FLATHEAD LAKE – Rivers and streams are akin to arteries and blood vessels in a human body, so monitoring the metabolic respiration and production rates of Earth’s freshwaters can help us understand the overall health of our planet.
Current and former researchers with the University of Montana’s Flathead Lake Biological Station were part of a scientific team that used modern environmental sensor technology to track stream vital signs in near real time.
The new system they developed acts almost like a Fitbit for monitoring the nation’s freshwater ecosystems. It allows researchers to better predict how freshwater vital signs might shift with land development, climate change, and other disturbances.
UM researchers Maite Arroita, Joanna Blaszczak, Alice Carter and Lauren Koenig, plus FLBS stream ecology Professor Bob Hall, were part of an effort led by Duke University Professor Emily Bernhardt. Their pioneering work was published recently in the prestigious Proceedings of the National Academy of Sciences.
Waterway scientists monitor fluctuations in oxygen and carbon that occur in streams as gases are absorbed and released by organisms like microbes, algae, insects and fish as they go about their basic life functions.
In the past to study stream metabolism, scientists relied on snapshot data composed of measurements taken from a small number of streams over a few hours or days. Now, by using years of data combined with new computational and statistical methods, a research team created an approach to convert water quality and environmental data into estimates of photosynthesis and respiration for specific rivers and river types.
Coming from more than 10 academic and government institutions, the scientists analyzed at least one year’s worth of data from over 220 rivers and streams across the United States. Environmental sensors recorded the dissolved oxygen and temperature every 15 minutes day and night. Study areas ranged from Arizona deserts and Puerto Rican rainforests to Midwest farmland.
Researchers compiled and uploaded the data to a web portal for public use.
“When we monitor a river continuously instead of just taking snapshots, a picture starts to emerge of what the life of the river is really like,” said Carter, an author on the study. “Disturbance and change are the norms. Measuring the ‘pulse’ of a river allows us to see how this influences the lives of organisms and how humans are changing these patterns.”
While analyzing the data, the researchers made an interesting discovery. Although changes in average annual temperature and precipitation often explain changes in terrestrial ecosystem productivity, for streams the most important controls are annual light availability and flow stability.
Streamflow changes seasonally, day to day, and even minute to minute with sudden storms, so stream organisms must contend with flows that range from a trickle to a torrent. Highly variable flows tend to dislodge algae and organic matter, lowering metabolic rates. High light stimulates photosynthesis.
The researchers contend focusing more attention on sunlight exposure and changes in water levels due to droughts or flooding will substantially improve scientists’ ability to predict river ecosystem dynamics in a way that may fundamentally change the way rivers are studied moving forward.
The study also found that streams respired more carbon than they produced, showing that organic matter transported from the land to water subsidizes metabolism in rivers.
“Our study provides a lens from which we can examine how changes in land use and climate can affect energy inputs to riverine food webs across many rivers through time,” said Hall, an FLBS stream ecologist. “Our approach will enable managers to monitor ecosystem processes in addition to water quality metrics such as dissolved oxygen.”
When it comes to the future of our stream ecosystems, their condition will likely depend on human activity. Study authors emphasize that changes to light and flows in streams greatly impact their communities and conditions. Changes in shade-producing riverbank vegetation, climate change-caused shifts in rainfall and streamflow regulation by dams can all affect how much energy is available for stream food webs.
If human-induced changes influence river and stream flows, then food webs, fish populations, outdoor recreation and other related industries that depend on our rivers may be impacted as well.
To put it another way, the researchers contend, whether it be 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 up to us.
This study was made possible by the National Science Foundation. For the complete study, visit https://www.pnas.org/doi/full/10.1073/pnas.2121976119. Data from the study are publicly available at https://data.streampulse.org/.
Contact: Alice Carter, UM Flathead Lake Biological Station postdoctoral research associate, 406-872-4557, firstname.lastname@example.org; Bob Hall, FLBS stream ecology professor, 406-872-4512, email@example.com.