Table 1: Densities of nitrate-dissimilating and nitrite-dissimilating bacteria in surface sediments in the German Bight, North Sea

At 24 stations in the Weser Estuary and the German Bight the Most Probable Numbers (MPN/g dry wt. sediment) of nitrate-dissimilating (= denitrifying) and of nitrate plus nitrite-dissimilating bacteria were recorded. The numbers of nitrite-dissimilating bacteria, i. e. denitrifiers not capable of reducing nitrate to nitrite, were calculated by subtraction of the MPN for nitrate-dissimilating from the MPN of nitrate plus nitrite-dissimilating bacteria. By determining the percentages of these bacteria in relation to the number of the heterotrophs, the ecological importance of denitrification, especially the nitrite dissimilation, was estimated. The results showed the MPN of nitrate-dissimilating bacteria to be in the range of 0-156 (up to 0.8 % of heterotrophic bacteria). An exception was the sediment of one station with a MPN of 1849, or 5.2 % of the heterotrophs. The amounts of nitrite-dissimilating bacteria were between 0 and 2352 (up to 13 % of heterotrophic bacteria). In the estuary the numbers of nitrate-dissimilating and of nitrite-dissimilating bacteria showed a decreasing tendency with distance from Bremerhaven. The highest numbers were found in the Weser off Bremerhaven and also at 3 stations in the German Bight, south of the Isle of Helgoland.

Table 1: Densities and snow loads for individual levels in 1967 and 1978

The deformation of a 20 m deep firn pit in the accumulation area of Kesselwandferner was surveyed over aperiod of 11 years. Six or seven surveying markers had been installed at each of 14 levels. The survey shows tImt the shear strain rate is independent of depth and the originally circular pit cross section was changed into an ellipse. In the direction of the glacier flow, the diameter was increased, the strain rate being approximately independent of depth. Transverse to the flow, however, the diameter decreased, the strain rate becoming higher as the depth increased. The vertical strain rates responsible for thinning of firn layers decrease with depth.

(Table 1) Rodent (lemming and vole) densities in 5 study areas in the Canadian Arctic

Lemmings construct nests of grass and moss under the snow during winter, and counting these nests in spring is 1 method of obtaining an index of winter density and habitat use. We counted winter nests after snow melt on fixed grids on 5 areas scattered across the Canadian Arctic and compared these nest counts to population density estimated by mark-recapture on the same areas in spring and during the previous autumn. Collared lemmings were a common species in most areas, some sites had an abundance of brown lemmings, and only 2 sites had tundra voles. Winter nest counts were correlated with lemming densities estimated in the following spring (r(s) = 0.80, P < 0.001), but less well correlated with densities the previous autumn (r(s) = 0.55, P < 0.001). Winter nest counts can be used to predict spring lemming densities with a log-log regression that explains 64% of the observed variation. Winter nest counts are best treated as an approximate index and should not be used when precise, quantitative lemming density estimates are required. Nest counts also can be used to provide general information about habitat-use in winter, predation rates by weasels, and the extent of winter breeding.