Oxygen Levels Tell Extent Of Ohio River’s Metabolism

The sun sets on the Ohio River in Louisville, Kentucky. (Credit: Louisville U.S. Army Corps of Engineers)

Few scientists have tried to gauge the metabolism of large, winding ecosystems like the Ohio River. Instead, many have chosen to zero in on lakes or smaller streams where their results can be more easily understood.

Metabolism in an organism is easily described: It’s a measure of all the catabolic and anabolic reactions inside its body. These would include chemical reactions involved in biological processes. For the Ohio River and other large systems like it, metabolism is defined a little differently. Its metabolism is linked to changes in dissolved oxygen levels, influenced by the consumption of oxygen by creatures living in its waters. While some take the oxygen in to live, including fish and other aquatic animals, others produce oxygen as a byproduct of making their own food. This segment typically includes aquatic plants and algae.

Luckily, measuring dissolved oxygen is fairly straightforward these days, as scientists have a variety of sensors out there to choose from. Jeff Kovatch, an associate professor of biological sciences at Marshall University, uses YSI 6600 V2-2 Multi-Parameter Water Quality Sondes to measure DO levels at two different points in the Greenup Pool of the Ohio River. He combines the data they collect with information on water temperature and solar radiation to estimate the metabolism of the Ohio River in an ongoing work.

“When you get the large, lotic systems like the Ohio, it’s something people have not looked at,” said Kovatch. “It involves new concepts and the metabolic theory of ecology. Combining those two things provides a way to study the main stem as a whole entity instead of fish and algae as individual units.”

The 10-year-old theory looks at the metabolic rates of organisms in an area to observe how they add to processes in their environments. Looking at the Ohio River from that standpoint is valuable because few others have done so in the past. The work is also revealing more about the river, including the makeup of its trophic structure and it may also help advance understanding of how other large rivers function around the world.

In addition to dissolved oxygen, the sondes collect information on the Ohio River’s temperature, turbidity, pH, conductivity and chlorophyll. Data on the extra parameters help with other investigations. The temperature and DO pieces to Kovatch’s model are easily added, but there is a little post-processing.

“With the data sonde technology, we measure the dissolved oxygen levels every 15 minutes,” said Kovatch. “Over a known geographic distance, we can do a volumetric extrapolation to get an idea of the total oxygen flux.”

Kovatch calculates the solar radiation data using time-tested methods that rely on latitude and longitude, light attenuation in the water and time of day. He and others in his lab collect the light data by going out to different sites on the river using boats. They drop sensors to a known depth and confirm how the light behaves in the water.

“By taking the radiation and the temperature, what I do is model changes over the day and night cycle to extrapolate what the physiologically active biomass in the Ohio might be,” said Kovatch. “Some of the estimates I came up with, the biomass is quite large.”

The results aren’t very surprising, says Kovatch, because of the sheer magnitude of the Ohio River. After all, its average discharge is around 8 cubic meters, which is quite large over its nearly one-thousand-mile length. In addition, his model doesn’t divide up organisms into consumers or producers of oxygen. It captures a glimpse of all the organisms in the river combined.

“It doesn’t tell you if it’s an autotroph or heterotroph,” said Kovatch. “It wouldn’t tell you if it was dominated by bacteria, fish or bivalve mollusks.”

Featured Image: The sun sets on the Ohio River in Louisville, Kentucky. (Credit: Louisville U.S. Army Corps of Engineers)