Distribution of aquatic gastropods across the Ordovician dolomite – Precambrian granite contact in southeastern Manitoba, Canada

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Abstract
Gastropod populations in 25 stream sites in southeastern Manitoba were studied over an 18-month period. Biological samples and water-quality samples were taken from each site at monthly intervals except during the winter. The gastropod distribution is described in relation to calcium concentration across a natural boundary. In addition to calcium, 16 other water-quality parameters were studied to ascertain whether these were important in regulating gastropod ecology. A multiple regression analysis indicated that the five most important of these were, in order of frequency of occurrence: calcium, nitrate and nitrite nitrogen, turbidity, magnesium, and alkalinity. Life history and additional conchological data are given for the 17 gastropod species encountered.