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river with mountain in the background

Are rivers big streams or flowing lakes?

New research published in the journal Biogeochemistry focuses on how mid-sized river nutrient cycling works. Is it more like a big stream or a flowing lake? Dr. AJ Reisinger, assistant professor of urban soil and water quality in the UF/IFAS Soil and Water Sciences Department, wanted to find out. He and colleagues spent four summers collecting data from 15 rivers in the western and midwestern United States.

Scientist standing in river in Utah.

Dr. AJ Reisinger filters a water sample during a nutrient uptake incubation at the Colorado River near Moab, UT. Fence posts in the river bed hold the incubation chambers in place. (Photo by Dr. Brittany Hanrahan)

The team measured nutrient uptake and metabolic activity (gross primary production and respiration) in the water column and at the whole-river scale. The rivers in five states (Idaho, Utah, Wyoming, Indiana, and Michigan) spanned nutrient and turbidity gradients.

“We wanted to figure out what happens in intermediate-sized rivers – ones that are too big to wade across, but not so big that you’d put a pontoon boat on it,” Reisinger explained. “We were particularly interested in figuring out if nutrient cycling in these mid-sized rivers was more like a stream or a lake.”

the view of a river from a bridge above it

Overhead view of the Manistee River in Western Michigan taken from the High Bridge Access Point within the Manistee National Forest. (Photo by AJ Reisinger)

In simple freshwater ecological terms, people who study streams – lotic or flowing systems – focus on processes on the streambed. Ecologists who study lakes – lentic or non-flowing systems – mostly focus on the water column. That is the area between the water’s surface and the bottom of the lake.

Results

“The results tell us that non-wadable rivers are a biogeochemical transition zone,” Reisinger said. “Ecologists who study streams need to continue working to incorporate the water column into our conceptual model of riverine nutrient and energy cycling.”

He points out that collecting river data from points that are hundreds of miles apart over the course of four years was a large undertaking.

This research was published in 2021 despite data collection starting in 2010 (and all data being collected and analyzed by 2015).

“I made life-long friends with my colleagues who worked on this project with me. My co-authors and the rest of the students and technicians on the project were amazing. I thank them for their support,” Reisinger said. “Persistence pays off!”

bottles in water collecting scientific data

Water column nutrient uptake incubation chambers (pictured above and below the water) were filled with river water, then amended with a nutrient of interest and allowed to sit in the river for 4-6 hours. The team collected water samples approximately every hour during this time period. They quantified the decrease in nutrient concentrations over time as a measure of nutrient uptake. The chambers are attached to fence posts during the experiment. (Photo by AJ Reisinger)

The research received primary funding from the National Science Foundation with the University of Wyoming-National Parks Services Research Station supporting a portion of the work.

You can read the full article here: https://link.springer.com/article/10.1007/s10533-021-00768-w