Lake Mahon nutrient testing was done in September. Water samples were taken at 4 lake locations on September 13, including near the 3 inflow streams. Phosphorous levels were low, but the ratio of nitrogen to phosphorous was high, and Eurasian milfoil apparently reacts to nitrogen but not phosphorous. Testing will be re-done in the Spring to see if results are much different then. 

Guide to attached results: 

• • Total phosphorous (TP) - results were low, ranging from 0.002 to 0.004 mg/L; for comparison, TP averaged 0.0066 mg/L (or 6.6 µg/L) in 2017 (see RSVL). TP less than 0.01 mg/L indicates an oligotrophic (young) lake.

  • Total nitrogen (TN) consists of organic nitrogen (tied up in organisms) plus inorganic nitrogen (ammonia, nitrate, nitrite).

  • TKN (Total Kjeldahl Nitrogen) - consists of organic nitrogen plus ammonia. TKN results ranged from 0.3 to 0.4 mg/L. The Rideau Valley Conservation Authority uses 0.5 mg/L as a guideline. Water not influenced by excessive organic inputs typically ranges from 0.1 to 0.5 mg/L. TKN results indicate a mesotrophic (middle-aged) lake. Organic nitrogen is naturally converted to a form of nitrogen readily available for use by plants.

  • Nitrate and Nitrite - both were below reporting levels. In oligotrophic lakes, nitrate would be expected to be less than 0.1 mg/L. Nitrate is usually much higher than nitrite. Nitrate is very low in forested and grassland areas, but for streams in (active) farm land, nitrate is usually substantially higher than organic nitrogen.

  • TN/TP ratio - the results imply a very high TN/TP ratio of at least 100:1, indicating that relatively low levels of phosphorous may be limiting the growth of algae and aquatic plants OTHER than Eurasian milfoil, which apparently reacts to nitrogen but not phosphorous.