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Phosphorus Reduction in Grenadier Pond

See also: Monitoring Water Quality

Excerpts from the Gartner Lee Report, 1995

High Levels of Phosphorus

The high levels of phosphorus in Grenadier Pond, in combination with high levels of nitrogen, relate directly or indirectly to many of the problems within the pond. High nutrient levels encourage the growth of both macrophytes and algae. In general, algae and aquatic macrophytes utilize nitrogen in the form of nitrate (ammonia can also be used, but is pH dependent). Some bluegreen algae have the ability to use molecular nitrogen as well, although this ability is enzymatically suppressed when concentrations of inorganic nitrogen are high.

A single analysis of the type of algae growing in Grenadier Pond was conducted by the MOEE in August 1994. Approximately 87% of the algae in the pond were blue-greens (mainly Aphanizomenon sp.), a less desirable food source of most zooplankton and only 6% were found to be green algae, which are readily consumed by zooplankton, with the remaining species a collection of diatoms and brown algae. Aphanizomenon sp. is known to be nitrogen fixer, however, it should be noted that their presence in the pond is not evidence that they are actually fixing nitrogen; appropriate testing would have to be conducted to confirm the biological activity of this algae. The general implication of this is that the system currently favours the growth of blue-green algae over other species.

Reduction of External Sources

Recommended measures in the 1995 Gartner Lee report included:

  • improvements within the watershed to reduce phosphorus inputs to storm water and increase ground water contributions [e.g. downspout disconnection]
  • bird control measures [e.g. reduction of number of Canada geese through measures such as habitat change and education to discourage feeding]
  • alteration of shoreline habitat, both shoreline and backshore (in part to support bird control) [much of this has been done since 1995]
  • create a storm treatment wetland in the pond at the southwest comer to capture and provide some treatment for the Catfish Pond outlet [completed in 2007]
 

Reduction of Internal Sources

The internal loading of phosphorus is one of the main sources of phosphorus contamination and therefore, all actions to remediate this loading are considered to be high priorities. Food web alteration can be applied through the stocking of the historically present predator fish, northern pike and largemouth bass. Funding from the. Canadian National Sportsmen's Show has allowed for the stocking of 200 largemouth bass and five northern pike in September 1994. Additional stocking of northern pike is scheduled for May 21, 1995. Although fish stocking will assist in the recovery of ecosystem balance, the successful reproduction of pike will likely not be observed until such time as the water levels are altered seasonally and shorelines are naturalized. Bass spawning can be enhanced by installing 50 spawning boxes along the south shore until such time as water quality improvements are realized.

More importantly, though, is the need to deal directly with the sediments in the pond. More information is required to allow a final determination of how to deal with the internal load. Specifically, additional information is required to delineate the depths, quality and consistency of the sediments to determine appropriate handling, as well as to obtain necessary permits or approvals. Trial plots for different sediment treatments could be undertaken to examine different alternatives prior to whole scale implementation.

Source: Gartner Lee Report, 1995

Proposals for the Rehabilitation of Grenadier Pond et al, Gartner Lee, 1995 Part 1,Part 2, Part 3, Part 4, Part 5, Part 6, Part 7, Part 8


Comments on Water Quality - 2013

Nutrient loading in Grenadier Pond was studied early in the 1990s culminating in the 1995 Gartner Lee report (see above).

Key findings:

  • phosphorus levels in Grenadier Pond are high
  • three sources were identified: storm sewers, wildfowl defecation especially Canada geese, and pond sediment, representing historical loading
  • storm sewer loading could be addressed by downspout disconnection and asking upstream homeowners to be careful about fertilizing their lawns and gardens, and geese could be discouraged by planting the shoreline with native plants, but there were no feasible solutions for removing the phosphorus in the sediment except encouraging a healthy population of predator fish. Reducing the phosphorus in the pond was therefore expected to be slow.

Observations:

  • mid-latitude lakes are bimictic (all the water mixes twice a year), including Grenadier Pond. This mixing has consequences for the oxygen levels below the thermocline (demarcation between top, stirred layer and bottom layer), which in turn affects the phosphorus levels (pond and lake chemistry is complicated). Thus, seasonal variations from low phosphorus in the spring to high levels at the end of the summer are normal and expected.
  • the phosphorus levels in Grenadier Pond spiked in 2011, but otherwise the levels are trending down.

Comments by Leslie Gooding


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Content last modified on June 26, 2013, at 06:40 PM EST