A team of Yale researchers will lead a five-year, $3 million study to determine whether an increase in extreme rain events is affecting the transport of dissolved organic matter (DOM) through the Connecticut River watershed, a phenomenon they say could alter the chemical composition and water quality of the watershed and Long Island Sound.
 
With funding from the National Science Foundation’s MacroSystems Biology program, researchers will collect data from dozens of points across the watershed, which begins in Canada and runs through five U.S. states, before emptying into Long Island Sound. Dissolved organic matter, a complex mix of compounds that leeches into waterways and gives rivers and streams their color, is a “master variable” in water systems; In addition to introducing both nutrients and pollutants, DOM influences the escape of carbon dioxide from the water and can impact the amount of light that penetrates the water. That, in turn, can affect levels of phytoplankton, a major food source for many organisms.
 
The researchers say that shifts in the transport of DOM could potentially impact mercury inputs to inland waters and the Sound, dissolved oxygen concentrations, and water clarity.

“Understanding how storms impact water quality and the delivery of materials to the coast is important to managing these vital ecosystems,” said lead investigator Peter Raymond, a professor of ecosystem ecology at the Yale School of Forestry & Environmental Studies.

Other contributors to the study include Jon Morrison and Jamie Shanley from the U.S. Geological Survey, Bill Sobczak from the College of the Holy Cross, and Aron Stubbins from the University of Georgia.
 
The study could also reveal new insights into the regional-scale dynamics of river systems. “The proposed work will test a new conceptual framework for drainage networks in order to understand how the chemistry of water changes as it moves from tiny streams to big rivers and how this change is impacted by precipitation events of different sizes,” Raymond said. 
 
While conventional theory holds that most DOM entering watersheds is naturally processed by organisms in “first order” streams — the smallest streams at the headwaters of river networks — the researchers suggest that these biogeochemical reactions might actually be occurring largely in the higher order rivers.
 
A critical reason is that major precipitation events are flushing an increasing amount of these materials directly into the larger, faster-moving rivers before there is time for those reactions to occur, Raymond said.
 
“Using the observations in conjunction with the computer modeling, we will project how things might change in the future — perhaps under more intense rainfall regimes or more frequent rainfall,” said James Saiers, a professor of hydrology at F&ES and investigator in the study.
 
The New England region is a predicted hotspot for more intense storms, or “hydrologic acceleration,” as a result of climate change, the researchers say.

Beyond simply exploring how heavy rain events affect the transport of materials, however, the study will also test traditional assumptions of how different components of river systems interact even under normal circumstances, said Henry Gholz, program director of National Science Foundation’s (NSF) Division of Environmental Biology.
 
“For about 40 years we have viewed moving freshwater systems, from the small headwater creeks to the mouths of major rivers, as linked in a relatively simple upstream to downstream continuum,” said Gholz. “This project will test a new conceptual model for that… While some material is moved down the system and is processed as it moves from top to bottom, there are also places in the river system where things happen more, or less, rapidly.
 
“This project really has global significance in terms of what the potential impacts could be for this field.”
 
The NSF’s MacroSystems Biology program supports large-scale projects exploring biological systems at regional to continental scales.