Emergence of seedlings of aquatic macrophytes from lake sediments

Sediment samples were collected in May 1980 from 11 stations at five sites in Lake Wabamun. Emergence of seedlings was recorded in a greenhouse at 19 °C for 120 days. The sediments were then chilled at 4 °C for 120 days and reexposed to greenhouse conditions for a further 90 days. Total seedling densities varied from 0 to 2335 m−2. Depth and sediment texture each accounted for 20% of the variance in seedling numbers. Discharge of thermal effluent from the Wabamun generating station also caused substantial variation in seedling number; seedling numbers at the shallowest Wabamun Outlet station were over four times those at any other site. Chilling of the sediment samples in the laboratory caused further emergence of seedlings from the four sites with the highest seedling densities in the initial treatment. Total numbers were up to 50% of those for seedlings that emerged during the initial exposure to greenhouse conditions. Potamogeton pectinatus and P. pusillus were most common among the seedlings of six species. Two of the three most common macrophytes in the lake were rare as seedlings, while no seedlings were recorded for the most common angiosperm, Myriophyllum exalbescens. Reproduction by seed makes a secondary contribution to the dynamics of the vegetation of Lake Wabamun.

The influence of substrate on the growth and morphology of Myriophyllum exalbescens and Myriophyllum spicatum

Stem cuttings, 30 cm long, of Myriophyllum exalbescens Fern. and M. spicatum L. were planted in three substrates: loam, sand, and peat. Growth responses of these species were compared in three independent experiments each of a duration of 50 days. In some cases M. spicatum grew more vigorously, but the previous growth conditions for the plant material at the start of the experiment influenced the total amount of growth. In all experiments the percentage of ash in M. exalbescens was greater than in plants of M. spicatum grown in the same environment. The two species remained distinct from one another in characteristics of leaf length, number of leaf divisions, and length of internodes near the apex of the main stem. Within each species a marked relationship between morphology and substrate was observed. On the nutrient-poor substrate, sand, leaves of M. spicatum converged in appearance towards leaves of M. exalbescens grown on the nutrient-rich substrate, loam.

Habitat selection by dabbling ducks in the Baie Noire marsh, southwestern Quebec

We monitored the waterfowl distribution in a recently flooded 260-ha marsh along the Ottawa River during 1974 and 1975. The birds (the three most important species were the black duck. Anas rubripes; the mallard, A. platyrhynchos; and the blue-winged teal, A. discors) did not distribute randomly among the five major habitats recognized, but clearly preferred a habitat dominated physiognomically by broken cattail (Typha angustifolia) cover but best characterized ecologically by ivy-leaved duckweed (Lemna trisulca), whitish water-milfoil (Myriophyllum exalbescens), and common bladderwort (Utricularia vulgaris). On average, broods (0.3/ha) and adult birds (6.6/ha) were four times more abundant per hectare there than in the next best habitat. This pattern of use was stable throughout the summer and throughout the daylight period as well. Multivariate analysis (correspondence factor analysis) enabled us to extract those ecological variables that played a determinant role in controlling plant distribution throughout the marsh. The observational and analytical techniques developed in this work could be applied to the development of marsh management plans designed to promote the expansion of the preferred waterfowl habitat.