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To assess the impacts of forest harvesting and fires on lentic fish assemblages in the Boreal Plains ecoregion (Alberta, Canada), we applied a reference condition approach to 37 lakes in burned, logged, or undisturbed catchments. Fish assemblages in the reference lakes were classified into two types: those dominated by large‐bodied piscivores and those dominated by small‐bodied fishes. A discriminant function analysis with only two environmental descriptors (lake maximum depth and average slope of the catchment) could correctly predict assemblage type in 84% of reference lakes. Depth likely reflects the influence that winter oxygen concentrations have on fish assemblage type, whereas catchment slope is correlated with a variety of landscape‐level features. Although potential effects of forest harvesting and fire can increase the susceptibility of lakes to winter hypoxia (via nutrient enrichment) and alter connectivity to the regional drainage network (via altered hydrology), fish assemblages in 93% of the disturbed lakes did not deviate from the discriminant function predictions, suggesting little, if any, assemblage‐level effects of the disturbances over the 1–2‐year time period of our study. Indeed, the level of disturbance in a catchment could explain less than 3% of the variation in assemblage structure, although a slight increase in the catches of white sucker Catostomus commersoni and a greater proportion of small individuals in white sucker populations may have reflected a modest enrichment effect in burned lakes. Current levels of landscape disturbance on the Boreal Plains appear to have minimal effects on lake fish assemblages but, because of the susceptibility of these lakes to winterkill, higher levels of terrestrial disturbance could prove detrimental.

Although theoretical foodweb models predict the presence of only three to four trophic categories, estimation of "potential" vertical foodweb structure from species lists and inferred feeding interactions suggest that as many as 7 trophic categories can occur in the pelagic foodwebs of North American glaciated lakes. A compilation of data on the nitrogen isotopic composition of zooplankton from 46 Canadian Shield lakes suggested the average existence of one "realized" trophic category in addition to that of filterfeeding, herbivorous cladocerans. When phytoplankton, planktivorous invertebrates, and plantivorous and piscivorous fish are included, the vertical foodweb structure in the pelagic zones of these lakes are greater than those hypothesized from some theoretical models.

The seed banks of six Lake Ontario shoreline marshes were investigated to assess the potential for natural regeneration of sparse submerged macrophyte populations in marshes subjected to anthropogenic disturbance. Twenty-six core samples were taken in each of three disturbed marshes with sparse submerged vegetation, and the number of seeds was compared with samples from three reference marshes containing abundant submerged vegetation. Six cores from each of six marshes were examined to determine whether there was a difference between disturbed and reference marshes in seed density or seed distribution, and germination assays were used to assess differences in seed viability. Seeds of five submerged macrophyte taxa were identified in substrate samples of the six marshes. Mean seed density was significantly higher in the three reference marshes (4082 – 47 623 seeds/m2) than in the three disturbed marshes (0–2041 seeds/m2). The density of seedlings of submerged macrophytes germinating in reference marsh samples ranged from 333 to 2406 seedlings/m2, whereas no seedlings germinated from disturbed marsh samples. The deeper sediments (7–14 cm sediment depth) in the reference marshes had comparable seed densities to those in the shallower sediments, whereas seeds were found in only the deeper sediments of the disturbed marshes. These data suggest that regeneration from buried seeds is unlikely in the disturbed marshes, even if improvements occur in the environmental conditions that have historically inhibited the growth of submerged macrophytes. Key words: submerged macrophytes, anthropogenic disturbance, Lake Ontario, seed banks, natural regeneration.

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