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LWTF News Archives: Winter 2008/09


Annual Monitoring Report for 2008 Shows Positive Results

Dr. Robert Kortmann, the Task Force's lead scientist, has delivered a detailed monitoring report for 2008 which shows encouraging results in several areas including water clarity, phosphorous, oxygen and algae. In addition, the Layer Aeration Systems appeared to operate effectively in 2008 despite delayed activation due to the Washington Boat Launch construction.

A summary of the Dr. Kortmann's report follows:

Lake Waramaug - Summary Report 2008, by Robert W. Kortmann, Ph.D.
Ecosystem Consulting Service, Inc. — February, 2009

Since the late 1970's the Lake Waramaug Task Force has been monitoring Lake Waramaug as part of its program of lake restoration. The following is a review of the findings and results for 2008. It addresses the key factors monitored by Ecosystems Consulting Services for the Lake Waramaug Task Force under the direction of Dr. Robert Kortmann.

Transparency / Water Clarity
Secchi disk transparency between Memorial Day and Labor Day (a measure of water clarity and light penetration) was the best recorded since management and monitoring began in the late 1970's. A modest fall algae bloom did result in reduced clarity and dying algae caused some floating algae scum. (See charts at right.)

Oxygen Levels
The annual spring
Diatom maximum was very productive in April 2008, resulting in very high dissolved oxygen saturation (up to 174%). When the Diatom population crashed in late May a "clear water phase" followed, and persisted for much of the summer. Dissolved oxygen remained at 6m through the summer, which sustained mid-depth habitat. A strong thermocline established at 5m, and descended in late summer.

As has been observed in prior years, oxygen loss ascends higher in the water column in more shallow areas of the lake (primarily due to proximity to the bottom and high sediment oxygen demand).

Phosphorus Levels
Total phosphorus concentrations remained relatively low, with a spring concentration of 21 ppb and summer concentrations between 14-20 ppb in surface water, setting the stage for "mesotrophic conditions". Nitrate-N was consumed early (typical) which favors N-fixing bluegreen algae.

Algae Report
Bluegreen algae remain the dominant phytoplankton group, especially N-fixing species.

Although bluegreen algae were dominant, the species that are most likely to cause nuisance blooms (Anabaena and Aphanizomenom) were not dominant most of the summer.

Phytoplankton densities have remained relatively low since 2000, and Diatoms have become more dominant during winter and spring.

Green algae have gained a greater fraction of the total phytoplankton since 2004, suggesting they are beginning to compete with the bluegreens. During the past two years green algae have reached 30% of the phytoplankton community. Total density has decreased, % Greens has increased.

Zooplankton Levels
Large-bodied Cladocera peaked in June (due to abundant Diatoms and Greens as a food resource. Although a larger population of these herbivorous animals ("algae eaters") is desirable the population is persisting and is able to respond to availability of food resources.

Layer Aeration System Operation
The Layer Aeration System in the deep basin of Lake Waramaug was activated somewhat later than normal due to delays in completing the new boat launch facility. However, the system was quite effective in 2008 (in combination with greater light penetration and resulting deeper photosynthetic oxygen production). The two Layer Aerators are set to function at somewhat different depth ranges. In June it was noted that most airflow was to the aerator closest to the compressor at the Washington town beach. This aerator functions in the 4.5-7 m depth range. Water clarity was very good at the time and the airflow was intentionally left alone ("If it isn't broken, don't try to fix it"). That was intended to manage the mid-depth layer more intensively. The approach was successful.

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