Degradation rates of aged petroleum hydrocarbons are likely to be mass transfer dependent in the field

Evidence for on site biodegradation may be difficult to provide at heterogeneous sites without additional experiments in controlled laboratory conditions. In this study, microbial activities measured as CO₂ and CH₄ production were compared in situ, in intact soil cores and in bottle microcosms containing sieved soils. In addition, biodegradation rates were determined by measuring the decrease in petroleum hydrocarbon concentrations at 7°C in aerobic and anaerobic conditions. Elevated concentrations of CO₂ and CH₄ in the soil gas phase indicated that both the aerobic and anaerobic microbial activity potentials were high at the contaminated site. Aerobic and anaerobic microbial degradation rates in laboratory experiments of petroleum hydrocarbons were highest in soils from the most contaminated point and degradation in the aerobic and anaerobic microcosms was linear throughout the incubation, indicating mass-transfer-dependent degradation. Different results for microbial activity measurements were obtained in laboratory studies depending on pretreatment and size of the sample, even when the environmental conditions were mimicked. These differences may be related to differences in the gas exchange rates as well as in changes in the bioavailability of the contaminant in different analyses. When predicting by modeling the behavior of an aged contaminant it is relevant to adapt the models in use to correspond to conditions relevant at the contaminated sites. The variables used in the models should be based on data from the site and on experiments performed using the original aged contaminant without any additions.     

Seasonal growth in Laminaria longicruris: Relations with dissolved inorganic nutrients and internal reserves of nitrogen

Observations have been made on seasonal fluctuations in dissolved inorganic nutrients, internal reserves of nitrogen and growth rates in Laminaria longicruris. The onset of winter growth in shallow-water stations (6 and 9 m) correlated well with improved dissolved nitrate conditions in the sea. During the winter, reserves of NO ₃ ^- were accumulated by the plants and reached maximum values of 150 moles per g fresh weight in March. This represents a concentration factor of approximately 28,000 over the ambient levels, or an internal nitrogen reserve of 2.1% of the dry weight of the tissue. Depletion of this nitrogen pool followed the disappearance of the external NO ₃ ^- with a lag period of up to 2 months. Rapid kelp growth was measured during this period. Reserves of organic nitrogen also reached maximum values in March and declined slowly throughout the summer into autumn. It is suggested that the combined inorganic and organic nitrogen reserves sustain the rapid growth rates into July and at reduced rate through the late summer. Fertilization of an experimental perimental kelp bed with NaNO₃ increased the internal plant reserves of NO ₃ ^- and produced a much improved summer growth rate. The enriched plants developed very small reserves of carbohydrate during the rapid summer growth phase.NRCC No. 15549.     

Settlement and recruitment of sea urchins (Strongylocentrotus spp.) in a sea-urchin barren ground and a kelp bed: are populations regulated by settlement or post-settlement processes?

I sampled recruitment of very small sea urchins (Strongylocentrotus spp.) by using the anesthetic magnesium chloride to remove individuals from substrata collected in sea-urchin barren grounds (barrens) and kelp beds at Naples Reef near Santa Barbara, California, USA. Preliminary sampling found low numbers of newly settled individuals(<0.6 mm test diam) from April–July in 1984 and 1985, and in April, 1986. In early May, 1986, I found many newly settled seaurchins (0.3 to 0.6 mm, 5 to 17 d old), and I compared the densities of the cohort on several types of natural substrata in barrens and kelp-bed habitats. Newly settled individuals of both purple sea urchins (S. purpuratus) and red sea urchins (S. franciscanus) were present in similar, high densities (1 000 S. purpuratus m^-2) on foliose red algal turf, a dominant substratum ofthe kelp bed, and on crustose coralline algae, the dominant substratum of an adjacent barrens. Larvae of S. purpuratus reared and tested in the laboratory showed high rates of settlement on both red algal turf and on crustose coralline algae, but significantly lower rates on rock. Larvae also settled in response to a partiallypurified extract of coralline algae. The reduced settlement on natural rock surfaces relative to either algal treatment and the significant settlement in response to the extract of coralline algae indicate that larvae discriminate between natural substrata and probably respond to a settlement cue other than, or in addition to, a simple microbial (bacterial) film. The similar densities of young recruits of S. purpuratus on dominant substrata of barrens and kelp bed show that, at least in this case, differential settlement cannot explain the high densities of sea urchins in the barrens habitat. Movement between barrens and kelp bed is unlikely given the small sizes of the newly recruited sea urchins relative to the large distances often involved. Reduced post-settlement mortality of newly settled individuals in the barrens remains the most likely mechanism leading to the higher densities of sea urchins in barrens relative to kelp-bed habitats.     

In situ water motion and nutrient uptake by the giant kelp Macrocystis pyrifera

Rates of NO ₃ ^- uptake by individual blades of Macrocystis pyrifera (L.) C. Agardh were measured at different flow rates in the laboratory. Dissolution rates of hemispherical, plaster buttons attached to the blade surface provided a relative measure of flow rates over blades used in uptake experiments and also over intact blades of adult kelp plants in situ (Laguna Beach, California, USA; 1981). Laboratory results indicated that uptake was saturated at a flow rate equivalent to 2.5 cm s^-1 current velocity. Flow rates over intact blades in situ always exceeded this uptake saturation level. Wave surge and movement of plant surfaces relative to the surrounding water provided sufficient flow to saturate uptake, even in a dense kelp canopy during low-current and calm sea-state conditions.     

Kelp (<Emphasis Type="Italic">Laminaria digitata</Emphasis>) increases germination and affects rooting and plant vigour in crops and native plants from an arable grassland in the Outer Hebrides,Scotland

Kelp and other seaweeds are traditionally used in many parts of the world as a soil amendment on arable fields. Seaweeds contain biochemical compounds that can act as plant growth regulators in terrestrial plants. In a low-intensity arable grassland in northwest Scotland an organic fertilizer, kelp (Laminaria digitata) has been used for hundreds of years, due to its anticipated positive effect as a soil conditioner and provider of plant nutrients. In this study the effects of kelp on germination and rooting of crops and native plants from this area were investigated in soil-free media. Germination was studied by incubation in the presence of kelp solutions. Rooting of plant cuttings was assessed after a pulse treatment with kelp solutions, and indole-3 acetic acid (IAA) as a reference plant growth regulator. Germination percentage of Plantago lanceolata, Trifolium repens and Avena strigosa seeds increased significantly when incubated with 0.05% kelp solutions. Total root weight and the individual weight of roots produced in cuttings of Vigna radiata and P. lanceolata were significantly increased when exposed to a 0.5% solution of kelp. Plant vigour, assessed visually, decreased significantly for P. lanceolata exposed to kelp at concentrations of 0.5 and 5.0% indicating the presence of a threshold level for an inhibitory effect of kelp at these concentrations, which may be due to high salinity. The results confirmed the presence of plant growth regulators in kelp, and indicates that amendment with kelp may potentially affect plant community composition. The threshold levels where some plants responded negatively to kelp amendment were close to or lower than the theoretical concentrations of kelp in soil water at field conditions with the current doses used on the machair, indicating that care should be taken in either administering kelp at the appropriate dose or leaching out salt before application.     

Growth of juvenile Macrocystis pyrifera (Laminariales) in relation to environmental factors

Instantaneous relative growth rates, (d^-1), were measured for juveniles of the giant kelp Macrocystis pyrifera transplanted to study sites in Southern California kelp forests between 1978 and 1982. Growth rates ranged from negative values (indicating loss of tissue) to 0.03 (doubling of total frond length every 19 d). Multiple regression analysis of growth versus irradiation, temperature, nitrogen concentration and amount of fouling revealed that all these factors had significant effects, together accounting for about 50% of the total variance. Elevated irradiation and nitrogen levels had strongly stimulatory effects (tissue nitrogen may have been more critical than ambient nitrogen for growth), while high temperature and fouling had strongly inhibitory effects. Irradiation was the most important factor influencing growth in 6 of the 8 transplant experiments. During these 6 experiments, the compensating irradiation level (below which there was no growth) was between 0.4 and 0.7 E m^-2 d^-1, and saturating irradiation was between 2 and 3 E m^-2 d^-1. During two of the experiments, growth was apparently limited by extremely high temperatures or low nitrogen levels. Quantum irradiation levels in the kelp forest were generally between the compensation and saturation levels. However, irradiation levels occasionally dropped below the compensation point for several months. Irradiation was occasionally low enough to limit the distribution of juvenile kelp by inhibiting growth, especially in the deeper portions of the kelp forest and under dense canopies formed by adult plants.     

Effects of petroleum products on bull kelp (Nereocystis luetkeana)

Although research has been conducted on the effects of oil on the giant kelp Macrocystis pyrifera, no similar studies have been completed on bull kelp, Nereocystis leutkeana, the dominant kelp in Washington State, British Columbia, and Alaska. The effects of three petroleum products [diesel fuel, intermediate fuel oil (IFO), and crude oil] were tested before and after weathering on N. luetkeana. Whole plants were exposed to petroleum product for 4 or 24 h and then transferred to the field; observations on the condition of the plants were made daily for 7 d. In addition, controlled bioassays were performed to measure the effects of petroleum exposure on net photosynthetic rate (NP) and respiration rate (R), using light-and dark-bottle techniques. These experiments verified the susceptibility of N. luetkeana tissue to the damaging effects of direct exposure to several oil types. The 4 h exposures to weathered diesel and unweathered IFO, and 24 h exposures to unweathered and weathered diesel and IFO resulted in moderate to severe damage to kelp tissue (i.e., clearly delineated bleached line accompanied by tissue necrosis). Weathered diesel was more toxic than unweathered diesel. The most severe damage to bull kelp was concentrated at the meristematic zone (junction of stipe and bulb) where new tissue growth occurs. Petroleum type significantly affected stipe and blade NP, R, and NP:R ratios. Diesel treatments had a greater negative effect on NP than did the IFO treatments. Based on these experiments, the relative ranking of the damaging effects of petroleum treatment on bull kelp are weathered diesel>unweathered IFO>unweathered diesel>weathered IFO>unweathered crude>weathered crude.     

Differential meiospore size and tolerance of ultraviolet light stress within and among kelp species along a depth gradient

 Kelp are differentially stratified along a gradient of UV exposure (as a function of water depth). The role of ultraviolet light in seaweed zonation has not been fully explored. This study found a significant meiospore size difference within and among the kelp species examined: Pterygophora californica Ruprecht (high to mid-subtidal), Macrocystis integrifolia Bory (high to mid-subtidal), Laminaria groenlandica Rosenvinge (high-subtidal), Alaria marginata Postels and Ruprecht (low-intertidal) and Hedophyllum sessile Setchell (mid-intertidal). This size difference was correlated with the depth distribution of adult plants, with the largest meiospores originating from shallow-dwelling adult kelp exposed to high UV light. Under UV stress in the laboratory, meiospores from adults growing in high-UV environments displayed greater germination and survival rates than the progeny of adult kelp occupying lower-UV environments. This suggested that in Barkley Sound, British Columbia, Canada, differential tolerance to UV (possibly determined by meiospore size) may limit the upper settlement position of kelp species and individuals. Tolerance to UV may be an important determinant of kelp zonation on rocky shores. Received: 16 June 1998 / Accepted: 6 January 2000     

Photosynthetic characteristics of giant kelp (Macrocystis pyrifera) determined in situ

Rates of net photosynthesis and nocturnal respiration by individual blades of the giant kelp Macrocystis pyrifera (L.) C. Agardh in southern California, were determined in situ by measuring oxygen production in polyethylene bags during spring/summer of 1983. Mature blades from different depths in the water column exhibited different photosynthetic characteristics. Blades from the surface canopy (0 to 1 m depth) exhibited higher photosynthetic capacity under saturating irradiance and higher photosynthetic efficiency at low irradiances than blades from 3 to 5 or 7 to 9 m depths. Saturating irradiance was lower for canopy blades than for deeper blades. Canopy blades showed no short-term photoinhibition, but photosynthetic rates of deeper blades were significantly reduced during 1 to 2 h incubations at high irradiances. Results of 1 to 2 wk acclimation experiments indicated that differences between photosynthetic characteristics of blades from different depths were primarily attributable to acclimation light conditions. Vertical displacement of blades within the kelp canopy occurred on a time-scale of 1 min to 1 h. Blades continually moved between the unshaded surface layer and deeper, shaded layers. Vertical movement did not maximize photosynthesis by individual blades; only a small proportion of blades making up a dense surface canopy maintained light-saturated photosynthetic rates during midday incubations. The relatively high photosynthetic rates exhibited by canopy blades over the entire range of light conditions probably resulted from acclimation to intermittent high and low irradiances, a consequence of vertical displacement. Vertical displacement also reduced the afternoon depression in photosynthesis of individual canopy blades. The overall effect of vertical displacement was optimization of total net photosynthesis by the kelp canopy and, therefore, optimization of whole-plant production.     

Toxic effect assessment of aminotetrazoles and high-energetic azotetrazole salts on soil microbial respiration

The influence of energetic heterocyclic high-nitrogen salts on microbial activity in soil enrichment was investigated. 5-Aminotetrazole, a sodium salt of 5-aminotetrazole, ammonium azotetrazolate, sodium azotetrazolate, guanidinium azotetrazolate, triaminoguanidine azotetrazolate and triaminoguanidine hydrochloride were examined. Respiration tests determined the amount and rate of production of CO₂, H₂ and H₂S from microbial activity. Aminotetrazoles, triaminoguanidine azotetrazolate and triaminoguanidine hydrochloride substantially reduced the amount and rate of microbial CO₂ production. The total amount of CO₂ produced in the soil enrichments was affected by the cation from the azotetrazole salt, whereas the azotetrazolate anion did not seem to inhibit microbial CO₂ production. In contrast, all applied compounds stopped the production of H₂S completely and modified the rate of H₂ production in the cultures compared with the control. The influence of ammonium azotetrazolate and sodium azotetrazolate on the activity of isolated sulfate-reducing bacteria was also determined. The compounds did not have bactericidal activity towards sulfate-reducing bacteria, but the compounds decreased the amount of H₂S produced or slowed the growth of these bacteria in comparison with the control.     

Effect of seawater velocity on inorganic nitrogen uptake by morphologically distinct forms of Macrocystis integrifolia from wave-sheltered and exposed sites

In conditions of low water motion (<0.06 ms^–1), the availability of essential nutrients to macroalgae, and thus their potential productivity, may be limited by thick diffusion boundary-layers at the thallus surface. The ability of macroalgae to take up nutrients in slow moving water may be related to how their blade morphology affects diffusion boundarylayer thickness. For the giant kelp, Macrocystis integrifolia Bory, morphological measurements indicate that blades of plants from a site exposed to wave action are thick, narrow and have a heavily corrugated surface. In contrast, blades from a site with a low degree of water motion are relatively thin, with few surface corrugations and large undulations along their edges. The aim of our work was to test the hypothesis that morphological features of M. integrifolia blades from a sheltered site allow enhanced inorganic nitrogen uptake at low seawater velocities compared to blades with a wave-exposed morphology. The rate of nitrate and ammonium uptake by morphologically distinct blades of M. integrifolia, from sites that were sheltered from and exposed to wave action, were measured in the laboratory at a range of seawater velocities (0.01 to 0.16 ms^–1), between March and May 1993. For both sheltered and exposed blade morphologies, nitrate and ammonium uptake rates increased with increasing seawater velocity, reaching a maximum rate at 0.04 to 0.06 ms^–1. Uptake parameters V _max (maximum uptake rate) and U _0.37 (the velocity at which the uptake rate is 37% of the maximum rate) were estimated using an exponential decay formula. These parameters were similar for both blade morphologies, at all seawater velocities tested. Additional measurements suggest that the nitrogen status of M. integrifolia blades from wavesheltered and exposed sites were similar throughout the experimental period, and thus nitrogen status did not affect the rate of nitrogen uptake in these experiments. on the basis of these results, we conclude that blade morphology does not enhance nitrogen uptake by M. integrifolia in conditions of low water motion. Potential effects of diffusion boundary-layers on kelp productivity are discussed.     

Changes in sea urchin populations after the destruction of kelp beds

In St. Margaret's Bay, Nova Scotia, Canada, there are large areas in which sea urchins (Strongylocentrotus droebachiensis) have eliminated beds of kelp (Laminaria spp.). Sites were identified where destruction of kelp beds had taken place 1, 2, 3, 3.5 and 4 years ago. With increase of time since kelp disappearance, the sea urchins showed decreased growth rate, reduced gonad size, but an increase in numbers resulting from high recruitment rates in the first two years after kelp bed destruction. These sea urchin populations, by their browsing, effectively prevent the regeneration of kelp. There is, as yet, no evidence of the sea urchin populations being starved out to allow the kelp to return.     

Mechanistic aspects of the thermal formation of halogenated organic compounds including polychlorinated dibenzo‐p‐dioxins part III†: Thermodegradation of organometallics and polymers

Thermodegradation of organometallics viz. RMX (where M = Mg, Ti, Pd, Sn, Si, Al; and X =halogen atom) provides corresponding haloorganics i.e. RX. 1,2‐Shifts of H and Cl on the carbene species like CH₂F. CF and CFCL₂, CF produced from R. CF. Si F₃ (R = CH₂F, CFCl₂) are preferred to that of fluorine. The thermolysis of R.CF₂. Si Cl₃ (R = CH₂F) produces chloroolefins via halogen exchange. Major products of thermal degradation of poly (vinyl chloride) (PVC) are HCl and benzene but the mechanism of PVC thermodegradation is still a matter of dispute. The thermal cracking of lignins yields substituted phenols.     

Growth and utilization of internal nitrogen reserves by the giant kelp Macrocystis pyrifera in a low-nitrogen environment

An adult giant kelp plant (Macrocystis pyrifera), moved from an inshore kelp forest to an offshore, low-nitrogen environment near Santa Catalina Island, California (USA), maintained growth for 2 wk on internal nitrogen reserves. Frond elongation rates decreased significantly during the third week, and plant growth rate (wet wt) dropped from an initial inshore rate of 3.6 to 0.9% d^-1. During this 3 wk period, nitrogen contents and free amino acid concentrations decreased, while mannitol and dry contents increased in frond tissues. After depletion of internal nitrogen reserves, the nitrogen content of lamina and stipe tissues averaged 1.1 and 0.7% dry wt, respectively. The experimental plant was exposed to higher ambient nitrogen concentrations during the last 2 wk. Rates of frond elongation and plant growth increased, but nitrogen content and amino acids in frond tissues remained low. Of the total nitrogen contained in frond tissue of the plant before transplantation, 58% was used to support growth in the absence of significant external nitrogen supply. Amino acids constituted a small proportion of these internal nitrogen reserves. Net movement of nitrogen occurred within large fronds, but not between different frond size classes. The nitrogen content of holdfast tissue remained relatively constant at 2.4% dry wt and accounted for 18 to 29% of the total nitrogen. Holdfast nitrogen was not used to support growth of nitrogen-depleted fronds. In comparison to Laminaria longicruris, which is adapted to long seasonal periods of low nitrogen availability, M. pyrifera has small nitrogen-storage capacity. However, internal reserves of M. pyrifera appear adequate to make nitrogen starvation uncommon in southern California kelp forests.     

Modelling the growth and harvest yield of the giant kelp Macrocystis pyrifera

The giant kelp Macrocystis pyrifera is one of the largest and fastest growing seaweeds and is dominant over large areas of the west coast of North America. A model of its growth has been developed which describes plant biomass and production over the course of a year as a function of environmental parameters which affect the light flux. Such parameters include water clarity, spacing between plants, bottom depth, latitude, harvesting activity, and photosynthetic response (P _max and I _k ). Model results for a standard set of conditions (latitude 33°N, 3 m plant spacing, water absorbance of 0.115 m^-1 and 12 m depth) yield a peak daily gross production of almost 6 g C m^-2 d^-1, peak daily net production of almost 3 g C m^-2 d^-1, and a peak specific growth rate of about 0.022 d^-1. Annual gross production for this case is 1 567 g C m^-2 yr^-1; annual net production is 537 g C m^-2 yr^-1. These values are comparable to those from field measurements. Size and timing of biomass and production peaks are affected by changes in the parameters describing the light field, with peaks usually occurring later in the year for more adverse circumstances. Inhigher latitudes, the seasonal variation is so extreme that the plant could not last the year at 53° N in 12 m of water, although it is able to survive the year in shallower water. Harvesting has severe effects on biomass and production. Model results suggest that light limitation is a very important constraint on kelp growth that should not be overlooked. This implies that differences in parameters describing two environments must be considered when comparing results obtained at different locales.     

Factors affecting methyl and inorganic mercury dynamics in mussels and shrimp

Radiotracer experiments were designed to study the effect of certain factors on the accumulation and loss of methyl and inorganic mercury in mussels (Mytilus galloprovincialis) and benthic shrimp (Lysmata seticaudata). Methyl mercury was accumulated from both food and water to a greater degree than inorganic mercury by both species. There was a tendency for small mussels to concentrate more mercury than larger individuals, but the reason for this difference remains unclear. A trend towards greater mercury accumulation at higher temperatures was noted for mussels, but the temperature effect was relatively small over a 10 C^o range between 8° and 19°C. Methyl mercury residues were eliminated by both species more slowly than those of the inorganic form. Loss from mussels was somewhat more rapid at higher temperatures; however, as in the case of accumulation, the effect of temperature was relatively small. Loss rates for small mussels were not significantly different from those for large individuals. Enhanced methyl mercury elimination was noted for the group of mussels maintained in their natural environment. The more rapid metal turnover in these individuals compared with mussels held in the laboratory was attributed to differences in the availability of natural particulate food matter and, hence, subsequent growth of the animals in the two experimental systems. The observed differences underscore the need for caution in predicting in situ flux of metals such as mercury in certain species based solely on data derived from laboratory experiments.     

Seasonal variation in the effects of food availability on gametogenesis in the purple urchin (<Emphasis Type="Italic">Strongylocentrotus purpuratus</Emphasis>)

The amount of food and when it is available affect both the timing of reproduction and the number of gametes produced by purple sea urchins, Strongylocentrotus purpuratus. To investigate this further, the effects of food availability on feeding rates, gonad growth, and gamete development were examined in S. purpuratus collected from the Point Loma kelp forest near San Diego, California, USA (32.69° N, 117.26° W) in September (Fall) 2007, and February (Spring) and July (Summer) 2008, using laboratory mesocosms. Each seasonal laboratory feeding experiment lasted 3 months, and different levels of food availability were established with different feeding frequencies (from 1 to 7 days week⁻¹). Gonad tissues of male and female urchins were staged at the end of each experiment using histological analyses. Reduced food availability resulted in increased daily consumption rates, especially in the Fall when gamete development began. Food limitation at this time resulted in failure to produce viable gametes, suggesting there is a critical period early in gonad development when food limitation affects reproductive competency. Food limitation later in gonad development did not stop viable gamete production, although it did reduce gamete output.     

Laboratory studies of the marine copepod Centropages typicus: egg production and development rates

Egg production and development rates of Centropages typicus (Krøyer) were studied in the laboratory under carying food and temperature conditions. Egg production rates in the laboratory ranged from 0 to 124 eggs female^-1 d^-1 and increased with food concentration up to a critical food concentration (P_c) above which egg production was constant. Egg production rates were influenced by temperature, with more eggs being produced at 15°C than at 10°C. Thalassiosira weisflogii and Prorocentrum micans were determined to be equally capable of supporting egg production at concentrations above P_c at 15°C. Rate of egg production was independent of adult female size when food and temperature were constant. Egg production rates of freshly captured females ranged from 0 to 188 eggs female^-1 d^-1 and were higher in April and May than in June or July. Hatching rates of eggs increased with increased temperature; 95% of the eggs at 15°C hatched within 48 h, while only 8% of the eggs at 10°C hatched within 48 h. Development rates, determined at 10°C in excess concentrations of T. weisflogii, were 23.0 d from egg release to copepodid state I, 27.0 d to stage II, 29.5 d to stage III, 32.2 d to stage IV, 38.5 d to stage V and 49 d to adulthood based on the average time required for 50% of the organisms in an experiment to attain a given stage. Adult males were usually observed 2 to 4 d before adult females, and therefore have a slightly faster rate of development. The effects of temperature, food type and food concentration on egg production and the seasonal appearances of diatoms in the New York Bight may account for the observed seasonal cycles in abundance of C. typicus in these coastal waters.     

Efficient adsorption of carbon dioxide and methane on activated carbon prepared from glycerol with potassium acetate

In the context of global warming and the energy crisis, emissions to the atmosphere of greenhouse gases such as carbon dioxide (CO₂) and methane (CH₄) should be reduced, and biomethane from landfill biogas should be recycled. For this, there is a need for affordable technologies to capture carbon dioxide, such as adsorption of biogas on activated carbon produced from industrial wastes. Here we converted glycerol, a largely available by-product from biodiesel production, into activated carbon with the first use of potassium acetate as an activating agent. We studied adsorption of CO₂ and CH₄ on activated carbon. The results show that activated carbon adsorb CO₂ up to 20% activated carbon weight at 250 kPa, and 9% at atmospheric pressure. This is explained by high specific surface areas up to 1115 m²g⁻¹. Moreover, selectivity values up to 10.6 are observed for the separation of CO₂/CH₄. We also found that the equivalent CO₂ emissions from activated carbon synthesis are easily neutralized by their use, even in a small biogas production unit.

     

Effects of an oil and gas-production effluent on the colonization potential of giant kelp (Macrocystis pyrifera) zoospores

Point sources of pollution (e.g. industrial and municipal outfalls) may produce ecological impacts at distant locations if pollutants affect dispersive propagules. We used laboratory experiments to determine how water-column exposure to produced water (=the aqueous fraction of oil and gas production that is typically discharged into coastal waters) influences the colonization potential of giant kelp (Macrocystis pyrifera) zoospores on the bottom. Zoospores were maintained in suspension at relatively low densities in 18-liter containers and exposed to one of five concentrations of produced water for varying amounts of time. Zoospore swimming generally decreased with increasing produced-water concentration and exposure duration; however, the specific pattern of decrease differed between experimental trials done on different dates. The effect of exposure duration on the ability of swimming zoospores to attach to plastic dishes placed on the bottom varied with produced-water concentration. Zoospores placed in produced-water concentrations of 1 and 10% showed a steady decline in their ability to attach with increased exposure; lower concentrations of produced water had no such effects. The percentage of zoospores that germinated after attachment varied tremendously with exposure duration and date of experimental trial. Zoospores that settled during the first 12 h after release had very poor rates of germination, indicative of a short precompetent period. Surprisingly, exposure of suspended zoospores to high concentrations of produced water during the first 12 h reduced this precompetent period and greatly improved germination success on the bottom. The magnitude of this enhancement, however, varied among dates. The results suggest that adverse effects of discharging produced water on planktonic zoospores of giant kelp would most likely be limited to the immediate vicinity of the outfall.