Ogden's Pondweed (Potamogeton ogdenii) COSEWIC assessment and status report: chapter 5

Habitat

Habitat requirements

Ogden’s pondweed is found in clear, slow-moving streams, beaver ponds, and lakes. The water is probably hard (alkaline) since both Ontario sites are associated with marble bedrock. Crow & Hellquist (2000) and Hellquist & Hilton (1983) report the habitat as “alkaline waters”. Hellquist & Mertinooke-Jongkind (2003) describe the habitat as “ponds and lakes with high alkalinity”. Although the species was not found by the author at the Davis Lock station in 2005, the location is well-described by the 1987 collection data. The quiet bays at the site support a diverse community of pondweeds including: P. strictifolius, P. robbinsii, and P. zosteriformis. The habitat on the Davis Lock specimen is “In 7-10 feet of water”.

The 1974 record of Ogden’s pondweed from Murphys Point Provincial Park is from one of a series of beaver ponds along a small creek with limited flow. In August of 2005, beavers were gone from most of the length of the creek and only a small, central watercourse remained. The only pondweed habitat consisted of shallow, scattered pools along the creek bed. Small populations of five other pondweed species were found in the creek: P. foliosus, P. illinoensis, P. natans, P. gramineus, and P. epihydrus. The habitat given for the Murphys Point collection is “Shallow waters of Black Creek, 1 m upstream from beaver dam”.

Habitat trends

With so few stations in the province and none re-located in 2005, not enough is known about general habitat trends for this species. It is clear, however, that the beaver pond habitats at the Murphys Point site have disappeared in recent years and indicates a reduction in available habitat.

Habitat protection/ownership

The Davis Lock station occurs in the navigable water of Sand Lake and the Rideau Canal, which is one of the National Historic Sites of Canada operated and maintained by Parks Canada. The Murphys Point station occurs in a provincial park that is owned by the provincial government and administered by Ontario Parks. The 1873 collection from “Hastings County” is too vague to comment on ownership.

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