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Recovery Strategy for the Engelmann's Quillwort (Isoetes engelmannii) in Canada (Proposed)


2.0 Threats

Understanding threats to Engelmann's quillwort is challenging given the inconspicuous nature of the species and the difficulty in studying them. However, excellent research has been conducted to date and with our current understanding of Engelmann's quillwort, ten broad categories of threats to this species are described. Table 1 illustrates whether the threat is actual or potential, human-induced or natural, and high, medium or low priority. Descriptions of each threat follow the table.

Table 1. Qualification of threats to Engelmann's quillwort given current understanding
ThreatActual/ PotentialHuman/ NaturalLevel of Importance
1. Mechanical Damage
Actual
Human/Natural
High
2. Nutrient Enrichment
Potential
Human
High

3. Herbicide Application

  • Aquatic Herbicide Application
  • Terrestrial Herbicide Application
Actual/Potential
Human
High
4. Competition
Potential
Natural/Human
High
5. Erosion
Potential
Human
Medium
6. Invasive Species
Potential
Human/Natural
Medium
7. Long-term Changes Water Levels
Potential
Human
Low
8. Other Water Contaminants
Potential
Human
Low
9. Predators
Potential
Natural
Low
10. Deliberate Removal
Potential
Human
High


2.1 Description of Threats

Mechanical damage (e.g. boat traffic, wave action, ice movement, dredging, raking, foot traffic, boat house and dock construction, and sand covering from beach creation) can cause damage to the site and individuals. Loss of habitat can occur if a dock covers a plant, which can destroy individuals and/or lower reproductive success. Such damage has been observed at locations in the Severn River, where boat traffic is significantly higher in comparison to the Gull River site (Heydon & Pidgen 2005).

Nutrient enrichment due to runoff and other sources can cause increased competition from other more aggressive species, which can result in local declines and extinctions. Increased levels of phosphorus at some locations may contribute to nutrient enrichment and the apparent proliferation of aquatic competitors and algae, which reduces the light available to submerged aquatic plants. Similar results were concluded in demographic field studies done on Isoetes lacustris in Western Europe (Voge, 1997).

Herbicide application, either for control of aquatic vegetation or from land runoff (i.e. terrestrial application), can potentially remove individuals or entire sub-populations (Heydon & Pidgen 2005).

Competition from other aquatic plants (native such as Eaton's quillwort and exotics) can cause declines in Engelmann's quillwort by out-competing them for essential components such as light and nutrients (Brunton 2001). Aquatic plants may be proliferating due to improved water quality from zebra mussel infestations and input of nutrients from surrounding land development.

Erosion from land sources such as shoreline development (i.e. construction of docks, construction of boathouses, building cottages, shorewall construction and removal of natural shoreline vegetation) and boat wake can result in site disturbance, reduction of sunlight, which then might result in decreased performance and recruitment (Heydon and Pidgen, 2005).

Invasive species such as Zebra mussels, which in recent years have become abundant in the Severn River site (Brunton 2001), can have negative impacts on quillworts. For example, encouragement of other competing macrophytes such as milfoil would be a negative impact. In addition, multiple attachments of mussels on the plants themselves may pose a physical threat to their leaves.

Long-term changes in water levels due to dam and hydroplant operation or changes in climate could potentially cause a loss of individuals and habitat. At the Severn River, the population is located directly upstream of a Trent-Severn Waterway lock where there is potential for excessive changes in water level in order to move boat traffic through. In addition, ice scouring is a potential effect of excessive water level fluctuations (Brunton 2001).

Other water contaminants (e.g. petroleum products, heavy metals, salt from roads) have caused the eradication of Engelmann's quillwort in major industrial areas in the eastern United States (Brunton 2003) and could potentially impact the survivorship of Canadian populations. Both the Gull River and Big Chute sites are located close to facilities (where accidental toxic spills could occur) potentially causing detrimental effects to the populations (Heydon & Pidgen 2005).

Predators, such as waterfowl and muskrats can physically damage sites and cause death to individuals through foraging activities.

Deliberate removal of individuals could seriously impair the viability of these populations. Removal might be an explanation for the surprisingly rapid decline in quillwort species that was observed at the Gull River site (Brunton, 2001).