OWLA: Mussels, nutrients and harmful algal blooms in our lakes

Late summer and early fall brought a burst of harmful algal blooms (HABs) for days on end throughout Owasco Lake and our neighboring Finger Lakes. We have all seen the headlines and heard the news. The technology in place with the city of Auburn and the skilled professionals at our treatment plant were able to contain the highly toxic microcystin from our drinking water supply. Roughly 70% of our community relies on Owasco Lake for its potable drinking water. The health and economic impacts of harmful algal blooms should be ever-present on our minds.

So, what has changed in our local ecosphere in the past few decades to cause us to now experience the plethora of toxic cyanobacteria? Personally, I rank climate change and the invasive dreissenid mussels (zebra/quagga) at the top of my list. Numerous studies published in scientific journals confirm the clear causal link between quagga mussels and zebra mussels with toxic algal blooms. In 2021, Michigan State University published in the scientific journal Ecosphere an on "Forecasting Earth's Ecosystem with Long Term Ecological Research." Their decades of experiments began with the arrival of zebra/quagga mussels within Michigan's lakes in the 1990s and have measured the shift in concentrations of algal organisms to the proliferation of blooms of cyanobacteria.

We all understand how phosphorus is a key nutrient for a healthy aquatic ecosystem. The University of Michigan has been conducting research on how quagga mussels have transformed the supply of legacy phosphorus in the sediment. In 2021, their research, funded by the U.S. National Science Foundation, was published in Science Daily. Over the decades, large amounts of phosphorus have accumulated in the biomass on the bottom of the lake, which now holds colonies of quagga mussels. One Great Lake study measured densities exceeding 10,000 individuals per square meter (six mussels per square inch). It can be postulated that dreissenid mussels are becoming the dominant life form in our Finger Lakes.

Over the years, a series of experiments were conducted that established a clear link between the invasion of zebra/quagga mussels and an increase in the late summer phytoplankton community dominated by microcystis. The strongest links were in lakes with low phosphorus concentrations, such as Owasco Lake. In addition to phosphorus, researchers also found that the concentration of toxin, or microcystin, produced by the microcystis increased in lakes when nitrogen is abundant, whether from farm fields, residential septic systems or even atmospheric deposition.

These small, hard-shelled organisms live on the lake floor and filter the water, removing phytoplankton and other small ps. These mussels recycle phosphorus with their excretions and feces, altering the natural rates at which phosphorus is exchanged between lake water and sediments. The University of Michigan study conducted in Lake Michigan found the mussels are removing phosphorus from the water 10 times faster than measured two decades ago. They are then resupplying the water column with eight times the amount of phosphorus than that which reaches the lake from the entire watershed. It is written in the report, "This kind of internal loading, effectively decouples the dynamics of phosphorus from the watershed inputs, leaving the system open to poorly predictable fluctuations when mussel populations increase or decrease."

The reality is Owasco Lake has firmly established colonies of quagga mussels throughout the lake bottom. The growing populations are capable of absorbing and excreting large quantities of phosphorus from the water column.

A Cayuga County farm is the recipient of the New York Agricultural Environmental Management-Leopold Conservation Award.

Controlling phosphorus input is an ongoing goal stated in our DEC-approved nine-element plan. A large percentage of our stakeholders within the watershed have bought in and play a central role dedicated to improving environmental stewardship, soil conservation and storm resiliency. Recently, our neighbors at Sunnyside Farms in Scipio were recognized for their leading example of how our agricultural community is helping meet this challenge. Brothers Greg and Neil Rejman were showcased as they received the revered New York Agricultural Environmental Management-Leopold Conservation Award. As you drive through the watershed you can see the conservation practices that they and other farms have implemented with sowing winter cover crops, reducing tillage, rotation of crops, improved management of manure storage and application, and investments in renewable energy sources. Congratulations on your well-earned award, and thank you for implementing sound land management practices that benefit us all.

Ann M. Robson is a past president of the board of directors of the Owasco Watershed Lake Association. For more information, or to join OWLA, visit owla.org .

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