Vegetation changes with falling water levels in the Delta Marsh, Manitoba

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Walker, Jennifer Mary
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Quantitative studies have been made on the vegetation of the fresh-water marsh at Delta, Manitoba, under falling water levels, from 1959 to 1961. Twenty widely distributed sites in the 15,000 hectare marsh were studied in detail. Twenty-seven prevalent species were found of which thirteen had a presence rating between 100% and 65%. Included in this group, in diminishing presence order, were: Phragmites communis var. berlandieri, Scolochloa festucacea, Atriplex patula, Chenopodium rubrum, Sonchus arvensis var. glabrescens, Aster brachyactis, Rumex maritimus var. fueginus, Carex atherodes, Hordeum jubatum, Typha latifolia, Scirpus paludosus, Ranunculus sceleratus, and Scirpus validus. Ecological descriptions of these species are given, with particular reference to the part they played in succession, within a season and from one season to the next. Emphasis is placed on those species with the highest presence values, and two groups of 'selective' species are described - those restricted to low and high conductivity sites. Submerged aquatic vegetation is discussed briefly. The soils of the marsh are a complex of Peaty Saline Rego Humic Gleysols and Organo and Saline Regosols. Samples were collected from all the sites and analyzed for pH, conductivity, physical composition, and available cations and anions. Sodium, potassium, calcium, magnesium, carbonates, bicarbonates, sulphates and chlorides were analyzed quantiatively. Topographical relief at Delta is slight but physiographic processes are striking and their influence on the vegetation is discussed.