraded in 96 hours versus only 4% of the methanogen lipid. Lipid degradation in both aerobic and anaerobic sediments was highly correlated to organic matter content with increasing amounts of organic matter inhibiting degradation. Long incubations (75 days) of the diphytanyl glycerol ether resulted in 51% degraded to CO₂ in low (0.5%) organic mangrove sediments while only 9% was mineralized in high (10.8%) organic marsh sediments. Physicochemical sorption of membrane lipids to the organic matrix is proposed as a mechanism which protects membrane lipids from microbial attack and degradation.     

Concentrations, potential sources and behavior of organochlorines and phenolic endocrine-disrupting chemicals in surficial sediment of the Shaying River, eastern China

Levels and distributions of organochlorine pesticides (OCPs) and phenolic endocrine-disrupting chemicals (EDCs) in surficial sediments of the Shaying River, the largest tributary of the Huaihe River in eastern China, were investigated to understand their relationship with the hydrodynamics. Concentrations of total hexachlorocyclohexane isomers (ΣHCHs) and dichlorodiphenyltrichloroethanes (ΣDDT) were in the range of 26.7–119 and 9.64–214 ng g^?1 with mean values of 104 and 80.7 ng g^?1, respectively. Residues of HCHs in sediments can be considered as originating from the application of both technical mixtures and lindane in the past. According to the spatial distribution of (DDD + DDE)/ΣDDT ratios, the influence of recent DDT inputs was dominant upstream, whereas DDD prevailed downstream, due to anaerobic degradation. Concentrations of total phenolic EDCs (ΣEDCs) including nonylphenol (NP), octylphenol (OP) and bisphenol A (BPA) ranged widely from 425 to 3,953 ng g^?1 with the highest level occurring in the middle reach. This accumulation could be attributed to the retransfer of surficial sediment from upstream, where the main sources are located. Spatial distribution of contaminants indicated that riverine hydrodynamics can significantly affect their behavior and fate in sediment. This evidence was further verified by multivariate statistical techniques such as Cluster Analysis (CA), Principle Component Analysis (PCA) and Discriminant Analysis (DA). The CA identified three distinct clusters reflecting the large complexity of river system like geography setting, hydrodynamic condition, etc. This finding was also confirmed by the DA. Furthermore, a PCA demonstrated that about 80.8 % of total spatial variance can be explained by the first three factors, which also indicated that contaminant spatial distributions are driven by local inputs, biodegradation and riverine hydrodynamics.