Anaerobic Layer Research Articles

Biofilms in pediatric respiratory and related infections

Bacteria can grow as free-floating, planktonic bacteria or complex communities called biofilms. Biofilms promote bacterial growth and diversity and offer bacteria unique environments, including aerobic and anaerobic layers, that facilitate resistance to antimicrobial therapies. Respiratory and related structures provide ideal environments for the development of bacterial biofilms, which predispose patients to recurrent and chronic infections. Biofilms are important for the persistence of chronic rhinosinusitis, pulmonary infections in cystic fibrosis, chronic otitis media, and device-related infections. Antimicrobial therapy that is proven effective against planktonic bacteria is often insufficiently effective against the defenses of biofilms. Furthermore, biofilms modify themselves following exposure to antimicrobial therapy, thus developing increased resistance. Understanding the nature of biofilms in common pediatric infections is essential to comprehending the expected course of bacterial illness and identifying treatments that are most likely to be beneficial against more resistant biofilms.

Vertical distribution and anaerobic biodegradation of polycyclic aromatic hydrocarbons in mangrove sediments in Hong Kong, South China

The vertical distribution of polycyclic aromatic hydrocarbons (PAHs) at different sediment depths, namely 0–2 cm, 2–4 cm, 4–6 cm, 6–10 cm, 10–15 cm and 15–20 cm, in one of the most contaminated mangrove swamps, Ma Wan, Hong Kong was investigated. It was the first time to study the intrinsic potential of deep sediment to biodegrade PAHs under anaerobic conditions and the abundance of electron acceptors in sediment for anaerobic degradation. Results showed that the total PAHs concentrations (summation of 16 US EPA priority PAHs) increased with sediment depth. The lowest concentration (about 1300 ng g − 1 freeze-dried sediment) and the highest value (around 5000 ng g − 1 freeze-dried sediment) were found in the surface layer (0–2 cm) and deeper layer (10–15 cm), respectively. The percentage of high molecular weight (HMW) PAHs (4 to 6 rings) to total PAHs was more than 89% at all sediment depths. The ratio of phenanthrene to anthracene was less than 10 while fluoranthene to pyrene was around 1. Negative redox potentials (Eh) were recorded in all of the sediment samples, ranging from − 170 to − 200 mv, with a sharp decrease at a depth of 6 cm then declined slowly to 20 cm. The results suggested that HMW PAHs originated from diesel-powered fishing vessels and were mainly accumulated in deep anaerobic sediments. Among the electron acceptors commonly used by anaerobic bacteria, sulfate was the most dominant, followed by iron(III), nitrate and manganese(IV) was the least. Their concentrations also decreased with sediment depth. The population size of total anaerobic heterotrophic bacteria increased with sediment depth, reaching the peak number in the middle layer (4–6 cm). In contrast, the aerobic heterotrophic bacterial count decreased with sediment depth. It was the first time to apply a modified electron transport system (ETS) method to evaluate the bacterial activities in the fresh sediment under PAH stress. The vertical drop of the ETS activity suggested that the indigenous bacteria were still active in the anaerobic sediment layer contaminated with PAHs. The biodegradation experiment further proved that the sediment collected at a depth of 10–15 cm harbored anaerobic PAH-degrading bacterial strains (two Sphingomonas, one Microbacterium, one Rhodococcus and two unknown species) with some intrinsic potential to degrade mixed PAHs consisting of fluorene, phenanthrene, fluoranthene and pyrene under low oxygen (2% O 2) and non-oxygen (0% O 2) conditions. This is the first paper to report the anaerobic PAH-degrading bacteria isolated from subsurface mangrove sediment.

Effects of vegetation, limestone and aeration on nitritation, anammox and denitrification in wetland treatment systems

Integration of partial nitrification (nitritation) and anaerobic ammonium oxidation (anammox) in constructed wetlands creates a sustainable design for nitrogen removal. Three wetland treatment systems were operated with synthetic wastewater (60 mg NH 3–N L −1) in a batch mode of fill – 1-week reaction – drain. Each treatment system had a surface flow wetland (unplanted, planted, and planted plus aerated, respectively) with a rooting substrate of sandy loam and limestone pellets, followed by an unplanted subsurface flow wetland. Meanwhile, three surface flow wetlands with a substrate of sandy loam and pavestone were operated in parallel to the former surface flow wetlands. Influent and effluent were monitored weekly for five cycles. Aeration reduced nitrogen removal due to hindered nitrate reduction. Vegetation maintained pH near neutral and moderate dissolved oxygen, significantly improved ammonia removal by anammox, and had higher TN removal due to coexistence of anammox and denitrification in anaerobic biofilm layers. Nitrite production was at a peak at the residence time of 4–5 d. Relative to pavestone, limestone increased the nitrite mass production peak by 97%. The subsurface flow wetlands removed nitrogen via nitritation and anammox, having an anammox activity of up to 2.4 g N m −3 d −1 over a startup operation of two months.

Characteristics of the microbial communities in the integrated vertical-flow constructed wetlands

Microorganisms play an important role in removing pollutants from constructed wetlands. We investigated the microbial characteristics in a novel integrated vertical-flow constructed wetland (IVCW), which has been in operation in Wuhan, China since 1998. We used phospholipid fatty acid (PLFA) and amoA gene to analyze the structure and diversity of the microbial community within the IVCW. PLFA results suggested that the amount of bacterial PLFA was significantly higher than that of fungal PLFA, but the total microbial biomass represented by PLFA index was low in the system. Microbial spatial distribution showed significantly higher bacterial (both G+ and G-) and fungal biomass in the surface than in the subsurface layers. The ratios of monounsaturated to branched PLFA demonstrated that an anaerobic layer sandwiched by two aerobic layers existed in the IVCW, consistent with the redox potential results. Analysis of the amoA revealed the presence of Nitrosomonas-like sequences in the surface substrate of the downflow chamber and apparent diversities of ammonia-oxidizing bacteria in the system. These results suggest that microorganisms, despite their relatively low biomass, have inhabited the IVCW, and the results will offer some valuable information on microbe to system designers and managers.

Active Bacterial Populations and Grazing Impact Revealed by an In Situ Experiment in a Shallow Aquifer

To elucidate bacterial population dynamics in an aquifer, we attempted to reveal the impact of protozoan grazing on bacterial productivity and community structure by an in situ incubation experiment using a diffusion chamber. The abundance and vertical distribution of bacteria and protozoa in the aquifer were revealed using wells that were drilled in a sedimentary rock system in Itako, Ibaraki, Japan. The water column in the wells possessed aerobic and anaerobic layers. Active bacterial populations under the grazing pressure of protozoa were revealed through in situ incubation with grazer eliminating experiment by the filtration. On August 19, 2003, the total number of bacteria (TDC) decreased from 1.5 × 106 cells ml− 1 at 2.2 m depth to 3.0 × 105 cells ml− 1 at 10 m depth. The relative contribution of the domain Bacteria to TDC ranged between 63% and 84%. Protozoa existed at a density of 4.2 × 104 to 1.9 × 105 cells ml− 1 in both aerobic and microaerobic conditions. A grazing elimination experiment in situ for 6 days brought about clearly different bacterial community profiles between the 2.2 m and 10 m samples. The bacterial composition of the initial community was predominantly β- and γ -proteobacteria at 2.2 m, while at 10 m β-, α - and γ -proteobacteria represented 56%, 26% and 13% of the community, respectively. The distribution of bacterial abundance, community composition and growth rates in the subsurface were influenced by grazing as well as by geochemical factors (dissolved oxygen and concentrations of organic carbon, methane and sulfate). Results of the in situ incubation experiment suggested that protozoan grazing contributes significantly to bacterial population dynamics.

Distribution and composition of extracellular polymeric substances in membrane-aerated biofilm

Extracellular polymeric substances (EPS) are one of the main components of the biofilm and perform important functions in the biofilm system. In this study, two membrane-aerated biofilms (MABs) were developed for the thin and thick biofilms under different surface loading rates (SLRs). Supplies of oxygen and substrates in the MAB were from two opposite directions. This counter diffusion of nutrients resulted in a different growth environment, in contrast to conventional biofilms receiving both oxygen and substrates from the same side. The compositions, distributions and physicochemical properties (solubility and bindability) of EPS in the MABs of different thicknesses under different SLRs were studied. The effect of dissolved oxygen (DO) concentration within the MAB on EPS properties and distribution was investigated. Experimental results showed the different biofilm thicknesses produced substantially different profiles of EPS composition and distribution. Soluble proteins were more dominant than soluble polysaccharides in the inner aerobic layer of the biofilms; in contrast, bound proteins were greater than bound polysaccharides in the outer anoxic or anaerobic layer of the biofilms. The biofilm-EPS matrix consisted mainly of bound EPS. Bound EPS exhibited a hump-shaped profile with the highest content occurring in an intermediate region in the thin MAB and relatively more uniformly in the one half of the biofilm close to the membrane side and then declined towards the biofilm-liquid interface in the thick MAB. The profiles of soluble EPS presented a similar declining trend from the membrane towards the outer region in both thin and thick MABs. The study suggested that not only EPS composition but also EPS distribution and properties (solubility and bindability) played a crucial role in controlling the cohesiveness and maintaining the structural stability and stratification of the MABs.

Removing the N and P in Dairy Effluent using Multi-Soil-Layer (MSL) Systems

The disposal of untreated dairy wastewater in Hawaii is a current concern because of possible contamination of surface, subsurface, and coastal water as well as increasing treatment costs resulting in the closure of many dairies. The objective of this study was to quantify the effectiveness of Multi-Soil-Layer (MSL) systems in removing nitrogen (N) and phosphorus (P) from the dairy effluent and to explore ways to increase MSL efficiency. Four MSL systems were constructed with replications of two treatments. Treatments were commercial Perlite or the Leilehua soil in the aerobic layer. A mixture of charcoal, sawdust, iron filings, and Honouliuli soil comprised the anaerobic layer in both treatments. Untreated dairy effluent was applied to each system at a flow rate of 505 L m-2 d-1 over a 4-month period. During the study, the removal of phosphate ranged 94% to 97% by the Leilehua MSL system in contrast to 47% to 97% by the Perlite MSL system. Effluent nitrogen (N) consisted of 98% ammonium and about 1% nitrate. Total inorganic N removal ranged 51% to 93% for the Leilehua and 46% to 96% for the Perlite MSL system. The results indicate that MSL systems can be effective in removing inorganic N and phosphate from dairy effluent. The MSL systems can be economical because of the nominal cost of the material used and the small amount of space needed.

Improving multi-soil-layer (MSL) system remediation of dairy effluent

Dairy effluent disposal is a serious problem in the Hawaiian Islands. Dairies often establish multiple settling lagoons to accumulate and store effluent. Occasionally, the overflow of lagoons leads to the transfer of nutrients, such as nitrogen (N) and phosphorus (P), and other contaminants, to hydrologically associated surface, subsurface, and coastal waters. This study was conducted to assess the removal of inorganic N and phosphate in dairy effluent using multi-soil-layer (MSL) systems. Four MSL systems were constructed with two replications of two treatments, which were Perlite and the Leilehua soil. Both materials were used separately for forming an aerobic layer in the MSL systems, whereas an anaerobic layer was formed from a mixture of charcoal, sawdust, iron filings and Honouliuli soil. The results of this study revealed that the removal of inorganic N was similar for the Leilehua and Perlite MSL system, which was 22–93% and 21–96%, respectively. Phosphate removal was higher in the Leilehua MSL system (64–99%) compared to the Perlite MSL system (9–97%). Additional aeration increased the removal of phosphate by the Leilehua MSL system. Sucrose application with a constant rate of aeration increased the removal of inorganic N both in the Leilehua and Perlite MSL systems and increased phosphate removal in the Perlite MSL system. The study demonstrated that MSL systems have the potential to remove high percentages of inorganic N and phosphate in dairy effluent enabling reuse of the water.

Indoor Vapor Intrusion with Oxygen-Limited Biodegradation for a Subsurface Gasoline Source

Development and results are presented for a subsurface soil to indoor air chemical vapor intrusion model that includes oxygen-limited biodegradation. The algebraic model incorporates a steady-state subsurface gasoline vapor source, diffusion-dominated soil vapor transport in a homogeneous subsurface soil layer, and mixing within a building enclosure. The soil is divided into a shallow aerobic layer including biodegradation and a deeper anaerobic layer in which biodegradation is neglected. Biodegradation of multiple chemicals is included, with aerobic first-order reaction kinetics estimated from measured data. Oxygen is supplied at the soil surface below the building foundation. Oxygen demand is attributed to a sum of multiple biodegrading chemicals and to baseline respiration of native soil organic matter. The model is solved by iteratively varying the aerobic depth to match oxygen demand to oxygen supply. Model results are calculated for ranges of source concentrations, unsaturated soil characteristics, and building parameters. Results indicate vapor intrusion of petroleum hydrocarbons can be significantly less than indicated by estimates that neglect biodegradation.

A biofilm model for engineering design

A biofilm model is presented for process engineering purposes--wastewater treatment plant design, upgrade and optimisation. The model belongs in the 1D dynamic layered biofilm model category, with modifications that allow it to be used with one parameter set for a large range of process situations. The biofilm model is integrated with a general activated sludge/anaerobic digestion model combined with a chemical equilibrium, precipitation and pH module. This allows the model to simulate the complex interactions that occur in the aerobic, anoxic and anaerobic layers of the biofilm. The model has been tested and is shown to match a variety of design guidelines, as well as experimental results from batch testing and full-scale plant operation. Both moving bed bioreactors (MBBR) and integrated fixed film activated sludge (IFAS) systems were simulated using the same model and parameter set. A new steady-state solver generates fast solutions and allows interactive design work with the complex model.

Modeling of P-dynamics and algal growth in a stratified reservoir—mechanisms of P-cycle in water and interaction between overlying water and sediment

A water quality model was designed to represent longitudinal and vertical concentration variations in narrow, stratified lakes/reservoirs and was applied to the Shimajigawa reservoir in Japan. In order to predict the concentrations of nutrients, DO, iron, and plankton, three models were combined. They consisted of a runoff model, a lake/reservoir flow-transport model, and an ecological model. It is thought that algal growth in reservoirs is increased by the release of phosphorus from the sediment and that both the formation and dissolution of an iron–phosphate complex are key factors controlling the rate at which phosphorus is released. Thus, to understand the dynamics of phosphorus in the lake/reservoir, the iron cycle and related redox reactions in the water and sediment column were taken into consideration. In addition, the processes of phosphorus adsorption/sedimentation under aerobic conditions and phosphorus desorption/release from the sediment were described by modeling the creation and decomposition of the iron-bound phosphate complex. Following the calibration of its parameters, the model was shown to be able to reproduce the actual oxygen profile, the dynamics of iron and nutrients, and algal growth. In particular, by combining the ecological model with the iron-bound phosphate sub-model, we were able to predict changes in PO 4-P concentrations in the hypolimnion. This shows that the combination of the iron-bound phosphate sub-model with the ecological model is very useful in understanding the dynamics of phosphorus in a lake/reservoir where a seasonal cycle between aerobic and anaerobic conditions occurs. In addition, the relationship between occasional algal blooms and phosphorus dynamics was investigated using the model. Algal densities in the reservoir were found to be strongly related to the amounts of phosphate transported from the lower layer to the epilimnion when turnover occurred, and were affected by the phosphorus dynamics of the lower layer. In turn, the amount of phosphate transported in this way was found to increase in accordance with the amount released from the sediment, which was found to depend on the development of an anaerobic layer.

Modeling nitrogen–carbon cycling and oxygen consumption in bottom sediments

A model framework is presented for simulating nitrogen and carbon cycling at the sediment–water interface, and predicting oxygen consumption by oxidation reactions inside the sediments. Based on conservation of mass and invoking simplifying assumptions, a coupled system of diffusive–reactive partial differential equations is formulated for two-layer conceptual model of aerobic–anaerobic sediments. Oxidation reactions are modeled as first-order rate processes and nitrate is assumed to be consumed entirely in the anoxic portion of the sediments. The sediments are delineated into a thin oxygenated surface layer whose thickness is equal to the oxygen penetration depth, and a lower, but much thicker anoxic layer. The sediments are separated from the overlying water column by a relatively thin boundary layer through which mass transfer is diffusion controlled. Transient solutions are derived using the method of Laplace transform and Green’s function, which relate pore-water concentrations of the constituents to their concentrations in the bulk water and to the flux of decomposable settling organic matter. Steady-state pore-water concentrations are also obtained including expressions for the extent of methane saturation zone and methane gas flux. A relationship relating the sediment oxygen demand (SOD) to bulk water oxygen is derived using the two-film concept, which in combination with the depth-integrated solutions forms the basis for predicting the extent of oxygen penetration in the sediment. Iterative procedure and simplification thereof are proposed to estimate the extent of methane saturation zone and thickness of the aerobic layer as functions of time. Sensitivity of steady-state solutions to key parameters illustrates sediment processes interactions and synergistic effects. Simulations indicate that for a relatively thin diffusive boundary layer, d, oxygen uptake is limited by biochemical processes inside the sediments, whereas for a thick boundary layer oxygen transfer through the diffusive boundary layer is limiting. The results show an almost linear relationship between steady-state sediment oxygen demand and bulk water oxygen. For small d methane and nitrogen fluxes are sediment controlled, whereas for large d they are controlled by diffusional transfer through the boundary layer. It is shown that the two-layer model solution converges to the one-layer model (anaerobic layer) solution as the thickness of the oxygenated layer approaches zero, and that the transient solutions approach asymptotically their corresponding steady-state solutions.

Nitrogen removal in the bioreactor landfill system with intermittent aeration at the top of landfilled waste

High ammonia concentration of recycled landfill leachate makes it very difficult to treat. In this work, a vertical aerobic/anoxic/anaerobic lab-scale bioreactor landfill system, which was constructed by intermittent aeration at the top of landfilled waste, as a bioreactor for in situ nitrogen removal was investigated during waste stabilization. Intermittent aeration at the top of landfilled waste might stimulate the growth of nitrifying bacteria and denitrifying bacteria in the top and middle layers of waste. The nitrifying bacteria population for the landfill bioreactor with intermittent aeration system reached between10 6 and 10 8 cells/dry g waste, although it decreased 2 orders of magnitude on day 30, due to the inhibitory effect of the acid environment and high organic matter in the landfilled waste. The denitrifying bacteria population increased by between 4 and 13 orders of magnitude compared with conventional anaerobic landfilled waste layers. Leachate NO 3 −–N concentration was very low in both two experimental landfill reactors. After 105 days operation, leachate NH 4 +–N and TN concentrations for the landfill reactor with intermittent aeration system dropped to 186 and 289 mg/l, respectively, while they were still kept above 1000 mg/l for the landfill reactor without intermittent aerobic system. In addition, there is an increase in the rate of waste stabilization as well as an increase of 12% in the total waste settlement for the landfill reactor with intermittent aeration system.

Sulfate-Reducing Bacteria in Gypsum Karst Lakes of Northern Lithuania

Microbiological studies were performed in three small gypsum karst lakes in northern Lithuania, most typical of the region. Samples were taken in different seasons of 2001. The conditions for microbial growth in the lakes are determined by elevated content of salts (from 0.5 to 2.0 g/l), dominated by SO(2-)4 and Ca2+ ions (up to 1.4 and 0.6 g/l, respectively). The elevated sulfate concentration is favorable for sulfate-reducing bacteria (SRBs). Summer and winter stratification gives rise to anaerobic water layers enriched in products of anaerobic degradation: H2S and CH4. The lakes under study contain abundant SRBs not only in bottom sediments (from 10(3) to 10(7) cells/dm3) but also in the water column (from 10(2) to 10(6) cells/ml). The characteristic spatial and temporal variations in the rate of sulfate reduction were noted. The highest rates of this process were recorded in summer: 0.95-2.60 mg S(2-)/dm3 per day in bottom sediments and up to 0.49 mg S(2-)/l per day in the water column. The maximum values (up to 11.36 mg S(2-)/dm3) were noted in areas where bottom sediments were enriched in plankton debris. Molecular analysis of conservative sequences of the gene for 16S RNA in sulfate-reducing microorganisms grown on lactate allowed them to be identified as Desulfovibrio desulfuricans.

Formation and structure of granulated microbial aggregates used in aerobic wastewater treatment

Granular microbial aggregates are used in aerobic treatment of wastewater. The granules have diverse microbial community and complex spatial structure. The structural elements are radial sub-aggregates, concentric layers, channels, pores, polysaccharide plugs, and an anaerobic core of lysed cells. Aerobic bacteria, consisting of 69–84% of microbial biomass, were concentrated in a layer to the depth of 550 μm from the surface of the granule. Facultative anaerobic bacteria, consisting of 9–13% of microbial biomass, dominated in a layer at a depth from 550 μm to 850 μm from the surface of the granule. Obligate anaerobic bacteria, consisting of 2% of microbial biomass, dominated in a layer on the depth from 850 μm to 1,000 μm from the surface of the granule. A core of dead and lysed cells was at a depth greater than 1,000 μm from the surface of the granule. The depth of the anaerobic layer correlated with the appearance of polysaccharide plugs in the pores. Enrichment cultures of microorganisms with high cell surface hydrophobicity or self-aggregation ability can be used to facilitate the formation of microbial granules.

Sorption Characteristics of Phosphorus in Peat Soils of a Semiarid Altered Wetland

We studied the adsorption characteristics of P in altered peat soils of the Hula Valley, Israel, which has undergone repeated drying and rewetting cycles. As a result, the water quality of Lake Kinneret, the only freshwater lake in Israel, may have been adversely affected. Peat sample collection was based on pedogenic evaluation of the wetland's history and on the redox potential of aerobic (Eh = 450 mV) and anaerobic (Eh < −220 mV) conditions. Extractable citrate–bicarbonate–dithionite iron (FeCBD) was a dominant mineral phase in the aerobic layers (29 ± 5 g kg−1). Mössbauer spectra suggested that hematite, goethite, ferrihydrite, and magnetite are the main Fe minerals in these peat soils. The sorption maximum (Smax) of the aerobic layers ranged from 670 to 1750 mg P kg−1, with a mean value of 1250 mg P kg−1, whereas the anaerobic layers ranged from 625 to 975 mg P kg−1, with a mean value of 775 mg P kg−1 The equilibrium phosphorus concentration (EPC0) values in the most anaerobic peat layers were several orders of magnitude higher (0.31 mg L−1) than in the aerobic layers (0.01 mg L−1). Only a weak to moderate correlation was found between the sorption attributes and the Fe content due to precipitation of Ca‐P phases. The main source of Ca in these soils is gypsum. Rewetting of the peat soils leads to a decrease in Smax and the buffer capacity, and an increase in EPC0, which could lead to higher P mobility. The increased potential of P mobility declined with a concurrent increase in Ca‐P precipitation due to enhanced dissolution of gypsum.

HELD EXPERIMENTS WITH MESOCOSM ON DIEL VERTICAL MIGRATION OF BLOOM OF GOIVYOSTOMUM SEMEN (RAPHIDOPHYCEAE)

By the field observation on water quality in Kawahara Lake, it was found that phytoplankton biomass, of which dominant species was Gonyostomum semen (G. semen), grew and aggregated densely in the middle layer in summer season. To clarify the influence factors on the diel migration of aggregated layer of G. semen, the field experiments with 3 mesocosms was conducted. A part of the lower water body in a mesocosm was transferred into the other mesocosm to change the condition of stratification for the water quality. In daytime G. semen aggregated at the depth of about 53m and in nighttime about 75m. As the results of the mesocosm experiment, it was found that G. semen moved downward for the nutrient salts at nighttime and stopped the downward migration when reached the anaerobic layer in strong reduction. Also, in daytime, the upward migration of G. semen was influenced by pH and the photon flux density.In addition, it was found that the bloom of G. semen was generated after the heavy rainfall from the frequent field researches, so that the trigger of a rapid proliferation of G. semen was the supply of NO3 with inflowing of river discharge.

Classification of soils supporting mangrove plantation in Kuwait

The State of Kuwait has initiated an ambitious national program to establish greenery in 20000 ha of open spaces in inland and coastal areas. Afforestation of intertidal zones with mangrove plants is being considered as a viable option for greening coastal areas. In view of this fact, experimental plantations were established using two ecotypes of Avicennia marina (Bahrain and UAE) and one ecotype of Avicennia germinans (Florida). The study consisted of two 10-year old plantations and two 2-year old plantations. Seedlings established successfully and grew vigorously on some of the locations within the site. Therefore, studies were conducted during 2002-2003 to describe and classify soils that supported maximum mangrove establishment and growth under the harsh arid coastal conditions of Kuwait. For this purpose, eight soil profiles (four each representing areas where seedlings established successfully and grew vigorously and where all seedlings died in the initial stages of establishment) were investigated and classified according to the soil taxonomy. The main soil types observed in the study site were: Typic Aquisalids, Typic/sodic Aquicambids and Calcic Aquisalids. Mangrove growth performance in relation to the landform, soil type and properties of the soil at various depths is discussed in the paper. The plant growth appeared to be the better on the typic Aquisalid soil than that on the Typic/sodic Aquicambid soils. The relative proportions of the coarse sand fraction, occurrence of the anaerobic layer in the profile and the surface layer salinity influenced both the establishment and growth of mangrove plants.

The Geochemistry of Phosphorus in Peat Soils of a Semiarid Altered Wetland

An understanding of P transformations in altered wetlands has mainly developed from temperate and humid regions with neutral to acidic soils. Little is known regarding downstream water quality impact of P transformations in semiarid wetlands that undergone repeated cycles of drying and rewetting. The P geochemistry was studied using the Hedley fractionation scheme in the altered peat soils of the Hula Valley, Israel. The peat soils were sampled according to the peat depth and redox potential characteristics. The mean total P concentration (Pt) in the surface peat horizons (1190 ± 300 mg kg−1) was significantly higher than in the anaerobic (EH < −220 mV) peat layers (650 ± 260 mg kg−1). The concentrations of P in all fractions except the most labile P were significantly higher in the aerobic (EH = 400 mV) peat layers. The predominant extractable fractions in the surface peat horizons were Ca‐P extracted by 1 M HCl (21–60% of Pt), Iron‐P extracted by 0.5 M NaOH (11–41% of Pt), and residual P extracted by H2SO4 (20–40% of Pt). The source of the Ca in the Ca‐P fraction was mainly from gypsum dissolution following the rewetting cycles. The results clearly showed that the drainage of these wetlands facilitated rapid organic matter (OM) oxidation, release of organically bound metals and P followed by sesquioxides and gypsum precipitation. These geochemical transformations enhanced the Pt concentration per mass of altered peat soil and changed the P distribution among the different pools. Most of the P is currently associated with Fe oxides and hydroxides and/or coprecipitated with Ca.

Mangrove, Avicennia marina, Establishment and Growth under the Arid Climate of Kuwait

The State of Kuwait is making concerted efforts to enhance greenery along its coastline. This study was conducted during 1999–2002 for identifying key soil factors associated with successful establishment and rapid growth in Avicennia marina. Based on the review of available data, repeated visits to potential sites, on-site assessment and laboratory characterization of soils, five sites (Shuwaikh, Sulaibikhat I, Sulaibikhat II, Doha, and Sabiya) were selected for establishing pilot plantations. Acclimatized seedlings were used to establish these plantations. Periodic data indicated wide variations both in seedling survival and growth both among sites and at different locations within each site. The highest seedling survival (71.0 to 81.2%) was observed in the Doha site and ranged from 16.1 to 78.0% in other sites. In general, seedlings planted along the tidal line showed the survivability and produced greater number of branches than those planted farther away from the tidal line. Postplanting on-site and laboratory analyses of soil samples showed that the highest seedling survival was associated with the presence of silty loam or fine-textured sand fractions in the upper 5 cm layer, medium to coarse textured sand material between 5 and 30 cm and an anaerobic silty loam or clayey layer below 30 cm depth. In contrast, greater proportion of gravel or clay fractions in the upper 30 cm layers increased seedling mortality and affected plant growth. Other factors such as low soil moisture, poor drainage conditions, high soil salinity and high sodicity also increased seedling mortality in some areas.