| Popis: |
The small fjord Lakselvvatn in North Norway, with a mean water-level 1 m above mean sea-level, was sampled 4 times in 1982–83. A layer of fresh water, normally 2 m, but up to 11 m thick, was found over brackish water of salinity increasing to 27 ‰. A halocline was always present somewhere between 7 and 13 m. Oxygen decreased with depth to zero at 30 m; this is judged to be a fairly permanent situation. A fresh-water fauna similar to that of nearby lakes was present in the littoral zone, and fresh-water planktonic crustaceans occurred in low numbers, generally above 2 m depth. Planktonic crustaceans of marine character were almost exclusively confined to polyhaline water, but Eurytemora affinis tolerated even fresh water. Twenty two taxa of macrobenthos showed a distinct vertical zonation above 30 m depth, strongly influenced by the salinity and oxygen gradients, and involving special vertical patterns of diversity and biomass. The established tolerance limits towards short exposures to fresh wate... |
