Removal of a high load of ammonia by a marine bacterium,Vibrio alginolyticus in biofilter

A newly isolated heterotrophic marine bacterium,Vibrio alginolyticus, was used to remove a high load of ammonia gas under non-sterile condition. The cells were inoculated onto an inorganic packing material in a fixed-bed reactor (biofilter), and a high bad of ammonia, in the range of ammonia gas concentration of 170 ppm to 880 ppm, was introduced continuously. Sucrose solution and 3% NaCl was supplied intermittently to supplement the carbon source and water to the biofilter. The average percentage of gas removed exceeded 85% for 107-day operation. The maximum removal capacity and the complete removal capacity were 19 g-N kg⁻¹ dry packing material day⁻¹ and 16 g-N kg⁻¹ dry packing material day⁻¹, respectively, which were about three times greater than those obtained in nitrifying sludge inoculated onto the same packing material. On day 82, the enhanced pressure drop was restored to the normal one by NaOH treatment, and efficient removal characteristics were later observed. During this operation, the non-sterile condition had no significantly adverse effect on the removability of ammonia byV. alginolyticus.     

Styrene degradation by <Emphasis Type="Italic">Pseudomonas</Emphasis> sp. SR-5 in biofilters with organic and inorganic packing materials

Pseudomonas sp. SR-5 was isolated as a styrene-degrading bacterium. In liquid culture containing 1% (v/v) styrene, more than 90% styrene was degraded in 53 h and the doubling time of SR-5 was 2 h. The removal of styrene gas was investigated in biofilters for 31 days using an organic packing material of peat and an inorganic packing material of ceramic inoculated with SR-5. The maximum-styrene-elimination capacities for peat and ceramic packing materials were 236 and 81 g m^–3 h^–1, respectively. The percentage of styrene converted to low molecular weight compounds including CO₂ in the peat and ceramic biofilters during a 10-day operation were estimated to be 90.4 and 36.7%, respectively. As the pressure drop in the peat bioflter at the end of experiment was significantly higher than that in ceramic biofilter, a biofilter using a mixture of peat and ceramic was tested. We determined that the maximum elimination capacity was 170 g m^–3 h^–1 and the production of low molecular weight compounds was 95% at a low pressure drop for this mixed packing material filter.     

Ulva rigida (Ulvales,Chlorophyta) tank culture as biofilters for dissolved inorganic nitrogen from fishpond effluents

Ulva rigida was cultivated in 7501 tanks at different densities with direct and continuous inflow (at 2, 4, 8 and 12 volumes d^–1) of the effluents from a commercial marine fishpond (40 metric tonnes, Tm, of Sparus aurata, water exchange rate of 16 m³ Tm^–1) in order to assess the maximum and optimum dissolved inorganic nitrogen (DIN) uptake rate and the annual stability of the Ulva tank biofiltering system. Maximum yields (40 g DW m^–2 d^–1) were obtained at a density of 2.5 g FW 1^–1 and at a DIN inflow rate of 1.7 g DIN m^–2 d^–1. Maximum DIN uptake rates were obtained during summer (2.2 g DIN M^–2 d^–1), and minimum in winter (1.1 g DIN m^–2 d^–1) with a yearly average DIN uptake rate of 1.77 g DIN m^–2 d^–1 At yearly average DIN removal efficiency (2.0 g DIN m^–2 d^–1, if winter period is excluded), 153 m² of Ulva tank surface would be needed to recover 100% of the DIN produced by 1 Tm of fish.Abbreviations DIN= dissolved inorganic nitrogen (NH _inf4 ^sup+ + NO _inf3 ^sup– + NO _inf2 ^sup– ); - FW= fresh weight; - DW= dry weight; - PFD= photon flux density; - V= DIN uptake rate     

Dolomite limits acidification of a biofilter degrading dimethyl sulphide

The applicability of dolomite particlesto control acidificationin a Hyphomicrobium MS3inoculated biofilter removingdimethyl sulphide (Me₂S) wasstudied. While direct inoculationof the dolomite particles with theliquid microbial culture was notsuccessful, start-up ofMe₂S-degradation in thebiofilter was observed when thedolomite particles were mixed with33% (wt/wt) of Hyphomicrobium MS3-inoculatedcompost or wood bark material.Under optimal conditions, anelimination capacity (EC) of 1680~g Me₂S m^-3 d^-1 wasobtained for the compost/dolomitebiofilter. Contrary to a wood barkor compost biofilter, no reductionin activity due to acidificationwas observed in these biofiltersover a 235 day period because ofthe micro environmentneutralisation of the microbialmetabolite H₂SO₄ with thecarbonate in the dolomite material.However, performance of thebiofilter decreased when themoisture content of the mixedcompost/dolomite material droppedbelow 15%. Next to this, nutrientlimitation resulted in a gradualdecrease of the EC andsupplementation of a nitrogensource was a prerequisite to obtaina long-term high EC (> 250 gMe₂S m^-3 d^-1) forMe₂S. In relation to thisnitrogen supplementation, it wasobserved that stable ECs forMe₂S were obtained when thisnutrient was dosed to the biofilterat a Me₂S-C/NH₄Cl-Nratio of about 10.Abbreviations:DW – dry weight,EC – elimination capacity,Me₂S – dimethyl sulphide,OL – organic loading rate,VS - volatile solids     

Annual productivity of Spirulina (Arthrospira) and nutrient removal in a pig wastewater recycling process under tropical conditions

An evaluation was made of the annual productivity of Spirulina (Arthrospira) and its ability to remove nutrients in outdoor raceways treating anaerobic effluents from pig wastewater under tropical conditions. The study was based at a pilot plant at La Mancha beach, State of Veracruz, Mexico. Batch or semi-continuous cultures were established at different seasons during four consecutive years. The protein content of the harvested biomass and the N and P removal from the ponds were also evaluated. Anaerobic effluents from digested pig waste were added in a proportion of 2% (v/v) to untreated sea-water diluted 1:4 with fresh water supplemented with 2 g L^–1 sodium bicarbonate, at days 0, 3 and 5. A straight filament strain of Spirulina adapted to grow in this complex medium was utilized. A pH value 9.5 ± 0.2 was maintained. The productivity of batch cultures during summer 1998 was significantly more with a pond depth of 0.10 m than with a depth 0.065 m. The average productivity of semi-continuous cultures during summer 1999 was 14.4 g m^–2 d^–1 with a pond depth of 0.15 m and 15.1 g m^–2 d^–1 with a depth of 0.20 m. The average annual productivity for semi-continuous cultures operating with depths of 0.10 m for winter and 0.15 and 0.25 m for the rest of the year, was 11.8 g m^–2 d^–1. This is the highest value reported for a Spirulina cultivation system utilising sea-water. The average protein content of the semi-continuous cultures was 48.9% ash-free dry weight. NH₄-N removal was in the range 84–96% and P removal in the range of 72–87%, depending on the depth of the culture and the season.     

Halotolerance of the oyster predator, Imogine mcgrathi, a stylochid flatworm from Port Stephens, New South Wales, Australia

The stylochid flatworm, Imogine mcgrathi was confirmed as a predator of the pteriid oyster Pinctada imbricata. Occurring at an average of 3.2 per oyster spat collector bag, the flatworms were found to consume oysters at a rate of 0.035–0.057 d^–1 in laboratory trials. Predation was affected by flatworm size with larger worms capable of consuming larger oysters and of consuming greater dry weights of oyster flesh. Irrespective of flatworm size, predation was generally confined to oysters less than 40 mm in shell height. Although all predation occurred at night, shading flatworms during the day did not significantly increase the rate of predation, but there were significant increases in the dry weight of oyster meat consumed. As a means of controlling flatworm infestations, salt, brine baths (250 g kg^–1) and freshwater baths were effective in killing I. mcgrathi. The ease of use of hyper- or hyposaline baths then encouraged assessments of I. mcgrathi halotolerance. The flatworms were exposed to solutions ranging in salinity from 0 to 250 g kg^–1for periods of from 5 min to 3 h. Despite showing both behavioural and physiological signs of stress, I. mcgrathi survived the maximum exposure time of 3 h at salinities in the range 7.5–60 g kg^–1, inclusive. Beyond this range, the duration of exposure tolerated by flatworms decreased until 0 and 250 g kg^–1, at which the flatworms no longer survived the minimum tested exposure of 5 min. Thus, despite the significant impact of other stylochids on commercial bivalves, at their current prevalence, I. mcgrathi can be controlled by exposing them to hyper- and hyposaline baths for the culture of P. imbricata in Port Stephens, NSW, Australia.     

Development and operation of a trickling biofilter system for continuous treatment of gas-phase trichloroethylene

A parallel trickling biofilter (TBF) system that consists of two TBFs units in parallel, one for biodegradation of trichloroethylene (TCE) and the other for reactivation of an inactivated biofilm, was developed and operated for continuous treatment of gas-phase TCE by Burkholderia cepacia G4. For inlet loadings below 8.6 mg TCE l^–1 d^–1, complete removal of TCE was achieved. The maximal TCE elimination capacity was 17 mg l^–1 d^–1.     

Water flux and energy use in wild house mice (Mus domesticus) and the impact of seasonal aridity on breeding and population levels

Summary Water turnover rate (WTR), urine concentration and field metabolic rate (FMR) were examined in house mice, Mus domesticus, permanently inhabiting roadside verge areas and seasonally invading crops in semi-arid wheatlands in South Australia. FMR was approximately proportional to body mass^0.5 and mean values varied from 4.8 ml CO₂ g^–1h^–1 (2.9 kJ g^–1d^–1) in autumn and winter, to 7.0 ml CO₂ g^–1h^–1 (4.2 kJ g^–1d^–1) in maturing crops during spring. WTR was independent of body mass, indicating that larger mice were selecting a diet containing moister foods. WTR was low in summer and high in winter, and in mice from crops varied from 165 ml l^–1 body water d^–1 (122 ml kg^–1d^–1) to 1000 ml l^–1d^–1 (725 ml kg^–1d^–1). Seasonal changes in WTR were less extreme on the roadside, where a greater diversity of food was available. In the crops, breeding occurred throughout summer during two of three years, but the population increased only in the one summer when mice had marginally higher WTR. On the roadside breeding and population growth were continuous during summer, except in a drought year. Avcrage urine concentration was inversely related to WTR, and varied from 2.0 to 4.8 Osm l^–1. The data indicate that the water conserving abilities of mice equal those of many desert rodents. The water conserving abilities of mice living in crops during summer were fully extended, and in some years aridity limited breeding success and population levels. The degree of moisture stress to which mice are exposed during summer appears to depend not only on rainfall but also on other factors such as availability of food and shelter, and the level of weed infestation in crops.     

The concentration of cadmium,lead, copper and zinc inChironomus gr.thummi larvae (Diptera,Chironomidae) with deformedversus normal menta

The concentrations of Cd, Pb, Cu and Zn inChironomus gr.thummi were determined for 4th instar larvae from the polluted Dyle River, tributary of the Scheldt River (Belgium). Comparison was made between larvae with deformed and normal menta. Deformed larvae showed higher overall metal concentrations than normal larvae. Especially Pb and Cu had higher concentrations in deformed larvae (16.22 mg kg^–1 dry weight and 39.66 respectively) than in normal larvae (12.80 mg kg^–1 dry weight and 35.70 respectively). No significant differences were found in the concentrations of Cd and Zn (mean [Cd] = 0.81 mg kg^–1 dry weight and mean [Zn] = 313.12 mg kg^–1 dry weight). There was no difference between the two larval groups as far as total length, dry weight and developmental stage of the imaginal discs are concerned.     

Preliminary compositional nutrient diagnosis norms for cowpea (Vigna unguiculata (L.) Walp.) grown on desert calcareous soil

This study calculated the compositional nutrient diagnosis (CND) norms of cowpea (Vigna unguiculata (L.) Walp.), as well as identified significant nutrient interactions of this crop growing in an irrigated calcareous desert soil. Three genotypes were distributed in rows in a 2-ha field. The soil showed high heterogeneity in its chemical properties. For statistical analysis, 86 foliar composite samples from healthy plants were used. Preliminary CND norms were developed using a cumulative variance ratio function and the ² distribution function. Means and standard deviations of row-centered log ratios V_X of five nutrients (N, P, K, Ca, and Mg) and a filling value R, which included all nutrients not chemically analyzed. Preliminary CND norms are: V_N^*=0.174±0.095, V_P^*=–2.172±0.234, V_K^*=–0.007±0.267, V_Ca^*=–0.022±0.146, V_Mg^*=–1.710±0.132, and V_R5^*=3.728±0.084. These CND norms are associated with dry bean yields higher than 1.88 t ha^–1, and are associated with the following foliar concentrations: 26.2 g N kg^–1, 2.5 g P kg^–1, 22.9 g K kg^–1, 21.6 g Ca kg^–1, and 4 g Mg kg^–1. Cowpea plants growing in desert calcareous soils took up lower amounts of N, P, and K than those considered as optimum in a previous report. Six interactions were strongly indicated for cowpea through principal component analyses: positive for Ca–Mg, and negative for N–Ca, N–Mg, Ca–P, Mg–P, and K–P. Furthermore, two interactions were identified using simple correlations, negative N–P and positive K–Ca.     

Culture ofGelidium sesquipedale (Clem.) Born.et Thur. in a chemostat system. Biomass production and metabolic responses affected by N flow

Gelidium sesquipedale is the most important raw material used for extraction of agar in Spain. Based on chemostats, a system of culture for macroalgae with a continuous flow of culture medium has been developed. A stressed morphotype from the South of Spain was cultured, and the effects of different rates of NO ₃ ^– flow on growth and internal constituents were investigated in the laboratory. Cultivation was successful after optimizing factors affecting growth, such as irradiance level, renewal rate and water movement. Mass production was dependent on N supply. With a flow of 35 mol NO₃ ^– g^–1 DW d^–1, optimal values of growth (2.1% d^–1) and biomass yield were obtained. In these conditions, biomass yield resembled the values observed in natural populations (about 500 g DW m^–2 y^–1). When the flow of N was reduced to 15 mol NO ₃ ^– g^–1 DW d^–1, growth rate and biomass yield were reduced three-fold, and were null when N was supplied as 7 mol NO ₃ ^– g^–1 DW d^–1. C:N ratio was an index of the physiological status of the tissue, remaining low when N was sufficient and raised to critical values when N supply was limited. Phycobiliproteins, kept at a constant irradiance level, were affected by N supply, acting as an internal nitrogen reserve, unlike chlorophylla. An effective phycobiliprotein synthesis took place when the flow of N was sufficient. Agar yield, on dry weight basis, was similar as a function of N flow, whereas agar yield of the culture was higher when N was sufficient as a result of growth not being limited by N.This system of culture, commonly used in microalgal studies, may have an important use in macroalgae as a system to obtain biomass of high quality as well as a good tool for physiological studies in conditions of continuous and controlled flow of nutrients.     

Process of simultaneous hydrogen sulfide removal from biogas and nitrogen removal from swine wastewater

The feasibility of a new flowchart describing simultaneous hydrogen sulfide removal from biogas and nitrogen removal from wastewater was investigated. It took 30 days for the reactor inoculated with aerobic sludge to attain a removal rate of 60% for H₂S and NO_x–N simultaneously. It took 34 and 48 days to attain the same removal rate for the reactor without inoculated sludge and the reactor inoculated with anaerobic sludge respectively. The reactor without inoculated sludge still operated successfully, despite requiring a slightly longer startup time. The packing material was capable of enhancing the removal efficiency of reactors. Based on the concentration of NO_x–N and H₂S in the effluent, the loading rate and the ability of the system to resist shock loading, the performance of the reactor filled with hollow plastic balls was greater than that of the reactor filled with elastic packing and the reactor filled with Pall rings.     

H2-Recycling system in mungbean Rhizobium in relation to N2-fixation

Thirty isolates of mungbean Rhizobium were tested for the presence of H₂-recycling system. All the isolates were preliminary screened for detecting H₂-recycling system in free culture using triphenyltetrazolium chloride reduction as screening procedure. The isolates which reduced the dye rapidly at early stages of growth were found to recycle hydrogen both in vivo as well as in vitro. Nitrogen fixing efficiency of hydrogenase positive, hydrogenase negative isolates and Hup^– mutants was compared by green house experiments. There was 13–56% increase in dry matter and 21–46% increase in total nitrogen of the plants inoculated with H₂-recycling isolates over the plants inoculated with non-recycling isolates. There was reduction in dry matter and total nitrogen content of the plants inoculated with Hup^– mutants as compared to plants inoculated with wild type strain. The per cent decrease due to inoculation with Hup^– mutants over wild type strain was 19–22 and 20–26 of dry weight and total nitrogen in plants, respectively.Abbreviations TTC triphenyltetrazolium chloride     

Pulmonary diffusing capacity in reptiles (Relations to temperature and O2-uptake)

Summary Pulmonary CO-diffusing capacity (D l _CO), lung volume, pulmonary perfusion and O₂-uptake were measured by non-invasive techniques in the lizardsVaranus exanthematicus andTupinambis teguixin (mean body weight 2.2 kg for both species).The CO-diffusing capacity was at 25–27°C 0.059 mlstpd·kg^–1·min^–1·Torr^–1 inVaranus, which is 47% greater than the value of 0.040 mlstpd·kg^–1·min^–1·Torr^–1 inTupinambis. The lung volume ofVaranus was 36 ml·kg^–1 and that ofTupinambis 20 ml·kg^–1. At 35–37°C the diffusing capacity of lizard lungs are about 25% of those for mammals of comparable size.InVaranus pulmonary CO-diffusing capacity increased with temperature from 0.027 mlstpd·kg^–1·min^–1·Torr^–1 at 17–19 °C to 0.075 mlstpd·kg^–1·min^–1·Torr^–1 at 35–37 °C. This change closely matched a concomitant increase of O₂-uptake. Pulmonary perfusion increased from 27 ml·kg^–1·min^–1 to 55 ml·kg^–1·min^–1 within this temperature range.The study emphasizes that pulmonary diffusing capacity cannot be fully evaluated without information on pulmonary perfusion and O₂-uptake. In reptiles and other ectotherms diffusing capacity must be reported at specified body temperature.     

Biofiltering efficiency in removal of dissolved nutrients by three species of estuarine macroalgae cultivated with sea bass (Dicentrarchus labrax) waste waters 1. Phosphate

The potential of three estuarine macroalgae (Ulvarotundata, Enteromorpa intestinalis andGracilaria gracilis) as biofilters for phosphate ineffluents of a sea bass (Dicentrarchus labrax) cultivationtank was studied. These seaweeds thrive in Cádiz Bay and were alsoselected because of their economic potential, so that environmental andeconomicadvantages may be achieved by future integrated aquaculture practices in thelocal fish farms. The study was designed to investigate the functioning of Pnutrition of the selected species. Maximum velocity of phosphate uptake (2.86mol PO₄ g^–1 dry wth^–1) was found in U. rotundata.This species also showed the highest affinity for this nutrient. At low flowrates (< 2 volumes d^–1), the three species efficientlyfiltered the phosphate dissolved in the waste water, with a minimum efficiencyof 60.7% in U. rotundata. Net phosphate uptake rate wassignificantly affected by the water flow, being greatest at the highest rateassayed (2 volumes d^–1). The marked decrease in tissue P shownby the three species during a flow-through experiment suggested that growth wasP limited. However, due to the increase in biomass, total P biomass increasedinthe cultures. A significant correlation was found between growth rates and thenet P biomass gained in the cultures. A three-stage design under low water flow(0.5 volumes d^–1) showed that the highest growth rates (up to0.14 d^–1) and integrated phosphate uptake rates(up to 5.8 mol PO₄ ^3– g^–1dry wt d^–1) were found in E.intestinalis in the first stage, with decreasing rates in thefollowing ones. As a result, phosphate become limiting and low increments oreven losses of total P biomass in these stages were found suggesting thatphosphate was excreted from the algae. The results show the potential abilityofthe three species to reduce substantially, at low water flow, the phosphateconcentration in waste waters from a D. labrax cultivationtank, and thus the quality of effluents from intensive aquaculture practices.     

Growth of dominant zooplankton species feeding on plankton microflora in Lake Shira

Batch cultures and continuous flow cultures were used to study the growth rates of zooplankton species from Shira lake, the rotifer Brachionus plicatilis Muller and calanoid copepod Arctodiaptomus salinus Daday, which were fed on phytoplankton and bacterioplankton from the lake. Analyses of the birth and survival rates were used to demonstrate that the lake phytoplankton, consisting mostly of cyanobacteria and diatomaceous algae, is inadequotes for optimal realisation of the reproductive potential of B. plicatilis when compared with the bacterial diet. The study revealed that the kinetic growth characteristics of the two zooplankters were similar: B. plicatilis r _max, 0.120 d^–1; S ₀, 0.253; and K _s, 0.114 mg dry mass l^–1; and for A. salinus r _max, 0.129 d^–1; S ₀, 0.240; and K _s, 0.171 mg dry mass l^–1. Fluctuations in natural food concentration reduced the growth rate of both species. Even though the threshold concentration of food for B. plicatilis and A. salinus were quite similar, the copepods were less sensitive to food limitation.     

The influence of invertebrates on the breakdown ofPotamogeton pectinatus L. in a coastal marina (Zandvlei,South Africa)

The influence of invertebrates upon the decomposition ofPotamogeton pectinatus L. in a coastal Marina system was examined over 112 days using litter bags. Invertebrate inclusion bags (2 mm mesh, 5 mm holes) registered a dry mass loss of 1% d^–1, while exclusion litter bags (80 µm mesh) produced a 0.4% mass loss d^–1 (a 2.5 fold difference). Losses of ash and N from inclusion bags were greater than those from exclusion bags (p < 0.05). There was a three fold difference between the two treatments in the time taken for litter to breakdown to half the initial stock: T_1/2 for inclusion bags = 43 d, exclusion bags = 130 d. In both treatments, minerals showed an expected rapid loss, due to leaching, with a subsequent slow increase relative to the dry material remaining. A total of nine invertebrate taxa was recorded from inclusion bags, with a peak biomass of 64 mg g^–1 dry massPotamogeton bag^–1 reached at 64 days after immersion. Grazing amphipods,Melita zeylanica Stebbing andAustrochiltonia subtenuis (Barnard), numerically dominated the litter bag fauna, whileM. zeylanica and nymphs of the zygopteran predatorIschnura senegalensis (Rambur) formed most of the biomass. Scanning Electron Microscopy indicated heavy grazing of micro-organisms by invertebrates, with major qualitative differences occurring 112 days after immersion. Invertebrates significantly accelerated the rate of litter breakdown through their feeding activities, assisting fragmentation and thus contributing to plant losses and also by increasing the surface area for microbial colonisation and attack.     

Quantitative traits associated with adaptation of three barley (Hordeum vulgare L) cultivars to suboptimal iron supply

A laboratory method was developed that allows determination of in situ net nitrification with high sensitivity and at high temporal resolution. Nitrate in soils is quantitatively converted into nitrous oxide under strictly anaerobic conditions in the presence of 10 kPa acetylene by the soil endogenous denitrifier population, with the N₂O detected by a gas chromatograph equipped with a ⁶³Ni electron capture detector. Thus, even low net nitrification rates, i.e. small net increases in soil nitrate concentrations can easily be detected. Comparison of results using this method with results obtained using the classical in situ incubation method (buried bag soil incubation) revealed excellent agreement. Application of the new method allowed both determination of the seasonal pattern of net nitrification as well as correlation analysis between in situ NO and N₂O flux rates and in situ net nitrification rates of the forest soils studied. Regardless of the forest site studied (spruce, spruce limed, beech), and during each year of a 3 years period (1995–1997), net nitrification varied strongly with season and was least during winter and greatest during summer. The long-term annual, mean rate of net nitrification for the untreated spruce site, the limed spruce site and the beech site were 1.54 ± 0.27 mg N kg^–1 sdw d^–1, 1.92 ± 0.23 mg N kg^–1 sdw d^–1 and 1.31 ± 0.23 mg N kg^–1 sdw d^–1, respectively. In situ rates of nitrification and NO and N₂O emission were strongly correlated for all sites suggesting that nitrification was the dominate source of NO as well as N₂O.     

Eichhornia crassipes-based tertiary treatment of Kraft pulp mill effluents in Chilean Central Region

This paper presents experimental results on the implementation of Eichhornia crassipes–based tertiary lagoon to treat effluents generated by a 300 ton d^–1 Kraft pulp mill in Chile. Results show that E. crassipes rapidly adapted to the tertiary lagoon conditions. Active growth was maintained even during a cold winter, protected by the wastewater heat content. A 1000 m² seeding area extended to 2300–6200 m² after a month of growth, with a monthly harvested biomass and nitrogen uptake were 1.1–5.4 ton (dry wt.), and 18–127 kg N, respectively. E. crassipes growth was adequately described by a first order model, with an estimated rate constant ca. 0.03 d^–1 and 0.06 d^–1, for winter and summer seasons, respectively. A management strategy based on such model, to account for seasonal variations in growth rate while keeping a constant nitrogen uptake capacity, is proposed here.     

Digestion and metabolism of a natural foliar diet (Eucalyptus punctata) by an arboreal marsupial, the koala (Phascolarctos cinereus)

Summary Digestion and energy metabolism in an arboreal marsupial, the koalaPhascolarctos cinereus, fed mature foliage from a common food tree, the grey gumEucalyptus punctata, were investigated. Six feeding (balance) experiments, at various times of year, and one slaughter experiment were performed and average daily oxygen consumption was measured.The average apparent digestibilities of dietary constituents were: dry matter 54%; total cell-contents 69%; available carbohydrate 92%; crude lipid 43%; total nitrogen 45%; total phenolics 91%; total cell walls 25%; hemicellulose 24%; acid-detergent fibre 25%; cellulose 31%; lignin 19%.Average digestible and metabolizable energy intakes were 0.50 and 0.43 MJ kg^–0.75 d^–1 respectively of which only 0.28 MJ kg^–0.75 d^–1 was expended in oxidative metabolism. The digestible energy intake required for maintenance was estimated to be 0.33 MJ kg^–0.75 d^–1, which is lower than that of eutherian and of other marsupial herbivores. The principal sources of metabolizable energy were non-structural carbohydrate and lipid.It is postulated that the ability of koalas to utilizeEucalyptus foliage as a sole source of nutrients is facilitated by their low requirement for energy and their ability to maximize intake of non cell-wall constituents.E. punctata foliage has a high digestible energy content compared with the foliage of many other trees and this may be a factor in its selection by koalas.Abbreviations DMI dry matter intake - DMD dry matter digestibility - DE digestible energy - ME metabolizable energy