Premium
Alkalinity and pH of tarns and streams in the English Lake District (Cumbria)
Author(s) -
SUTCLIFFE D. W.,
CARRICK T. R.
Publication year - 1988
Publication title -
freshwater biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.297
H-Index - 156
eISSN - 1365-2427
pISSN - 0046-5070
DOI - 10.1111/j.1365-2427.1988.tb00340.x
Subject(s) - alkalinity , streams , altitude (triangle) , slates , geology , acid deposition , acid rain , hydrology (agriculture) , ecology , geochemistry , chemistry , soil water , biology , soil science , geometry , mathematics , computer network , geotechnical engineering , organic chemistry , computer science
SUMMARY. 1. The distribution of softwater and acid tarns and streams in central Cumbria is briefly summarized and compared for the periods 1983‐85 and 1949‐56. 2. Fifty‐three upland tarns (altitude >350m) and forty lowland tarns (altitude <320m) were sampled on Skiddaw Slates, the Borrowdale Volcanic Series, and igneous intrusions. On these bedrocks, tarns and streams would be highly sensitive to further acidification if acid deposition increases above current levels. Twenty‐six upland and seven lowland tarns are permanently acid with zero or negative alkalinity values throughout the year; mean pH ranged from 5.3 to 4.2. The other sixty upland and lowland tarns had positive mean Alk in the summers of 1983‐85, ranging from 7 to 1227μequiv. I −1 Alk and mean pH5.7 to >7.0. Thirty‐one of the sixty tarns had mean Alk < 100μequiv. I −1 in summer (May‐September); sixteen became temporarily acid (negative Alk) for varying periods in winter. Acid episodes also occurred in the tarns in 1949‐56. 3. Acid and very low alkalinity tarns and streams commonly occur on the high western, central and northern fells. Few occur on the high eastern felts, where there are veins of calcite in exposed rocks. 4. Seventy‐five lowland tarns were sampled on Silurian Slates in southern Lakeland. On these bedrocks, tarns and streams are not highly sensitive to further acidification. Only six tarns had summer mean Alk <100μequiv. 1 −1 . No permanently acid tarns or streams were found. 5. Over a mean span of about 30 years. Eel Tarn appears to have become slightly more acid and Harrop Tarn slightly less acid. The remainder of all tarns surveyed in 1983‐85 have altered little, although there is a heavy load of acidic deposition on to the catchments and some tarns contain very low concentrations of Alk. Rapid acidification in recent years has been prevented by the neutralizing capacity of volcanic and sedimentary rocks. These rocks produce relatively high concentrations of Alk, up to 650μequiv.l −1 in some spring‐fed streams on the central fells and even more at lower altitudes. Absence of coniferous