Effects of Liming on the Aquatic Fauna in a Norwegian Watershed: Why Do Crustaceans and Fish Respond Differently?

摘要

We studied the effects of liming on fish and crustaceans in a watershed which is in a region known to have one of the highest diversity of aquatic biota in Norway.This watershed,Enningdal,is shared between Norway (1/3) and Sweden (2/3) and includes 61 lakes > 1.0 ha in Norway.Liming started on a large scale in the 1980s.Currently,a total of 26 of lakes (43%) are limed,covering 93% of the total lake area.The mean value +-S.D.of pH and the concentration of inorganic labile Al in these lakes is 6.62+-0.35 and 3 +-4 mu g l-1 respectively.Historical data of fish communities have been obtained from surveys,while test-fishing and sampling of crustaceans were conducted in 24 lakes in recent years (2002-2004).The present study shows that crustaceans to a greater extent than fish has responded to improved water quality after more than 20 years of liming.Of a total of 120 fish populations,42 (35%) have gone extinct.Only five of the lost fish populations (12%) have been re-established,all due to human re-introductions.Physical barriers are considered to be the main factor preventing fish from invading limed lakes.In contrast,crustaceans have been re-established in most limed lakes.This may be mainly due to their good spreading capacity.However,they might also have survived in refuges within the watershed,or as resting-eggs in the sediment.