Acidification in Cumbrian waters: Past and present distribution of diatoms in local lakes and tarns.
Report No DWI0629

Final Summary

We have examined the present diatom distribution and that of the recent past in order to assess the rate and extent of acidification in Cumbrian lakes and tarns.

The survey of present distribution in waters of less than pH 7.5 reveals a complex mosaic of over 500 diatom taxa. There is clearly a difference in diatom assemblages between sites with and without any alkalinity (+ pH 5.5) but additional factors determine the pattern of assemblages in waters with pH above 6.0. mere is also evidence for morphological variation in taxa related to environmental changes.

Recent sediments of 5 sites all indicate some changes within the last 200 years, the more acid ones showing pH decreases within the present century. Although all sites are in upland grasslands, there is evidence of disturbance since Romano-British times.

Spatial and temporal distributions all require further work in order to maximize the information from such a large amount of data.

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