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Clear As Mud - Cayuga Lake Modeling Project Incomplete


Cayuga Lake from the South Hill overlook. The Cayuga Lake Modeling Project is looking at phosphorus levels in the lake and its tributaries, as well as point sources: the water treatment plants, and Cornell's Lake Source Cooling plant.

A public presentation of the Cayuga Lake Modeling Project's findings was held Nov. 13 in the Old Jail meeting room on Court Street. Elizabeth Moran, Ph.D. and president of EcoLogic, gave out the project's findings to a room packed with local officials and concerned residents. Three years into the CLMP, the study appears to have raised as many questions as it answers: studies of temperature, phosphorus load and their effect on algae growth all lead to new questions on what these measurements really mean to the health of the lake.

Moran explained that CLMP is run by Cornell under Department of Environmental Conservation auspices, as a condition of Cornell's permit for the Lake Source Cooling Plant. The Lake Source Cooling plant, on East Shore Drive, pipes water from Cornell to the plant, where it meets (but doesn't mix with) cooler water piped up from the depths of the lake. Although the project doesn't add water to the lake, it does contribute a temperature rise and brings phosphorus up from cooler levels of the lake to warmer ones. The DEC's concern with LSC is this rise in phosphorus content.

Phosphorus is a problem because it leads to plant growth and algal growth; the DEC's limit for total phosphorus load (Total P) is 20 micrograms per liter for recreational water bodies. “Phosphorus is a common constituent of agricultural fertilizers, manure, and organic wastes in sewage and industrial effluent. It is an essential element for plant life, but when there is too much of it in water, it can speed up eutrophication (a reduction in dissolved oxygen in water bodies caused by an increase of mineral and organic nutrients) of rivers and lakes.” (Source: United States Geological Survey.) Cayuga Lake was placed on an EPA list of impaired water bodies in 2002 because Total P in the south end of the lake occasionally goes over this limit, said Moran.

The modeling project, which has completed Phase One (gathering data, planning) and is now in Phase Two (modeling) should wrap up in 2016. In 2013 a major finding was that 97 percent of the bioavailable phosphorus was from non-point sources. Point sources are easy to find: the water treatment plants and LSC, mainly. These are heavily regulated and their output monitored. Non-point sources are less easy to monitor: parking lots, lawns, agricultural areas, and golf courses contribute both fertilizer runoff and organic matter, like rotting leaves. “We're also looking in great detail at the watershed to see what the sources of phosphorous are,” said Moran.

However, said Moran, there's another issue, which is whether that phosphorous is bioavailable. “The elevated Total P concentrations are entering during runoff events,” she said, using a chart to demonstrate. “They come with the mud, which means they have low bioavailability.” The DEC limits don't take into account the difference between bio-available and low bioavailable P, said Moran. Sediment or low bioavailable P is strongly bound to mineral or organic sediment, and has the potential to become available with time, but bioavailable P can be immediately used by algae as fuel for growth.

“Total P is a flawed indicator of algal growth potential, dominated by muds with low bioavailability,” said Moran.

Time was another factor. The CLMP has found “Lake circulation is dynamic and complex,” said Moran. “There's a lot more exchange between the main lake and the shelf (at the south end). This has implications for algae.” Cooler water from the north end or middle of the lake exchanges with the warmer water in the south end, a process accelerated by wind. “The flushing is pronounced, relative to the growth rate of phytoplanktons. Algae need three days to grow, and by then the water's mixed up with the rest of the lake.” This may be why the south end is not seeing harmful algae blooms, she explained.

Finally, another interesting finding has come up: “Cayuga Heights and Ithaca Wastewater Treatment Plants reduced (their) phosphorous (output) by 80 percent, but the massive reduction from the WWTPs has not reduced chlorophyll a.” Measurements of chlorophyll a are used to estimate algae populations.

Before taking questions from the audience, Moran outlined what will happen next. The CLMP continues for another year, until December 2016. In the meantime, the project managers expect to “review the regulatory status with the DEC and EPA,” including commenting on the difference between bio-available P and sediment P; and “advocate for a robust watershed management approach, reflecting detailed scientific investigations” into non-point sources.

Moran noted that studying phosphorous content in water bodies is a developing and emerging field, and projects such as this one are uncommon. How to measure, and what the measurements mean, is still evolving.

Local environmental watchdog Walter Hang raised a question. “LSC is contributing about 6 percent of phosphorous to the lake. Doesn't that confirm that the LSC shouldn't have gotten a permit, because it's contributing phosphorous to an impaired section of the lake?”

Robert Bland, a Cornell engineer who has been involved with LSC from the beginning, responded: “I think you've raised that question many times with the DEC, and that's (partly) why we're doing the study. There's going to be an outcome of this model that will answer that.” He went on, “That six percent is a dry weight of phosphorous... some amount of phosphorous is essential to life; without any phosphorous it would be a sterile lake.”

Bill Foster asked, “What about the role of turbidity in the south end of the lake, in terms of algal growth?”

Moran said, “The model is looking at that.”