Temporal shifts in the allocation of energy in the arrow squid,<Emphasis Type="Italic"> Nototodarus gouldi</Emphasis>: sex-specific responses

Squid typically display considerable intra-specific plasticity in size and age-at-maturity in response to ambient environmental conditions, yet little is known of the mechanisms driving these variations. We examined the intra-specific variability in Nototodarus gouldi reproductive traits to determine patterns of energy allocation between somatic and reproductive processes over short temporal scales. Females caught during the cool months of May and July were larger, had slower lifetime growth, lower gonad investment, and better somatic condition than females caught during the warmer months, suggesting a trade-off between gonad investment and somatic condition in females. On the other hand, males showed a tight coupling between somatic condition and gonad investment for most months, with increases in somatic and gonad tissue occurring concurrently. In male squid, an increase in lifetime growth rate was coupled with an increase in the relative weights of somatic and reproductive structures, whereas in females, percent increase in body weight per day was correlated only with gonad development. Patterns of repro-somatic investment in mature females had implications for spawning strategies, since female squid with higher levels of gonad investment apparently released batches of eggs together as a group, regardless of body size, whereas females with low gonad investment possibly spawned their eggs independently of one another. In terms of life-history theory, male squid were able to respond rapidly to environmental fluctuations without compromising either the gonad or the soma. However, although mature females did not appear to respond as quickly to ambient conditions, female squid possibly produced two different reproductive strategies, possibly to maximise offspring survival in either a stable or a variable environment. It seems from our study that monthly variations in ambient conditions may have large effects on life-history strategies.Communicated by M.S. Johnson, Crawley     

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.     

Species- and stage-specific differences in trace element tissue concentrations in amphibians: implications for the disposal of coal-combustion wastes

Information on species- and stage-specific patterns of contaminant accumulation is generally lacking for amphibians, yet such information could provide valuable knowledge on how amphibians interact with contaminants. We assessed concentrations of As, Cd, Cu, Ni, Pb, Se, Sr, and Zn in whole bodies of larval, recently metamorphosed, and adult life stages in Bufo terrestris and Rana sphenocephala from a site that currently receives coal combustion waste (CCW) discharge, a site where CCW was formerly discharged that has undergone natural attenuation for 30 years, and a nearby reference site. For the majority of elements (As, Cd, Cu, Ni, Pb, Zn), concentrations were highest in larvae, but Se and Sr concentrations remained elevated in later life stages, likely because these elements are S and Ca analogs, respectively, and are thus retained throughout structural changes during metamorphosis. Element concentrations were generally higher in B. terrestris than in R. sphenocephala. Concentrations of As, Se, and Sr were up to 11-35 times higher in metamorphs emigrating from CCW-polluted wetlands compared to unpolluted wetlands, suggesting metamorphosed amphibians can transport trace elements from aquatic disposal basins to nearby uncontaminated terrestrial habitats. In addition, anurans utilizing naturally revegetated sites up to 30 years after CCW disposal ceases are exposed to trace elements, although to a lesser degree than sites where CCW is currently discharged.     

Transfer of selenium from prey to predators in a simulated terrestrial food chain

Little is known about the accumulation and effects of selenium in reptiles. We developed a simplified laboratory food chain where we fed commercial feed laden with seleno-D,L-methionine (30 microg/g dry mass) to crickets (Acheta domestica) for 5-7 d. Se-enriched crickets (approximately 15 microg/g Se [dry mass]) were fed to juvenile male and female lizards (Sceloporus occidentalis) for 98 d while conspecifics were fed uncontaminated crickets. Lizards fed contaminated prey accumulated Se concentrations ranging from 9.3 (in female carcass) to 14.1 (in female gonad) microg/g compared to <1.5 microg/g in tissues of controls. Female gonad concentrations approached the highest of thresholds for reproductive toxicity in oviparous vertebrates. However, we observed no consistent effect of dietary treatment on sublethal parameters or survival. Our simplified food chain proved to be an ecologically relevant method of exposing lizards to Se, and forms the foundation for future studies on maternal transfer and teratogenicity of Se.     

Nutrient losses by surface run-off following the application of organic manures to arable land. 1. Nitrogen

Research was conducted on nitrogen (N) surface run-off losses following organic manure applications to land, utilising a purpose-built facility on a sloping site in Herefordshire under arable tillage. Different rates and timing of cattle slurry, farmyard manure and inorganic N and phosphorus (P) fertiliser were compared, over a 4-year period (1993-97). P losses from the same studies are reported in a separate paper. The application of cattle slurries to the silty clay loam soil increased the loss of solids and NH4(+)-N in surface water flow compared to control plots receiving inorganic fertiliser only, or no treatment, but had little effect on NO3(-)-N losses by this route. Results were consistent with other observations that rainfall events immediately after manure applications are particularly likely to be associated with nutrient run-off losses. Losses via subsurface flow (30 cm interflow) were consistently much lower than via surface water movement and were generally unaffected by treatment. Increasing slurry application rate and, in particular, slurry solids loading, increased solids and NH4(-)-N losses via surface run-off. The threshold, above which the risk of losses via surface run-off appeared to be greatly increased, was ca. 2.5-3.0 t/ha slurry solids, which approximates to the 50 m3/ha limit suggested for slurry within UK 'good agricultural practice'. Sealing of the soil surface by slurry solids appears to be a possible mechanism by which polluting surface run-off may occur following slurry application on susceptible soils. Total losses of NH4(+)-N and NO3(-)-N during the 4-year monitoring period were insignificant in agronomic terms, but average soluble N concentrations (NH4(+)-N + NO3(-)-N) in run-off, ranging from ca. 2.0 mg/l, up to 14.0 mg/l for the higher rate slurry treatments. Peak concentrations of NH4(+)-N > 30 mg/l, are such as to be of concern in sensitive catchments, in terms of the potential for contribution to accelerated eutrophication and adverse effects on freshwater biota.     

An assessment of the risks associated with PCDDs and PCDFs following the application of sewage sludge to agricultural land in the UK

A model has been developed to describe the transfer of PCDDs and PCDFs from sludge-amended soils to the human foodchain. The model is conservative and assumes that all foods consumed by an individual are derived from sludge-amended soils. Predicted concentrations of PCDDs and PCDFs in potatoes, cereals, root vegetables and leafy vegetables were in close agreement with mean concentrations reported in the food survey conducted by MAFF in the UK. Predicted concentrations in milk were well below the Maximum Tolerable Concentration adopted by MAFF. Assuming a half-life of ten years in sludge-amended soils, the maximum estimated incremental daily intake (IDI) predicted by the model following ten applications of sludge to agricultural land was 0.80 pg I-TEQ kg⁻¹ day⁻¹, representing an increase of approximately 45% on current levels of background exposure. For an individual whose diet is solely derived from sludge-amended soils, the total exposure is predicted to be approximately 181 pg I-TEQ day⁻¹ or 2.6 pg I-TEQ kg⁻¹ day⁻¹. This compares with an average background exposure of approximately 2 pg I-TEQ kg⁻¹ day⁻¹, well within the TDI of 10 pg I-TEQ kg⁻¹ day⁻¹ and indicates that the application of sewage sludge to agricultural land under the conditions assumed would not appear to present a significant health risk under the conservative scenarios considered in this assessment.     

The effect of two applications of atrazine on the water quality of freshwater enclosures

To simulate runoff from agricultural lands, atrazine was applied to aquatic enclosures (112 m(3)) on 1 June 1983 at a concentration of 0.1 mg litre(-1). Thirty-five days later the nominal concentration was increased to 0.155 mg litre(-1). Treated enclosures became clearer with Secchi disc readings of 3.6 m compared to non-treated controls (2.9 m). Less than 5% of the first atrazine addition disappeared during the first 35 days and little effect on biological activity was observed. However, with the second enrichment the rate of loss of atrazine was rapid (t(1/2) = 150 days), ammonium, calcium, dissolved inorganic carbon and nitrate levels were higher, while oxygen, chlorophyll, dissolved organic carbon and particulate organic carbon concentrations were lower in the treated enclosures. These water quality changes cannot be explained by herbicide-water chemistry interactions alone, thereby suggesting an indirect effect as a consequence of atrazine inhibition on photosynthesis and possibly other microbial processes.     

Mobility of polychlorinated aromatic compounds in soils contaminated with wood-preserving oil

Greater understanding of the mobility of polychlorinated aromatic compounds in soils is needed to investigate contamination and design suitable remediation strategies for sites contaminated with wood-preserving oil. The objectives of this study were (1) to develop a suitable aqueous batch extraction method for soil containing wood-preservative residues; (2) to determine partition coefficients for the primary contaminants [pentachlorophenol (PCP), polychlorinated dibenzo-p-dioxins (PCDDs), and polychlorinated dibenzofurans (PCDFS)] in oil, soil, and aqueous phases; and (3) to evaluate the potential soil migration of the primary contaminants. In a three-phase oil-soil-water mixture, PCP, PCDDs, and PCDFs were partitioned to the greatest extent in the oil phase. These results suggest that the migration of contaminants can occur in a saturated subsurface soil zone containing an oil phase at a wood-preserving site. In the absence of a free oil phase, PCDDs and PCDFs were highly partitioned onto soil and were considered non-leachable in the aqueous phase. However, PCP was considered highly leachable from contaminated soil containing only an aqueous liquid phase. Results from this study indicate that removal of any free oil phase present in subsurface soil should have highest priority during the cleanup of contaminated wood-preserving sites.