1972. Distribution of aquatic gastropods across an interface between the Canadian Shield and limestone formations. Can. J. Zool. 50: 1433J. Zool. 50: -1445 This quantitative study gives a convincing demonstration in situ of the direct relationship which exists between the distribution and density of aquatic gastropods and the calcium concentration of their natural waters. The area chosen, in the Gravenhurst-Barrie district of southern Ontario, north of Lake Simcoe, provided a well-demarcated natural gradient across the interface between limestone formations and the calcium-poor rocks of the Pre-Cambrian Shield. Monthly quantitative samples over a 14-month period at 25 stations showed that most pulmonates, notably Physa gyrina and Helisoma anceps, had high densities in hard and medium water, whereas the prosobranchs Amnicola limosa and Campeloma decisum showed a reverse pattern, with highest densities in soft and medium water and very low densities in hard. Most pulmonates showed a slower individual growth rate in soft water and a lower proportion of large individuals. MCKILLOP, W. B., et A. D. HARRISON. 1972. Distribution of aquatic gastropods across an interface between the Canadian Shield and limestone formations. Can. J. Zool. 50: 1433-1445.Des Btudes quantitatives ont permis de demontrer in situ que la rkpartition et la densite des gasteropodes aquatiques sont fonction directe de la concentration de calcium dans l'eau du milieu. La region choisie, dans le district Gravenhurst-Barrie, en Ontario du Sud, au nord du lac Simcoe, est un gradient nature1 bien dktermine, a la jonction des formations calcaires et des roches pauvres en calcium du Bouclier Canadien. Des khantillons quantitatifs, prelevBs A tous les mois durant 14 mois, en 25 stations diffBrentes, ont montrB que la plupart des pulmones, notamment Physa gyrina et Helisoma anceps, ont des densitBs plus grandes en eau a duretk Blevke ou moyenne, alors que l'inverse se produit chez les prosobranches Amnicola limosa et Campeloma decisum, dont les densitBs sont BlevBes, en eau douce ou A duretC moyenne, et trbs basses en eau dure. En eau douce, la croissance individuelle est plus lente chez la plupart des pulmones et l'importance relative des gros individus est moindre.[Traduit par le journal]

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.

No abstract

Fluctuations in the level of Lake Agassiz are dated at two sites in northwestern Ontario. A radiocarbon date on a modern shell sample indicates dates on freshwater molluscs from the area are about 440 ± 100 years (GSC-3281) too old due to the hard-water effect. An adjustment of 400 years to two fossil freshwater mollusc dates of 11 400 ± 410 (GSC-3114) and 10 400 ± 100 years BP (GSC-2968) makes them compatible with radiocarbon dates on wood from deposits in other parts of the Lake Agassiz basin. The two new dates indicate the beginning of the low-water Moorhead Phase of Lake Agassiz started about 11 000 years BP. The high-water Emerson Phase started when the water level rose to form the Upper Campbell beach approximately 10 000 years BP. The red clay widely distributed throughout northwestern Ontario was deposited during the Emerson Phase when the ice margin lay along the Hartman, Dog Lake, and Marks moraines.

Stratigraphie and paleoecological analyses at five sections, together with age determinations based on 19 previously published and 21 new radiocarbon dates, provide a detailed late Holocene history of the Red River, Manitoba. Ecological information, such as age frequency analysis, relative abundance, diversity and association of species was drawn from 19 mollusc species. These data indicate that the Red and Assiniboine rivers cut the valleys they occupy today within a thousand years of the regression of Lake Agassiz. In the south, up to 14 m of alluvium has accumulated during the last 7000 years. A decrease in the sedimentation rate at 1400 BP is coincident with the shift in the position of the Assiniboine from the valley of the La Salle River to its present position. Overbank sedimentation did not start in the northern part of the area until ca. 5200 BP. Initial rapid sedimentation rates in this area are attributed to increased precipitation and a brief eastward excursion of the Assiniboine River into the Red. In spite of increased precipitation, flood frequencies remained low in the north until 1400 BP. Increased overbank sedimentation after 1400 BP is attributed to the northward shift in the position ot the Assiniboine.

Can. Ent. 113: 251-253 (1981) Vapour degreasing and cleaning of entomological specimens proved to be a viable alternative to standard methods. Defined change in colour upon degreasing clearly portrayed the effectiveness of this new technique.

Post-Lake Agassiz raised beaches have been identified 6 m above the present level of Lake Winnipegosis. The level, termed the Dawson level, is radiocarbon dated at 4870 f 80 years BP (GSC-4138) and 4900 + 70 years BP (GSC-4139) at Dawson Bay and at 5050 + 100 years BP (BGS-1126) at Denbeigh Point. The dates are estimated to be 350 years too old due to the hard-water effect and the Dawson level is believed to have formed about 4550 years ago. The 6 m drop in the level of the northern part of Lake Winnipegosis is attributed to isostatic tilting. The fossil assemblages of the beaches are the same and are dominated by the extinct gastropod Marstonia gelida. Two marine invertebrates, the foraminifer Elphidium gunteri and the ostracod Cytheromorphafuscata, are present in the samples. These marine animals are believed to have been brought into the area by migrating waterfowl and to have survived because of the high salinity of the lake.Les plages soulevkes, postkrieures au lac Agassiz, ont Ct C identifikes B 6 m au-dessus du niveau actuel du lac Winnipegosis. Le niveau, appelk niveau Dawson, est datC au radiocarbone B 4870 f 80 ans Av.P. (GSC-4138) et 4900 + 70 ans Av.P. B la baie de Dawson et B 5050 f 100 ans Av.P. (BGS-1126) i la pointe Denbeigh. Les dates accusent 350 ans de trop B cause del'effet de la duretC de l'eau, et le niveau Dawson semble s'gtre formCe il y a approxirnativement 4550 ans. L'abaissement de 6 m du niveau de la partie nord du lac Winnipegosis est attribuC au mouvement isostatique. Les assemblages de fossiles des plages sont identiques et dominks par le gastkropode Bteint Marstonia gelida. Deux invertkbks marins, le foraminifere Elphidium gunteri et l'ostracode Cytheromorpha fuscata, sont prksents dans les Cchantillons. L'apparition de ces animaux marins dans cette kgion est probablement due la migration des oiseaux aquatiques et leur survivance fut assuke par la forte salinitC du lac.[Traduit par la revue]Can.

Can. Ent. 113: 255-258 (1981) Frequently descriptive entomology suffers from a lack of precise data on specimen colour. Since colour is rarely defined and since an effective technique is available, the authors suggest that greater consideration be given colour analysis. A simple procedure is outlined in relation to colour analysis of specimens undergoing degreasing. RCsumeL'absence de donntes precises sur la couleur des spicimens est souvent un problkme en entomologie descriptive. Parce que la couleur est rarement prtcisie bien qu'une technique efficace soit disponible i i cet effet, les auteurs proposent d'accorder plus d'importance a l'analyse de la couleur. Une mtthode simple est dtcrite pour analyser la couleur de sptcimens devant ktre dtgraissts.