Picture this: a secret underworld beneath our lakes and oceans, where the muddy floors of these waters are quietly unleashing nutrients that spark explosive algal growth, poisoning ecosystems and turning idyllic spots into hazardous zones. It's a crisis that's costing us wildlife, recreation, and even property values—but what if we could finally see what's really happening down there? Buckle up, because Florida Atlantic University's groundbreaking CAROSEL device is about to change the game in water quality monitoring, and it might just reveal surprises that challenge everything we thought we knew about these underwater dynamics.
At the heart of this hidden world are the sediments on the bottom of lakes and coastal areas, which act like a natural time capsule, storing records of an ecosystem's health over time. But their most critical role involves something called 'benthic fluxes'—the way nutrients like nitrogen and phosphorus seep from these sediments into the water above. For beginners, think of it as a slow-release fertilizer from the lake bed that can supercharge algae, leading to harmful algal blooms (commonly known as HABs). These aren't just ugly green slimes; they're toxic events that can kill fish, make water unsafe for swimming, and even disrupt tourism. In essence, they degrade water quality on a massive scale. Traditionally, scientists have struggled to measure these fluxes accurately because old methods are time-consuming, expensive, and require boats, ships, and teams of people for just one snapshot of data. Newer automated tools hold promise, but few have delved into how sediments fuel or maintain HABs—a crucial gap in protecting our aquatic environments. Take Florida's Lake Okeechobee, for example, a vast, murky water body where benthic nutrient releases are the primary driver behind the algae explosions that plague it.
Enter Florida Atlantic University's Harbor Branch Oceanographic Institute researchers, who are pioneering a continuous tracking system for nutrient exchanges between sediments and overlying water. Their innovation focuses on nitrogen in its various forms, providing real-time insights into how ammonium (NH₄⁺)—a favorite food for blooming algae—is released from the bottom multiple times daily over weeks or months. This offers an unparalleled, granular understanding of nutrient flows that traditional methods could never capture.
The star of the show? CAROSEL, which stands for Chamber ARray for Observing Sediment Exchanges Long-term. This clever underwater gadget is an autonomous system that monitors how nutrients and other substances shuttle between lake or ocean bottoms and the water column without needing constant human intervention. Forget the old-school approach of sending out boats twice for a single data point; CAROSEL operates on its own, collecting measurements several times a day for extended periods, revolutionizing how we study these processes. It's like having a tireless underwater detective constantly on the case, logging details that were previously impossible to obtain.
For their recent study, the team deployed CAROSEL in a shallow freshwater retention pond at the FAU Harbor Branch campus in Fort Pierce. Their aim was to dissect the complex dance between nutrients and oxygen across daily and longer cycles, revealing how much nitrogen is available depending on the time of day or weather patterns. As a bonus, it provided better estimates of how nutrients are stripped from these pond systems over time. These retention ponds, dotted across Florida, are a standard environmental strategy—known as Best Management Practices (BMPs)—mandated by state regulations to filter out nutrients before they reach sensitive coastal estuaries. By trapping pollutants like excess fertilizers from farms or runoff, they help prevent downstream disasters, but CAROSEL is shedding light on just how effectively they're working.
The findings, published in the journal Limnology & Oceanography, uncovered fascinating rhythms in the water. Oxygen levels rose during daylight hours thanks to plant photosynthesis, then dipped at night as organisms respired. Meanwhile, sediments were always soaking up oxygen from the water above. Ammonium was steadily released from the sediments throughout the study, but in the water column, nitrogen was added during the day and broken down at night—a twist, since you'd expect daytime plant growth to gobble up nutrients like a hungry teenager at a buffet. And this is the part most people miss: after rainstorms, fluxes of ammonium and nitrate shifted dramatically, exposing how vulnerable these processes are to weather changes. Nitrogen removal via nitrification (converting ammonia to nitrate) and denitrification (turning nitrates into gases) was vigorous but erratic, which could explain why some BMPs aren't performing as hoped.
But here's where it gets controversial: CAROSEL's high-frequency data exposed rapid, unpredictable swings in nutrient and oxygen exchanges, flipping the script on the idea that sediment processes are slow and steady. Could this mean our current models for water management are oversimplifying things, potentially leading to ineffective policies? Some might argue that sediments are the unsung heroes (or villains) of ecosystems, covering 70% of Earth's surface yet often overlooked in conservation efforts. Imagine if we treated sediment health like we do air or soil—would that spark a revolution in how we protect our waters?
"What's most exciting is that CAROSEL gave us a detailed, hour-by-hour view of how weather and environmental changes directly affect the chemistry between the lake bottom and the water above," said Jordon Beckler, Ph.D., senior author, an associate research professor at FAU Harbor Branch and an FAU Sensing Institute (I-SENSE) fellow. "That level of detail helps us untangle the complex chain reactions happening in lakes and estuaries – something that's been incredibly hard to do until now with such low-resolution conventional benthic flux data. We see this technology as a powerful new tool for understanding how these fluxes drive ecosystem dynamics, especially given the explosion of harmful algal blooms globally over the last few decades. I see sediments, which cover about 70% of the Earth's surface, as the next water, soil or air – for which we already have developed an appreciation for their health and conservation."
This up-close perspective will empower scientists to grasp how swiftly nutrients cycle and how elements like sunlight, heat, and storms influence them—vital for enhancing water quality oversight and strategies. CAROSEL shows real promise in tackling challenges such as nutrient pollution, HABs, oxygen-deprived 'dead zones,' carbon movements, and even contaminants like organics or heavy metals in a changing climate. For instance, in areas prone to droughts or floods, this could help predict and prevent outbreaks before they spiral out of control.
"What makes the CAROSEL especially valuable is its versatility – it's designed to work in both freshwater and marine environments and can be adapted to monitor a wide range of substances, from nutrients like ammonium and nitrate to other parameters such as carbon dioxide or dissolved organic carbon. We've specifically designed the CAROSEL to accept any underwater sensor that exists on the market today," said Mason Thackston, first author and graduate research assistant at FAU Harbor Branch. "That flexibility means we can tailor the system to different ecosystems and research needs. I'm currently gearing up for two new funded projects, one to establish a baseline for benthic nutrient fluxes in an area planned to be dredged in the Northern Indian River Lagoon, and another to directly monitor legacy nutrient fluxes in Lake Okeechobee. We also see great promise for improving our understanding of the nutrient dynamics of BMPs in Florida, which are presently underperforming with respect to expectations."
Study co-authors are Donald Nuzzio, Ph.D., president of Analytical Instrument Systems, Inc.; and Csaba Vaczo, a mechanical engineer at FAU Harbor Branch.
This work was supported by the Harbor Branch Oceanographic Institute Foundation and an FAU I-SENSE seed grant, as well as the Florida Department of Environmental Protection Innovative Technologies for HAB Mitigation Program, for supporting research directly leading to the conception of the CAROSEL (Grant #MN016).
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What do you think? Does technology like CAROSEL represent a game-changer for environmental protection, or are we putting too much faith in gadgets without addressing root causes like pollution? Do sediments deserve more attention in global conservation efforts, or is this just hype? Share your thoughts in the comments—do you agree, disagree, or have your own counterpoints to add?
