An introduction to critical loads

The critical loads approach to emission controls of gaseous pollutants is a concept with a short but eventful history. Despite difficulties with definitions and agreed values, its acceptance within the UN-ECE Convention on Long Range Transboundary Air Pollution has provided the impetus for developing methods to put critical loads to a practical use-the revision of the UNECE emission protocols for sulphur and nitrogen. Methodologies first focus upon quantifying a pollutant threshold at which harmful effects occur on particular sensitive receptors (usually biological species). This threshold is known as the critical load for deposited pollutants, and as the critical level for gaseous pollutants acting on receptors. To calculate a critical load, biological effects are usually 'translated' to critical chemical values, e.g. harmful effects on fish 'translate' to alkalinity or aluminium concentrations in water; thus, critical load calculations may be based upon the chemistry of a system. Such calculations may be performed using simple, steady-state models, whilst the use of more complex, dynamic models provides an insight into the past and future trends. Maps of critical loads can be drawn using calculated values, and maps of pollutant deposition data will then show geographical areas where critical loads are exceeded. Spatial emission-deposition models can identify sources contributing to areas of excess loads and quantify necessary emission reductions. Optimization procedures applied to such models can derive abatement strategies related to economic costs and critical load effects. The critical load calculations may also be used to underpin the setting of target loads; these are pollutant loads, determined by political agreement, which take account of social, economic and political considerations.     

Case study of augmenting livelihood of fishing community at Sagar Island,India, through solar thermal dryer technology

Environment, Development and Sustainability - Drying of fish at the Sagar Island (21.7269° N, 88.1096° E) is generally carried out in open sun on the seashore on plastic sheets or mat of...     

Population structure and sex-change in the coral-inhabiting snailCoralliophila violacea at Hsiao-Liuchiu,Taiwan

Surveys of the coral-inhabiting snailCoralliophila violacea (Lamarck) (=C. neritoidea Kiener) were made on shallow fringing reefs (<8 m deep) around Hsiao-Liuchiu, Taiwan, between July and October 1990. The snails were aggregated into patches on the surface of massive poritid coral colonies. Coral colonies >40 cm in diameter were more likely to bear patches of snails than smaller colonies, and also to have more snails. The coralliophilids ranged from 5 to 30 mm in aperture length. The sex ratio of the population was biased toward males (539:279), with only a few small individuals of indistinguishable sex. Snails between 6 and 10 mm were all males, while most snails with aperture lengths 20 mm were females. Judging from the distinct size ranges of males and females within patches and from the observed degeneration of the penis, the snails may have changed sex from male to female with increasing size. Sex-change may occur across a wide size range (10 to 20 mm). The correlation of smallest female size and largest male size among patches indicates that snail size at sex-change is peculiar to each individual patch. Those females in patches with a single female (but many males) were significantly smaller than females in multiple-female patches. It is likely that in the absence of females males change sex at a smaller size, whereas in the presence of large females males delay sexchange until they have reached a larger size. The plasticity of size at sex-change may be adaptive and a result of natural selection at the individual level.     

Dry aerial fallout of organochlorine insecticide residues in Delhi, India

Monitoring of airborne dust in Delhi during May to July 1985 revealed residues of DDT varying from 1.3 to 7.14 ng mg(-1) (4.06-22.31 ng m(-2) day(-1)) with an average of 3.32 ng mg(-1) (10.38 ng m(-2) day(-1)), and HCH which ranged from 0.46 to 2.35 ng mg(-1) (1.44-7.34 ng m(-2) day(-1)) with a mean of 1.16 ng mg(-1) (3.63 ng m(-2) day(-1)). The concentration of total DDT was almost 3 times greater than that of HCH.     

Reversibility of stemflow-induced soil acidification in Swedish beech forest

Stemwater running down the trunks of beech (Fagus sylvatica L.) has an acidifying effect on soil near the stem. The deposition of acidifying substances may be two to four times higher close to the stem compared to in the stand in general. To study reversibility of soil acidification, 72 stumps of beech trees were chosen from five different year classes of felling (3, 6, 9, 14-15, 25-30), representing the years when stemflow ceased to affect the soil. The H(+) concentration (pH KCl) in the topsoil (0-5 cm) differed between the distances 10-30 cm and 230-250 cm from the stumps, the soil close to the stem being more acid. The longer the time since felling the smaller the differences in H(+) concentration became. This reduction in soil acidity amounted to ca. 50% after 15 years, and only small further changes occurred over the next ten years. This indicates that soil may not recover fully from acidification, or does so at a rather slow rate after the initial 15 years of recovery.     

Impact of repeated application on the binding and persistence of [14C]-DDT and [14C]-HCH in a tropical soil

An Indian sandy loam soil was initially treated with 1 kg a.i. ha(-1) of either [(14)C]-p,p'-DDT or [(14)C]-gamma-HCH during winter. DDT concentration after 30 days declined to 75.3%, which included 2.1% soil-bound residues. After 150 days, DDT levels further decreased to 42.4% with a concomitant increase in bound residues amounting to 5.9%. Identical treatment with HCH caused the residue levels to be reduced to 67.4 and 23.6%, after 30 and 150 days, respectively. During this period, the soil-bound residues of HCH increased from 5.2 to 12.8%. Repeat application to pre-treated soils in summer and subsequent field exposure for 30 days reduced the concentration of DDT to 52.1% and that of HCH to 42.4% of the total concentration following the second treatment. In parallel control experiments, which received only a single treatment, DDT levels declined to 61.3%, while HCH slumped to 45.3%, indicating a slower dissipation rate than in the corresponding repeated treatments. In repeat experiments, the soil-bound residues of DDT and HCH showed only a 1.07 to 1.08-fold increase in 30 days, as compared to three to ten-times increase in the control experiments. The results amply demonstrate that pre-treatment of tropical soils with DDT or HCH enhances their rate of dissipation and significantly reduce the formation of their soil-bound residues.