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The purpose of this study was to evaluate the potential toxic effects of chronic sublethal polychlorinated biphenyl (PCB) exposure on feral fish, using histopathology as an endpoint. Histopathological study of bream (Abramis brama) and asp (Aspius aspius) living in a PCB-polluted freshwater lake revealed abnormal cellular changes in the renal corpuscle of both species. Dilation of glomerular capillaries (DGC), mesangial edema (ME), an adhesion between visceral and parietal layers of Bowman's capsule (ABC), and filling of Bowman's space (FBS), were highly prevalent features in lake fish. The prevalence of each of these lesions was significantly lower, or totally absent in fish caught from reference locations. Cellular alterations in liver, gill, gonads, spleen, and intestine were all linked to seasonal changes. The results suggest that some of the observed histopathological changes in renal glomeruli, particularly DGC and ME, could possibly indicate a prolonged chemical stress caused by PCBs and related compounds. It is also possible that chronic PCB exposure may have suppressed and weakened the immuno systems of exposed fish making them more vulnerable to secondary parasitic infections.
An evaluation of the negative effects caused by anthropogenic influence on lake ecosystems was performed, using data from 143 catchments in Uppsala County, Sweden. The study included i) technical encroachments; i.e. construction of dams, dikes, etc. as well as effects of drainage of land; ii) pollution, i.e. eutrophication, acidification, and contamination by toxic substances; iii) introduction of nonnative species; and iv) exploitation of species populations. Severe damage was caused mostly by drainage of land followed by pollution by toxic substances and, to a smaller extent, introduction of nonnative species and eutrophication. Most lakes were subject to several types of disturbances, interacting in a complex pattern, which made it difficult to link the visible effects to the true causes of the disturbance. Future lake management should include analyses of all disturbances to the lake catchments, taking into account the historical perspective, in order to balance the threats/damages, in an analysis of the possibilities for maintaining biodiversity and sustainability in the eco-systems.
Three deep basins were chosen for this study and the most recent changes that are reflected in the uppermost 15 to 35 cm are reported. The Gotland Basin, the largest continuous sedimentation basin in the southern Baltic Sea, was chosen for the present study. Simultaneously, a quite large basin, the North Central Baltic Basin was investigated and chemical data are reported for the first time. In the southern Baltic Sea the Bornholm Basin was investigated. All 3 basins are different as regards the physicochemical conditions in the area. The investigated elements were divided into different groups according to their origin and geochemical behavior: elements of natural terrestrial origin; nutrients; elements that are confined to early diagenetic minerals; and in the near-surface zone the anthropogenic elements including several harmful metals. Although there seems to be a decreasing trend in the surface zone the metal concentrations are still clearly elevated.
San Quintin, Mexico, provides a useful site for integrated analyses of material fluxes and socioeconomic constraints in a geographically isolated system. Natural resource utilization on the land is dominated by groundwater exploitation for cultivation of horticulture crops (primarily tomatoes). Irrigation exceeds water recharge minus export by a factor of 6. Resource utilization in the bay is dominated by oyster culture; food for the oysters is provided by tidal exchange of bay and ocean water. Consideration of oyster respiration and system respiration suggests that the present level of aquaculture is about 40% of the sustainable level. A “physical unsustainability index” (PhUI) was developed to measure the proportional departure of utilization of the most limiting resource for sustainability: 6 on land; 0.4 in the bay. Based on PhUI and measures of economic development, we conclude that aquaculture is more viable than agriculture.
Watershed Development Programmes (WDPs) have been initiated in India to improve and sustain productivity and the production potential of the dry and semiarid regions of the country at higher levels, through adoption of appropriate production and conservation techniques. The aim is also to meet the needs of rural communities for food, fuel, fodder, and timber and, thereby, reduce pressure on natural forests. In view of their potential for growth, for improving income, and the natural resource base of the disadvantaged regions of the country, WDPs are being accorded importance in the development plans for India and by donor agencies. This paper presents a social cost-benefit appraisal of a watershed development project in Karnataka, India. Using alternate viability measures, i.e. Net Present Value (NPV), Benefit-Cost Ratio (BCR) and Internal Rate of Return (IRR), and rigorous tests and sensitivity analyses, the results show that if expected full benefits are realized, the benefits derived from the watershed project are quite high, with the IRRs ranging from 19 to 96%. If, however, expected full benefits were to fall short by 25%, and net costs of (including the opportunity cost of grazing benefits foregone by the villagers on account of establishing community woodlots on degraded forestlands and village commons used earlier for free grazing of their cattle) the project will report losses. Even these losses can be contained if the direct benefits from some community woodlots, for which information was not available, and other indirect benefits, mostly of an environmental nature, are included. The findings of this study suggest that watershed development projects initiated to improve the economy and ecology of India's dry and semiarid regions are economically viable and socially desirable.
High-elevation sites in the tropics may be particularly sensitive to rapid climate change. By sampling treeline populations, I have developed the first extensive (> 300 years) tree-ring chronology in tropical North America. The site is Nevado de Colima, at the western end of the Mexican Neovolcanic Belt, and the species studied is Mexican mountain pine (Pinus hartwegii). Despite past logging in the area, 300 to 500-year old pines were found at 3600–3700 m elevation, about 300 m below the present treeline. The Nevado de Colima tree-ring chronology is well replicated from 1600 to 1997. Calibration with Colima climatic records points to summer monsoon precipitation as the strongest dendroclimatic signal. Most trees also exhibit extremely low growth in 1913 and 1914, following the January 1913 Plinian eruption of the Volcan de Colima. Because P. hartwegii is found on top of high mountains from Mexico to Guatemala, there is potential for developing a network of tropical treeline chronologies.