"Reference Biospheres" for solid radioactive waste disposal: the BIOMASS methodology

The BIOMASS Theme 1 project has developed a methodology for the logical and defensible construction of 'assessment biospheres': mathematical representations of biospheres used in the total system performance assessment of radioactive waste disposal. The BIOMASS Methodology provides a systematic approach to decision making, including decisions on how to address biosphere change. The BIOMASS Methodology was developed through consultation and collaboration with many relevant organisations, including regulators, operators and a variety of independent experts. It has been developed to be practical and to be consistent with recommendations from ICRP and IAEA on radiation protection in the context of the disposal of long-lived solid radioactive wastes. The five main steps in the methodology are described in this paper. The importance of a clear assessment context, to clarify intentions and to support a coherent biosphere assessment process within an overall repository performance assessment, is strongly emphasised. A well described assessment context is an important tool for ensuring consistency across the performance assessment as a whole. The use of interaction matrices has been found to be helpful in clarifying the interactions between different habitats within the biosphere system and the significant radionuclide transfer pathways within the biosphere system. Matrices also provide a useful means of checking for consistency.     

Modelling and experimental studies on the transfer of radionuclides to fruit

Although fruit is an important component of the diet, the extent to which it contributes to radiological exposure remains unclear, partially as a consequence of uncertainties in models and data used to assess transfer of radionuclides in the food chain. A Fruits Working Group operated as part of the IAEA BIOMASS (BIOsphere Modelling and ASSessment) programme from 1997 to 2000, with the aim of improving the robustness of the models that are used for radiological assessment. The Group completed a number of modelling and experimental activities including: (i) a review of experimental, field and modelling information on the transfer of radionuclides to fruit; (ii) discussion of recently completed or ongoing experimental studies; (iii) development of a database on the transfer of radionuclides to fruit; (iv) development of a conceptual model for fruit and (v) two model intercomparison studies and a model validation study. The Group achieved significant advances in understanding the processes involved in transfer of radionuclides to fruit. The work demonstrated that further experimental and modelling studies are required to ensure that the current generation of models can be applied to a wide range of scenarios.     

Morpho-functional patterns of photosynthesis and UV sensitivity in the kelp <Emphasis Type="Italic">Lessonia nigrescens</Emphasis> (Laminariales,Phaeophyta)

The photosynthetic responses of the south Pacific kelp Lessonia nigrescens of the coast of Valdivia, Chile (40°S), were investigated by exposing its different thallus parts, fronds, stipes and holdfasts, to UV radiation in the laboratory. Biologically effective doses (BED_{photoinhibition300}) between 400 and 800 kJ m⁻² were required for a 40% inhibition in photosynthesis under UVA+UVB radiation. At BED_{photoinhibition300} close to 250 kJ m⁻² (in treatments without UVB), the inhibition of photosynthesis did not exceed 20%. These UV doses were in the range of current daily doses measured in Valdivia on cloudless summer days. In general, exposure to UVB for periods longer than 12 h reduced photosynthesis, measured as maximal quantum yield (F _v/F _m) and electron transport. The fronds were the most UV-sensitive section of this alga, coinciding with the highest pigments contents and carbon fixation. Evidence of a photodamage was also seen. After a 48 h exposure to PAR+UVA+UVB, a decrease of F _v/F _m in the fronds was close to 41%, while in the stipes and holdfasts it was 12 and 18%, respectively. Although the thalli from the different size classes showed marked differences in their morphology and morphometry, no obvious differences in the UV tolerance of the fronds were detected. The results indicated that the UV-related responses are integrated in the suite of morpho-functional adaptations of the alga. Although the fronds are spatially more exposed to solar radiation than basal structures (stipes and holdfast), due their high turnover rate they may compensate better detrimental effects of UV. In contrast, stipes and the holdfast are key support structures characterized by low replacement rates and designed to confer hydrodynamic resistance to drag forces.     

The search for indigenous dune stabilizers: Germination requirements of selected South African species

The coastline of South Africa is characterized by extensive dune fields which are threatened by development, and thus the demand of stabilization of drift sand will increase. The non-invasive alien grass speciesAmmophila arenaria is at present the dominant sand stabilizer. Due to its foreign origin and invasiveness in North America its use was criticized and indigenous sand-binding species would be preferred. The germination requirements of the nativeArctotheca populifolia, Ipomoea pes-caprae. Myrica cordifolia andScaevola plumieri were investigated. The results showed that for all four species the total germination time and germination phase could be shortened and germination success (number of germinated seeds) improved. The different scarification and stratification treatments broke the dormancy ofI. pes-caprae, M. cordifolia andS. plumieri, whereas the seeds ofA. populifolia were not dormant. Seeds ofI. pes-caprae andM. cordifolia had induced an innate dormancy, respectively, whereas the type of dormancy in seeds ofS. plumieri dormancy processes remained unknown.     

Diel trophic interactions between vertically-migrating zooplankton and their fish predators in an eelgrass community

Diel changes in the composition of crustacean zooplankton and the diets of fish predators from an intertidal eelgrass flat were monitored concurrently. The zooplankton is characterized by two major components. The obligate zooplankters (holoplanktonic calanoid copepods and meroplanktonic decapod larvae) appear to exhibit vertical migration, being present in higher densities near the surface of the water column at night. The facultative zooplankton (amphipods and ostracods) are benthic during the day, but move up into the water column at night. Planktivorous midwaterdwelling fish consume calanoid copepods and decapod larvae during the day and cease feeding or switch their diet to amphipods at night. Benthic-dwelling fish consume some amphipods during both day and night. The factors important in prey selection by fish and the functional significance of vertical migration in both components of the zooplankton are discussed in the light of the changing patterns of fish predation.This paper is Publication No. 183 in the Ministry for Conservation of Victoria, Environmental Studies Series.     

Respiration rates of<Emphasis Type="Italic"> Beroe ovata</Emphasis> in the Black Sea

Metabolic rates of the ctenophore Beroe ovata within the length range from 0.4 mm (newly hatched larvae) to 60 mm were investigated. At 20° the respiration rates (Q, µg O₂ ind.^–1 h^–1) of individuals with wet weights (W, mg) less than or greater than 100 mg changed according to the equations Q=0.093W^0.62 and Q=0.016W^0.99, respectively. The weight-specific respiration rate of the juvenile ctenophores with wet body weights of 0.021–100 mg diminished approximately 20-fold (from 0.35 to 0.017 µg O₂ mg^–1 h^–1, respectively), but did not change within the range from 100 to 30,000 mg. The difference in the slope of the regression lines seems to be attributable to the ontogenetic changes in B. ovata metabolism. For the tested temperature range of 10–28°, the mean Q₁₀ coefficient was equal to 2.17±0.5. The basal metabolism of B. ovata narcotised by chloral hydrate was 4.5±0.9 times lower than total metabolism. Such a metabolic range is considered to be characteristic of aquatic invertebrates with high levels of locomotory activity.Communicated by O. Kinne, Oldendorf/Luhe     

Interception and dispersal of artificial food falls by scavenging fishes in the abyssal Northeast Atlantic: early-season observations prior to annual deposition of phytodetritus

The hypothesis that the behaviour of deep-sea scavenging fishes is influenced by seasonal input of organic matter from the ocean surface was investigated by observing responses to baits placed on the sea floor at 4800 m depth in the NE Atlantic (48°50′N; 16°30′W) during spring (April 1994). Data from the present study are compared with those from previous studies of the same location made in summer 1989. The first fishes to arrive at baits were the grenadier Coryphaenoides (Nematonurus) armatus and the eel Histiobranchus bathybius, after delays of 28 and 29 min, respectively; these results are not significantly different from those of summer 1989. Similarly, other indices of activity (staying time and swimming speed) showed no evidence of differences between years/seasons. However, the rate of radial dispersal of bait (0.009 m s⁻¹) by C. (N.) armatus was much slower than in all previous studies. A change in the size distribution of C. (N.) armatus to smaller individuals in spring 1994 was also evident. It is suggested that the fish on the abyssal plain may not comprise a steady-state population and that major episodic or seasonal migrations may occur. Received: 18 October 1996 / Accepted: 20 December 1996     

Advanced age for sexual maturity in the ocean quahog Arctica islandica (Mollusca: Bivalvia)

A study of gonadal state in 39 small specimens of Arctica islandica Linné collected in April 1976 from the Middle Atlantic shelf of North America suggests that sexual maturity is reached at a later age than has been reported for other shelf bivalves. Eight of the specimens had gonads in the undifferentiated state. On the basis of annual internal growth banding in the shells of these immature specimens, age ranged between 4 and 14 years. Average age was 9.38 years (standard deviation, s,= 3.54). Shell length ranged from 24 to 47 mm (average 38.85 mm, s=9.25). Differentiated gonads were found in specimens as young as 6 years. Age of maturity shows a wide range and may be dependent upon growth rate and locality.     

Bacterial populations as components of oceanic ecosystems

The production of bacterioplankton in tropical waters is shown to be a major food source for filter feeders. Since this production greatly exceeds autotrophic production by phytoplankton, the external energy source is believed to be soluble organic material transported from temperate latitudes. In the latter environment this material is produced as part of excessive autotrophic production, but its destruction by bacteria is inhibited at low temperature. The organic material is transported by global circulation to warm tropical waters, where it is utilized to form particulate organic aggregates which serve as food for filter feeders.