Pollution-related changes in diets of two insectivorous passerines

Insectivorous birds living in polluted areas are not only exposed to pollutants but they may also be affected by changes in their invertebrate food. The populations of many invertebrate species are affected by environmental pollution and such changes may lead to differences in the diet of insectivorous birds. We examined nestling food quality (invertebrate composition and heavy metal levels) and breeding performance of two cavity-nesting passerines, the Great tit, Parus major, and the pied flycatcher, Ficedula hypoleuca, in an area with long-term heavy metal pollution by a copper smelter. There were no differences in feeding frequencies or the amount of food that parents provided to their nestlings between polluted and unpolluted sites, but food quality in a polluted area differed from that of the control area in both bird species. P. major took more beetles and variable “flying insects” and less caterpillars (of smaller size) and moths in the polluted area as compared to the unpolluted one. F. hypoleuca ate more beetles and larvae and less moths and spiders in the polluted area. Breeding success of P. major was better when the nestling diet contained a large proportion of caterpillars and the relationship was especially strong in the polluted area. On the contrary, F. hypoleuca broods succeeded equally well with variable diets. Our data suggest that a more opportunistic forager, F. hypoleuca, is less vulnerable to a changing invertebrate composition caused by human environmental impacts than a caterpillar specialist, P. major. In a heavy metal polluted area, F. hypoleuca seems to be more sensitive to a decreased amount of Ca rich food items (e.g. snails) while P. major suffers especially from the lack of carotenoid rich caterpillars. Our results emphasize the importance of secondary environmental changes, like food quality, in addition to direct impacts of pollutants.     

Polluted environment and cold weather induce laying gaps in great tit and pied flycatcher

We studied the occurrence of laying gaps in free-living populations of the pied flycatcher, Ficedula hypoleuca, and the great tit, Parus major, in a pollution gradient of a copper smelter in south-west Finland. Laying gaps were 2.8 times more common in F. hypoleuca than in P. major. The probability of laying gaps was highest in the heavily polluted zone and lowest in the unpolluted zone for both bird species. Cold weather at the time of laying increased the number of laying gaps in both species, but in P. major this effect was most pronounced in the heavily polluted environment. In the most heavily polluted environment the laying gaps were more likely to occur near the beginning of the laying sequence in both species. The laying gap probability increased with increasing laying date in P. major but not in F. hypoleuca. We suggest that the increased number of laying gaps in the polluted environment results from limited Ca availability and the interference of heavy metals with Ca metabolism in laying females.     

Density dependent effects between three competitive bird species

Summary Density and breeding success of the great tit Parus major, blue tit Parus caeruleus and collared flycatcher Ficedula albicollis were studied in nest box colony in oak forest over a period of 19 years.Intraspecific density dependent clutch size reduction was found with blue tit and great tit. In interspecific relation the high density of blue tits reduced the clutch size of great tits.In the hatching period neither intraspecific nor interspecific density dependence were showed between the tits when the third competitive species, collared flycatcher was present. The collared flycatcher significantly reduced the hatching success of both tit species and the number of fledglings of great tit.The effects of the great tits and combined density of the great and blue tits on the hatching failure and number of fledglings of collared flycatcher were found when the density of the tits was high. There were not significant relationships to the single density of blue tits.The temporal variability of the competition of the three bird species is discussed.     

Nest desertion: a trade-off between current and future reproduction

Life history theory predicts that parents should desert a reproductive attempt if the costs of rearing this brood exceed the expected benefits. Thus, if the value of the current breeding attempt is reduced, for example through an unexpected reduction in size, parents are expected to reconsider whether it is worth continuing investing in their brood. With regard to nest desertion behaviour two predictions can be made: individuals are (1) more likely to desert if the reduction in clutch size is large and (2) less likely to desert if the reduction is at a late stage of breeding. We investigated the threshold at which nest desertion takes place by experimentally reducing great tit, Parus major, clutches to different sizes and at different stages of the incubation period. The results were in accordance with the predictions: clutch desertion rates were negatively related to the number of eggs that remained in the nest, and nest desertion was less likely nearer the end of the incubation period. In addition, we estimated the fitness consequences of nest desertion behaviour. For this purpose we made one group of birds desert in favour of a replacement clutch and another group rear a reduced brood. The latter were more likely to produce a second clutch after the first-brood fledglings had left the nest. As a consequence, the number of fledglings produced over the entire breeding season did not differ between the two experimental groups. We also counted the number of recruits and breeding adults in the following breeding season and found that the experimental groups did not differ in local recruitment and adult survival. Therefore, the results did not indicate that parents improved their fitness by deserting a reduced clutch.Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved .     

Yeasts from Marine and Estuarine Waters with Different Levels of Pollution in the State of Rio de Janeiro, Brazil

Yeast counts were made at 24 marine and estuarine sites in the vicinity of Rio de Janeiro, Brazil. Mean salinities of estuarine sites ranged from 14.2 to 27.4‰, and mean temperatures ranged from 25 to 28°C. Total coliform counts varied from 80% above 100,000 colony-forming units (CFU)/100 ml at heavily polluted sites to 100% below 100 CFU/100 ml at unpolluted sites. Total yeast counts above 100 CFU/100 ml were typical of heavily and moderately polluted water but atypical of lightly polluted and unpolluted water. Mean total yeast counts were 2,880 CFU/100 ml for heavily polluted sites, 202 CFU/100 ml for moderately polluted sites, and 3 CFU/100 ml for lightly polluted and unpolluted sites. Total yeast counts had a positive response to increased pollution levels, and Candida krusei and phenotypically similar yeasts as a group were prevalent in polluted estuarine water but rare in unpolluted seawater. The 549 strains of yeasts and yeast-like organisms isolated were grouped into 67 species, of which the 21 most prevalent made up 86% of the total yeast population. The prevalent genera in the polluted estuary were Candida, Rhodotorula, Torulopsis, Hanseniaspora, Debaryomyces, and Trichosporon.     

Decline of Eulia ministrana (Lepidoptera: Tortricidae) in polluted habitats is not accompanied by phenotypic stress responses

Environmental pollution is currently identified as one of the major drivers of rapid decline of insect populations, and this finding has revitalized interest in insect responses to pollution. We tested the hypothesis that the pollution-induced decline of insect populations can be predicted from phenotypic stress responses expressed as morphological differences between populations inhabiting polluted and unpolluted sites. We explored populations of the brassy tortrix Eulia ministrana in subarctic forests along an environmental disturbance gradient created by long-lasting severe impacts of aerial emissions of the copper–nickel smelter in Monchegorsk, northwestern Russia. We used pheromone traps to measure the population densities of this leafrolling moth and to collect specimens for assessment of three morphological stress indices: size, forewing melanization, and fluctuating asymmetry in wing venation. Wing length of E. ministrana increased by 10%, and neither forewing melanization nor fluctuating asymmetry changed from the unpolluted forest to the heavily polluted industrial barren. However, the population density of E. ministrana decreased 5 to 10 fold in the same pollution gradient. Thus, none of the studied potential morphological stress indicators signaled vulnerability of E. ministrana to environmental pollution and/or to pollution-induced environmental disturbance. We conclude that insect populations can decline without any visible signs of stress. The use of morphological proxies of insect fitness to predict the consequences of human impact on insect populations is therefore risky until causal relationships between these proxies and insect abundance are deciphered.     

Decline in the frequency and benefits of multiple brooding in great tits as a consequence of a changing environment

For multiple-brooded species, the number of reproductive events per year is a major determinant of an individual''s fitness. Where multiple brooding is facultative, its occurrence is likely to change with environmental conditions, and, as a consequence, the current rates of environmental change could have substantial impacts on breeding patterns. Here we examine temporal population-level trends in the proportion of female great tits (Parus major) producing two clutches per year (‘double brooding’) in four long-term study populations in The Netherlands, and show that the proportion of females that double brood has declined in all populations, with the strongest decline taking place in the last 30 years of the study. For one of the populations, for which we have data on caterpillar abundance, we show that the probability that a female produces a second clutch was related to the timing of her first clutch relative to the peak in caterpillar abundance, and that the probability of double brooding declined over the study period. We further show that the number of recruits from the second clutch decreased significantly over the period 1973–2004 in all populations. Our results indicate that adjustment to changing climatic conditions may involve shifts in life-history traits other than simply the timing of breeding.     

Effects of high density on spacing behaviour and reproduction in Akodon azarae: A fencing experiment

We studied the short term spacing behavioural responses of Pampean grassland mouse (Akodon azarae) with regard to population density in four 0.25 ha enclosures (two control and two experimental) in the 2011 breeding season. Based on the hypothesis that A. azarae breeding females exhibit spacing behaviour, and breeding males show a fusion spatial response, we tested the following predictions: (1) home range size and intrasexual overlap degree of females are independent of population density values; (2) at high population density, home range size of males decreases and the intrasexual home range overlap degree increases. To determine if female reproductive success decreases at high population density, we analyzed pregnancy rate, size and weight of litters, and period until fecundation in both low and high enclosure population density. We found that both males and females varied their home range size in relation to population density. Although male home ranges were always bigger than those of females in populations with high density, home range sizes of both sexes decreased. Females kept exclusive home ranges independent of density values meanwhile males decreased home range overlap in high breeding density populations. Although females produced litters of similar size in both treatments, weight of litter, pregnant rate and period until fecundation varied in relation to population density. Our results did not support the hypothesis that at high density females of A. azarae exhibit spacing behaviour neither that males exhibit a fusion spatial response.     

Productivity differences between dandelion (Taraxacum officinale; Asteraceae) clones from pollution impacted versus non-impacted soils

Common dandelions (Taraxacum officinale Weber, sensu lato; Asteraceae) introduced to North America form an assemblage of asexual (agamospermous), clonal lineages derived from Eurasian mixed sexual and asexual populations. We investigated whether selection for more pollution tolerant clonal lineages occurs at polluted sites and selection for more pollution intolerant lineages occurs at unpolluted sites. We tested the above hypothesis by performing reciprocal greenhouse productivity experiments in which unique dandelion clones (12 clones, identified by DNA fingerprinting, from each site type) sampled from two unpolluted and two polluted (moderately enhanced Cu, Pb and Zn soil concentrations) sites were grown pairwise in both unpolluted (nutrient solution only) and polluted (nutrient solution + Cu, Pb and Zn) media (n?=?48 paired tests for each media type). Dandelion clones from polluted sites produced fewer and smaller leaves, shorter roots and smaller root diameters, reduced shoot and root dry weights, and reduced total biomass compared to clones from unpolluted sites when clones were grown in unpolluted-media (P?≤?0.05). In contrast, clones taken from unpolluted sites were shown to produce significantly fewer and shorter leaves, shorter roots and smaller root diameters, reduced shoot and root dry weights, reduced total biomass, a reduced shoot : root biomass ratio, and have much lower survival compared to clones from polluted sites when both were grown in polluted-media (P?≤?0.05). These results reveal that there was increased selection against unpolluted-site clonal lineages in polluted-media and against polluted-site clonal lineages in unpolluted-media. Across all treatments, clones from unpolluted sites growing in unpolluted-media had the highest proximate measures of fitness. Overall, these findings provide insight into the relationships among anthropogenic environmental contamination and the consequent effects of selective forces acting on dandelion clones and their population genetic architecture.     

Leaf fluctuating asymmetry of common plantain as an indicator of habitat quality

Abstract

Although developmental instability (DI), measured as fluctuating asymmetry (FA), is expected to be positively related to environmental stress and negatively to habitat quality, the pattern found here was the reverse. Developmental instability of leaf traits (leaf width and vein distances within a leaf) was estimated (using two indices of FA: FA₄ and σ_i ²) and compared between three populations of Plantago major L. (Plantaginaceae) from northern Serbia. Two of the populations are from chronically polluted areas (Karaburma & Zemun), while Crni Lug is from an unpolluted, natural area. Results obtained using both FA indices were the same; higher asymmetry levels in the unpolluted area than in the polluted sites, were found for both traits. Between the two polluted sites, FA values were significantly higher in Karaburma site for vein distances within a leaf. Concerning differences in FA₄ values between samples, in two cases, results are similar to those found for σ_i ² values, for vein distances within leaf. These are the first quantitative data on P. major indicating that (i) plants living in the stressful sites are more symmetrical and (ii) leaf FA for plant species with wide ecological distribution such as P. major should be considered as an ‘index of habitat quality.’     

Egg shell quality,clutch size and hatching success of the great tit (Parus major) and the pied flycatcher (Ficedula hypoleuca) in an air pollution gradient

Egg shell thickness, egg volume, clutch size and hatching success of Parus major and Ficedula hypoleuca were studied at 14 study sites around a copper smelter complex in Harjavalta, south-west Finland, in 1991–1993. In 1991–1992 unhatched eggs were collected to measure shell quality. F. hypoleuca was more susceptible to pollutants than P. major, the response of which was weaker in all aspects studied. Egg shells of F. hypoleuca were about 17% thinner and eggs were about 8% smaller in volume near the factory than at a distance of 10 km. The clutch size of F. hypoleuca was significantly smaller and hatching success markedly lower at a study site next to the factory complex than at all other sites. In P. major, variation in shell thickness and egg volume was not significantly related to the distance from the pollution source. Clutch size and hatching success of P. major did not significantly differ among study sites, although the trend in hatching success was in the same direction as in F. hypoleuca. Clutches of both species contained less shell material and both species had more nests without eggs near the factory than further away. The surface structure of the eggshells was studied by scanning electron microscope. Especially in F. hypoleuca, the egg shell surface was more rough and porous near the factory. The roles of Ca and heavy metals in shell thinning are discussed.     

Strong evidence for selection for larger brood size in a great tit population

We measured the selection pressure on brood size in a recentlyestablished population of great tits (Parus major L.) in thenorthern Netherlands by manipulating brood size in three years(1995: n = 51, 1997: n = 66, 1998: n = 51), and we estimatedfitness consequences in terms of local survival of both offspringand parents. Enlarged broods had highest fitness; the offspringfitness component was positively affected by manipulation andthe parental fitness component was unaffected. Parental survivaland the probability that parents produced a second clutch werenot affected by the treatment. However, parents that had raisedenlarged broods produced their second clutch later in the season.Clutch size, brood size, and laying date of birds recapturedin the next breeding season were largely independent of thetreatment. We conclude that there is strong evidence for selectionfor larger brood size and reject the individual optimizationhypothesis for this population because the number of young inthe nest predicts fitness independently of the manipulationhistory.     

SHORT NOTES

Earlé, R. A. 1981. Factors governing avian breeding in Acacia savanna, Pietermaritzburg, Part 3: Breeding success, recruitment and clutch size. Ostrich 52:235-243.

The clutch size and breeding success of eight species of birds were monitored over a two year period in Acacia savanna. The mean clutch size fluctuated within the breeding season and four patterns of clutch size variation were noted. A smaller proportion of large clutches were laid in the 1979 season when less food was available. Breeding success was higher in the dry 1979 season but fewer breeding attempts were made and the overall recruitment was thus lower. At the peak of the breeding season, in mid-November, breeding success was at its lowest. Predation on nests was the greatest factor reducing breeding success although rain and strong winds affected some species.     

THE INFLUENCE OF THE ENVIRONMENT ON BREEDING SUCCESS OF A SUBURBAN POPULATION OF CRESTED BARBETS TRACHYPHONUS VAILLANTII

Van Zyl, A.J. 1994. The influence of the environment on the breeding success of a suburban population of Crested Barbets Trachyphonus vaillantii. Ostrich 65: 291–296.

I studied the breeding biology of the Crested Barbet Trachyphonus vaillantii in Colbyn, a suburb east of Pretoria, South Africa, for nine breeding seasons from 1981 to 1989 to examine patterns in annual breeding success, breeding attempt success in multiple broods, and rainfall. The modal incubation period was 14 days and the nestling period ranged from 28 to 31 days. Average clutch size for all the years was 3,3 eggs/clutch and there was no significant difference in clutch size or number of young fledged/nest between years. On average, Crested Barbet pairs made 2,4 breeding attempts/season. There was no difference in clutch size or breeding success between the breeding attempts. Crested Barbets nesting in natural nests laid on average larger clutches than those in artificial nestboxes, but had non-signficantly lower breeding success. Failure to raise Crested Barbet chicks was attributed to parasitism by Lesser Honeyguides Indicator minor, bee swarms occupying nestboxes, and flooding of natural nests. Breeding performance was not correlated with rainfall or adult body size. The suburban environment may be less variable than a natural environment, resulting in a stable breeding Crested Barbet population.     

Assessment of Water Pollution using Diatom Community Structure and Species Distribution — A Case Study in a Tropical River Basin

A study on biological assessment of water pollution using diatom community structure and species distribution was carried out in the Linggi River Basin, Malaysia which was polluted by various urban, industrial and agricultural wastes. A total of 86 diatom taxa belonging to 21 genera were recorded from all eight sampling stations located in the basin, of which 70 species were found on artificial substrates; the remaining 16 species were recorded exclusively on natural substrates. The number of diatom species observed between the stations varied from 22-47 species. The dominant diatom species in decreasing order of abundance were Eunotia vanheurckii, Nitzschia palea, Achnanthes saxonica, Gomphonema parvulum and Achnanthes minutissima. The most common clean water species were Achnanthes minutissima, A. linearis and Synedra rumpens. The most tolerant species were Nitzschia palea followed by Gomphonema parvulum and Pinnularia braunii. Eunotia vanheurckii and Navicula cryptocephala occurred in high densities at both unpolluted and polluted stations and can be considered as the common facultative or indifferent species. Although a large number of species were recorded at the unpolluted stations, equivalent number of species were also found at the moderately polluted stations. However, the number of species was reduced at grossly polluted stations. Nevertheless, a marked variation in species association exists between the unpolluted and polluted stations, but not among the polluted stations to distinguish the type and degree of pollution.     

Untersuchungen über die Auswirkung kommunaler Abwässer auf das benthische Ökosystem mariner Watten

The influence of domestic sewage on intertidal sand and mud flat benthic communities has been studied at three minor outfalls around the North Sea island of Sylt (F. R. Germany) and at the main outfall of Vancouver, B. C. (Canada). During high tide, domestic waste water was found at the water surface due to its lower specific gravity. Consequently, O₂ depletion and salinity decrease occured mainly in surface waters. Oxygen deficiency prevailed in the sediment-water layer, when settled sewage particles were re-suspended by strong tidal currents. This resulted in anaerobic conditions at the sediment surface for up to 40% of the day. Substantial pH decrease and increase in seston load of the water were observed only along the sewage channels and around the outlets when large quantities of sewage were discharged. The amount of particulate organic material increased up to 10% and more in muddy sediments due to sedimentation of sewage sludge. Considerable eutrophication of the mud flats resulted from nutrient load of the sewage and from decomposition of faecal material deposited on the sediments. The vertical distribution of microalgae in the sediment was not influenced by sewage. Primary productivity of microalgae on the sediment surface was positively correlated with the degree of pollution. In heavily and mediumly polluted zones, heterotrophic bacterial production exceeded primary production rates at the sediment surface. Compared with unpolluted intertidal flats the number of macrobenthic species was not reduced in polluted mud flats. In regard to overall species abundance, the macrofauna associations of the disposal area showed three distinct zones: (1) Heavy pollution around the outfall resulted in a degradation zone either without benthic invertebrates or with a very low density of individuals; (2) medium polluted areas were characterized by a zone of maximum density; (3) with decreasing or diminishing pollution the number of individuals returned to normal values (background values). The distribution of species within these zones indicated a significant difference between the response of the channel fauna and the flat fauna to pollution: while the number of species increased continously inside the channels with decreasing pollution, the species variety of the tidal flats was positively correlated with the number of individuals. The diversity of the benthos inside the channels was negatively correlated with the degree of pollution, whereas the diversity indices for the fauna on the tidal flats increased quickly from the centre of pollution, remained at a high level in the medium polluted zone, and decreased again to the area of diminishing pollution. The number of dominating species in the sewage channel increased from the outlet towards the low-tide level, with ratios of 0.9 to 0.33; on the flats the number remained constant throughout the three zones, with maximum ratios of 0.5, demonstrating that no qualitative changes for the macrobenthos of intertidal flats result from domestic sewage disposals. In polluted intertidal flats the macrobenthos is dominated by muddy-sand species whose adaptability to varying sedimentary factors, such as grain size distribution and content of organic material (coefficients of variability: 50.7 and 45.7%, respectively), is relatively high compared with mud and sand species. A special indicator community for polluted intertidal areas does not exist. Intensified waste-water treatment prior to discharge reduced the size of the degradation zone around the outfalls while it simultaneously caused a lower density of the macrobenthos in the medium polluted zone.

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Dissertation aus dem Fachbereich Biologie der Universität Hamburg.     

Impact of wastewater discharge on the plant diversity,community structure and heavy metal pollution of range plants in eastern Saudi Arabia

The main objectives of this study were to determine the floristic composition of the vegetation cover and to find the effects of wastewater pollution on the plant community structure in eastern Saudi Arabia. 28 stands which were distributed among polluted and unpolluted sites, were chosen for this study. A total of 42 plant species were recorded (14 in the polluted and 28 in the unpolluted sites). The recorded plants comprised of 13 perennial plant species and 29 annual plant species. Seven vegetation communities were determined using TWINSPAN and DCA classification and ordination techniques. Three in the polluted sites, two in the unpolluted sites and the remaining two were mixed communities. The (Sarcopoterium spinosum – Pistacia len‐tiscus) community in the polluted sites, had the highest values of soil moisture, salinity, sulphate, calcium and potassium. On the other hand, Juniperus phoenicea – Olea europaea community in the unpolluted site, had the lowest value of organic matter, salinity and magnesium. In respect of genetic diversity, the community of Foeniculum vulgare - Nicotiana glauca in the unpolluted site, was the most diverse, while Ricinus communis - Chrysanthemum coronarium in the polluted sites was the least one. Both soil and wastewater heavy metal analysis indicated that Pb, Cd, Cr, Cu and Ni concentrations in the polluted sites were significantly higher than those in the unpolluted ones. The impact of wastewater discharge led to the appearance of new invasive plant species that may significantly affect plant diversity and community structure in eastern Saudi Arabia. Finally wastewater discharge in open rangelands could adversely affect the growth of plant species in the rangelands and thus adversely affect plant community structure and diversity.     

Impact of climate change and prey abundance on nesting success of a top predator, the goshawk

Contemporary research has documented a large number of shifts in spring phenology and changes in distribution range although the average spring temperatures have increased by only 0.3–0.6 °C over the past 100 years. Generally, earlier breeding birds have larger clutch sizes, and the advancing spring could thus potentially increase breeding success. Shifts in spring phenology can, however, be crucial for bird reproduction, and mistiming the breeding event may even have negative consequences for population development. Our aim was to explore how weather and prey abundance relates to the breeding performance of a north European top predator, the northern goshawk Accipiter gentilis. Our nationwide dataset from Finland, spanning the period 1989–2004, shows that ambient weather has a greater impact on the timing and success of breeding than the density of grouse Tetraonidae, the main prey of goshawks. Higher early spring temperatures were associated with advancing hatching date of goshawks. Correspondingly, grouse density and temperature during laying and brooding were positively associated with brood size, while precipitation showed a negative connection. Applying our models to a future scenario of climate warming, combined with a 50 % reduction in grouse density, suggests that average breeding dates will advance only 2.5 days and average breeding success would remain the same. Notably, breeding success was not spatially equal throughout Finland, as northern and eastern populations suffered most from declining grouse densities. The observed pattern is thus the opposite to what is expected from a population situated at the northern edge of its distribution range, and thus may help to understand why populations may not increase at the northern edge of their thermal distribution due to climate change.     

Superficial and hyporheic oligochaete communities as indicators of pollution and water exchange in the River Moselle, France

Benthic oligochaetes were sampled on three occasions (June, August and October 1992) in the upper (0–10 cm) and hyporheic (35–45 cm depths) sediments at five sites of the River Moselle, from upstream of the town of Epinal to Velle-sur-Moselle. The first site (upstream from Epinal) is considered as unpolluted and the four remaining sites are polluted by industrial effluents. The most polluted stations were generally dominated by the pollution tolerant taxon Limnodrilus. Numbers of individuals of this taxon decreased at the less polluted last site in recovery zone, and were also scarce in the first unpolluted site. It is noteworthy that these tendencies were observed in both superficial and hyporheic substrates and to the greatest degree in hyporheic ones. At the unpolluted site, the hyporheic habitat is dominated by the groundwater species Propappus volki, Pristina spp., Pristinella spp. At the less polluted site (last site), the deep sediments are dominated by groundwater species and the Tubificidae without hair setae decrease from June to October. As a result of water exchange between superficial and subterranean waters, superficial substrates of the first and the last stations tend to be colonised by a high proportion of hyporheic species that suggests that flow is primarily from subterranean to superficial waters. The contrary is the case at other polluted stations which are characterised by the invasion of hyporheic substrates by the pollution tolerant superficial taxa Limnodrilus. This suggests that water flows from the river to the deeper groundwater. These two stations are located near drinking water plants which utilise groundwater, thus increasing the vulnerability of groundwater to surface contaminants.     

Scots pine (<Emphasis Type="Italic">Pinus sylvestris</Emphasis> L.) wood properties in an alkaline air pollution environment

This paper examines the long-term influence on pine (Pinus sylvestris L.) wood properties of alkaline dust pollution (pH 12.3–12.7) emitted over 135 years from a cement plant in Estonia. A study of stemwood physical and mechanical properties in 70–80-year-old Scots pines growing in three zones of different air pollution levels showed serious deviations in comparison with a relatively healthy forest in an unpolluted area. Specimens from polluted trees evidenced smaller sapwood annual ring widths than those from the control trees. At the same time, the number of growth rings in sapwood at breast height increased under pollution. In the polluted areas, percentage of latewood in the annual ring widths was higher than in the unpolluted area. Small amounts of cement dust, which contains elements essential for the mineral nutrition of the trees, might have acted as fertilizer. Pine wood in the polluted stands exhibited increased density, bending strength across the grain, compression strength along the grain and, in some instances, hardness along the grain.