Analysis of the cause of shifts in algal taxa and abundance over 50 years in an oligotrophic lake in central NY
This paper analyzes 50 years of algal data from Skaneateles Lake to determine that the observed population shifts in 1991 were primarily caused by methodological changes in surveys, while the 2008 shifts were driven by environmental factors such as longer growing seasons and invasive mussels.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
Imagine a 50-year-old time capsule of water, sitting deep in the Finger Lakes of New York. This is Skaneateles Lake, a crystal-clear, nutrient-poor (oligotrophic) body of water that has served as the unfiltered drinking source for Syracuse since 1894. For half a century, the City of Syracuse has been taking a daily "algal census," counting the tiny, floating plants (phytoplankton) living in the water.
The researchers who dug into this massive dataset found that the lake's microscopic population didn't just slowly drift over time; it threw two massive, sudden parties where the guest list changed completely. The first wild shift happened in 1991, and the second in 2008. But who invited the new guests, and who kicked the old ones out? The answer is a mix of detective work, microscope magic, and invasive species drama.
The Great 1991 Switch: A Case of "Better Glasses"
The first big surprise was a massive explosion in the number of tiny, single-celled cyanobacteria called Synechocystis. Before 1991, they were practically invisible, making up less than 0.1% of the count. Suddenly, in 1991, they skyrocketed to an average of 93.0% of the cyanobacteria population.
Was the lake suddenly overrun by these tiny bugs? The paper suggests no. Instead, the authors point to a change in the "eyes" watching the lake. In 1988, a new technician took over the counting job. This new person started using a microscope with higher magnification (200x instead of the old 100x).
Think of it like this: The first technician was looking at the lake through a pair of binoculars, while the second technician switched to a high-powered telescope. The tiny Synechocystis cells are so small (about 1–2 µm) that they were essentially invisible to the "binoculars." The new "telescope" didn't create more bugs; it just finally allowed the observers to see the ones that were already there. The paper argues that this 1991 shift was likely a methodological change—a change in how we looked, not necessarily a change in the lake itself.
The 2008 Shift: The Real Ecological Drama
If 1991 was a trick of the light, 2008 was a real ecological earthquake. This time, the changes weren't just about seeing tiny things better; the entire community structure of the lake actually changed.
The Invaders Arrive
The paper highlights the arrival of invasive mussels as a major suspect. Zebra mussels first showed up around 1995, but by 2008, they were being replaced by their cousins, the quagga mussels.
- The Analogy: Imagine the lake as a giant buffet. The zebra mussels were like diners who only sat at the tables near the edge (the shallow, rocky parts). But the quagga mussels are the diners who can sit anywhere, even on the soft, deep floor of the lake. Since Skaneateles Lake is deep and cold, the quagga mussels took over the whole buffet.
- The Effect: These mussels are super-efficient filters. They eat up the "normal" algae (like diatoms and green algae) but often leave the cyanobacteria alone because they are too small or taste bad. By 2008, the mussels had cleared the table of the competition, leaving the cyanobacteria to feast and multiply.
The Warm-Up
While the mussels were doing their work, the lake was also getting a cozy blanket of warmth. The paper notes that the water temperature in the summer months (May through September) has been rising by 0.8°C per decade. The "growing season"—the time the water stays above 15°C—has stretched from an average of 116 days in the 1970s to 143 days in the 2020s.
- The Analogy: Cyanobacteria are like sunbathers who love the heat. The longer the summer lasts, the more time they have to throw a party. The paper suggests that while the heat didn't directly cause a spike in numbers on its own, it removed the "barriers" that used to stop them from growing, giving them a competitive edge.
The Nutrient Mystery
You might expect that more food (nutrients) caused the party. The paper looked at phosphorus levels, which are usually the main fuel for algae.
- The Twist: The data shows that total phosphorus (TP) levels stayed low for most of the record. However, there was a weird, temporary spike starting around 2014, where levels rose to 15.5 µg L-1 (about three times the baseline).
- The Connection: This spike coincided with the first sighting of a different, potentially harmful cyanobacteria called Microcystis in 2014, which led to the first documented harmful algal bloom (cHAB) in 2017. The paper suggests this nutrient bump might have helped Microcystis get a foothold, but it's unclear if this was a permanent change or just a temporary glitch.
What the Paper Rules Out
It's important to know what didn't cause the changes. The authors explicitly checked and ruled out a few things:
- Rain and Runoff: They looked at huge storm events and inflows. While a massive storm in 2015 did cause a temporary spike in algae, there was no consistent link between rain and the long-term shifts in 1991 or 2008.
- Just Temperature: While the lake got warmer, the paper found no direct correlation between the temperature and the number of algae cells in the years after 1992. The heat helped, but it wasn't the sole driver.
- Nutrients as the Only Cause: The paper argues against the idea that phosphorus alone controls everything. The big shifts happened before the nutrient spikes, and the lake changed even while staying "oligotrophic" (low nutrient).
The Verdict
So, what happened in Skaneateles Lake over 50 years?
- 1991: We got better microscopes and realized the tiny bugs were there all along.
- 2008: The lake actually changed. Invasive quagga mussels moved into the deep water, ate the competition, and let cyanobacteria take over. Warmer, longer summers gave them extra time to party.
- 2014: A temporary nutrient spike might have helped a specific, harmful type of cyanobacteria (Microcystis) arrive, leading to the first real "bad bloom" in decades.
The paper concludes that we can't blame just one thing. It wasn't just the weather, and it wasn't just the nutrients. It was a perfect storm of better counting methods, invasive species, and climate shifts working together. The lesson? To understand a lake, you need to look at the whole picture, not just one piece of the puzzle.
Drowning in papers in your field?
Get daily digests of the most novel papers matching your research keywords — with technical summaries, in your language.