 |
Lower Beverley LakeWater Quality Test Results Through 2003Water ClarityClarity measurements are made with a Secchi disc to determine the depth of effective light penetration into the lake. The greater the measured depth, the clearer the water. If the Secchi disc reading is less than 3 metres, the lake is considered "enriched” (too many nutrients). Data available back to 1971 indicate LBL measurements have been consistently in the enriched range at less than 3 metres, but generally improving since 1990. Clarity sampling was expanded in 1994 to include Kendricks Bay and the area north of Black Jack Island (input from Cooligan Creek), in addition to Oak Bay (the area south of the Narrows near the mouth of Morton Creek). In 1998, measurements were initiated at the Upper Lake dam in Delta to monitor additional input into LBL, and indicate Upper Beverley Lake water clarity is generally consistent with measurements in Lower Beverley. Clarity measurements benefit from low rainfall and low lake levels. Results deteriorated in 1998, due in part to unusually high water levels in early July that resulted in increased watershed runoff. Clarity improved in 1999 consistent with a regional trend attributed to low rainfall, and nutrients staying on land and in wetlands. Environment Canada reported that 2001 was the driest year since 1972 and LBL water levels were unusually low, contributing to the best clarity since 1998. Unusual conditions continued in 2002 with extraordinary low levels in August, which along with evidence of Zebra Mussel infestation contributed to the best clarity measurements ever recorded in LBL. The trend continued in 2003 with further improvement in clarity measurements in the Oak Bay/Blackjack Island test sites.
Algal LevelWater clarity is an indirect measure of the algal density in the lake, which is affected by the level of nutrients present. Water samples are chemically analyzed to determine the nutrient level; the lower the level the better. Chlorophyll concentration measurements (an indicator of the amount of microscopic algae in the water) were used through 1995: 4 or more micrograms/Litre indicates high algal density and is considered “enriched” (too many nutrients). LBL measurements were above this level through 1995. In 1995 the Ministry changed the analysis to phosphorus concentration (TP, the single most important nutrient governing the level of algae in the water). On phosphorus measurements, we improved and fell into the "moderately enriched" (some nutrients) category (equivalent to 2 to 4 mg/L on the combined Chlorophyll / Phosphorus chart below), until our improving trend reversed in 1998. In 1999 nutrient levels fell in many Ontario lakes, and measurements in Kendricks Bay matched this trend regaining a moderately enriched condition, although Oak Bay and Black Jack Island remained enriched. Measurements were at or above the enriched threshold through 2001. We participated in an MOE study in 2002 and 2003 expanding phosphorus measurements at selected off-shield lakes to provide full season coverage in all test locations, the first time precise TP data had been collected for these lakes. LBL nutrient levels in 2002 and 2003 were the lowest since 1999.
The expanded phosphorus testing provided weekly profiles of nutrient levels as the lake progressed through its seasonal cycle. Off-shield lakes typically exhibit lower TP levels in spring due to being “flushed” by spring runoff. By the end of June, higher concentrations build through late summer contributing to late season algal blooms. In 2003, phosphorus measurements in Lower Beverley increased modestly in July and August, near the threshold of moderately enriched [11-20mg/L] and enriched [>20 mg/L] status.
ZEBRA MUSSELSWe participated in the Invading Species Watch 2003, a volunteer based monitoring program to detect presence/absence of aquatic nuisance species. As expected, the analyses confirmed Zebra Mussel activity in all areas sampled in Lower Beverley Lake (many cottagers reported significant infestation in 2002 and 2003), but found no indication of spiny water fleas that are spreading into inland waterways from the Great Lakes. WATER TESTING OVERVIEWBoth Lower and Upper Beverley Lakes are among more than 20% of over 800 lake locations sampled across Ontario in 2003 classified as “enriched” (high in nutrients) with comparatively poor clarity (less than 3 metres). Invading species also can affect clarity, and LBL was highlighted among lakes that exhibit improving water clarity with recent Zebra Mussel infestation. Maintaining and evaluating long-term data is the heart of the Lake Partner Program philosophy and crucial to understanding lake quality trends. Our current testing program includes clarity and phosphorus measurements at Oak Bay (unsettled area/infrequent input through Morton Creek from the Rideau chain), Kendricks Bay (LBL deep basin), Black Jack Island (input from Cooligan Creek), and Upper Lake dam (inlet). |
|
This page was last updated Tuesday, March 8, 2005
© 2007 Eton Systems |
