For decades, scientists have studied freshwater ecosystems using indicators such as pH, temperature, salinity, and nutrient content.
“This untapped measure in nature can give us a lot of really useful information.”
But a new paper published in Science argues that chemical diversity (chemodiversity) could be a way to better gauge and analyze freshwater ecosystem health. The paper encourages ecologists to use high-resolution mass spectrometry to uncover the characteristics of dissolved organic matter, or DOM.
“This untapped measure in nature can give us a lot of really useful information,” said Andrew Tanentzap, an ecologist at Trent University in Peterborough, Ont., Canada, and a coauthor on the new paper.
DOMinating Ecosystem Functions
Measuring chemodiversity hinges on understanding DOM, a group of carbon-containing compounds ubiquitous in nature.
Different types of DOM play important roles in freshwater systems. Some block light from passing through water, which affects how plants and algae grow as well as water temperature. Others bind to toxic compounds, making them either more or less available for other freshwater organisms to consume or absorb. When bound to DOM, nutrients such as nitrogen and phosphorus are more bioavailable and can promote the growth of harmful algae that impair water quality.
“Until now, we’ve really treated dissolved organic matter like it’s kind of a black box,” Tanentzap said. Scientists typically measure the concentration of DOM in water samples and can get some idea of its bulk makeup. But identifying the specific characteristics of DOM requires high-resolution mass spectrometry, which shows scientists the molecular composition of individual compounds.
The method has gone underused in biology and ecology, said Krista Longnecker, a marine chemist at the Woods Hole Oceanographic Institution who was not involved in the research. It wasn’t until recent decades that mass spectrometers evolved enough to allow scientists to identify different types of molecules within an ecosystem, she said.
“People for years have said, ‘Okay, let’s look at the biodiversity, let’s look at the biology,’” Longnecker said. “But that’s only half the story. The other half is what the chemicals and molecules are doing.”
Pinning Down Pollution
The paper hypothesizes that greater chemodiversity leads to greater biodiversity and a healthier ecosystem. That makes sense, said Juliana D’Andrilli, an environmental chemist at the University of North Texas who peer-reviewed the paper: Like humans, she said, microbes are happier when there’s a wide array of chemicals available to them to metabolize. And in general, healthier microbe populations lead to healthier ecosystems.
“By using the molecular characteristics of the organic matter, you can work out its origins.”
High-resolution mass spectrometry can also help ecologists identify the sources of freshwater pollution from DOM because DOM from one source may have a slightly different makeup than DOM from another source. “Mass spectrometry is almost like a fingerprinting technique,” Tanentzap said. “By using the molecular characteristics of the organic matter, you can work out its origins.”
For example, a previous study by Longnecker and other researchers used high-resolution mass spectrometry to determine that phosphorus pollution in Lake Erie originated from agricultural fields and wastewater treatment plants.
Applying high-resolution mass spectrometry to questions of ecosystem health is especially important as aquatic ecosystems undergo rapid changes brought on by human influence and climate change, Longnecker said.
A lack of cross-disciplinary understanding has delayed this type of research, Tanentzap said. Chemists aren’t generally interested in the ecological functions of DOM, and biologists often aren’t familiar with the techniques used to identify them, he added. Getting biologists and chemists on the same page could accelerate the kind of research he hopes will come out of the new paper.
Holding workshops to unify language across disciplines, training researchers to improve their science communication skills, and cultivating enthusiasm for cross-disciplinary work are all ways to encourage the conversations necessary for the new paper’s ideas to become reality, according to D’Andrilli.
—Grace van Deelen (@GVD__), Staff Writer