To understand maintenance of the within-habitat diversity of closely related species, I investigated 11 Carex species growing along rivers in the south-western St. Lawrence Valley of Quebec. Microenvironments within a half meter of focal plants characterized for Carex comosa, C. crinita, C. grayi, C. intumescens, C. lacustris, C. lupulina, C. pseudocyperus, C. retrorsa, C. tuckermanii, C. typhina, and C. vesicaria revealed significant differences among the species in their environmental affinities. Species appear to fall into groups based on their tolerance of flooding and are secondarily differentiated on other environmental gradients such as insolation, soil pH and soil organic matter. Several traits were related to the environments that species inhabit: diaspore weight, diaspore floating duration, and root aerenchyma. The absence of any phylogenetic trend in niche differences for pairs of species supports the idea that evolutionary differentiation of the alpha-niche is the basis for coexistence of congeners.

Toxic antifouling agents such as tributyltin (TBT) and triphenyltin (TPT) have been released in aquatic ecosystems through the use of antifouling paint applied to ship hulls, pleasure crafts and fish nets. The purpose of this study was to assess the use of zebra mussels (Dreissena polymorpha ) as a biomonitor for investigating the geographical variations of organotin bioavailability along the St. Lawrence River. Organotins TBT and TPT and their degradation products were first measured in the soft tissues of zebra mussels collected from along the River. High concentrations of TBT were found in mussels from Bassin Louise, a marina in Quebec City (1442 ng/g wet weight). TPT concentrations were elevated at 2 sites near Quebec City (252 and 530 ng/g wet weight). A follow-up study assessed the extent of the distribution of organotins from the contaminated marina to the River system by measuring organotin concentrations in zebra mussels and in sediments collected River near Quebec City. The highest concentration of TBT was found in Bassin Louise (1078 ng/g wet weight) and elevated concentrations were found in two other marinas. The concentrations decreased sharply to background levels just outside the marinas. All butyltins were detected in all sediments analysed. There was a significant correlation between TBT in sediments and mussels. These studies suggest that organotin contamination may remain a problem in localized freshwaters in the St. Lawrence River.

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St. Barnabé fault, in St. Hyacinthe plain of the St. Lawrence lowlands, was postulated by Clark (1947) on his geological study of this area. Structural features of this type are of great interest to the geophysicist to establish relation between physical quantities measured at the surface and geometry of such structures. A subsurface fault can be diagnosed, under density contrast condition, with surface gravity measurements. The present detailed gravity survey was undertaken to determine if such a condition existed, to correlate geological information with gravity data, and to assess this data in terms of possible parameters of the fault structure. The field work was carried out in the summer months of 1964 with a Worden gravimeter. [...]