Concentrations and amounts of methylmercury in water and fish in the limed and acid basins of a small lake

Three months after neutralization concentrations of methylmercury (MeHg) were higher in the water of the limed than in the control basin of a small lake. After two years, the concentrations in the limed basin were somewhat lower than in the control (0.056–2.19 ng L^?1 and 0.129–2.65 ng L^?1, respectively). The highest concentrations were found in the anoxic hypolimnia. The total amount of MeHg in the water mass of the lake varied from 19 to 68 mg, showing a drop after spring and autumn overturns and a maximum during stratification periods. The total Hg concentrations of fish in L. Iso Valkjärvi varied from 0.06 to 0.14 μg g^?1 (ww) in whitefish to 0.1 to 0.7 μg g^?1 in perch and to 0.2 to 1.4 μg g^?1 in pike. The total amount of MeHg bound in the fish of the lake was quite similar to that in the water column, 43 to 59 mg in 1990–1993, 33 to 47 mg of which was in the perch population.     

The reliability of whitefish (Coregonus lavaretus (L.)) age determination - differences between methods and between readers

Abstract— Age determinations of whitefish ( Coregonus lavaretus (L.)) were compared in two different tests. In the first test, the readers determined the age of each individual from one calcified structure (scale, otolith, or opercular bone) at a time. The samples from three populations, 50 specimens in each, were mixed so that the readers did not know which population each calcified structure was from. A sample of known-age whitefish was used in the second age determination test, where information such as time of catch, length, weight, and sex was available to the readers. In each of the 50 envelopes the reader got scale impressions and two otoliths, one of which had been burned and ground. In the first test, the precision of the readers was low both between readers and between different structures. In the samples of slow-growing populations, the determinations made from the otoliths showed older ages than the determinations from the scales. In the second age determination test the results were better; 73-90% (average 82%) of the determinations were correct. The use of two calcified structures and the knowledge of the material were considered to improve the accuracy. Age determination bias may occur that affects the age distribution: even though 80% of the fish were aged correctly, an exceptionally strong or weak year class could remain unidentified. The estimation of growth rate seemed less sensitive to incorrect age determination than age distribution.     

Recovery of the Perch (Perca Fluviatilis) in an Acidified Lake and Subsequent Responses in Macroinvertebrates and the Goldeneye (Bucephala Clangula)

The perch population of Lake Vähä Valkjärvi, a two hectare clear-water lake in southern Finland, decreased due to acid precipitation during the 1980s. During the early 1990s a decrease in acidic deposition resulted in slight improvement of water quality of the lake. This was followed by recovery of the reproduction of perch starting in 1991. A mark and recapture experiment in spring 1995 indicated a hundred fold increase in the population size of perch in a four year period. A decrease in the abundance of aquatic invertebrates was recorded during 1989–1996. This decrease well coincided with the recovery of the perch population, suggesting that increased predation by fish was responsible for the decrease. The occurrence of goldeneye young also dropped in L. Vähä Valkjärvi since 1993. This was thought to be due to increased food competition with perch.     

What can perch population data tell us about the acidification history of a lake?

In this study an attempt was made to describe the acidification history of a lake through the changes in the population structure and the growth of perch (Perca fluviatilis L.). The lake was generally considered fishless at the beginning of the 80s. Our catches in 1985 consisted mostly of large, old perch but there was also a younger year-class present, born in 1983. The oldest perch of (he catch were twenty years old. The slow growth of old perch suggests that the density of the population was quite high in the late 60s and early 70s. We caught only a few perch bom in the 70s, suggesting that reproduction was more or less completely unsuccessful then. The few that we did catch showed extremely high growth rates. This was interpreted as due to good feeding conditions, such as no competition for food in a sparse population. We concluded that the acidification-induced decrease in the perch population of Lake Orajärvi took place mainly during the 70s. This is supported by paleolimnological and modelling studies, In 1992, a higher number of 2+ perch were caught indicating successful reproduction in 1990. Since then, we have sampled the lake annually and recorded 0+ and 1+ fish every year. Perch in these new year-classes are clearly growing slower than those born in the last decade.This suggests that the population density has essentially increased. Successful reproduction in perch in recent years has been possible because of improvements in water quality due to decreased acid deposition and/or exceptional hydrological conditions during the 1990s.     

Losses and recoveries of fish populations in acidified lakes of southern Finland in the last decade

Acid-induced fish damage in small lakes in southern Finland was studied in a fish status survey of eighty lakes from 1985–1987. Later, twenty of these lakes were selected for further monitoring. A sampling of these lakes from 1988–1989 showed that the decrease in some perch (Perca fluviatilis L.) and roach (Rutilus rutilus L.) populations still continued. The results from the same lakes in 1992 showed that successful reproduction had taken place with many of the perch populations that had been close to extinction in 1985. In contrast, no signs of recovery in the roach populations were detected. The explanation for the appearance of new cohorts of perch could have been the decrease in acid deposition but the exceptional hydrological conditions of winters in the early 1990s may also have affected them. The different responses of the perch and roach populations were interpreted as a consequence of the different sensitivity of these two species to acidification. Even a slight improvement in the water quality has resulted in the appearance of strong new year-classes of perch, but not of roach. Therefore, more improvement in water quality is needed until a sensitive species like roach can reproduce again.     

A mutation in PRKAG3 associated with excess glycogen content in pig skeletal muscle

A high proportion of purebred Hampshire pigs carries the dominant RN- mutation, which causes high glycogen content in skeletal muscle. The mutation has beneficial effects on meat content but detrimental effects on processing yield. Here, it is shown that the mutation is a nonconservative substitution (R200Q) in the PRKAG3 gene, which encodes a muscle-specific isoform of the regulatory gamma subunit of adenosine monophosphate-activated protein kinase (AMPK). Loss-of-function mutations in the homologous gene in yeast (SNF4) cause defects in glucose metabolism, including glycogen storage. Further analysis of the PRKAG3 signaling pathway may provide insights into muscle physiology as well as the pathogenesis of noninsulin-dependent diabetes mellitus in humans, a metabolic disorder associated with impaired glycogen synthesis.     

Detection of the effective refractive index of thermally modified Scots pine by immersion liquid method

The purpose of this study was to determine the effective refractive index of thermally modified Scots pine (Pinus sylvestris L.) wood specimens as a quantitative measure regarding the change of wood density which is due to the thermal modification. The refractive index of thermally modified Scots pine wood was obtained by introducing pine wood powder into an immersion liquid and measuring light backscattering with a homebuilt multifunction spectrophotometer. The present method provides useful information that in principle can be applied, for example, in the optimization of the thermal modification process and inspection of the quality of thermally modified wood.     

Isolation and characterization of a reovirus from common eiders (Somateria mollissima) from Finland

Samples of brain, intestine, liver, lung, spleen, and bursa of Fabricius were collected from five common eider (Somateria mollissima) duckling carcasses during a die-off in the western Gulf of Finland (59 degrees 50'N, 23 degrees 15'E) in June 1996. No viral activity was observed in specific-pathogen-free chicken embryos inoculated with tissue suspensions, but samples of bursa of Fabricius from three birds were positive when inoculated into Muscovy duck (Cairina moschata) embryo fibroblasts. The isolates were characterized as nonenveloped RNA viruses and possessed several characteristics of the genus Orthoreovirus. Virus particles were icosahedral with a mean diameter of 72 nm and were stable at pH 3.0; their genome was separated into 10 segments by polyacrylamide gel electrophoresis. Mallard (Anas platyrhynchos) ducklings experimentally infected with the eider reovirus showed elevated serum activities of aspartate aminotransferase, creatine kinase, and lactate dehydrogenase enzymes and focal hemorrhages in the liver, spleen, and bursa of Fabricius. During 1997-99, the prevalence of neutralizing antibodies to the isolated virus ranged from 0 to 86% in 302 serum samples collected from incubating eider hens at three nesting areas along coastal Finland. The highest seroprevalence was found in Hanko in 1999, just weeks before reports of an uninvestigated mortality event resulting in the death of an estimated 98% of ducklings at that location. These findings raise the question of potential involvement of the virus in poor duckling survival and eider population declines observed in several breeding areas along coastal Finland since the mid-1980s.     

Modeling the dynamics of pressure propagation and diameter variation in tree sapwood

A non-steady-state model of water tension propagation in tree stems was developed. The model is based on the cohesion theory and the assumption that fluctuating water tension driven by transpiration together with the elasticity of wood cause variations in the diameter of a tree stem. The change in xylem diameter can be linked to water tension in accordance with Hooke's law. The model was tested against field measurements of the diurnal change in xylem diameter at different heights in a 180-year-old Scots pine tree at Hyyti?l?, southern Finland. Model predictions agreed well with measurements. The effect of tree dimensions on pressure propagation was examined with the model. The model outcomes were also consistent with results of several field measurements presented in the literature.     

Dendroclimatological analysis of seeded and thinned Scots pine (<Emphasis Type="Italic">Pinus sylvestris</Emphasis> L.) stands at the coniferous timberline

Radial growth was examined in two Scots pine stands that were seeded during the 1920s and 1930s due to reforestation and afforestation activity on the timberline of northern Finnish Lapland. Tree-rings of seeded pines were calibrated against the instrumental records of local weather and large-scale atmospheric patterns and further compared to pines of natural origin on the timberline. The studied stands were shown to contain common growth variability that differed from the variability of natural pines. Deviating growth of seeded pines was attributed to their only moderate growth dependence on mid-summer (July) temperatures and, likewise, their strong dependence on the autumn climate in the previous year, and linked to the different genetic origin of artificial stands due to southern seeds. Stands were thinned for different densities in 1985 and 1986. The growth response to thinning was markedly better than could be expected according to previous studies. We found that the positive growth reaction conceivably benefited from the ameliorated winter conditions, expressed as warmed (March) temperatures and the prolonged positive phase of the Arctic Oscillation (February). The results emphasize the determining influence of climatic fluctuations on reforestation and afforestation near the distributional limits of tree species.