. The Canadian field-naturalist. 42 The Canadian Field-Naturalist Vol. 89 creek • = Scirpus validus L. o = other aquatic species > sludge accumulation zone. k zone with little sludge Figure 1. Highly simplified diagram illustrating basic topographical relationships discussed in text. toward the river, with scattered patches of this species occurring for a further kilometre to- wards the center of the river. For a distance of about 75 m from the discharge point of Watts Creek, Scirpus validus is essentially the only rooted aquatic plant found. (Floating duckweeds, Lemna minor L. and Spirodel
. The Canadian field-naturalist. 42 The Canadian Field-Naturalist Vol. 89 creek • = Scirpus validus L. o = other aquatic species > sludge accumulation zone. k zone with little sludge Figure 1. Highly simplified diagram illustrating basic topographical relationships discussed in text. toward the river, with scattered patches of this species occurring for a further kilometre to- wards the center of the river. For a distance of about 75 m from the discharge point of Watts Creek, Scirpus validus is essentially the only rooted aquatic plant found. (Floating duckweeds, Lemna minor L. and Spirodela polyrhiza (L) Schleiden, also grow profusely in this area, as do microscopic algae.) The substrate of this region is an oozy sewage deposit, hereafter termed "; At the limits of this zone, the substrate changes very noticeably to a sandy sediment, and several other rooted higher aquatic plant species are found in addition to S. validus. These include the emergent aquatic species Typha latifolia L., Sparganium eurycarpum Engelm., Ponte- deria cor data L., Sagittaria rigida Pursh, and Sagittaria latifolia Willd., the floating-leaved Nymphaea odorata Ait., and the submersed species Ceratophyllum demersum L., Ana- char is canadensis (Michx.) Rich. Heteranthera dubia (Jacq.) Macm., Potamogeton perfo- liatus L., and Vallisneria americana Michx. Methods Samples of sediments and leaves were col- lected August 20-24, 1973. Sampled plants of Scirpus validus were consistently chosen growing in water less than a metre in depth, and extending at least a metre out of the water. The top 50 cm of leaves, well out of the water, were collected. Massed collections of about 100 leaves were made at 32 sites, and at each site a sample of soil representing the top 15 cm of substrate, was collected. Thirteen sites in the heavily-polluted sludge zone, where only Scirpus validus is found, were sampled. An additional 19 sites of growth of S. validus, representing less-polluted areas
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