Three Decades of Research at Acton Lake

A multi-disciplinary team at Miami University, Ohio, has been studying the environmental change at Acton Lake for over three decades. Using three different NexSens buoys over this time, the team has an incredible archive of data that is helping build a picture of Acton’s past, present, and future.

Until recently, a NexSens CB-50 buoy was used alongside other environmental monitoring at Acton Lake. In May 2025, the Miami team deployed a new XB-200 buoy, future-proofing their ongoing monitoring using real-time buoy systems.

Acton Lake, a small hypereutrophic reservoir in southwest Ohio, covers 2.4km² and has a maximum depth of about 8m. The dam was built in 1956, and the lake has a large agricultural watershed.

Historically, erosion of soil–mainly from farmland–has washed vast amounts of sediment into Acton Lake, causing it to slowly fill.

In 1992, the United States Department of Agriculture Soil Conservation Service developed a watershed management plan encouraging conservation tillage through economic incentives for farmers, aiming to reduce sedimentation in the lake.

Mike Vanni, Professor Emeritus at Miami University, has worked on Acton Lake since the 1990s. He explains, “From 1990 to 2000, the amount of conservation tillage in the watershed more or less quadrupled from around 15% to 60% of cropland area and that’s been pretty stable since then. And those trends mirror regional trends all over the Midwest.”

NexSens Applications Scientist Joe Davidson assisting the Miami University team with the deployment of the XB-200 data buoy. (Credit: Josh Pene / DreamBox Studio)

Developing Monitoring at Acton Lake

A variety of environmental monitoring methods are used at Acton Lake to track its changing ecosystem.

Around 2010, the Miami University team deployed their first NexSens buoy, the MX-300, which was later replaced by the CB-50 buoy. Positioned close to the dam at the south end of the lake, it measures oxygen concentration and temperature through the water column, forming the foundation of much of the team’s long-term monitoring.

During its service, the buoy has transmitted real-time data via cell and hosted various additional sonde configurations, including conductivity, temperature, chlorophyll, and turbidity. Across the duration of monitoring, sondes have been added, removed and replaced from the buoy–something made easy by the system’s flexibility.

As well as the buoy, there is a longstanding weather station at Acton Lake, with new ones planned for installation this year.

Hydrological monitoring efforts in the rivers that drain into Acton Lake use simple methods, including pressure transducers in wells to measure water level and automated water samplers that collect samples every seven hours. Manual grab samples requiring lab analysis remain an important part of the team’s monitoring efforts.

The NexSens CB-450 buoy after it was first deployed in 2019. The CB-450 was the second NexSens buoy deployed at Acton Lake, and through its years of service, it has contributed to a long-term data set. (Credit: Mike Vanni)

Emerging Trends at Acton Lake

Vanni states that over the last two decades, research has focused on “how the lake and streams are responding to changes in agriculture–mostly a change in tillage.”

Before this, research monitored fluvial inputs and lake health, but didn’t focus on longer-term changes related to agriculture.

The shift that catalyzed the beginning of the long-term monitoring program was “fortuitous,” as Vanni highlights, “We didn’t really think we’d see any change, because we know how noisy environmental data are. And we didn’t know how successful the movement towards conservation tillage would be.”

“But we just happen to notice these changes in the streams and then in the lake. After about six or eight years, when we were monitoring the streams, we noticed that the concentrations of sediment and phosphorus were declining in the way you’d predict, consistent with less tillage. So that set the stage for doing this long term study,” he explains.

In 2002, the Miami team secured funding from the US National Science Foundation’s Long Term Research in Environmental Biology (LTREB) Program for a long-term project exploring the impact of changes on streams and Acton Lake. Since that initial grant, the project has continued to receive LTREB funding.

Lesley Knoll (right) and Amy Weber, Research Associate, deploying the Acton Lake buoy for the 2024 season. (Credit: Mike Vanni)

Long-Term Monitoring Begins

The Acton Lake ecosystem is shaped by complex, interlinked factors. Agricultural land use affects sediment, phosphorus, and nitrogen levels, while precipitation determines stream water input.

In the first decade after conservation tillage began in the watershed, environmental changes were clearly observed. While suspended sediment decreased as expected, some surprising trends emerged.

Although conservation tillage was expected to reduce phosphorus and algal blooms, Vanni notes that Acton Lake had the “exact opposite response” and actually became “much greener” in the first 10–12 years.

The team hypothesized this was because of gizzard shad, a fish that feeds on bottom sediment containing nitrogen and phosphorus, and excretes them into the water.

Vanni explains that in summer, when stream input is low and fish populations are high, “more phosphorus comes from the fish than the streams.”

The correlation between increased fish populations and lake greening led the team to conclude that “there’s more light and more fish, and we’re getting more algae because of that.”

Indeed, this 15-year study showed that gizzards supported an average of 18% of primary production during the phytoplankton growing season, and about 30% during summer (July-September) when algal biomass is highest, though there was significant variation inter- and intra-annually.

Aerial view of the dam adjacent to Acton Lake. (Credit: Josh Pene / DreamBox Studio)

Beneath the Surface at Acton Lake

Lesley Knoll is an Acton Lake local and Assistant Professor of Biology at Miami University who has been studying the lake since the beginning of her academic career.

Now working with an extensive 31 years of data, Knoll’s work focuses on long-term trends and dissolved oxygen (DO) in the deepest parts of the lake.

A global trend in decreasing lake-bottom DO has been linked to factors such as an increase in productivity, decomposition of organic matter, and rising temperatures, which exacerbate temperature stratification.

At Acton, Knoll’s research has uncovered that the lake’s “anoxic factor”–which takes into account the spatial and temporal trends of hypoxic events–has not changed over time.

But, she highlights, “What’s interesting is that it does seem like the amount of suspended sediments in the water is playing a role in the oxygen dynamics”–an area often overlooked in research.

She continues, “If you have more suspended sediments in the water there’s less anoxia. When you have more suspended sediments, you have less algae. If you don’t have as much algae, you don’t have as much fuel for decomposition.”

Knoll emphasizes that research is still very much in progress to untangle the complex, transboundary relationships of DO at Acton. “There seems to be a relationship between what’s going on in the watershed with the erosion from the farm fields and the oxygen,” she notes.

Davidson demonstrating how to prepare the XB-200 for deployment. (Credit: Josh Pene / DreamBox Studio)

Acton Lake Inputs

Miami University’s approach to studying Acton Lake has been cross-departmental, allowing for a more holistic interpretation of data and a deeper understanding of the complex interconnectedness of the lake and its environment.

Bartosz Grudzinski is a hydrologist and geomorphologist at Miami University interested in factors influencing water quality and hydrology in the rivers that feed Acton Lake.

He explains that changes in hydrological and meteorological patterns are impacting the watershed. Although there hasn’t been a significant change in total precipitation, there has been a shift in seasonality, more intense flooding, and temperature increases.

Grudzinski remarks that there have been “plenty of surprises” unearthed from the data collected. For example, there is variability in the response of streams to extreme flooding, an unexpected difference considering their close geographical proximity.

One study explored how water quality changes as water flows through a state park–a pocket of forest that contains natural vegetation on untilled soil–hemmed in by agricultural land.

Grudzinski says, “When water flows through that park, we’re noticing that nutrient levels significantly decrease within several streams that drain into the lake.”

He continues, “We cleared out all the forest to allow agriculture to expand, but we still have some pockets of forest. Hopefully we’ll conserve more in the future, and that could have benefits to water quality.”

The NexSens XB-200 data buoy deployed in Acton Lake. (Credit: Josh Pene / DreamBox Studio)

The Future of Monitoring at Acton Lake

At the beginning of May 2025, the Miami University team deployed a new NexSens XB-200 buoy, which will improve the spatial resolution of data collection at Acton Lake.

With a temperature string and YSI EXO2 multi-parameter sonde on board, real-time data is transmitted via the X3 data logger.

The data from the new buoy will supplement the existing dataset and contribute to a fuller environmental picture–something particularly important in the context of climate change.

“If you have a wet year now, we’re probably going to get more sediment coming into the lake than we did in a dry year in the 90s, even though the concentrations of sediment are lower. Basically, weather overwhelms agricultural management,” Vanni says.

Davidson assisting the Miami University team with the deployment of the XB-200 data buoy. (Credit: Josh Pene / DreamBox Studio)

The Benefits of Better Data

One of the immense benefits of the long-term data at Acton Lake is that it has enabled a whole variety of applications–some unexpected–and offered windows into multiple research areas.

Despite the already extensive continuous dataset and its many applications, Knoll notes, “I think we need more data. […] We’re finding that 31 years [of data] might not be enough for some of these things, because there’s so much variability year to year.”

The long-term dataset from Acton Lake has already provided significant scientific value and shed light on an ecosystem in flux–with sometimes surprising results. Looking to the future, it’s exciting to consider what the team might discover with a new buoy on the water.