摘要:

Blanket mires extend over approximately 22,500 km2of the north and west of the British Isles, and are of both national and international importance. Blanket peat started to form locally in some regions 9400 years ago, but the period of most active spread was between 5100 and 3100 BP. Clearance of forest and scrub by human activity probably triggered peat formation in many areas, though the influence of longer term changes in climate can be detected both in the times of peat initiation and in subsequent peat growth. High-quality blanket mires can be characterized by the presence of distinctive plant communities, well-defined microtopographic differentiation of the mire surface, and a diplotelmic structure to the peat mass. Many blanket mires, however, currently have a modified, damaged, or eroded vegetation cover. British and Irish blanket mires are used for a variety of purposes: year-round grazing (mainly sheep), game stocking (red grouse and red deer), water catchment, plantation forestry, domestic and commercial peat extraction, military training, recreation, and conservation. The associated management practices can have significant effects on the composition and structure of the vegetation, the bird and invertebrate faunas, and the physical and chemical properties of the underlying peat. A major part of the British blanket mire resource is affected and modified by grazing, burning, and drainage; only approximately 4000 km2may remain in a near-natural state. An estimated 3500 km2is afforested and a further 3500 km2is eroded. Atmospheric pollution has been shown to have had significant effects on the blanket mire vegetation only in the Southern Pennines, but substantial areas in Wales, northern England, and southwestern Scotland are potentially at risk from high levels of sulphur and nitrogen deposition. The peat mass is very susceptible to erosion from natural agents: frost, drought, rain, and wind. However, erosion normally occurs only when the plant cover is damaged. Severely eroded peat is found in all blanket mire regions of the British Isles and is most common above 450 to 500 m altitude, where it is associated with the development of gully systems within the peat mass. Erosion has almost certainly increased in intensity in the last 200 years, as land-use pressures have intensified, but there is evidence from a number of regions that active gully systems were present by at least AD 1500-1700. Damage and erosion of the blanket mire vegetation has considerable economic and amenity consequences: loss of grazing land, infilling of reservoirs with sediment and periodic discolouration of water supplies, loss of distinctive wildlife (particularly birds), and impaired recreational value. Techniques are now available for the revegetation and restoration of badly damaged blanket mire, but they are very costly. Government schemes that provide incentives for less-intensive management of blanket mires offer a potentially more viable way of meeting our international conservation obligations.Key words: blanket bog, peat, grazing, pollution, burning, afforestation.

ISSN:1208-6053    

DOI:10.1139/a98-006

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

The effects of salinity and pH on the partitioning behaviour and toxicity of ionizable and neutral organics and organotin compounds in aquatic ecosystems are reviewed. The pH and pKaare of importance for the distribution overn-octanol and water (Dow) of ionizable compounds.Dowincreases with salinity for ionized organics up to 3 times and for organotins up to 1000 times. Neutral acids partition more strongly to the phospholipids than their ions; however, differences are smaller than forDow. For dissociated phenols, the distribution over the membrane and water (Dmw) depends on counterion concentration. For pentachlorophenol (PCP) and organotins, the uptake rate constant (k1) for the neutral form is up to a factor 10 higher than for the ion. The formation of ion_counterion pairs at higher salinity does not contribute to a higher uptake rate. The adaptation to salinity does not result in different bioconcentration kinetics. There is no general intrinsic susceptibility difference between salt water and freshwater organisms. For ionized organic acids, an increase in toxicity up to 4 times with decreasing salinity is reported frequently. Differences in pH are important for toxicity for compounds with a pKabetween 6 and 9. For organophosphates a toxicity increase up to 2.5-fold with salinity was found. Bioconcentration and toxicity of ionizable organics aren't influenced by salinity in the way thatDowis influenced. Quantitative structure activity relationships developed for neutral compounds cannot be used to estimate the bioconcentration or toxicity of partly ionized organics. The deviating partitioning behaviour over water and octanol is no reason to set separate quality criteria for ionizable compounds for marine water and freshwater. However, their toxicity can differ as a result of pH differences. Toxicity data for fresh and marine organisms should always be compared, because unexpected differences in sensitivity can be detected in this way.Key words: salinity, sensitivity, acids, bases, organotin compounds.

ISSN:1208-6053    

DOI:10.1139/a98-007

出版商:NRC Research Press    

年代:1998

数据来源: NRC