Vertical distribution of organic constituents in an Antarctic lake: Lake Vanda

Vertical distribution of organic constituents, i.e. total organic carbon (TOC), extractable organic carbon with ethyl acetate (EOC), hydrocarbons, phytol, sterols, fatty acids and phenolic acids in Lake Vanda was studied to elucidate their features in relation to the stratification of lake water and the distribution of lake organisms. The concentrations of TOC, EOC and sterols increased with depth and attained the maximum values of 25 and 1.5 mgC l^–1 and 1.4 g l^–1 in the bottom, respectively, while those of fatty acids showed the maximum value of 61 g l^–1 at a depth of 55.4 m, along with the highest value of the ratio of unsaturated (UC₁₆, uC₁₈) to saturated (C₁₆, C₁₈) acids (8.5) and with the highest carbon preference index (35). Hydrocarbons were only found in the bottom layers (60.4 and 65.9 m) and bottom sediment. These results suggest strongly that the vertical distribution of lake organisms and their activity are quite different due to depth. In the bottom warm anoxic layers the degradation of organic materials must have occurred significantly and thus refractory organic materials should be concentrated.     

Biogeochemical study of organic substances in Antarctic lakes

The features of organic constituents in Antarctic lakes and ponds of the McMurdo, Syowa and Vestfold oases are summarised from a biogeochemical viewpoint. Total organic carbon or dissolved organic carbon contents in saline lakewaters are generally extremely high and much higher than those in freshwater lakes. The concentrations and/or compositions of hydrocarbons, fatty acids, sterols, phenolic acids and hydroxy acids in lake and pond waters and sediments vary markedly, probably reflecting differences in biological activity and source organisms. Long-chain alkenes, such as n-C_29:2 (carbon chain length: numbers of unsaturated bonds) are found as the major hydrocarbons in some anoxic lake sediments. Unusually, long-chain n-alkanoic acids are abundant in some Antarctic lake sediments and 24-ethylcholest-5-en-3-ol is the most prominent sterol in most of the lakes studied. It is suggested that some bacteria, and cyanobacteria and algae are important sources of long-chain n-alkanoic acids and 24-ethylcholest-5-en-3-ol, respectively, as previously reported from environments of the mid and lower latitudes. The dominance of p-hydroxybenzoic acid among the phenolic acids found together with the absence of syringic, p-coumaric and ferulic acids in the Antarctic lakes reflects the absence of vascular plants in the areas studied.In three Antarctic saline lakes (Vanda, Fryxell and Ace) the kinds and amounts of organic constituents differ with depth due to the zonation of microorganisms. The maximum fatty acid contents are found at depths just above the anoxic layer, corresponding to the photosynthetic maxima in the lakes, and the depths of maximum phytoplankton populations. In the bottom sediments of the lakes, the composition of organic substances is significantly different from that in the water columns, indicating that the sinking organic substances are degraded rapidly by microorganisms on the lake bottom.     

The physical, chemical and biological characteristics of the holomictic sulphated Lake Arcas-2 (Cuenca, Spain)

The main limnological features of Lake Arcas-2 were followed through two consecutive stratification periods. Its morphometrical characteristics, such as the high relative depth (31%) and steep basin walls, enhance the sharp water stratification with the formation of an oxic-anoxic boundary at 8.8–9 m and a sulphide-rich hypolimnion during the thermal stagnation. The ionic sequence was SO ₄ ^2- >Alkal.>Cl^- and Ca²⁺>Mg²⁺>Na⁺>K⁺ and the mineralization was high, with water conductivity higher than 2500 S cm^-1. It is mesotrophic with epilimnetic chlorophyll a concentrations of 2–5 g l^-1 and metalimnetic of 8 g l^-1. The depth of the euphotic zone was established at around 8 m. Phosphorus concentration in the oxic waters was low but largely accumulated in the anoxic hypolimnion, together with other compounds such as ammonium, silicate, sulphide, etc. Nitrate was abundant in the oxic waters and is related to the use of fertilizers in the surrounding fields. A fine-layer sampler was used to study the oxic–anoxic interface where a dense plate of Chromatiaceae developed. The dominant species, Chromatium weissei, reached a maximum integrated biomass of 121 gWW m^-2 during August. Thiocapsa sp., representing less than 1% of total purple bacteria, had an integrated biomass of 0.8 gWW m^-2 and Amoebobacter sp. (1%) had 1 gWW m^-2. Other populations were sharply stratified i.e. Oscillatoria cf. ornata and Cryptomonas erosa. Those organisms, and mainly the cyanobacterium, accounted for the high chlorophyll a concentrations (>100 g l^-1) recorded in the anoxic waters of the hypolimnion. Green bacteria were scarcely developed due to the shadowing effect caused mainly by the purple bacterial bloom.     

TOC fluctuations in a humic lake as related to catchment acidification, season and climate

Studies of fluctuations in total organic carbon (TOC) were performedin both the reference basin and the acidified basin of experimental LakeSkjervatjern, in order to separate effects of various catchment and in-lakeprocesses. Nearly five years of catchment acidification did not inducesignificant changes in TOC. TOC concentrations was not related clearly toprecipitation or runoff. In both basins, there was a regular, seasonal patternwith a gradual increase in TOC concentrations from spring to late autumn.Minima in concentrations occurred during periods with frozen ground inwinter, irrespective of discharge patterns. The decrease from 10 mg C l^-1 in autumn to 1--2 mg C l^-1 in latewinter, was only seen in surface layers. Runoff was the major loss routefor surface TOC in the lake. Photo-oxidation, bacterial oxidation, andsedimentation combined yielded maximum loss rates of 3%of surface TOC d^-1. Below a depth of 1 m 0.5%d^-1 was lost to these same processes. The surface microlayerhad 5--10 times more TOC than the bulk water on average, and could haveeffects on gas exchange and sub-surface light. Despite the oxidation ofTOC, the short residence time of the lake and rapid replacement of TOCfrom the catchment was the major determinant of lake water TOC.     

Effects of elevated CO2 and increased nitrogen deposition on photosynthesis and growth of understory plants in spruce model ecosystems

We studied the effects of atmospheric CO₂ enrichment (280, 420 and 560 l CO₂ l^–1) and increased N deposition (0,30 and 90 kg ha^–1 year^–1) on the spruce-forest understory species Oxalis acetosella, Homogyne alpina and Rubus hirtus. Clones of these species formed the ground cover in nine 0.7 m² model ecosystems with 5-year-old Picea abies trees (leaf area index of approx 2.2). Communities grew on natural forest soil in a simulated montane climate. Independently of N deposition, the rate of light-saturated net photosynthesis of leaves grown and measured at 420 l CO₂ l^–1 was higher in Oxalis and in Homogyne, but was not significantly different in Rubus compared to leaves grown and measured at the pre-industrial CO₂ concentration of 280 l l^–1. Remarkably, further CO₂ enrichment to 560 l l^–1 caused no additional increase of CO₂ uptake. With increasing CO₂ supply concentrations of non-structural carbohydrates in leaves increased and N concentrations decreased in all species, whereas N deposition had no significant effect on these traits. Above-ground biomass and leaf area production were not significantly affected by elevated CO₂ in the more vigorously growing species O. acetosella and R. hirtus, but the slow growing H. alpina produced almost twice as much biomass and 50% more leaf area per plant under 420 l CO₂ l^–1 compared to 280 l l^–1 (again no further stimulation at 560 l l^–1). In contrast, increased N addition stimulated growth in Oxalis and Rubus but had no effect on Homogyne. In Oxalis (only) biomass per plant was positively correlated with microhabitat quantum flux density at low CO₂, but not at high CO₂ indicating carbon saturation. On the other hand, the less shade-tolerant Homogyne profited from CO₂ enrichment at all understory light levels facilitating its spread into more shady micro-habitats under elevated CO₂. These species-specific responses to CO₂ and N deposition will affect community structure. The non-linear responses to elevated CO₂ of several of the traits studied here suggest that the largest responses to rising atmospheric CO₂ are under way now or have already occurred and possible future responses to further increases in CO₂ concentration are likely to be much smaller in these understory species.     

Lipid composition of water and surface sediments in Takapoto atoll lagoon (French Polynesia)

Dissolved, particulate and sedimentary lipid compounds were analyzed in samples collected in May 1988 at three sites in the lagoon of the closed atoll of Takapoto (Tuamotu archipelago, French Polynesia). The study provides background information dealing with water quality and the nature and concentration of lipids. Non-aromatic hydrocarbons and fatty acids were isolated from lipids and analyzed by gas chromatography/mass spectrometry. Non-aromatic hydrocarbon concentrations did not exceed 1000 ng l^-1 in water, and 2300 ng g^-1 in surface sediments and are among the lowest encountered in pristine marine environments. No noticeable petroleum pollution was evidenced in the lagoon. Nevertheless, traces of petroleum-derived compounds were detected at the central site for both surface and deep water. Total fatty acid concentrations varied in the range 6.3–14.4 g l^-1 for the particulate phase and in the range 0.5–3.2 g l^-1 for the dissolved phase. The molecular fingerprints of fatty acids and hydrocarbons evidenced a predominant algal, and to a lesser extent microbial, origin of the organic matter present in water and sediments. Mono- and polyunsaturated fatty acids, which are essential components for animal metabolism, were identified in noticeable amounts in suspended matter (1.8–4.6 g l^-1), and at highly variable levels in the dissolved phase (0.08–1.21 g l^-1).     

Selective feeding by the aquatic oligochaete Tubifex tubifex (Tubificidae,Clitellata)

The particle size distribution of faecal pellets produced by the tubificid worm Tubifex tubifex in laboratory culture, was measured with a Coulter® Multisizer. The faecal material from worms cultured in a range of sediments was composed of particles with a mean diameter of less than 63 m, and only a few isolated larger particles were found by microscopic analysis. This suggests that this species actively selects the silt-clay fraction, avoiding larger sand particles. A more detailed analysis of faeces revealed that about 75%, by volume, was composed of particles with a mean diameter < 25m, and the mode was < 10m. T. tubifex fed selectively on the organic rich particles of the sediment, and this feeding was independent of particle size. Measurement of the organic content of faeces (measured as % loss on ignition) showed that they had a consistently higher organic content than the sediment, considered as whole sediments or the <63 m sieved fraction. On the basis of these results, we hypothesise that this species exhibits two levels of selectivity in its feeding behaviour. Thus selection is primarily based on particle size, avoiding the ingestion of sand particles and also, on the preferential selection of particles associated with organic material, within the fine (silt-clay) fraction of the sediment.     

Relation between phosphate and organic matter in fish-pond sediments of the Deroua fish farm (Béni-Mellal, Morocco): implications for pond management

An experimental approach of the phosphate exchange across the water–sediment interface in fish ponds of the Deroua farm (Béni-Mellal, Morocco) is needed to understand the phosphate dynamics in these ponds in relation to their water quality. During this study, we conducted experiments to determine the P-fractions of the different pond sediments and to estimate the release from these sediments of phosphate available for algal uptake. We also determined the amount of phosphate needed to saturate the sediments of two different fish ponds under anoxic and oxic conditions. Phosphate release from sediments comes mainly from Fe(OOH)P and is more important in ponds lined with sheets. The accumulation of organic matter in sediments favours the installation of anoxic conditions and enhances the phosphate release from CaCO₃P, labile in these pond sediments. Under experimental conditions, org-P plays a minor role in the P-release. Oxic conditions, to the contrary, have an inhibitory effect on the P-release from sediments. About 80–98% of the P-adsorbed onto different pond sediments was recovered in the inorg-P-fractions. Aeration induces the oxidation of FeS to Fe(OOH) which can adsorb phosphate from solution. Besides, the presence of bacteria in pond sediments was essential to promote phosphate release under anoxic conditions by controlling the oxidation state of iron and the mineralization of the organic matter. Sheet-lined ponds, when insufficiently dried, accumulate a large quantity of organic matter in their sediments. After a decrease in pH, P is released from CaCO₃P and enhances the phytoplankton productivity responsible for renewed accumulation of organic matter. Org-C concentrations in sediments over 20 mg g^–1 d.w. favour the formation of toxic factors (Fe²⁺, Mn²⁺, NO₂ ^– and H₂S) harmful for carp growth. An extended period of drying efficiently enhances the mineralization of organic matter.     

Dynamics of seston constituants in the Ariège and Garonne rivers (France)

Water contents of suspended matter, algal pigments, particulate organic carbon and particulate phosphorus were measured in the rivers Garonne (2 sites) and Ariège (1 site) throughout an annual cycle. The general trend of the parameters was similar at the three sites. Depending on the sites, the period of algal growth (chlorophyll a + phaeopigments > 25 µg l^–1), lasted from two to six weeks in August–September. The algal peaks reached 50 to 90 µg 1^–1 of total pigments. High contents of particulate organic carbon (> 2 mg 1^–1) occurred at the end of summer (coinciding with algal growth), and during the November and May floods. In summer 50–75 % of the suspended matter was organic, in spring this was 10 times less. The high linear correlation between particulate organic carbon and pigment contents (r = 0.87; P = 0.0001) suggested an algal origin of at least part of the particulate carbon. Algal carbon was minor in the annual fluxes of particulate carbon (25 to 39% depending on the sites), but relatively high in comparison with other rivers. The mean particulate phosphorus content calculated over the year was 24 µg l^–1 ; it varied from 15 µg l^–1 during the high water period to 28 µg 1^–1 during the low water period. Likewise the percentage of particulate phosphorus in the suspended matter varied from 0.17 to 0.40. A negative linear correlation existed between particulate phosphorus content and specific discharge (r = – 0.46; P = 0.0001).The very marked seasonal trend of the parameters and the interactions led us to differentiate two modes of the rivers' functioning: a hydrologic phase and a biological phase. The hydrologic phase (high water) was dominated by the processes of erosion and transfer over the whole catchment area and the flood plain, while the biological phase was characterized by a high primary production in the river bed.     

The manganese cycle in Lac Léman,Switzerland: the role ofMetallogenium

The manganese pathways in Lac Léman have been investigated on the basis of chemical analyses undertaken on water, suspended solids, bottom sediments and interstitial water samples. The various modes of occurrence of Mn have been determined by means of visual examination using SEM and TEM (scanning and transmission electron microscopy), by microanalysis (EDAX) of various sediment fractions, by chemical analysis of the dissolved phase, and by chemical speciation and XRD of bottom sediments. Fluxes to and from the sediment have also been computed. The time-depth variations of Mn in the water column are characterized by (a) a very steep gradient of Mn sol. from the sediment interstitial water (15 mg l⁻¹) to the overlying water, 2 m above the bottom(500 μg l⁻¹), (b) an accumulation of Mn part. between 280 m and the interface at 310 m, consisting of mineralized colonies ofMetallogenium. The abundance ofMetallogenium colonies is inversely related to O₂ concentration; the optimal value for the bacterium Mn fixation is around 1 mg l⁻¹. Because of the quasi-anoxic state of the bottom sediments and overlying water, Mn diffuses from a ‘source layer’, 2–5 cm below the interface (a) upwards across the interface, before being taken up byMetallogenium, and (b) downwards to a ‘sink layer’, in which large amounts of Mn-carbonate precipitate. Particulate Mn sedimentation rates measured in traps show that downwards Mn flux due toMetallogenium settling approximately balances the upwards soluble flux due to diffusion. Quantitatively, the process of Mn cycling in Lac Léman is, therefore, limited to the lowermost part of the hypolimnion. Although Zn and Cd seem to follow the same cycle as Mn, Fe behaves in a different manner; it was not taken up byMetallogenium at the time of our study.     

Microbial sulfate reduction in a brackish meromictic steppe lake

Patterns of sulfate reduction were studied in water and sediments of Lake Shira, South Siberia, Russia. The lake was characterized by a high level of sulfate (91-116 mM). The concentration of hydrogen sulfide in the anoxic waters of the lake reached 0.6 mM. In summer the sulfate reduction rate in the water column, measured by radiometric technique, varied from 0.25 to 9.81 mol sulfate l^-1 d^-1. There were two peaks of sulfate reduction activity: just below the chemocline and near the sediment surface. Sulfate reduction rate in the profundal silts ranged from 4.1 to 90.6 mol l^-1 d^-1. The zone of the most active sulfate reduction was restricted to the surface sediment layers. The acceleration of sulfate reduction rate (up to 236 mol l^-1 d^-1) and the increase of density of viable sulfate reducers (up to 2 x 10⁵ cells ml^-1) were recorded in the littoral sediments adjacent to the mouth of the Son River and sewage discharge. It was apparently caused by the input of allochthonous organic substrates and also by a high environmental temperature. On an areal basis, sulfate reduction rate in the water was approximately 8 times higher than that in the profundal sediments. Sulfate reduction was the most important process of anaerobic oxidation of organic carbon in Lake Shira. In summer in the profundal zone of the lake, sulfate reducers were able to mineralize about 67% of the daily integrated primary production of phototrophic and chemotrophic organisms.     

High density culture of the freshwater rotifer,Brachionus calyciflorus

The freshwater rotifer, Brachionus calyciflorus is one of the live food organisms used for the mass production of larval fish. In this study possibility of obtaining high density cultures of the freshwater rotifer B. calyciflorus were investigated. The two culture systems used differed in their air and dissolved oxygen supplies using three temperatures in each case: 24, 28 and 32 °C. Rotifers were batch-cultured using 5 l-vessels and fed with the freshwater Chlorella. The growth rate of rotifers significantly increased with an increase in temperature. The maximum density of the rotifers with air-supply at 24 °C, 6500 ind. ml^–1, was significantly lower than those cultured at 28 and 32 °C, i.e. 8600 and 8100 ind. ml^–1, respectively. Dissolved oxygen levels decreased with time and ranged from 0.8 to 1.4 mg l^–1 when the density of freshwater rotifer was the highest at each temperature. The highest density (19200 ind. ml^–1) of freshwater rotifer was obtained in cultures with a supply of oxygen at 28 °C. Densities of 13500 and 17200 ind. ml^–1 were found at 24 and 32 °C, respectively. Levels of NH₃-N increased with time and a dramatic increase of NH₃-N was observed at high temperatures. Levels of NH₃-N at 24, 28 and 32 °C were 13.2, 18.5 and 24.5 mg l^–1, respectively. These levels coincided with the highest rotifer density at each of the three temperatures. When rotifers were cultured with an oxygen-supply and pH was adjusted to 7, the maximum density of rotifer reached 33500 ind. ml^–1 at 32 °C . These results suggested that high density culture of freshwater rotifer, B. calyciflorus could be achieved under optimal conditions with DO value of exceeding 5 mg l^–1 and NH₃-N values of lower than 12.0 mg l^–1.     

A laboratory study on biochemical degradation and microbial utilization of organic matter comprising a marine diatom,land grass,and salt marsh plant in estuarine ecosystems

We studied the biochemical degradation of organic matter comprising marine diatom, land grass, and salt marsh plant in estuarine ecosystems in two laboratory microcosms consisting of estuarine sediments and coastal seawater. The materials were incubated separately and together under controlled oxic and anoxic conditions to test effects of co-metabolism and redox on overall degradation of organic matter. We followed variations of bulk parameters [total organic carbon (TOC), total nitrogen (TN), C/N ratio, δ¹³C_TOC, and δ¹⁵N_TN], fatty acid concentrations, and compound-specific δ¹³C values over 3 months. Coexistence of marine diatom (relatively labile) with land grass/salt marsh plant (relatively refractory) in the microcosms yielded a negative co-metabolism effect (retardation rather than acceleration) on the overall degradation of organic matter. The ratios of oxic to anoxic degradation rate constants (k _ox/k _an) of TOC and most fatty acids were in a range of 1.1–1.7, implying that redox conditions per se had a limited influence on degradation of fresh organic materials in estuarine ecosystems. Variations of two bacteria-specific fatty acids (iso- and anteiso-15:0) and their δ¹³C values indicated that bacterial metabolism could use organic carbon (OC) from any available material when only one single-source material was dominant in the ecosystems. However, bacteria probably utilized OC preferentially from labile marine diatom when multiple-source materials were almost equally present in the ecosystems.     

Two mathematical models for the development of a single microbial pellet

A mathematical model for pellet development of filamentous microorganisms is presented, which simulates in detail location and growth of single hyphal elements. The basic model for growth, septation and branching of discrete hyphae is adopted from Yang et al. [2, 23]. Exact solutions to the intracellular mass-balance equations of a growth-limiting key component is given for two types of either branched or unbranched cellular compartments. Furthermore, the growth model was extended in regard to the external mass-balance equations of limiting substrates (oxygen, glucose) under the assumption that the substrates can enter the denser regions of the pellet only diffusively. Penetration of the substrates into the more porous outer regions of the pellet occurs more easily due to microeddies in the surrounding fluid. Chipping of hyphae from the pellet surface by shear forces was included in the model as well. The application of shear forces leads to a marked smoothing of the simulated pellet surface. The development of pellets from spore germination up to late stages with cell-lysis due to shortage of substrates in the pellet centre can be described. The effects of various model parameters are discussed.List of Symbols A _i algebraic coefficient (i = 1, 2,..., 6) - B _i algebraic coefficient (i = 1, 2,..., 6) - C _i mass-concentration of component i (i = O₂, S) (gl^–1) - C _i,crit concentration of substance i critical for lysis (i=O₂, S) (gl^–1) - C _i,stop concentration of substance i below which cells are inactivated (gl^–1) - C(l _i,t) intracellular concentration of the key component at site l _i and time t (gl^–1) - C _m maximal intracellular concentration of the key component (gl^–1) - C _X Concentration of dry biomass (gl^–1) - D intracellular diffusion coefficient of the key component (m² h^–1) - D _max,i maximal molecular diffusion coefficient of substrate i (i = O₂, S) (m² h^–1) - D _eff,i effective diffusion coefficient of component i (i = O₂) (m² h^–1) - d _h cross-sectional diameter of hyphae (m) - k production coefficient for the key component (h^–1) - K _s Monod coefficient for glucose (gl^–1) - k ₀ Monod coefficient for oxygen (gl^–1) - L _c total length of a compartment (m) - L _i total length of branch i (i=1, 2, 3) (m) - l _i position on branch i (i=1, 2, 3) - L _m maximal length of a segment (m) - m _i maintenance coefficient of substrate i (h^–1) - N _m maximal number of segments in a compartment - n _iR number of tips of type i in layer R, i=1, 2 - p auxiliary variable (see Eq. (7)) - P _Br probability that a hypha is chipped off (%h^–1) - pO ₂ partial pressure of oxygen in the liquid phase (%) - Q auxiliary variable (see Eq. (8)) - Q _i uptake rate of substrate i (i = O₂, S) (gl^–1 h^–1) - q auxiliary variable (see Eq. (7)) - R index of radial layer (R=1, 2, 3,..., R _max) - r radius (m) - r _crit critical radius, Eq. (15) (m) - r _max pellet radius (m) - r _tip distance from the pellet centre to the tip position (m) - r _thr threshold radius (m) - s auxiliary variable (see Eq. (7)) - S index for glucose - t time (h) - v _R volume of layer R (1) - Y _Mi observable yield coefficient of biomass on substrate i (gg^–1) - Y _Xi yield coefficient of biomass on substrate i (gg^–1) Greek Letters _i actual tip expansion rate (m h^–1) - _i,m actual maximal extension rate of tip i (i=1, 2) (m h^–1) - _1y lysis rate (h^–1) - _m maximal tip extension rate (m h^–1) - auxiliary variable in Eq. (2) - auxiliary variable in Eq. (3) - auxiliary variable defined in Eq. (4) (m^–1) - _shear shear force parameter - _R overall specific growth rate in layer R (h^–1) - _m maximal specific hyphal growth rate (h^–1) - cell volume density (l cell volume per 1) - _crit critical cell volume density in Eq. (15) - _S shear force parameter - _X cell mass density (g dry weight per 1 wet cells) - (C _i) growth kinetics on substrate i - proportional factor in Eq. (34) (l g^–1) We thank the Deutsche Forschungsgemeinschaft (DFG) for financially supporting parts of this work.We thank the Deutsche Forschungsgemeinschaft (DFG) for financially supporting parts of this work.     

Fermentation ofCandida utilis for uricase production

Summary Conditions for the production of microbial uricase byCandida utilis were studied. For the selected strain, hypoxanthine proved to be the most effective inducer of uricase formation. The highest values of biomass as well as uricase activity in the mechanically agitated fermentor were obtained under the following conditions: 50 h, rotation impeller speed 7 s^–1, air flow rate 1.25×10^–5 m³s^–1, concentration of inducer 0.1%.List of symbols b width of baffle, m - c length of baffle, m - D diameter of cylindrical fermentor, m - d diameter of impeller, m - d ₁ diameter of impeller disc, m - Fr _m impeller Froud number - g gravitional acceleration, ms^–2 - H height of batch surface above bottom, m - H ₂ height of impeller disc above bottom, m - h height of impeller blade, m - Kp _g flow rate number - L length of impeller blade, m - N rotational speed of impeller, s^–1 - Re _m impeller Reynolds number - T time, h - V volume of batch, m³ - V _g air (gas) flow rate, m³s^–1 - x mass fraction of the dry matter of cells - x ₀ initial value of the mass fraction of the dry matter of cells - _r volume fraction of the dry matter of cells - <eta<₁ viscosity of pure liquid, Pa s - viscosity of batch (suspension of microbial suspension), Pa s - density of batch, kg m^–3     

Mineralization of hexachlorocyclohexane in soil during solid-phase bioremediation

Soil containing hexachlorocyclohexane (HCH) was spiked with ¹⁴C--HCH and then subjected to bioremediation in bench-scale microcosms to determine the rate and extent of mineralization of the ¹⁴C-labeled HCH to ¹⁴CO₂. The soil was treated using two different DARAMEND amendments, D6386 and D6390. The amendments were previously found to enhance natural HCH bioremediation as determined by measuring the disappearance of parent compounds under either strictly oxic conditions (D6386), or cycled anoxic/oxic conditions (D6390). Within 80 days of the initiation of treatment, mineralization was observed in all of the strictly oxic microcosms. However, mineralization was negligible in the cycled anoxic/oxic microcosms throughout the 275-day study, even after cycling was ceased at 84 days and although significant removal (up to 51%) of indigenous -HCH (146 mg/kg) was detected by GC with electron capture detector. Of the amended, strictly oxic treatments, only one, in which 47% of the spiked ¹⁴C-HCH was recovered as ¹⁴CO₂, enhanced mineralization compared with an unamended treatment (in which 34% recovery was measured). Other oxic treatments involving higher amendment application rates or auxiliary carbon sources were inhibitory to mineralization. Thus, although HCH degradation occurs during the application of either oxic or cycled anoxic/oxic DARAMEND treatments, mineralization of -HCH may be inhibited depending on the amendment and treatment protocol.     

Brassinolide improves embryogenic tissue initiation in conifers and rice

Somatic embryogenesis (SE), the most promising technology for the large-scale production of high-value coniferous trees from advanced breeding and genetic engineering programs, is expected to play an important role in increasing productivity, sustainability, and the uniformity of future U.S. forests. To be successful for commercial use, SE technology must work with a variety of genetically diverse trees. Initiation in loblolly pine (Pinus taeda L.), our main focus species, is often recalcitrant for desirable genotypes. Initiation percentages of loblolly pine, Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco], and Norway spruce (Picea abies L., Karst.) were improved through the use of brassinolide. Brassinosteroids, which include brassinolide, are a relatively new group of natural plant growth regulators that are found in many plant species. They have been shown to have diverse, tissue-specific, and species-specific effects, including the stimulation of cell elongation and ethylene production and increasing resistance to abiotic stress. In our media, brassinolide was effective at concentrations ranging from 0.005–0.25 M. Using control medium (no brassinolide) and brassinolide-supplemented (0.1 M) medium, we achieved improved initiation percentages in loblolly pine, Douglas-fir, Norway spruce, and rice—15.0% to 30.1%, 16.1% to 36.3%, 34.6% to 47.4%, and 10%, respectively. Brassinolide increased the weight of loblolly pine embryogenic tissue by 66% and stimulated initiation in the more recalcitrant families of loblolly pine and Douglas-fir, thus compensating somewhat for genotypic differences in initiation. Initiation percentages in loblolly pine were improved through the combination of modified 1/2-P6 salts, 50 mg/l activated carbon (AC), adjusted levels of Cu and Zn (to compensate for adsorption by AC), 1.5% maltose, 2% myo-inositol (to raise the osmotic level, partially simulating the megagametophyte environment), 500 mg/l casamino acids, 450 mg/l glutamine, 2 mg/l -naphthaleneacetic acid, 0.63 mg/l 6-benzylaminopurine, 0.61 mg/l kinetin, 3.4 mg/l silver nitrate, 10 M cGMP, 0.1 M brassinolide, and 2 g/l Gelrite. Across 12 open-pollinated families of loblolly pine, initiation percentages ranged from 2.5% to 50.7%, averaging 22.5%.Abbreviations AC Activated carbon - BA 6-Benzylaminopurine - 8-Br-cGMP Guanosine 3,5-cyclic monophosphate, 8-bromo-, sodium salt - 2,4-D 2,4-Dichlorophenyloxyacetic acid - NAA -Naphthaleneacetic acid Communicated by G.C. Phillips     

Distribution of iron in Lake Banyoles in relation to the ecology of purple and green sulfur bacteria

The distribution of iron both in suspended sediment and in the water column has been studied during summer stratification in Lake Banyoles. In this lake, near bottom springs, a very fine material suspended sediment remains in suspension. Dissolved Fe²⁺ in interstitial water of this suspended sediment, is related to redox potential and to the bottom water inflow. In the water column, soluble iron is present in the hypolimnion of the six different basins forming Lake Banyoles. Under those conditions Fe²⁺ is partially removed by sulfide produced in the anoxic sediment. In addition, a peak of Fe²⁺ found at the density gradient level in basins C-III, C-IV and C-VI. A three compartment model on the dynamics of the processes involving iron in Lake Banyoles is proposed. The bottom springs supply oxygen to the anoxic hypolimnion affecting chemical processes of the iron cycle. The presence of phototrophic sulfur bacteria in the anoxic monimolimnion of basins C-III and C-IV can be related to the kinetics of Fe²⁺ and sulfide. In C-III sulfide concentration exceeds Fe²⁺ concentration whereas in C-IV sulfide is not detectable and iron reached values up to 60 mM. The presence of phototrophic sulfur bacteria in iron-containing environments with no detectable sulfide is explained by the ability of such microorganisms to use FeS as electron donor instead of H₂S.     

Carapace movements aid air breathing in the semaphore crab,Heloecius cordiformis (Decapoda: Brachyura: Ocypodidae)

Summary While on land and recirculating branchial water the Australian semaphore crab Heloecius cordiformis (Decapoda: Ocypodidae), a semi-terrestrial airbreathing mangrove crab, sequentially depresses and elevates its carapace in a regular pump-like manner. The functional role of these carapace movements in aerial oxygen consumption is investigated. Carapace immobilisation (reversible and non-injurious) did not appear to affect branchial water circulation. In dry crabs (branchial water removed) carapace immobilisation had no effect on the rate of oxygen consumption (VO₂), heart rate or whole-body lactate (WBL) levels. In wet crabs (with branchial water) carapace immobilisation caused VO₂ to drop by 38% from 81 to 46 l O₂ · g^-1 · h^-1, heart rate to decline by 32%, from 2.5 to 1.7 Hz, and WBL levels to increase over 2.5-fold, from 0.27 to 0.67 mg · g^-1, after 3 h of carapace immobilisation. The (VO₂) of carapace-immobilised crabs with branchial water was similar to lung-occluded crabs with branchial water. Severe hypoxia induced physiological responses similar to those of carapace-immobilised crabs with branchial water. After 3 h of severe hypoxia, heart rate had declined by 80%, from 2.2 to 0.43 Hz, and the incidence of carapace pumping slowed by 85%, from 2.4 to 0.37 cycles · min^-1. It is concluded that in the absence of carapace movements branchial water in some way inteferes with lung ventilation. Under normal circumstances water circulation and lung ventilation are mutually exclusive processes (due to their singular dependence on the scaphognathites), yet in Heloecius these processes must be carried out simultaneously. Carapace movements may alleviate this conflict.Abbreviations FF, FR, SF, SR fast-forward, fast-reverse, slow-forward, slow-reverse scaphognathite pumping - MEA Milne Edwards aperture - VO₂ rate of oxygen consumption - WBL whole-body lactate     

δ13C signature of organic carbon in estuarine bottom sediment as an indicator of carbon export from adjacent marshes

The ¹³C signature of organic carbon in estuarine bottom sediment in Louisiana Barataria Basin was used for estimating carbon flux from adjacent marsh. The stable carbon isotope composition of plants, soils and sediments from the basin were determined. The ¹³C content of marsh vegetation ranged from -26.3 to -27.8% for C₃ freshwater vegetation in the upper basin to -13.0 to -13.3% for C₄ vegetation in the lower basin. The ¹³C content of the highly organic marsh soils were similar to ¹³C content of vegetation present. The ¹³C content of organic carbon from bottom sediment of open water bodies ranged from 27.3 in the upper basin (freshwater) to 16.4 in bottom sediment of salt marsh ponds. The¹³C signature of organic carbon in bottom sediment from saline regions corresponded to the size of the body of water. The smaller salt marsh ponds contain sediment with ¹³C values close to that of the C₄ plantSpartina alterniflora. Results suggest that phytoplankton rather thanSpartina alterniffora is the likely organic source in bottom sediment of the larger bay near the coast (e.g. Caminada Bay).