What is pond? Study yields first data-driven definition

Almost anyone can identify a pond, but what exactly sets it apart from a lake or a wetland? A new study, co-led by Cornell, provides the first data-driven, functional definition of a pond and evidence of the clear ecological function of ponds, which could have broad implications for science and policy.

“The Lack of a Universal” pond definition causes a lot of confusion, from people wondering what the difference is between a pond and a Laketo aquatic monitoring programs of varying definitions at government agencies, even to accurately modeling global carbon budgets,” said Meredith Holgerson, assistant professor of ecology and evolutionary biology and co-first author of “A Functional Definition to Distinguish Ponds from Lakes and wetlands,” published June 21 in Scientific Reports†

“We wanted to evaluate how scientists and policymakers define ponds and investigate whether ponds are functionally different from lakes and wetlands,” Holgerson said.

Their conclusion: Ponds are small and shallow water bodies, with a maximum surface area of ​​five hectares, a maximum depth of 5 meters and less than 30% emerging vegetation.

There are hundreds of millions or even billions of ponds worldwide — over 95% of the world’s still water bodies are small (less than 10 acres) — but the humble pond has been underexposed and largely disregarded by federal and state surveillance and conservation programs. This is partly because their numbers make monitoring difficult, but also because agencies do not define them or distinguish them from lakes or wetlands. The neglect affects the accuracy of climate modeling, as ponds emit high levels of greenhouse gases and their contribution to the global carbon budget is uncertain.

Holgerson and her team examined how scientists defined pond in more than 500 relevant scientific papers, coded them for different descriptors, such as area or depth, and whether the descriptions were qualitative or quantitative.

“We found that there wasn’t one definition that researchers all cited, and the definitions were often qualitative, describing a pond as ‘small,’ for example,” Holgerson said.

The team also conducted a survey of government agencies responsible for monitoring and conserving water bodies. Half the states had laws referring to ponds, but only one state (Michigan) defined ponds. Other states have designated ponds as state water or lumped them together with lakes or wetlands.

However, the researchers found that ponds are not the same as lakes or wetlands. Closer examination of the literature revealed that ponds have different ecological structures and functions that make their categorization with lakes or wetlands problematic.

Holgerson and her team have mapped the relationships between surface area and various measures of ecological structure or function. “We looked at parameters such as gross primary production, respiration, chlorophyll levels, emission of greenhouse gassesdie temperature ranges and the rate of gas exchange with the atmosphere,” Holgerson said. “Nine out of 10 ecosystem parameters relate nonlinearly to the surface, suggesting that ponds really work differently.”

They also examined how these ecosystem metrics related to depth and emerging vegetation — plants rooted in the soil and extending to the surface — and again found nonlinear relationships. They used the thresholds for where water body functions started to change with surfacedepth and emerging vegetation to arrive at their definition.

The clear profile and characteristics of ponds mean they shouldn’t be held to the same monitoring standards as lakes or wetlands, Holgerson said. “For example, ponds may naturally have higher nutrient concentrations and higher methane fluxes. We may need to develop unique water quality standards for pond monitoring.”

More research is needed to sharpen the definition, especially to better understand water bodies on the boundary between wetlands and ponds, and ponds and lakes, and how size, depth, vegetation – and other variables such as how sheltered a water body is – affect the functioning of the pond and its categorization.

“At the beginning of the study, we weren’t sure whether our research would allow us to propose a new definition that we were confident in, but we think the numbers we offer are solid and a good starting point for further research.” research,” said Holgerson. “We’re calling for more research, especially to look at the boundaries between wetlands, ponds and lakes.”

Holgerson hopes the new definition will also draw attention to ponds as distinct, important ecosystems worth studying, monitoring and protecting. “Research and monitoring of ponds can help us figure out how these globally abundant water bodies function. There is also an essential human element,” Holgerson said. “So many people have connections with ponds — they have childhood stories about catching frogs or learning to fish in a nearby pond.”