The prenatal diagnosis of the cerebro-hepato-renal syndrome of Zellweger

The prenatal diagnosis of the cerebro-hepato-renal syndrome of Zellweger (CHRS) was made by assaying the levels of very long chain fatty acids (VLCFAs) in amniotic fluid cell cultures, obtained by amniocentesis at 16 1/2 weeks of pregnancy. The family-at-risk, because they had previously borne a child with CHRS, accepted these results as indications of an affected fetus, and chose to terminate the pregnancy at 20 1/2 weeks of gestation. The diagnosis was confirned by the phenotype of the aborted fetus and the presence of markedly elevated levels of VLCFAs in fetal liver homogenates. The prenatal diagnosis of CHRS, which can now readily be determined from amniotic fluid cell cultures, is an important step in genetic counselling of families-at-risk for this disease.     

An approach and preliminary model of integrating ecological and economic constraints of environmental quality in the Guayas River estuary, Ecuador

We describe conceptual and simulation models of land use within the intertidal zone of the Guayas River estuary to quantify the contribution of mangrove wetlands to maintaining environmental quality of a tropical estuary. The goal of this exercise is to demonstrate the important consideration of ecological constraints in determining economic and management decisions; and how modeling can be used to quantify impacts of land use such as loss of mangrove wetlands on environmental quality. Our conceptual model treats solar energy, river flow, and tides as forcing functions that control the properties of estuarine ecosystems, but also describes market forces and cultural policies as constraints on properties of socioeconomic systems. The controversy of coastal resource management in Ecuador centers around the relative impacts of shrimp pond construction and management as negative feedbacks to the environmental quality of the Guayas River estuary. Unique oceanographic processes and land use changes contribute to complex issues of water and habitat quality in this tropical estuary, the largest estuarine complex on the Pacific coast of South America. A dynamic box model was developed for the estuary and calibrated with data collected from a 14 month survey of water quality parameters throughout the estuary. Scenarios included conversion of mangroves to shrimp ponds in three regions of the estuary, and the construction of a dam by varying three different rates of river discharge at 100, 50 and 10% of 1989 base flow. Good water quality is maintained by the low residence time of water in the estuary (11 d) because of seasonally high river flow and tidal exchange. With a 90% reduction of mangrove forests in the estuary caused by shrimp pond construction, total nitrogen concentrations increased 5 fold. However, as river discharge decreased to 10%, the same construction caused a 60 fold increase in nitrogen concentrations to 250 μM. Increases in nitrogen concentrations were higher in the upper estuary region, with much less change in the lower estuary. Thus the sensitivity of environmental quality to changes in land use in the intertidal and upland zone are linked to the hydrography of the estuary and is site specific. In the future, the combinations of these ecological models together with economic analyses of the goods and services of mangroves may provide better techniques to evaluate the economic impacts of specific coastal zone management decisions.     

Influence of body condition and weather on departures of first-year European robins, <Emphasis Type="Italic">Erithacus rubecula</Emphasis>, from an autumn migratory stopover site

How migratory birds decide when to leave a stopover site is important to the understanding of bird migration strategies. Our study looks at how body condition and the weather affect the decision to depart on nocturnal migratory flight. During two autumn migration seasons (2002–2003), we radio tracked 51 first-year European robins, Erithacus rubecula, at a stopover site on the Courish Spit (Eastern Baltic) from the first day after landing until their migratory departure. The tagged robins stopped over for 1–14 days. There was no clear relationship between stopover duration and energetic condition on arrival. Weather conditions (wind, precipitation, and cloud cover) on departure differed measurably between years. In 2002, robins took off mainly under following winds and clear skies. In 2003, there were mainly light head winds and partially cloudy or overcast skies. This could be explained by the year-specific role of weather factors in making the decision to depart. In both years, robins making short (1–2 days) stopovers took off in more varied weather situations than those individuals with long stopovers. This suggests that robins from the former group were more inclined to continue with migration than longer-stay birds that, apart from re-fuelling, could be waiting for favourable weather. The lack of a relationship between stopover duration and body condition and some departures under unfavourable weather conditions suggest that endogenous spatiotemporal programmes may play an important role in controlling stopover duration in robins.     

Regional differences in duration of the planktonic larval stage of reef fishes in the eastern Pacific Ocean

Regional variation in the duration of the planktonic larval phase of three species of reef fishes, Thalassoma lucasanum (Labridae), Stegastes flavilatus, and Microspathodon dorsalis (Pomacentridae) was investigated between 1982 and 1991 at several sites in the tropical eastern Pacific over a distance of 3500 km, encompassing virtually their entire range of distribution. Durations of the larval phase, determined from counts of daily otolith increments, were significantly different (1.3 to 1.6 x) between sites. Populations of all three species had a consistently shorter larval life at the most northern site, Cabo San Lucas (Mexico) compared to Panamá and the offshore islands of Galápagos and Cocos. Analyses of otolith increment width over the precompetent period revealed that this disparity in larval duration primarily reflected differences in larval growth rates: faster growing fish spent less time in the plankton. In T. lucasanum, some of the variation in larval duration between Panamá and offshore sites (Galápagos Islands and Cocos Island) may be accounted for by a higher frequency of individuals delaying metamorphosis at the offshore sites. These data indicate that conditions in the planktonic environment are not homogeneous throughout the tropical eastern Pacific and may have a profound effect on aspects of the larval ecology of reef fishes in this region.     

Duration of the planktonic larval stage of one hundred species of Pacific and Atlantic wrasses (family Labridae)

The planktonic larval durations of a preliminary sample of one hundred species of wrasses from both the Pacific and Atlantic Oceans were estimated with the use of the daily otolith-increment aging-technique. Larval durations were determined by counting the number of daily increments between the center of the otolith and the mark corresponding to settlement. The duration of the planktonic larval phase of wrasses appears to be extremely variable between species, ranging from 15 d in Diproctacanthus xanthurus to 121 d in a specimen of Thalassoma ballieui. Larval durations within species were also variable, especially in species with relatively long durations. Congeners tended to have similar larval durations and similar otolith-increment characteristics. Hawaiian and Eastern Pacific species had longer larval durations than their Caribbean or Western Pacific congeners. Similarly, Hawaiian populations had significantly longer larval durations than their Western Pacific conspecifics. The implications of these findings for biogeographical studies are discussed.     

Social-ecological resilience and social conflict: institutions and strategic adaptation in Swedish water management

Dealing with uncertainty and complexity in social-ecological systems is profoundly dependent on the ability of natural resource users to learn and adapt from ecological surprises and crises. This paper analyzes why and how learning processes are affected by strategic behavior among natural resource users and how social conflict is affected by social and ecological uncertainty. The claim is that social conflict among natural resource users seriously inhibits the possibilities of learning and adaptation in social-ecological systems. This is done combining insights from political science, experimental economics, and social-psychology and an analytical case study elaborating social conflict and institutional change in Swedish water management institutions. This paper also discusses the crucial role the institutional context plays in defining the outcome of learning processes in Swedish water management institutions and hence highlights previously poorly elaborated political aspects of learning processes and institutional change in social-ecological systems.     

Modelling of silica diffusion experiments with Si in Boom Clay

A mathematical model describing the dissolution of nuclear glass directly disposed in clay combines a first-order dissolution rate law with the diffusion of dissolved silica in clay. According to this model, the main parameters describing the long-term dissolution of the glass are ηR, the product of the diffusion accessible porosity η and the retardation factor R, and the apparent diffusion coefficient D_app of dissolved silica in clay.For determining the migration parameters needed for long-term predictions, four Through-Diffusion (T-D) experiments and one percolation test have been performed on undisturbed clay cores. In the Through-Diffusion experiments, the concentration decrease after injection of ³²Si (radioactive labelled silica) was measured in the inlet compartment. At the end of the T-D experiments, the clay cores were cut in thin slices and the activity of labelled silica in each slice was determined. The measured activity profiles for these four clay cores are well reproducible.Since no labelled silica could be detected in the outlet compartments, the Through-Diffusion experiments are fitted by two In-Diffusion models: one model assuming linear and reversible sorption equilibrium and a second model taking into account sorption kinetics. Although the kinetic model provides better fits, due to the sufficiently long duration of the experiments, both models give approximately similar values for the fit parameters. The single percolation test leads to an apparent diffusion coefficient value about two to three times lower than those of the Through-Diffusion tests.Therefore, dissolved silica appears to be strongly retarded in Boom Clay. A retardation factor R between 100 and 300 was determined. The corresponding in situ distribution coefficient K_d is in the range 25–75 cm³ g⁻¹. The apparent diffusion coefficient of dissolved silica in Boom Clay is estimated between 2×10⁻¹³ and 7×10⁻¹³ m² s⁻¹. The pore diffusion coefficient is in the range from 6×10⁻¹¹ to 1×10⁻¹⁰ m² s⁻¹.     

Agricultural soil as a potential source of input of organochlorine pesticides into a nearby pond

A study was conducted in the southeastern region of Buenos Aires province, Argentina, to assess an agricultural soil as a potential source of organochlorine (OC) pesticides for the aquatic biota of a nearby pond. We analyzed gamma-HCH (lindane), still in use, and the following banned compounds: DDT, DDE, DDD heptachlor, heptachlor epoxide, aldrin, dieldrin and endrin in soil, bulrush, grass shrimp and fish using gas chromatography with electron capture detection (GC-ECD). Among the OC pesticides, lindane was most dominant in the soil (32.6 ng/g dry wt in the upper and 173.9 ng/g dry wt in the lower horizon) and bulrush (1.9 pg/g lipid). Macrophyte also accumulated high levels of heptachlor epoxide (1.5 pg/g lipid). Heptachlor, although present in the soil, was below the detection limit in all aquatic biota studied. Its primary degradation product, heptachlor epoxide, was found in both soil and biota samples. DDT was found at low levels in the surface soil (6.8 ng/g dry wt), but at higher concentrations in fish (3.6 pg/g lipid), although levels were still below permissible levels for human consumption. Since most of the compounds were found in both soil and aquatic biota, our study suggests that agricultural soil could be an important source for OC pesticides in the nearby pond.