No description available.

The brook trout population in a 4.7 hectare subarctic lake was sampled in 1986 and intensively fished in 1987, 1988 and 1989 in order to study the effect of stock depletion on fish parasite transmission. Population density was originally high, with slow individual growth rates, and small maximum size. Brook trout bore infections of Eubothrium salvelini, Phyllodistomum umblae, Crepidostomum farionis and Diplostomum sp. as well as some rare parasites. After intensive fishing the growth rates and size of the remaining fish increased. In 1987 all parasites increased in abundance. E. salvelini decreased in 1988 whereas the abundance of the other parasites remained high. In 1989 two new parasites, Echinorhynchus lateralis and Philonema sp. appeared. Parasite community changes and improves fish growth were related to trout diets and the pattern of intermediate host consumption. In 1987 zooplankton feeding increased. It then declined in 1988 and 1989 as populations of large benthic invertebrate prey increased. Feeding shifts may also have been mediated in part by intraspecific competition and aggression.

A detailed study of the water balance of a lichen-heath tundra underlain by permafrost was begun in September 1976 near Schefferville, Quebec. The study was centred on a 0.9 ha hillside and an adjacent 100 ha catchment. The study revealed that the transfer of latent heat by moisture transport occurs during the development of the active layer as well as during freeze-up. The transfer of sensible and latent heat does not have a major impact on the maximum depth of the active layer on hillslopes, but does strongly control the maximum depth of thaw in the valley bottoms. The study also demonstrated that a simple form of the Priestley-Taylor model yields accurate estimates of evapotranspiration from several types of surfaces. A water budget model based on the Priestley-Taylor model gave an accurate estimate of the seasonal runoff from the experimental catchment. A daily water budget model indicated that a significant proportion (31%) of the net runoff (precipitation minus evapotranspiration) is stored within the still-frozen part of the active layer (primarily in the valley bottoms) early in the thaw season. That stored water is released only when the active layer approaches its maximum depth of thaw.

No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

No description available.