Aerobic Layer Research Articles

Benthic Bacterial and Fungal Productivity and Carbon Turnover in a Freshwater Marsh

Heterotrophic bacteria and fungi are widely recognized as crucial mediators of carbon, nutrient, and energy flow in ecosystems, yet information on their total annual production in benthic habitats is lacking. To assess the significance of annual microbial production in a structurally complex system, we measured production rates of bacteria and fungi over an annual cycle in four aerobic habitats of a littoral freshwater marsh. Production rates of fungi in plant litter were substantial (0.2 to 2.4 mg C g(-1) C) but were clearly outweighed by those of bacteria (2.6 to 18.8 mg C g(-1) C) throughout the year. This indicates that bacteria represent the most actively growing microorganisms on marsh plant litter in submerged conditions, a finding that contrasts strikingly with results from both standing dead shoots of marsh plants and submerged plant litter decaying in streams. Concomitant measurements of microbial respiration (1.5 to 15.3 mg C-CO2 g(-1) of plant litter C day(-1)) point to high microbial growth efficiencies on the plant litter, averaging 45.5%. The submerged plant litter layer together with the thin aerobic sediment layer underneath (average depth of 5 mm) contributed the bulk of microbial production per square meter of marsh surface (99%), whereas bacterial production in the marsh water column and epiphytic biofilms was negligible. The magnitude of the combined production in these compartments (approximately 1,490 g C m(-2) year(-1)) highlights the importance of carbon flows through microbial biomass, to the extent that even massive primary productivity of the marsh plants (603 g C m(-2) year(-1)) and subsidiary carbon sources (approximately 330 g C m(-2) year(-1)) were insufficient to meet the microbial carbon demand. These findings suggest that littoral freshwater marshes are genuine hot spots of aerobic microbial carbon transformations, which may act as net organic carbon importers from adjacent systems and, in turn, emit large amounts of CO2 (here, approximately 870 g C m(-2) year(-1)) into the atmosphere.

Sensitivity analysis with a phosphorus diagenesis model (SPIEL)

Sensitivity analysis is an important part of the modelling procedure. In this paper, sensitivity analysis of a phosphorus diagenesis model (SPIEL) was used for determining the most important parameters and forcing functions, as well as the potential influence of technical in-lake measures on phosphorus (P) release from the sediment. The model “Sedimentary Phosphorus In Eutrophic Lakes” (SPIEL) includes sub-modules for calculating the aerobic layer thickness, the iron–sulphur cycle and the free aluminium sorption capacity. The results of a detailed sensitivity analysis for different module combinations were compared. By means of graphical representation of the cause and effect chains, the synergistic and compensatory effects of different processes on P release in Lake Sempach were discussed. The importance of the iron–sulphur cycle and of the aerobic layer thickness for the P release in this lake is demonstrated.

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.

Gas Diffusion Coefficient of Undisturbed Peat Soils

Determination of the gas diffusion coefficient D s of peat soils is essential to understand the mechanisms of soil gas transport in peatlands, which have been one of major potential sources of gaseous carbons. In the present study, we aimed at determining the D s of peat soils for various values of the air-filled porosity a and we tested the validity of the Three-Porosity Model (Moldrup et al. 2004) and the Millington-Quirk model (1961) for predicting the relative gas diffusivity, the ratio of D s to D 0, the gas diffusion coefficient in free air. Undisturbed peat soil cores were sampled from aerobic layers in the Bibai mire, Hokkaido, Japan. The MQ model reproduced the measured D s/D 0 curves better than the TPM. The TPM, a predictive model for undisturbed mineral soils, overestimated the D s/D 0 values for peat soils, implying that in the peat soils the pore pathways were more tortuous than those in the mineral soils. Since the changes in the D s/D 0 ratios with the a values of a well-decomposed black peat soil tended to be more remarkable than those of other high-moor peat soils, the existence of a positive feedback mechanism was assumed, such that peat soil decomposition itself would increase the soil gas diffusivity and promote soil respiration.

Influence of Campsurus notatus bioturbation on oxygen profile and uptake in sediments of an Amazonian lake impacted by bauxite tailings

Oxygen uptake rates and vertical profiles were determined in sediment taken from natural areas and areas impacted by bauxite tailings in Lake Batata, and in the U-shaped burrows constructed by the nymphs of the benthic ephemeropteran Campsurus notatus, under laboratory conditions. Sediment from impacted and natural areas containing different densities of nymphs of C. notatus (0 to 1,200 ind. m -2 ) were incubated in acrylic cores. In sediment from the natural area, O 2 was present only in the upper 3.5 mm. In the impacted area, the aerobic layer was deeper, with O 2 detected down to 6.5 mm depth. O 2 uptake was twice as high in sediment from the natural area (1.11 mmol O 2 m -2 h -1 ) as from the impacted area (0.61 mmol O 2 m -2 h -1 ). In cores containing nymphs of C. notatus, O 2 uptake was significantly higher than in sediments without C. notatus. The increase in the rates of O 2 uptake was positively correlated with the biomass of the nymphs (g DW m -2 ). The presence of C. notatus resulted in alteration of the O 2 profiles in the sediment of both areas, indicating the importance of these larvae in structuring O 2 profiles in the sediments of Lake Batata.

Microbial production of methane in the aerobic water layer of the Black Sea

Microbial production of methane in the aerobic water layer of the Black Sea

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.

The development of experimental procedures for the evaluation of additives to attenuate manure odour, and the impact of these additives on workers, animals and the environment

The objective of this project was to develop a laboratory research protocol to evaluate the effect of additives on manure odour and physico-chemical characteristics, and establish conditions that are representative of those found in farm storage structures (temperature, solids content, pH, ventilation above the manure surface, storage period). The results suggested that system configuration might have an impact on additive effect. An open system should be used when it is recommended that additives be applied in the animal diet or the gutters. Additionally, the surface/depth ratio of the gutter should be respected, since it will impact on the relative importance of the aerobic layer and on ammonia volatilization. On the other hand, a closed system should be used when the additive is applied to the manure storage tank, especially if the tank has a cover. Odour analysis still requires fundamental research to establish reliable procedures and protocols, especially in the area sample collection and dilution levels required to decrease H2S concentration to safe levels for the panellists. Odour analysis should also be conducted in triplicate, because of the possible large experimental error due to dilution, the human factors, and also instrumental error.

SPIEL—a model for phosphorus diagenesis and its application to lake restoration

The internal phosphorus (P) cycle of a lake can delay the effects of external P load reduction. Thus, some in-lake measures are used to speed up the recovery process by influencing the P retention in the sediment. The P retention is determined by the quantity and composition of settling seston and the P diagenesis. Existing diagenetic models do not include all important processes of the P diagenesis, or the control parameters of in-lake measures as input variables. Therefore, a deterministic P diagenetic model (SPIEL) has been developed for lake sediments of eutrophic lakes, to predict the development of the P release after an in-lake measure has been carried out. This tool helps to analyse the complex biological and chemical processes in the sediment, and to determine the appropriate measure for a lake. The model is structured in modules, reflecting the control variables of the measures and their effects on the steering factors of the P diagenesis. The main module calculates the P cycle within the sediment; other sub modules can be added to calculate the aerobic layer thickness, the iron–sulphur cycle, the P sorption capacity of aluminium, the change in porosity, or the P concentration in the overlying water body. Thus, it is possible to create measure-specific models by combining different modules, for example, for oxidation with oxygen or nitrate, precipitation with iron or aluminium, capping, hypolimnetic withdrawal and measure combinations. The model has been calibrated and verified for Lake Sempach, Switzerland. Scenarios have been calculated to show the effects of different in-lake measures on the P retention. The model results indicate that the most suitable measures for Lake Sempach regarding the P retention would be a P precipitation with aluminium or iron. Aluminium has the advantage of a longer lasting effect on the P release than iron.

Simulating biodegradation of toluene in sand column experiments at the macroscopic and pore-level scale for aerobic and denitrifying conditions

Heterotropic bacteria can degrade organic substrates utilizing different terminal electron acceptors. The sequence of electron acceptor utilization depends on the energy yield of the individual reaction pathway, which decreases as the redox potential decreases. Due to these differences in energy yield, and an inhibiting activity of oxygen on some enzymatic processes, the simultaneous utilization of oxygen and nitrate as terminal electron acceptors may not occur for many degradation processes, unless the oxygen concentration falls below a given threshold level (about 0.2 mg/l). Two sand column experiments were conducted, with toluene as the carbon source, and showed an apparent simultaneous utilization of oxygen and nitrate as electron acceptors in regions where the oxygen concentration was significantly higher (⩾1.1 mg/l) than the above mentioned threshold concentration. Results from aerobic and anaerobic plate-count analyses showed growth of both aerobes and denitrifiers in the zone of the column where simultaneous utilization of oxygen and nitrate was observed. From these observations, it was postulated that the porous media contained oxygen-free microlocations where the denitrifiers were able to degrade the toluene. To simulate the observed dynamics, a dual biofilm model was implemented. This model formulation assumes that the biofilm is composed of two distinct layers, where the outer layer is colonized by aerobic bacteria and the inner layer by denitrifying bacteria. The thickness of the aerobic layer is such that oxygen is depleted at the boundary of these two layers, resulting in oxygen-free microlocations that allows denitrification to proceed, even though oxygen is still present in the bulk fluid phase. The model simulations compared well to the experimental profiles. Model analyses indicated that changes in physical, chemical, and hydrologic parameters could change the length and location of the zone where at the macroscopic level, oxygen and nitrate are utilized simultaneously. Comparisons of the proposed model to macroscopic modeling approaches showed that a dual biofilm model is able to describe the simultaneous utilization of oxygen and nitrate more accurately.

Vertical Distribution and Abundance of Gymnamoebae (Rhizopoda) in Bottom Sediments of the Brackish Water Nivå Bay (Baltic Sea, The Sound)

The sandy sediments of Nivå Bay (Baltic Sea, The Sound, Denmark) are often covered with the mats of sulphur bacteria and are temporarily anoxic. The vertical distribution and abundance of naked amoebae species in three sediment cores from this bay were studied. Amoebae were most abundant and diverse in the upper 1 cm of sediment, and their number and diversity decreased with increasing depth into the sediment. Amoebae were recovered from both upper oxygenated and deep anoxic layers of sediments. The species composition and abundance of amoebae was very heterogeneous, even at spatial scales of several centimeters, suggesting the existence of microhabitats selectively occupied by particular species. All species found were recorded from aerobic cultures and some of these amoebae occur in both the aerobic and anaerobic layers of the sediment. Minimal possible number of amoebae in the sediments, estimated for the first time as areal abundance integrated for depth was: core 1 -597 cm(-2); core 2 -1,110 cm(-2); core 3 -1,430 cm(-2). These abundances are probably best regarded as "potential" abundances of amoebae hidden in the sediments, as the question of the ratio between active and resting amoebae remains open.

The Influence of Microphytobenthos on the Northern Adriatic Ecosystem: A Modelling Study

Whilst studies have demonstrated that unicellular phytobenthic organisms can be locally important, little is known of their influence on their ecosystem, especially in terms of modifying benthic trophic dynamics and influencing the coupling between the benthos and pelagos. It may be hypothesized that the controlling influence on microphytobenthos would vary seasonally, with incident light, shading, nutrient depletion and grazing all playing a role. In order to elucidate some of these questions a theoretical model of microphytobenthos has been added to the European Regional Seas Ecosystem Model (ERSEM), coupled to a 1D vertically resolved water column model. Several water columns, extending in depth from 5 to 25m have been simulated along an offshore transect at approximately 44°18′N. The microphytobenthos are predicted to contribute in excess of 50% of primary production in shallow (<5m) depths, with light limitation reducing the potential growing season to zero at around 25m. Light availability is the key factor limiting microphytobenthos, with self-shading dominating this effect in established populations. Grazing is shown to be a significant control on microphytobenthic populations. Nutrient stress is not a major limiting factor of microphytobenthic populations due to the availability of benthic nutrient pools. Although nutrient uptake and cycling via the microphytobenthos is not significant compared with regional inputs, the microphytobenthos significantly impact nutrient regeneration rates, aerobic layer processes and benthic trophic dynamics. Effects on the pelagic ecosystem are minimal.

Seasonal fluctuations in live and dead biomass of Phragmites australis as described by a growth and decomposition model: implications of duration of aerobic conditions for litter mineralization and sedimentation

We developed a model of Phragmites australis growth and decomposition to evaluate the material budget and nutrient cycles of a reed stand in Neusiedlersee, Austria. The model describes the growth of each organ of P. australis, the collapse of standing dead shoots, the decomposition of leaves and stalks, and nutrient uptake and release during these processes. The model was calibrated using growth and decomposition data from the literature, and subsequently applied to predict the effects of P. australis stands on a marsh ecosystem. From the start of its decomposition in water, the litter was assumed to stay in the aerobic water layer for 6, 12 or 24 months before entering the anaerobic sediment layer. Because decomposition increases with increasing oxygen and temperature, the aerobic decomposition rate (before the litter was transferred to the anaerobic substrate) increased markedly, especially from spring to autumn. The model predicted that between 33 (6 months aerated) and 48% (24 months aerated) of the annual aboveground production would decompose within 1 year, while the rest would remain in the anaerobic substrate. Rates of nitrogen and phosphorus release were 1.4 times higher between late spring and the end of summer than during autumn and winter. A higher proportion of phosphorus than nitrogen was expected to remain trapped in the anaerobic layer. The uptake of nitrogen and phosphorus during the growing season exceeded release during decomposition 4–6 and 5–7-fold, respectively. The model is useful for quantifying the nutrient cycles of reed-dominant marshes.

Compartmental model for organic matter digestion in facultative ponds

A model has been developed for the digestion of organic matter in facultative ponds in tropical regions. Complete mixing has been assumed for the aerobic and anaerobic compartments. Settling, aerobic layer oxidation, and anaerobic layer methanogenesis are the main processes for organic matter removal in the water column. Exchange processes between layers are dispersive or soluble exchange, solubilization and transport of organic matter from sediments to water column are also taken into account. Degradation of organic matter in the sediments produces gaseous emissions to the water column. The exchange between bubbles ascending and the water column was measured. The model was calibrated with data obtained from a pilot facultative pond built in Muña Reservoir in Bogotá. The pond was sampled during 4 months to compare data between its water hyacinth covered section and uncovered section. The results clearly show the relative importance of different BOD removal processes in facultative ponds and suggest modifications to further improve performance. The results from the model suggest that internal loadings to facultative ponds due to solubilization and return of organic matter from the sediments to the aerobic layer greatly influence the soluble BOD effluent concentration. Aerobic degradation activity in the facultative pond does not affect significantly the effluent concentration. Anaerobic degradation activity in the facultative pond can more easily achieve increases in the removal efficiencies of BOD.

Oxygen Dynamics in Crude Oil Contaminated Salt Marshes: II. Carbonaceous Sediment Oxygen Demand Model

The role of carbonaceous sediment oxygen demand (CSOD) due to oxidation of sulfides reduced in oxygen dynamics in crude oil contaminated salt marshes was investigated through a mathematical model. An existing CSOD model was calibrated from laboratory data sets through nonlinear regression. The effect of oil and fertilizer on CSOD was quantified by comparing three treatments (i) control (no oil and fertilizer amended) (ii) fertilized, and (iii) oiled and fertilized sediments. CSOD was directly proportional to sulfate reduction. Higher CSODs under oiled/fertilized and fertilized conditions were primarily due to increased sulfate reduction rates under these conditions. Reaction velocity for oxidation of dissolved sulfide in the aerobic layer, κH2S,d1, was significantly greater than that of particulate sulfide oxidation, κH2S,p1. This indicates that dissolved sulfides are dominant over particulate sulfides and directly related to CSOD in salt marshes. The CSOD was linearly dependent on the overlying dissolved oxygen concentration when crude oil and fertilizer were added.

Feedback control of the rate of peat formation.

The role of peatlands in the global carbon cycle is confounded by two inconsistencies. First, peatlands have been a large reservoir for carbon sequestered in the past, but may be either net sources or net sinks at present. Second, long-term rates of peat accumulation (and hence carbon sequestration) are surprisingly steady, despite great variability in the short-term rates of peat formation. Here, we present a feedback mechanism that can explain how fine-scale and short-term variability in peat-forming processes is constrained to give steady rates of peat accumulation over longer time-scales. The feedback mechanism depends on a humpbacked relationship between the rate of peat formation and the thickness of the aerobic surface layer (the acrotelm), such that individual microforms (hummocks, lawns, hollows and pools) expand or contract vertically in response to fluctuations in the position of the water table. Hummocks (but not hollows) 'evolve' to a steady state where changes in acrotelm thickness compensate for climate-mediated variations in surface wetness. With long-term growth of a topographically confined peat deposit, the steady state gradually shifts to a thicker acrotelm (i.e. taller hummocks) and lower rates of peat formation and carbon sequestration.

Degradation of herbicides in two sandy aquifers under different redox conditions

We examined the potential for complete degradation (mineralisation) of the four [ring-U- 14C]herbicides mecoprop, isoproturon, atrazine, and metsulphuron-methyl in two sandy aquifers representing aerobic, denitrifying, sulphate-reducing, and methanogenic conditions. Slurries with sediment and groundwater were set-up aerobically or anaerobically in the presence of the electron-acceptor prevailing at the sampling site, amended with 25 μg l −1 herbicide, and incubated at 10°C. Considerable mineralisation was only observed in sediment from the plough layer incubated aerobically. Here, 30% of 14C-mecoprop was recovered as 14CO 2 after 15 days and 15% of isoproturon was recovered as 14CO 2 after 267 days. Only 7% of mecoprop was recovered as 14CO 2 after 313 days in sediment from the aquifer below sampled at 1.95–3.00 mbs (m below the surface). In denitrifying and methanogenic slurries, 3% of 14C added as mecoprop was recovered as 14CO 2. Isoproturon was not mineralised except in the aerobic plough layer, and atrazine and metsulphuron-methyl were not mineralised under any of the conditions applied.

Characterisation of phosphorus in sediments from waste stabilization ponds

The waste stabilization pond (WSP) systems are useful for the treatment of wastewater. Despite a good knowledge of these systems, the dynamics of phosphorus elimination in these systems are not well known, especially concerning the forms of phosphorus in the sediment. Phosphorus dynamics were studied with data collected from the three stabilization ponds of the Mèze (France) system. A conceptual model based on theoretical considerations was developed, and applied to each pond. The percentage of observed variation described by these models ranged between 46.2% and 74.1%. The results showed that the principal variables affecting orthophosphate in WSP systems were phosphorus input and particulate phosphorus. When the model was applied to high rate algal pond (HRAP) data, the role of photosynthesis on pH increase and P precipitation was clear. Sediments sampled in the three facultative ponds were characterised with a fractionation scheme, currently used for sediments of natural aquatic ecosystems. Inorganic phosphorus accounted for 92-94% of total sediment phosphorus, with 57–59% bound to iron hydroxides and 33–37% bound to calcium. Surprisingly, organic phosphorus represented only between 6 and 8%. Polyphosphate was detected. Phosphorus concentration was greatest in the sediment from the third pond, where an aerobic layer at the sediment surface prevented phosphorus release.

Non-steady variations of SOD and phosphate release rate due to changes in the quality of the overlying water

A dynamic model, which predicts non-steady variations in the sediment oxygen demand (SOD) and phosphate release rate, has been designed. This theoretical model consists of three diffusion equations with biochemical reactions for dissolved oxygen (DO), phosphate and ferrous iron. According to this model, step changes in the DO concentration and flow velocity produce drastic changes in the SOD and phosphate release rate within 10 minutes. The vigorous response of the SOD and phosphate release rate is caused by the difference in the time scale of diffusion in the water boundary layer and that of the biochemical reactions in the sediment. Secondly, a negative phosphate transfer from water to sediment can even occur under aerobic conditions. This is caused by the decrease in phosphate concentration in the aerobic layer due to adsorption.

Transformations of nitrogen-15-labelled urea in a flooded soil as affected by floodwater algae and green manure in a growth chamber

The effects of floodwater algae and green manure on transformations of 15N-urea were studied in columns of a sandy loam soil in a growth chamber. The columns were flooded and either kept in the light, to allow algal growth, or in the dark (control) for 17 days before adding the labelled urea. Changes in urea-, NO3–- and NH4+-N levels and the pH of the floodwater were measured over the subsequent 41-day period, during which the control column remained in the dark and those containing algae were maintained either in the dark to cause the death of the algae or in the light. Volatilized NH3 was monitored, and on termination of the experiment the distribution of 15N between NO3–, NH4+ and organic forms was measured in the soil. Urea hydrolysis was most rapid in the presence of both living algae and green manure, followed by dead algae, and was slowest in the control. The concentration of NH4+-N in the floodwater was, however, reduced in the presence of algae due to assimilation and NH3 volatilization owing to the raised day-time pH in the floodwater. NH3 volatilization for the first 10 days was rather high in the columns kept in the light compared to those in the dark. Total volatilization plus denitrification losses were greatest where dead algae were present, owing to the absence of live algae which assimilated more than half of the applied N. Algal growth in floodwater increased the depth of the aerobic soil layer present at the soil-water interface. Subsequently, under dark conditions, stimulated algal growth reduced the depth of the aerobic layer causing less nitrification, which resulted in lower losses of N due to denitrification, i.e. 17% of the applied urea-N as compared to 39% in the light treatments. Although the presence of green manure caused a marked increase in the rate of hydrolysis, algal assimilation prevented excessive N losses via volatilization, indicating that the retention of higher quantities of NH4+-N may have increased fertilizer-N use efficiency.