The extent of semi‐natural grassland has diminished considerably across lowland landscapes of England and Wales during the second half of the twentieth century. Locating, describing and evaluating the dwindling cover has been a major challenge for conservationists. A concentrated vegetation survey effort at grassland sites has been mounted within different parts of Britain since the late 1970s. Plant community recognition has benefited considerably from the development of the contemporary National Vegetation Classification, and its widespread adoption permits national inventory of comparable vegetation data. Findings of a range of surveys (ninety‐eight in total), undertaken between 1978 and 1996 in England and Wales covering different forms of unimproved lowland grassland, are collated and reviewed. Vegetation data were abstracted from internally published survey reports. Calcicolous and neutral grasslands have been covered more thoroughly than acidic and wet or marshy grasslands. Cover data are summarized at community level. Overall estimates from survey results indicate that there are some 27 500–40 000 ha of calcicolous grassland, 7500–15 000 ha of unimproved neutral pasture and hay meadow, 8000–15 000 ha of acidic grassland and 9000–17 500 ha of wet grassland in lowland England and Wales; these represent only 1–2% of the cover of permanent lowland grassland. Some communities have additional representation in heathlands, mires and upland environments. Although they require further refinement, the cover data for individual communities provide a context for assessing priorities in site‐based and agri‐environment conservation programmes. It is concluded that, as well as arresting further depletion, it will be necessary to restore and expand lowland grassland habitats to counteract the negative impacts of fragmentation and isolation of various community types, such as the Centaureo–Cynosuretum, which is widely but thinly distributed. Habitat rehabilitation schemes also need to assimilate local patterns of community diversity characteristic of both wet and dry grasslands. It is suggested that reversal of the recent successional trends that followed relaxation of grazing at certain sites might produce a more appropriate balance in the relative cover of coarse tall grasslands and fine short turf. Vegetation surveys provide a source of spatial data for identifying local aggregations of semi‐natural grassland remnants.
The effect of stomaching time on release of epiphytic bacteria from two species of submerged macrophytes was investigated, and the proportion of total epiphytes released from three species by stomaching was determined. A duration of 5 min was found to be an adequate stomaching time; the proportion released (mean ca 0.4) varied considerably between sites and sampling occasions.
i. Concentration of total suspended bacteria and heterotrophic activity (as turnover rate and turnover rate per bacterium for glucose assimilation by a trace-addition approach) were determined at distance intervals along four high-trophic-status calcareous headstreams in the Yorkshire Wolds and along four low-trophic-status acid headstreams in the Galloway Hills.2. Mean concentration of suspended bacteria was marginally greater in the calcareous streams while turnover rate and turnover rate per bacterium were substantially greater.3. Further determinations of heterotrophic activity (as turnover rate, turnover rate per bacterium, I/^MX
ABSTRACT1. This study collated information relating to acidification of running and standing waters on Sites of Special Scientific Interest (SSSIs) throughout Britain in acid-sensitive areas.2. Of those SSSIs which occur in acid-sensitive areas of Britain, 196 have water bodies. The following information was obtained for each site if available: details of local geology and soils, types of land use and management, water quality data and data relating to biological components of both the aquatic and riparian habitats.3. In addition, samples from 112 water bodies were collected for water chemistry and epilithic diatom analysis. Results from each site were placed into existing critical loads and species response models to determine whether acidification had occurred.4. Results showed that the fresh waters on 141 SSSIs had probably suffered acidification. This was most acute in north Wales, with mid Wales, south-west and north-east Scotland and northern England also being badly affected. 5.A wide variety of changes in the biological status of water bodies relating to acidification were found to have been recorded on SSSIs, ranging from phytoplankton, invertebrate and macrophyte community changes to decline of fish, amphibian, bird and mammal populations.6. Catchment afforestation may be a problem in poorly buffered areas and has probably contributed to freshwater acidification on 40 SSSIs. 7.Comparison with critical loads maps for acidity in UK fresh waters reveals that existing commitments on acidifying emissions (the EC Large Combustion Plant Directive) will not be sufficient to prevent further acidification on a number of SSSIs. In order to achieve a protection of the nature conservation interest of fresh waters further commitments to emission reductions will be necessary. INTRODUCTION
1. Concentration of suspended bacteria in a calcareous headstream increased linearly from the source to 48 m; this indicated a diffuse origin of bacteria.2. Drift loss of suspended bacteria and glucose-mineralization capacity from this length of stream were measured, and estimates were also made of the total number and glucose-mineralization capacity of epiphytic bacteria associated with the luxuriant submerged aquatic vegetation.3. Mean drift loss per day represented 11-12% of total epiphytic bacteria and 8-18% of epiphyte glucose-mineralization capacity, hence the epiphytic population should be well able to sustain the observed downstream losses.4. In a 90 m length of a contrasting acid, granitic, headstream, in which submerged vegetation was principally a leafy liverwort, there was no downstream change in concentration of suspended bacteria. 5. A substantial population of epiphytic bacteria was found in the acid stream, sufficient for only a 1-2% daily release to produce a doubling in concentration of suspended bacteria; reasons are suggested for the apparent non-release of epiphytes.
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