Growth and biochemical characterization of microalgal biomass produced in bubble column and airlift photobioreactors: studies in fed-batch culture

Relatively large (0.19 m column diameter, 2 m tall, 0.06 m³ working volume) outdoor bubble column and airlift bioreactors (a split-cylinder and a draft-tube airlift device) were compared for monoseptic fed-batch culture of the microalga Phaeodactylum tricornutum. The three photobioreactors produced similar biomass versus time profiles and final biomass concentration (4 kg m⁻³). The maximum specific growth rate observed within a daily illuminated period in the exponential growth phase, had a value of 0.08 h⁻¹ on the third day of culture. Because of night-time losses of biomass, the specific growth rate averaged over the 4-days of exponential phase was 0.021 h⁻¹ for the three reactors.

The biomass in the vertical column reactors did not experience photoinhibition under conditions (photosynthetically active daily averaged irradiance value of 1150±52 μE m⁻² s⁻¹) that are known to cause photoinhibition in conventional thin-tube horizontal loop reactors. Because of good gas-liquid mass transfer, the dissolved oxygen concentration in the reactors at peak photosynthesis remained <120% of air saturation; thus, oxygen inhibition of photosynthesis and photo-oxidation of the biomass did not occur. Carbohydrate accumulation (up to 13% w/w) by the biomass was favored during light-limited linear growth. A declining light intensity caused a more than five-fold increase in cellular carotenoids but the chlorophylls increased only by about 2.5-fold during the course of the culture. In the stationary phase, up to 2% of the biomass was chlorophylls and carotenoids constituted up to 0.5% of the biomass dry weight.     

Effect of sulfide to nitrate ratios on the simultaneous anaerobic sulfide and nitrate removal

Present investigation deals with the effect of sulfide to nitrate (S/N) molar ratio on the simultaneous anaerobic sulfide and nitrate removal on capacity, stability and selectivity of the process. The volumetric sulfide-sulfur and nitrate-nitrogen removal rates at molar S/N ratio of 5:2 were 4.86 kg (m³ d)⁻¹ and 0.99 kg (m³ d)⁻¹, respectively, which were higher than those at S/N molar ratios of 5:5 and 5:8. Moreover, the fluctuations in the effluent at S/N ratio of 5:2 were less than those at the other two tested ratios. During the operation, the ratio of converted sulfide to converted nitrate tended to approach 5:2. The selectivity for elemental sulfur and dinitrogen was improved when the S/N molar ratio was set at 5:2 rather than 5:5 or 5:8. The process became unstable if the influent sulfide surpassed its critical concentration. The electron balance between reactants was also analyzed for different S/N molar ratios.     

Anaerobic treatment of highly concentrated aniline wastewater using packed-bed biofilm reactor

The performance of packed-bed biofilm reactor (PBBR) with self-floating bio-carriers was investigated to treat highly concentrated organic nitrogenous aniline wastewater with a COD value as high as 24,000 mg/L. With 45 vol% of carrier charge inside the reactor, the aniline wastewater can be effectively treated with 94% of COD removal efficiency at a low organic loading rate (OLR) of 0.9 kg COD/(m³ d). The removal efficiency decreased gradually down to 75% when OLR increased to 12.27 kg COD/(m³ d) that corresponded to 1 day of HRT. Separate tests with biofilm alone showed that the conversion contribution of the biofilm was about half of the overall COD conversion by the biofilm plus sludge system at the same OLRs of 3–4 kg COD/(m³ d), and that the biofilm had higher activity than suspended sludge. Ammonium released from decomposed aniline was increased gradually from 500 to 1700 mg/L with the OLR increase from 0.9 to 12.27 kg COD/(m³ d), which resulted in inhibitory effect to the microorganism due to the toxicity of free ammonia. Batch anaerobic toxicity tests showed that the biofilm was less sensitive to toxic compounds than suspended sludge and could tolerate higher concentration of free ammonia.     

The effects of rate and timing of N fertilizer on growth, photosynthesis, N accumulation and yield of mustard (Brassica juncea) subjected to defoliation

Mustard (Brassica juncea L.) is characterized by large number of broad oblong shaped leaves in the lower layers. Our earlier studies have shown that removal of these shaded lower leaves on mustard plant axis enhanced growth, photosynthetic capacity and yield of the crop. We now present evidence that soil-applied nitrogen (N) at pre- or post-flowering stage following defoliation of lower leaves influences plant growth, photosynthesis and assimilation balance. Following defoliation at pre-flowering, i.e. 40 d after sowing (DAS) and N applied at the rate of 100 kg ha⁻¹ at the time of sowing and 50 kg ha⁻¹ at post-flowering (60 DAS) enhanced the characteristics maximally. The defoliation treatment together with N combinations and the time of its application, N at 150 kg ha⁻¹ applied as single dose at the time of sowing or N applied in split; 100 kg ha⁻¹ at the time of sowing and 50 kg ha⁻¹ at 40 DAS or 75 kg ha⁻¹ at the time of sowing or 75 kg ha⁻¹ at pre- or post-flowering time proved less effective. The plants which were not defoliated and received 75 kg N ha⁻¹ at the time of sowing and 75 kg ha⁻¹ at 60 DAS showed lowest values. Furthermore, N assimilation was more efficient in plants following defoliation at 40 DAS. The results suggest that split N application (100 kg ha⁻¹ at sowing and 50 kg ha⁻¹ at post-flowering) enhances substantially growth, photosynthesis, N assimilation and yield of mustard following defoliation. This management practice could be adopted in mustard culture for increasing seed yield together with minimizing N loss.     

Protein-based complex medium design for recombinant serine alkaline protease production

This work reports on the design of a complex medium based on simple and complex carbon sources, i.e. glucose, sucrose, molasses, and defatted-soybean, and simple and complex nitrogen sources, i.e. (NH₄)₂HPO₄, casein, and defatted-soybean, for serine alkaline protease (SAP) production by recombinant Bacillus subtilis carrying pHV1431::subC gene. SAP activity was obtained as 3050 U cm⁻³ with the initial defatted-soybean concentration C_soybean^o=20 kg m⁻³ and initial glucose concentration C_G^o=8 kg m⁻³; whereas, addition of the inorganic nitrogen source (NH₄)₂HPO₄ decreased SAP production considerably. Further increase in SAP production (3850 U cm⁻³) was obtained when sucrose was replaced with glucose at C_sucrose^o=15 kg m⁻³ and C_soybean^o=20 kg m⁻³. Nevertheless, when molasses was replaced with sucrose, the maximum activity was obtained with molasses having 10 kg m⁻³ initial sucrose concentration and C_soybean^o=15 kg m⁻³as 2130 U cm⁻³; moreover, when casein was replaced with defatted-soybean SAP production decreased considerably (ca. 250 U cm⁻³). Thereafter, the effects of inorganic ionic compounds were investigated; and except phosphate, inorganic compounds supplied from defatted-soybean were found to be sufficient for the bioprocess. The highest SAP activity was obtained as 5350 U cm⁻³ in the medium that contained (kg m⁻³): C_soybean^o=20, C_sucrose^o=15, C_Na2HPO4^o=0.021, and C_NaH2PO4^o=2.82, that was 6.5-fold higher than that of the SAP produced in the defined medium. By using the designed complex medium, oxygen transfer characteristics of the bioprocess were investigated; and, Damköhler number that is the oxygen transfer limitation increases with the cultivation time until t=14 h; and, at t>20 h both mass transfer and biochemical reaction resistances were effective. Overall oxygen transfer coefficient varied between 0.010 and 0.044 s⁻¹; volumetric oxygen uptake rate varied between 0.001 and 0.006 mol m⁻³ s⁻¹; and specific oxygen uptake rate varied between 0.0001 and 0.0022 mol kg⁻¹ DW s⁻¹ throughout the bioprocess.     

Tangential finger forces use mechanical advantage during static grasping

When grasping and manipulating objects, the central controller utilizes the mechanical advantage of the normal forces of the fingers for torque production. Whether the same is valid for tangential forces is unknown. The main purpose of this study was to determine the patterns of finger tangential forces and the use of mechanical advantage as a control mechanism when dealing with objects of nonuniform finger positioning. A complementary goal was to explore the interaction of mechanical advantage (moment arm) and the role a finger has as a torque agonist/antagonist with respect to external torques (±0.4 N m). Five 6-df force/torque transducers measured finger forces while subjects held a prism handle (6 cm width × 9 cm height) with and without a single finger displaced 2 cm (handle width). The effect of increasing the tangential moment arm was significant (p < .01) for increasing tangential forces (in >70% of trials) and hence creating greater moments. Thus, the data provides evidence that the grasping system as a rule utilizes mechanical advantage for generating tangential forces. The increase in tangential force was independent of whether the finger was acting as a torque agonist or antagonist, revealing their effects to be additive.     

Decline of the African lungfish (Protopterus aethiopicus) in Lake Victoria (East Africa)

Catch and effort data for the period 1973–1990 demonstrate a dramatic decline of lungfish in the Tanzanian waters of Lake Victoria. Bottom trawl catches in the Mwanza Gulf showed a decline in catch rates from 67.5 kg h⁻¹ in 1973 to 5.5 kg h⁻¹ in 1986. Trawling of commercial vessels in the Speke Gulf revealed a decline in lungfish catches from 1.3 kg h⁻¹ in 1986 to 0.07 kg h⁻¹ in 1990. The development of anoxia in the deeper waters of Lake Victoria, the algal blooms, and the decline of water transparency, all associated with eutrophication, are not likely to have contributed to the decreased catch rate. However, the lungfish decline may reflect the interaction of overexploitation by the fishery and a low level of Nile perch predation that restricts lungfish to wetland refugia. We suggest that this may have been reinforced over the past few decades by large-scale conversion of wetlands to agricultural land and harvesting of nest-guarding male lungfish leading to decreased recruitment of young.     

Changes in organic carbon distribution with depth in agricultural soils in northern Belgium, 1960–2006

In most studies concerning the carbon (C) exchange between soil and atmosphere only the topsoil (0–0.3 m) is taken into account. However, it has been shown that important amounts of stable soil organic carbon (SOC) are also stored at greater depth. Here, we developed a quantitative model to estimate the evolution of the distribution of SOC with depth between 1960 (database 'Aardewerk') and 2006 in northern Belgium. This temporal analysis was conducted under different land use, texture and drainage conditions. The results indicate that intensified land management practices seriously affect the SOC status of the soil. The increase in plough depth and a change in crop rotation result in a significant decrease of C near the surface for dry silt loam cropland soils, (i.e. 1.02 ± 0.23 kg C m⁻² in the top 0.3 m between 1960 and 2006). In wet to extremely wet grasslands, topsoil SOC decreased significantly, indicating a negative influence of intensive soil drainage on SOC stock. This resulted in a decline of SOC between 1960 and 2006 in the top 1 m, ranging from 3.99 ± 2.57 kg C m⁻² in extremely wet silt loam soils to 2.04 ± 2.08 kg C m⁻² in wet sandy soils. A slight increase of SOC stock is observed under dry to moderately wet grasslands at greater depths corresponding to increased livestock densities in the region. The increase of SOC in the top 1 m under grassland ranges from 0.65 ± 1.39 kg C m⁻² in well drained silt loam soils to 2.59 ± 6.49 kg C m⁻² in moderately drained silt loam soils over entire period.     

Anaerobic digestion of solid slaughterhouse waste (SHW) at laboratory scale: Influence of co-digestion with the organic fraction of municipal solid waste (OFMSW)

Mesophilic anaerobic digestion of slaughterhouse waste (SHW) and its co-digestion with the organic fraction of municipal solid waste (OFMSW) have been evaluated. These processes were carried out in a laboratory plant semi-continuously operated and two set-ups were run. The first set-up, with a hydraulic retention time (HRT) of 25 days and organic loading rate (OLR) of 1.70 kg VS m⁻³ day⁻¹ for digestion, and 3.70 kg VS m⁻³ day⁻¹ for co-digestion, was not successful. The second set-up was initiated with an HRT of 50 days and an OLR of 0.9 kg VS m⁻³ day⁻¹ for digestion and 1.85 kg VS m⁻³ day⁻¹ for co-digestion. Under these conditions, once the sludge had been acclimated to a medium with a high fat and ammonia content, it was possible to decrease the HRT while progressively increasing the OLR to the values used in the first set-up until an HRT of 25 days and OLRs of 1.70 and 3.70 kg VS m⁻³ day⁻¹, for digestion and co-digestion, respectively (the same conditions of the digesters failures previously). These digesters showed a highly stable performance, volatile fatty acids (VFAs) were not detected and long chain fatty acids (LCFAs) were undetected or only trace levels were measured in the analyzed effluent. Fat removal reached values of up to 83%. Anaerobic digestion was thus found to be a suitable technology for efficiently treating lipid and protein waste.     

Seasonal nitrogen dynamics of Miscanthus×giganteus and Panicum virgatum

There is a tradeoff to consider when harvesting perennial biomass crops: harvest too late and yield declines, harvest too early and risk higher mineral contents, particularly nitrogen (N). Allowing the crop to completely senesce and recycle nutrients has several advantages, including improved feedstock quality and reduced fertilizer requirements, but it comes at a risk, particularly in temperate climates where snow and ice can reduce or destroy harvestable biomass. The effect of harvest time on the N concentration ([N]) and biomass of Panicum virgatum and Miscanthus × giganteus was evaluated at three sites in Illinois over two years. In both species [N] of standing biomass significantly declined with time ( P <0.0001). Interestingly, there was no significant interaction effect of species and sample date on [N] ( P =0.2888), but there was a highly significant interaction effect on the total N in standing biomass ( P <0.0001). The amount of standing N was directly related to biomass yield. Seasonal changes in standing N differed among locations, suggesting that harvest time recommendations for N management depend on location. P. virgatum would have potentially removed as much as 187 kg N ha⁻¹ if harvested green, and as little as 5 kg N ha⁻¹ if harvested in late winter. Because of higher biomass yields, M . × giganteus standing N ranged from 379 kg N ha⁻¹ in June to <17 kg N ha⁻¹ in February. Importantly, there was little overall change in [N] between an early winter (December) harvest and a late winter (February/March) harvest, indicating the benefits of N cycling in the system can be realized by end of the growing season and thus, at least from an N economy perspective, there is no reason to risk yield losses by delaying harvest over the winter.     

Barrier and surface properties of chitosan-coated greaseproof paper

Greaseproof papers with different air permeances were coated with chitosan, both on a bench scale and on a pilot scale to study the conditions necessary to obtain a packaging material with good barrier properties towards oxygen, nitrogen, carbon dioxide and air. In addition, barrier properties against grease and water were measured. The results showed that an oxygen permeability in the same range as that of poly(ethylene terephthalate) was obtained at coat weights exceeding 5 g/m². The oxygen permeability was not substantially affected by temperature changes, provided that the air permeance of the base paper was low. Carbon dioxide and nitrogen permeabilities were low enough to be measurable only at a coat weight exceeding 5 g/m² and only on the two base papers with the lowest air permeance. The mechanical properties were characterized by tensile strength and fracture strain. The tensile strength was not affected by the coat weight, whereas the fracture strain was highest for coat weights exceeding 5 g/m². High grease resistance values were also obtained at this coat weight, whereas the water resistance deteriorated slightly due to the hygroscopic character of the chitosan. However, a coat weight as high as 5 g/m² could only be achieved on a bench scale. On a pilot scale, the maximum coat weight was 0.2 g/m² because the solids content of the coating solution used was limited to 1.0 wt% due to the high molecular weight of the chitosan used and the resultant high viscosity of the polymer solution. The coating on a pilot scale was performed using the metered size press technique.     

Limb work and joint work minimization reveal an energetic benefit to the elbows-back,knees-forward limb design in parasagittal quadrupeds

Quadrupedal animal locomotion is energetically costly. We explore two forms of mechanical work that may be relevant in imposing these physiological demands. Limb work, due to the forces and velocities between the stance foot and the centre of mass, could theoretically be zero given vertical limb forces and horizontal centre of mass path. To prevent pitching, skewed vertical force profiles would then be required, with forelimb forces high in late stance and hindlimb forces high in early stance. By contrast, joint work—the positive mechanical work performed by the limb joints—would be reduced with forces directed through the hip or shoulder joints. Measured quadruped kinetics show features consistent with compromised reduction of both forms of work, suggesting some degree of, but not perfect, inter-joint energy transfer. The elbows-back, knees-forward design reduces the joint work demand of a low limb-work, skewed, vertical force profile. This geometry allows periods of high force to be supported when the distal segment is near vertical, imposing low moments about the elbow or knee, while the shoulder or hip avoids high joint power despite high moments because the proximal segment barely rotates—translation over this period is due to rotation of the distal segment.     

High organic loading influences the physical characteristics of aerobic sludge granules

Aims:  The effect of high organic loading rate (OLR) on the physical characteristics of aerobic granules was studied.
Methods and Results:  Two column-type sequential aerobic sludge blanket reactors were fed with either glucose or acetate as the main carbon source, and the OLR was gradually raised from 6 to 9, 12 and 15 kg chemical oxygen demand (COD) m⁻³ d⁻¹. Glucose-fed granules could sustain the maximum OLR tested. At a low OLR, these granules exhibited a loose fluffy morphology dominated by filamentous bacteria. At higher OLRs, these granules became irregularly shaped, with folds, crevices and depressions. In contrast, acetate-fed granules had a compact spherical morphology at OLRs of 6 and 9 kg COD m⁻³ d⁻¹, with better settling and strength characteristics than glucose-fed granules at similar OLRs. However, acetate-fed granules could not sustain high OLRs and disintegrated when the OLR reached 9 kg COD m⁻³ d⁻¹.
Conclusions:  The compact regular microstructure of the acetate-fed granules appeared to limit mass transfer of nutrients at an OLR of 9 kg COD m⁻³ d⁻¹. The looser filamentous microstructure of the glucose-fed granules and the subsequent irregular morphology delayed the onset of diffusion limitation and allowed significantly higher OLRs to be attained.
Significance and Impact of the Study:  High organic loading rates are possible with aerobic granules. This research would be helpful in the development of aerobic granule-based systems for high-strength wastewaters.     

How swift are swifts Apus apus?

Swifts Apus apus are renowned for their fast flight manner which has fascinated people in all times. However, previous studies of swifts in flight during migration and roosting flights have shown that the birds operate over a narrow range of flight speeds compared with most other birds studied. In this study we have focused on the special flight behavior often called 'screaming parties'. During these flights the birds appear to reach very high speeds and therefore we used a stereo high speed camera setup to measure the flight speeds of the birds during this behavior with high accuracy. The birds were found to fly at much higher speeds during 'screaming parties' than during migration or roosting, on average twice as fast, 20.9  ms⁻¹ (±5.1  ms⁻¹) in horizontal speed. The highest record was 31.1  ms⁻¹ which is the highest measured yet for a swift in self powered flight. Furthermore, the birds were performing steep climbing flights, on average 4.0  ms⁻¹ (±2.8  ms⁻¹) in vertical velocity. A clear trade-off between horizontal speed and vertical speed was found, suggesting that the birds are operating at their maximum.     

Performance of anaerobic baffled reactor (ABR) treating synthetic wastewater containing p-nitrophenol

In this study, the effect of increasing p-nitrophenol (PNP) concentrations on the performance of anaerobic baffled reactor (ABR) (chemical oxygen demand (COD), removals, volatile fatty acid (VFA), p-aminophenol (PAP) and methane gas productions) was investigated through 240 days. The PNP concentrations were raised to 700 from 10 mg/L corresponding to PNP loading rates of 0.97 and 67.9 g/m³ day. The PNP and COD removal efficiencies were 99 and 90% at PNP loading rates as high as 33.9 g/m³ day, respectively, through the acclimation of anaerobic granular sludge. After this loading rate, the removal efficiencies decreased to 79%. The COD removal efficiencies were high in compartment 1 (E = 78–93%) while a small amount of COD removal was achieved in compartments 2 and 3. The PNP removal efficiencies were approximately 90% in all PNP loading rates except for loading rate of 0.97 g/m³ day. The maximum PNP removal efficiency was measured as 99% at a loading rate of 8.32 g/m³ day. The optimum PNP loading rate for maximum COD, PNP removals and methane yield was 8.32 g/m³ day. The total, methane gas productions and methane percentages were approximately 2160–2400 mL/day and 950–1250 mL/day and 44–52% for the PNP loading rates varying between 4.36 and 33.9 g/m³ day, respectively. For PNP loading rates varying between 33.9 and 67.9 g/m³ day, the total, methane gas productions and methane percentages were approximately 2160 and 960 mL/day and 44%, respectively. The highest total volatile fatty acid (TVFA) concentrations were found in the first compartment with fluctuated values varied between 50 and 200 mg/L indicating the acidogenesis. p-Aminophenol was found as the main intermediate through anaerobic degradation of PNP which later was broken down to phenol and ammonia.     

Influence of defect locations and nitrogen doping configurations on the mechanical properties of armchair graphene nanoribbons

The effect of defect locations on the mechanical properties of armchair graphene nanoribbons (AGNRs) and the various configurations of nitrogen (N) doping on the mechanical properties of AGNRs were examined using molecular dynamics (MD) simulations. The variation of the Young’s modulus (YM) and the ultimate tensile strength (UTS) of pyridinic-N, graphitic-N, and pyrrolic-N by increasing the concentration of N doping was investigated. The results of MD simulations show that the defect location has a significant effect on the UTS and failure strain (FS) of AGNRs in both vertical and horizontal directions. In the horizontal direction, variations of the UTS and FS are lower than in the vertical direction. On the other hand, the variations of the YM is almost similar in vertical and horizontal directions. The results of this work indicate that the UTS and FS of AGNRs are more sensitive than the YM of AGNRs for different defect directions. Pyridinic-N improves the mechanical properties of the defective AGNR and performs better YM and UTS values than the graphitic-N. Substitution N atoms, which are located at the defective sites and/or at the edges of AGNRs, are mechanically more favorable. Pyrrolic-N configuration has the lowest mechanical properties among the other configurations. Furthermore, pyrrolic-N with Stone-Wales-1 (SW-1) type of defect has higher mechanical properties than pyrrolic-N with Stone-Wales-2 (SW-2) type of defect.     

The effect of torque direction and cylindrical handle diameter on the coupling between the hand and a cylindrical handle

Pheasant and O'Neill's torque model (1975) was modified to account for grip force distributions. The modified model suggests that skin friction produced by twisting an object in the direction of fingertips causes flexion of the distal phalanges and increases grip force and, thus, torque. Twelve subjects grasped a cylindrical object with diameters of 45.1, 57.8, and 83.2 mm in a power grip, and performed maximum torque exertions about the long axis of the handle in two directions: the direction the thumb points and the direction the fingertips point. Normal force on the fingertips increased with torque toward the fingertips, as predicted by the model. Consequently, torque toward the fingertips was 22% greater than torque toward the thumb. Measured torque and fingertip forces were compared with model predictions. Torque could be predicted well by the model. Measured fingertip force and thumb force were, on average, 27% less than the predicted values. Consistent with previous studies, grip force decreased as the handle diameter increased from 45.1 to 83.2 mm. This may be due not only to the muscle length-strength relationship, but also to major active force locations on the hand: grip force distributions suggest that a small handle allows fingertip force and thumb force to work together against the palm, resulting in a high reaction force on the palm, and, therefore, a high grip force. For a large handle, fingertip force and thumb force act against each other, resulting in little reaction force on the palm and, thus, a low grip force.     

Swimming activity of seabass: comparing patterns obtained in natural environment and in re-circulating tanks under high density

Seabass ( Dicentrarchus labrax ) swimming activity was compared between natural environments and aquaculture facilities. Behaviour under natural conditions was assessed in a saltmarsh pond (250 m², 18 × 14 × 0·8 m) using acoustic telemetry. From several surveys, we documented the diel activity rhythm and demonstrated group effects on swimming patterns and amplitudes by comparing activity of solitary fish with that of a fish living in a group of 60. Consequences of weather variability were also analysed and revealed a high sensitivity of fish to atmospheric conditions for both swimming and demand‐feeding behaviour. Behaviour in fish tanks was also studied using acoustic telemetry, as part of the EUREKA EU1 960 'Aqua‐Maki 2' project investigating aspects of fish culture in re-circulating tanks under high density. A re-circulating hexagonal tank (5·4 × 5·4 m, 1·8 m depth, 48 m³) was equipped with positioning and demand‐feeding systems, oxygen and temperature probes. Initial density was 50 kg m³ in March and rose to 90 kg m³ at the end of the experiment in May. During this period, the movements of nine fish were continuously recorded for 24 h each, reaching a total of six 24 h episode at eight days interval. Swimming activity was analysed in terms of activity rhythms and space occupation specially around feeding events. The two data set and main results will be presented and compared to assess seabass behavioural plasticity and sensitivity to husbandry conditions.     

Terrestrial export of highly bioavailable carbon from small boreal catchments in spring floods

1. We assessed the terrestrial export of organic carbon, which effectively supported aquatic bacterial production (BP), from small boreal catchments during spring flood. We analysed stream runoff from nine small catchments with different proportions of peat mires and coniferous forests by monitoring the dissolved organic carbon (DOC) flux in combination with conducting bacterial bioassays.
2. Multiple linear regression analysis showed that BP during 7-day-dark bioassays (BP₇; μg C L⁻¹day⁻¹) was explained by both the quantity and quality (low-molecular weight fractions) of the DOC. BP₇ can be used as a measure of export of terrestrial organic carbon that is highly bioavailable.
3. Total export of DOC during spring flood from the different catchments ranged from 20 to 27 kg ha⁻¹ and was negatively correlated to forest cover (%). However, the export of BP₇ carbon was positively correlated to forest cover and varied from about 0.1 kg ha⁻¹ in mire-dominated streams to about 0.2 kg ha⁻¹ in forest-dominated streams.
4. The high bioavailability of forest carbon suggests that forests are the main contributors of BP-supporting carbon in boreal streams although mires have higher area-specific export of DOC.     

External forces and torques generated by the brachiating white-handed gibbon (Hylobates lar)

We compared the kinetics of brachiation to bipedal walking and running. Gibbons use pectoral limbs in continuous contact with their overhead support at slow speeds, but exhibit aerial phases (or ricochetal brachiation) at faster speeds. This basic interaction between limb and support suggests some analogy to walking and running. We quantified the forces in three axes and torque about the vertical axis generated by a brachiating White-handed gibbon (Hylobates lar) and compared them with bipedal locomotion. Handholds oriented perpendicular to the direction of travel (as in ladder rungs) were spaced 0.80, 1.20, 1.60, 1.72, 1.95, and 2.25 m apart. The gibbon proportionally matched forward velocity to stride length. Handhold reaction forces resembled ground reaction forces of running humans except that the order of horizontal braking and propulsion were reversed. Peak vertical forces in brachiation increased with speed as in bipedal locomotion. In contrast to bipedalism, however, peak horizontal forces changed little with speed. Gait transition occurred within the same relative velocity range as the walk-run transition in bipeds (Froude number = 0.3-0.6). We oriented handholds parallel to the direction of travel (as in a continuous pole) at 0.80 and 1.60 m spacings. In ricochetal brachiation, the gibbon generated greater torque with handholds oriented perpendicular as opposed to parallel to the direction of travel. Handhold orientation did not affect peak forces. The similarities and differences between brachiation and bipedalism offer insight into the ubiquity of mechanical principles guiding all limbed locomotion and the distinctiveness of brachiation as a unique mode of locomotion.