A Lake-Dwelling Robot Fights Toxic Algae Blooms

March 20, 2019 | Story | No Comments

Satellites do an incredible job of mapping algal blooms, the green mats that spread over lakes and oceans during warm, nutrient-rich summers. But the hypnotic, swirling images from space can't tell if toxins are lurking in a carpet of cyanobacteria, threatening the safety of water.

Ecologists and hydrologists can test water's drinkability by boating through the blooms—though collecting samples off the side of a power boat is tricky and inconvenient. So this year, scientists are monitoring Lake Erie with a robot, 18 feet below the water’s surface.

The so-called Environmental Sample Processor, ESPniagara, sits on the floor of Lake Erie’s western basin. It collects algae from the surrounding water, analyzes microcystin (a small, circular liver-toxic protein), and uploads results for researchers at the end of every test. They're watching this toxin closely, because elevated levels of it could swiftly poison the water supply for humans and wildlife in the surrounding area.

A no-frills charm dominates the ESPniagara's aesthetic. “It kind of looks like a trash can,” says Tim Davis, a molecular ecologist at NOAA in Ann Arbor. Tentacles of clear plastic tubing for sample processing swirl around the lab-in-a-can’s lower half, while circuits and wiring snake between the components above. Those electronics and the machine’s batteries—400 D cell batteries power the unit—understandably need some protection to sit at the bottom of the lake. “The metal trashcan is essentially a pressure case that can withstand very, very high pressures, and essentially keeps it dry,” Davis says.

Staying dry isn’t the only requirement for the lab capsule. ESPniagara also needs to stay put, remain upright, and avoid sinking too deeply into the gunky mud. So NOAA recruited applied physicists at the University of Washington to design the 1,000-pound frame encasing the unit. By their calculations, even if Hurricane Sandy-level winds hit Michigan, the water sampling could continue. And at the lake’s surface, a round orange data buoy relays information from its tests via a cellular modem, like the one in your phone.

So far ESPniagara has been testing the water every other day. But as of August 1, with the risk of harmful blooms steadily rising, it began testing on a daily schedule. It pulls lake water in, concentrating algae cells onto a filter. When the filter is clogged with plenty of algae to measure, the biology begins.

While full-scale labs use temperature-controlled water baths, freezers, and centrifuges to run these kinds of experiments, the ESPniagara accomplishes the same tests with a few carefully formulated protocols. Each toxicity measurement happens within a quarter-sized puck that’s about an inch and a half tall.

To measure the algae’s microcystins, it’s important to know that the cyanobacteria hold most of their toxins inside their cells. “So in order to get accurate concentrations, you need to be able to break the cells open,” Davis says. A bit of methanol-Tween-20 (basically dish detergent) does the trick, along with some heat and pressure. And once the cells are cracked open to reveal all the toxins, the ESPniagara dots samples into a four-by-five grid for quantification.

The toxin detection relies on antibodies that fluoresce when they’ve bound a specific substance. In this case, the antibodies that don’t bind a toxin light up, so brighter dots mean safer water. An internal camera photographs the test array, and at the end of this whole process—it takes roughly four hours—the data buoy sends off that photo. The results end up with collaborators all the way across the country, at the Monterey Bay Aquarium Research Institute servers. Then Davis and his team download them for their own analysis.

Once they've got toxicity data, they combine it with satellite measurements for algal biomass and hydrodynamic models of windspeed and current. That full picture tells them how toxic the bloom is, and where the toxins will end up next. Knowing that strong winds are about to send more toxins into the water supply, for example, helps treatment plants decide how to act. When more microcystins arrive, they’ll know to roll out extra filtration steps—like particle activated charcoal neutralization—to keep drinking water safe. It’s almost like the ESPniagara gives water treatment plants … extrasensory perception.