Liming to improve the living conditions for fish
Decreased acid deposition and thereby decreased exceedance of the criticl load, as has been evident the last few years, will have significant impact on the amounts of limestone powder that should be used to deacidify surface waters. Also, the acidified area will decrease and eventually make liming unnecessary in some areas. As a consequence of deposition scenarios according to the commitments of the UN sulphur protocol liming in Norway will be reduced to one third some time after year 2010.
Calcium-carbonates as finely ground dry powder may stabilize pH at intermediate levels (pH 6-8), are cheep and easy to handle and are most widely used. Carbonates dissolve and neutralize the water as a function of pH, powder size distribution and time and conditions for dissolution.
Both lake liming, limedosers and terrestrial liming may be used to deacidify acid waters. A mix of different liming techniques is often recommended. Terrestrial liming techniques such as whole-catchment liming or wetland liming have several advantages compared to other liming techniques. Most important is terrestrial retention of aluminium and deacidification of melt water during the winter time and spring.
Dosers for dry limestone powder or slurried powder are used in both small streams and large rivers. The most advanced are equipped with automatic dosing control based on pH upstream or downstream and water flow. Data are transmitted, stored in database and used for dose control. Close-downs may be detrimental, especially to salmon populations if no other liming measures are included. Special control programmes are necessary in such cases.

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