Heavy metals (Cu and Zn) in recent sediments of Llangorse Lake,Wales: non-ferrous smelting,Napoleon and the price of wheat — a palaeoecological study

Elevated concentrations of Cu and Zn have been found in the upper part of three sediment cores collected from Llangorse Lake, in south Wales. Palaeomagnetic evidence from one of the cores and ²¹⁰Pb analysis of another, suggests that the increase in sediment Cu and Zn concentrations began during the eighteenth century. A sharp increase in the concentrations of these metals in the sediment profile appears to have occurred during the latter part of the eighteenth century and these concentrations remained high until the mid to late nineteenth century.The absence of known ore deposits and industry around the lake suggests that the lake and catchment soils were increasingly contaminated by long-range aerial transport of emissions from the expanding activity of Cu and Zn smelters located some 80 km upwind in the Swansea area during the Industrial Revolution. Evidence from agricultural crop returns indicates a significant increase in the amount of land devoted to tillage in the catchment, particularly to cereal production, during the late eighteenth and the first half of the nineteenth century which included the Napoleonic Wars. This agricultural shift appears to coincide with increased concentrations of Cu and Zn in the lake sediments. It is suggested that newly ploughed soils, contaminated with metals for many years by long-range aerial transport from the Swansea area, eroded, and were carried into the lake by catchment run-off and added to the sediment burden of Cu and Zn. A subsequent decline of Cu and Zn emissions due to the collapse of the non-ferrous smelting industry and reduced soil erosion because of a 50% reduction of tillage due to an agricultural depression in the second half of the 19th century may explain the fall in Cu and Zn concentrations in the upper part of the sediment profile. The most recent sediments (20th century) show the increase in heavy metals characteristic of many lakes around the world.     

Macrobenthic community structure before and after pollution abatement in the Neches River estuary (Texas)

Macrobenthos and physicochemical conditions in the lower 39 km of the Neches River estuary were studied from August, 1984 to May, 1985. The results were compared with data collected in 1971–1972. Between 1972 and 1984 the permitted BOD waste load in the tidal Neches River was reduced from 123 125 kg d to 8717 kg d. River discharge and dissolved oxygen concentrations were consistently higher and salinity was lower, during the same seasons, during the 1984–1985 study. A total of 50 taxa of macrobenthos were collected in 1971–1972 and 104 taxa were collected in 1984–1985. The numbers of taxa per collection at each station in 1984–1985 were at least twice those found in 1971–1972. Minimum densities in 1984–1985 were much higher than the maximum densities in 1971–1972 at all stations. Patterns of dominance, Sorenson's similarity index, and diversity ( ) values indicated improved water quality in 1984–1985. Statistical analysis of macrobenthic diversity indicated significant differences between upper estuary and lower estuary stations in 1971–1972. No significant differences were found in 1984–1985. Significant differences in numbers of taxa, macrobenthos densities, and values between the two studies were found. Reductions of waste loads, increased river discharge, and deepening of the navigation channel were among the factors that probably contributed most to the changes in community structure of the macrobenthos observed.     

土壤重金属污染的酶学诊断:紫色土Cd、Cu、Pb和As对水稻根系脱氢酶的影响

本文通过酸性紫色土和石灰性紫色土中不同浓度Cd、Cu、Pb、As对水稻根系脱氢酶的影响研究,揭示了脱氢酶受抑制与产生抗性的过程。在低浓度时,土壤Cd、Cu、Pb、As对脱氢酶的影响较敏感,能因元素的不同性质反映土壤类型影响的差别。最后,以脱氢酶受抑制与初始抗性峰出现的转折点相应的土壤浓度为依据,确定了两种紫色土Cd、Cu、Pb、As的临界浓度。     

Aspects of seagrass ecology along the western Arabian Gulf coast

Results of semi-quantitative observations and quantitative sampling of seagrasses at coastal and offshore sites along the western Arabian Gulf are presented. Overall seagrass cover (all species together) shows significant positive correlation with latitude, but not with salinity, temperature or depth. The same pattern is shown by Halodule uninervis (Forsk.) Aschers., the dominant species. Mean seagrass biomass ranged from 53–235 g m^-2 (dry weight). These values are comparable with biomass estimates from regions in which environmental conditions are generally less extreme than in the Gulf. Seagrass biomass is significantly negatively correlated with depth and sediment grain size. No significant correlation is apparent between seagrass biomass and factors such as season, salinity, or concentrations of nutrients and heavy metals measured. It is pointed out that any correlations observed are not necessarily taken to imply causality.     

Effects of paper mill effluents on the fish fauna of stony shores of Lake Päijänne

The fish fauna of the stony littoral in the central parts of L. Päijänne was studied by electric fishing on four occasions during 1988–1989. Ten fish species and 1681 individuals (14.5 kg) were caught in the 15 fishing sites (4096 m²) which gives a mean density of 0.41 ind. m^–2 and biomass of 3.5 gm^–2. Effluent from two large paper mills causes a clear zonation of the fish fauna in the area. In the most polluted shores, only burbot and perch occurred regularly and the reproduction of other species was inhibited. In the semipolluted area (5–15 km from the Kaipola paper mill), burbot and stone loach occurred regularly, but owing to low numbers of perch and bullhead the total densities were usually low.The clean shores were characterized by an abundance of stone loach and bullhead and locally also of minnow, which seemed to be very sensitive to pollution. The strong floods during summer 1988 had positive effects on the reproduction of perch and pike, but the densities of other species were highest during the normal water level in autumn 1989.     

Biological nitrogen fixation for sustainable agriculture: A perspective

The economic and environmental costs of the heavy use of chemical N fertilizers in agriculture are a global concern. Sustainability considerations mandate that alternatives to N fertilizers must be urgently sought. Biological nitrogen fixation (BNF), a microbiological process which converts atmospheric nitrogen into a plant-usable form, offers this alternative. Nitrogen-fixing systems offer an economically attractive and ecologically sound means of reducing external inputs and improving internal resources. Symbiotic systems such as that of legumes and Rhizobium can be a major source of N in most cropping systems and that of Azolla and Anabaena can be of particular value to flooded rice crop. Nitrogen fixation by associative and free-living microorganisms can also be important. However, scientific and socio-cultural constraints limit the utilization of BNF systems in agriculture. While several environmental factors that affect BNF have been studied, uncertainties still remain on how organisms respond to a given situation. In the case of legumes, ecological models that predict the likelihood and the magnitude of response to rhizobial inoculation are now becoming available. Molecular biology has made it possible to introduce choice attributes into nitrogen-fixing organisms but limited knowledge on how they interact with the environment makes it difficult to tailor organisms to order. The difficulty in detecting introduced organisms in the field is still a major obstacle to assessing the success or failure of inoculation. Production-level problems and socio-cultural factors also limit the integration of BNF systems into actual farming situations. Maximum benefit can be realized only through analysis and resolution of major constraints to BNF performance in the field and adoption and use of the technology by farmers.     

Effects of acid wastes from titanium dioxide production on biomass and species richness of benthic algae

Titanium dioxide wastes are suspected to be toxic to rocky shore communities in an estuary in southeast Norway. An experimental project lasting two years examined whether titanium dioxide wastes affected recolonization by rocky shore organisms. The experiments were performed in situ in six tanks (each with 9 m³ brackish water) at two different levels of salinity. Three different concentrations of industrial waste water were used. The growth season in 1986 was dry and sunny compared to 1987, causing reduction of growth on exposed granite chips compared to controls. At the two highest waste concentrations in the tanks, Fucus serratus was observed with necrotic tissue both years, and in 1986 benthic diatoms were scarce.