FLATHEAD LAKE – Rivers and streams are similar to arteries and blood vessels in a human body, so monitoring metabolic respiration and production rates of Earth’s freshwater can help us understand the overall health of our planet.
Current and former researchers at the University of Montana’s Flathead Lake Biological Station were part of a scientific team that used modern environmental sensor technology to track river life signs in near real time.
The new system they developed works almost like a Fitbit to monitor the country’s freshwater ecosystems. It allows researchers to better predict how freshwater vital signs might change with land development, climate change and other disturbances.
UM researchers Maite Arroita, Joanna Blaszczak, Alice Carter and Lauren Koenig, and FLBS Professor of Bach Ecology Bob Hall were part of an effort led by Duke University professor Emily Bernhardt. Her groundbreaking work was recently published in the prestigious Proceedings of the National Academy of Sciences.
Waterway scientists monitor fluctuations in oxygen and carbon that occur in rivers as gases are absorbed and released by organisms such as microbes, algae, insects and fish as they go about their basic life functions.
Historically, to study river metabolism, scientists have relied on snapshot data, which consisted of measurements taken over a few hours or days on a small number of rivers. Now, by using years of data combined with new computational and statistical methods, a research team has developed an approach to convert water quality and environmental data into estimates of photosynthesis and respiration for specific rivers and river types.
The scientists come from more than 10 academic and government institutions and analyzed at least a year’s worth of data from more than 220 rivers and streams in the United States. Environmental sensors recorded dissolved oxygen and temperature every 15 minutes, day and night. The study areas ranged from the deserts of Arizona and the rainforests of Puerto Rico to the farmlands of the Midwest.
Researchers compiled the data and uploaded it to a web portal for public use.
“When we continuously monitor a river, rather than just taking snapshots, a picture of what the river’s life is really like begins to emerge,” said Carter, an author of the study. “Disruption and change are the norm. By measuring the “pulse” of a flow, we can see how it affects the life of organisms and how humans are changing these patterns.”
Analyzing the data, the researchers made an interesting discovery. Although changes in mean annual temperature and precipitation often explain changes in terrestrial ecosystem productivity, the key controls for streams are annual light availability and flow stability.
Stream flow changes seasonally, day-to-day, and even minute-to-minute during sudden storms, requiring stream organisms to contend with flows ranging from a trickle to a torrent. Highly variable currents tend to remove algae and organic matter, lowering metabolic rates. High light stimulates photosynthesis.
The researchers claim that paying more attention to solar radiation and changes in water levels due to drought or flooding will greatly improve scientists’ ability to predict river ecosystem dynamics in a way that will fundamentally change the way rivers are studied in the future could change.
The study also found that streams breathed more carbon than they produced, showing that organic matter transported from land to water subsidizes metabolism in rivers.
“Our study provides a lens through which we can examine how changes in land use and climate over time may affect the energy input to river food webs in many rivers,” said Hall, a river ecologist with FLBS. “Our approach will allow managers to monitor ecosystem processes in addition to water quality metrics such as dissolved oxygen.”
When it comes to the future of our river ecosystems, their condition will likely depend on human activities. The study authors emphasize that changes in light and flows in streams have major impacts on their communities and conditions. Changes in shade-providing riparian vegetation, shifts in precipitation caused by climate change, and regulation of runoff by dams can affect how much energy is available for river food webs.
When man-made changes affect the flows of rivers and streams, food webs, fish populations, outdoor recreation, and other related industries that depend on our rivers can also be affected.
Put another way, researchers claim, whether it’s a river in the rainforests of Puerto Rico or the sun-dappled icy flows of the Flathead River here in Montana, the future ecological health of our rivers is in our hands.
This study was made possible by the National Science Foundation. The full study can be found at https://www.pnas.org/doi/full/10.1073/pnas.2121976119. Data from the study is publicly available at https://data.streampulse.org/.