Perhaps the clearest insight to emerge from Robert’s decade of monitoring is the cycle linking cyanobacteria (or blue-green algal blooms) to water column oxygen concentrations. Through photosynthesis, algae consume dissolved carbon dioxide and nutrients—especially phosphorus—and pump oxygen into the surface waters. However, when an algal bloom exhausts the available nutrients and collapses, the organisms sink. In the benthic zone, decomposers break them down, consuming oxygen in the process and resulting in an expansion of an oxygen-poor anoxic layer. 

“A big bloom occurs when there are high concentrations of nutrients, warm temperatures, and bright sun,” Robert explained. “As the bloom ramps up, the algae consumes these nutrients, and when there’s no longer enough nutrients to support the bloom biomass, there is a mass die-off that rains down to the bottom. As a result, oxygen concentrations plummet throughout the water column, creating significant stress to fish and other organisms that rely on oxygen.”

With Surfer, these shifts are visible. The annual contour plots of dissolved oxygen (DO) at depth reveal oxygen-rich periods in vivid blue and oxygen-depleted zones in stark black. These plots use date (X-axis), depth (Y-axis), and DO concentration (Z-axis) to tell the story of when and where oxygen vanishes. As the black zones expand across the plots, they point to times when severe oxygen depletion has occurred. And when the entire water column drops below 2 mg/l, the lake reaches a state of hypoxia, and observed fish kills occur.

Robert also created time series plots in Grapher to showcase insights across multiple parameters. He often plotted several datasets against time, layering in both his weekly field samples and data logger outputs that recorded every 30 minutes. The DO weekly sample comparison with the continuous DO logger data revealed diurnal cycling of dissolved oxygen that the infrequent weekly checks would’ve missed. 

“I’m using this multiparameter plot to show how several different data sources can be used to examine interdependence,” Robert said. “After looking at everything, I can say, ‘Okay, what happens when there’s a rain event, or how does smoke from wildfires impact the lake? What happened to the oxygen with light penetration? Or what’s the relationship between phosphorus and oxygen?’ This process of visual comparison helps to tease out insights that warrant further analytical study of the impact of the specific parameters measured. Now with ten years of data, the analysis can expand to weekly, seasonal, and even decadal time scales to look for patterns and trends.” 

Of course, while Robert has insights he can lean on to detect the bigger trends, not all the annual data tells the same story. Weather, temperature, and nutrient cycling all play major roles, making it tough to identify long-term climate-driven trends. 

“Lakes are complex,” Robert said. “One year’s wet and cold; the next is hot and dry. Teasing out a single process to know if there’s a trend is difficult.”

However, one pattern that appears to be common year to year is that Swan Lake seems to be at its lowest point of resilience during late summer. By August or September, as daylight hours start to decrease, the lake’s dissolved oxygen concentrations are low, leaving the overall lake health more vulnerable. A smoke event from a nearby fire once managed to push it over the edge, as the oxygen dropped across the entire water column, resulting in a fish kill. Fortunately, that wasn’t the end of the story for Swan Lake.

“Once the fish kill occurred, the lake had restoring forces that kicked in—coupled with the fall winds and cooler temperatures—and the fall lake turned over,” Robert said.