Scientists Go With the Flow to Collect Better Freshwater Data

On a clear, sunny afternoon this September, two of Trout Lake Station’s green-hued jon boats were out on Sparkling Lake, just off of highway 51. For CFL faculty member, Emily Stanley, and grad student, Luke Loken, it was like a lot of other days at the office. For Scott Ensign, however, the outing was the first lake-based field test for what could be a big advancement in aquatic scientific equipment.

Scott Ensign displays a HydroSphere he recovered from Sparkling Lake. Photo: Emily Stanley
Scott Ensign displays a HydroSphere he recovered from Sparkling Lake. Photo: Emily Stanley

Earlier in the week Ensign, a co-founder of Planktos Instruments, had dropped two hard-plastic spheres containing thousands of dollars of instrumentation into the crystal clear waters of Sparkling Lake. He calls the devices “HydroSpheres” and their job is to float along with currents in the lake like some sort of free-range buoy and collect data on the lake’s temperature, water chemistry and productivity.
Ensign’s company had already honed the HydroSphere’s spherical design to sit at neutral buoyancy just below the water’s surface and travel down rivers, specifically the Neuse and Cape Fear Rivers in North Carolina, where the company is based. But Sparkling was their first attempt at a lake.

“We did two things that we’ve been waiting to do for a long time,” Ensign says. “One was having a HydroSphere floating at the surface to measure the movement of water as it’s getting blown around and the second was to get one to sit at the thermocline (where the warm, upper water sits on top of the cold, deeper water).”
That second objective didn’t exactly go to plan, as Ensign eventually had to pull that hydrosphere up off the bottom of the lake. But, he says, “for some period of time, at least, we got it to sit on the thermocline and measure the movement of water in deeper layers and see how that’s reacting relative to the surface.”

John Gardner searches for a signal from the second HydroSphere. Photo: Emily Stanley
John Gardner searches for a signal from the second HydroSphere. Photo: Emily Stanley

After that retrieval, John Gardner, a Duke University PhD student working with Planktos Instruments, donned the headphones of a radio receiver and, antenna in hand, began to direct one of the boats toward the second HydroSphere’s signal.
The true promise of these instruments, says Emily Stanley, are that they can move with the current inside of a particular “packet” of water as it heads downstream or around a lake, a process that, she says, while “fundamental” to the way scientists about these systems, is generally “not done.” Scientists usually work around these limitations by taking samples at multiple points along a river, for example. But Stanley says, a tool like the HydroSphere can allow researchers to really get a better sense of what’s going on in the water, allowing them to “record data as they drift with currents to figure out how chemistry evolves along these journeys.”
This will be immensely beneficial as it is notoriously difficult to get a true “big picture” of many freshwater ecosystems. Previous work at the CFL done by former grad student, Matt Van de Bogert, with Steve Carpenter and Paul Hanson, showed that using a buoy to measure primary productivity in a lake can be quite problematic. For example, Stanley says, “If I put a dissolved oxygen (DO) sensor in one spot in the middle of the lake, I assume I’m measuring what’s going on right in the immediate vicinity. But the wind can move water around and water that washes over the DO sensor might have come from some really productive shoreline area and cause the DO to go up. Later on, when I look at the data and see the spike, I’ll probably think that there was an increase in primary production. But, in fact, there wasn’t. There was just water moving from a productive part of the lake to an unproductive part of the lake.”
The HydroSphere should help clear things like this up, Ensign says. For example, the devices could someday help researchers track an algae bloom as it moves around a lake, or a pollution plume as it moves downriver. There is already intense interest in understanding the dynamics of changes in water quality, he says. For example, citizen monitoring groups and environmental non-profits may be tracking developments in polluted waterways, or municipalities industries could be working to comply with federal discharge permits. “There is so much data being collected for regulatory reasons,” Ensign says, “and we’re trying to figure out how, with minimal expense and time, we can expand those data sets and get much more meaningful data.“
The wandering HydroSphere is brought safely back to shore. Photo: A. Hinterthuer
The wandering HydroSphere is brought safely back to shore. Photo: A. Hinterthuer

Back on Sparkling Lake, Gardner hones in on the second HydroSphere. The wind has pushed it up under some bushes on Sparkling Lake’s shoreline. It bobs, unharmed, in the shallows and Gardner leans over to drag it on board. He lets the water drain from the clear outer housing, then stows the device safely in a bin. Ensign and his team hope this trial run will help them figure out how to keep the spheres floating freely in a lake and fine-tune their design.
While this round may not have gone completely according to plan, these two HydroSpheres still collected amounts of data just by going with the flow, which is a new way of doing things.
“The bottom line is that this device should provide us with a new frame of reference for studying lakes and rivers,” says Stanley. “And fresh perspectives often lead to big advances as they get us away from conventional wisdom and force us to look at things differently.”

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