Box 142, Westport, Ontario K0G 1X0
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Box 142, Westport, Ontario K0G 1X0 |
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Water Quality, 2007
Water Chemistry
Water quality was tested on 7 occasions in 2007. Deep-water samples, taken on May 29th, June 16th, July 22nd and August 29th, were analyzed for total phosphorus (TP) concentration through the Lake Partners Program (Ministry of the Environment). In addition, both deep and shallow-water samples were taken on May 15th, July 5th and October 16th and analyzed for TP, E. Coli, and total organic nitrogen through the Rideau Valley Conservation Authority (RVCA). The results are summarized in Tables 1 and 2.
Water Sampling Sites for Wolfe Lake
Table 1: TP Concentration, µg/L (Lake Partners Program Data)
Interpretation of Results
Deep-water samples for the Lake Partners Program are taken at a depth that is twice that of the Secchi disc reading (approximately 13 – 14 m), and are considered to reflect the general phosphorus status of the lake at that point in time. Over the 4 summer months, deep-water TP concentrations averaged 9.0 µg/L and ranged between 7.5 and 10.6 µg/L. The July value is graphically presented in Figure 1, along with July data dating back to 1996 (the earliest results that we have). As can be seen, TP concentrations in our lake have not increased since 2001 and even appear to have declined slightly since then. Since phosphorus is the main nutrient for algal growth in lakes in our region, the lower its concentration, the clearer and more odour-free the water in that lake.
E. Coli. Escherichia coli (E. Coli) are bacteria that live in the gastrointestinal tracts of warm-blooded animals and birds. Most E. Coli pose no health risk to humans, but their presence in water is an indication that fecal matter (which may contain disease-causing organisms) has entered the water. E. Coli concentrations are conventionally expressed as the number of organisms (Colony Forming Units, or cfu) per 100 ml of water, but since the standard assay does not determine their species of origin, it is unknown whether they are from an animal or a human source. It is thus not unusual to detect low levels of E. Coli (up to 10 cfu/100 ml) in clean uncontaminated lakes that support a normal population of waterfowl such as loons, ducks and gulls. For swimming, the “safe limit” in Ontario, above which public beaches are closed, has been set at 100 cfu/100 ml.
Shallow-water testing for E. Coli is an effective method of determining whether there may be faulty septic systems in that vicinity. With the exception of the October sample at site #4, all values (Table 2B) can be considered as falling well within the “acceptable” range. Since previous samples at site #4 were normal, it is likely that the sample was contaminated by a waterfowl source and should not be interpreted as a cause for alarm.
Water Clarity
Secchi disc readings at sites B and C ranged from 5.8 to 7.1 m over the course of the summer. July Secchi disc readings for the past 17 years are graphically presented in Figure 2. Since readings greater than 5 m are generally considered to indicate “excellent” clarity, it is apparent that our lake continues to be one of the clearest in the region. It should be noted, however, that some of that clarity may be attributable to the presence of zebra mussels.
Year
Zebra Mussels
Now for the bad news. Even though we knew that there would be a major increase in the number of zebra mussels in 2007, the population explosion was considerably greater than expected. In early summer, your Lake Association placed a number of concrete monitoring pads at various locations along the shore and periodically checked them for the presence of adult mussels. These results appear in Glen Ewen’s article, elsewhere in this newsletter.
As summarized in last year’s water quality report, the life span for a zebra mussel is 2-3 years in Ontario lakes. They begin to reproduce when water temperature warms to approximately 12° C, which, in Wolfe Lake, is normally sometime in May. Adult females can produce 40,000 to 1,000,000 eggs per summer. Once fertilized, these develop into microscopic larvae, called veligers. At this stage, they are invisible to the naked eye and can only be detected under a microscope. The veligers float at the surface feeding on plankton, growing rapidly in size and are dispersed about the lake according to currents and predominant wind conditions. After 2 to 5 weeks, they become too heavy to float and sink to the bottom to attach to a hard surface, such as rocks, submerged logs or native clam shells. If they are unable to find a hard surface, they die within a few days. Those that have attached begin growing shells and at this stage appear like grains of sand. After about 4 months, they are approximately 1/5 of an inch in length and brown in colour with their characteristic darker stripes. By the second summer they are mature (about the size of your little fingernail) and ready to reproduce. Reproduction rates are influenced by water temperature and dissolved calcium. Calcium concentration in our lake was measured in July by the RVCA and the average value was 28 mg/L. Unfortunately this falls exactly on the threshold for rapid reproduction.
A number of people on the lake have told me that they have been looking for zebra mussels at their waterfronts and failed to find them. This is usually because they assume them to be much larger than they really are and because they are not looking on the sides and the undersides of the rocks. Believe me, they are there. By September of last year, approximately 8 out of 10 softball-sized rocks that I picked up (in 1-3 feet of water) in the vicinity of our cottage had adult mussels on their undersides. There was also a sharp increase in numbers in late summer and early fall, probably due to the unusually warm water temperatures that we had until the end of October. When I brought in my water line in mid-October, the foot-valve was clogged with several hundred mussels. Some were full-sized, but most were immature – a bad sign for this coming summer.
Duncan MacDougall
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