Researcher gathers stream data from Mack Creek, on the H.J. Andrews Experimental Forest in Oregon. Credit: Tom Iraci, U.S. Forest Service
CORVALLIS, Ore. Mar.
19, 2013. For the first time, a study has compared water quality
trends in forested streams across the country that are largely
undisturbed by land use or land cover changes.
The study, which
draws on decades’ worth of data from reference
streams in six U.S. states and Puerto Rico, underscores the value
of long-term data in understanding the patterns and causes of water
quality changes in streams and rivers. It is published in the current
issue of the journal Environmental Research Letters.
Much of what we know about changes in stream water quality comes
from studies where basins have been impacted by human activity,” said
Alba Argerich, a postdoctoral research associate with Oregon State
University and the study’s lead author. “Our work intentionally
focused on relatively undisturbed streams, the very reference sites
that serve as benchmarks for evaluating water quality trends.”
the study, Argerich and colleagues analyzed concentrations of stream
nitrogen, which, despite regulations, have been on the rise
across the country as energy and food production release reactive
forms of the compound into waterways. Once there, reactive nitrogen—nitrate
and ammonium—can alter stream function and cause substantial
changes in stream communities.
The study focused on sites that
are part of the USDA Forest Service’s
Experimental Forest and Range network, a system of 80 locations
across the country that provide settings for long-term science
studies. Many of the sites have long-term monitoring programs and
data sets spanning decades and so provide unique opportunities
to evaluate long-term trends.
These long-term water quality data from experimental forests are
a treasure,” said Sherri Johnson, a research ecologist with
the Pacific Northwest Research Station and a co-author of the study. “Some
sites have over 40 years of weekly data.”
analyzed 559 years of stream nitrate and 523 years of stream ammonium
data from 22 streams in 7 experimental forests
across the country. They found that even these near-pristine forested
streams are subject to change, as stream nitrate has declined in
the Pacific Northwest, in the Northeast, and in Puerto Rico, but
has increased in the Mountain West and the South. They also observed
that, within a forest, trends were not always in sync—at
some sites, two streams within an experimental forest had opposing
for the same type of nitrogen for the same period of time, suggesting
that the controls on stream nitrogen concentrations may vary among
and within sites.
Understanding how nutrient concentrations are changing over time
in reference streams is vital for informing best management practices
that are aimed at protecting water resources,” Argerich said.
learn more about the study, visit http://iopscience.iop.org/1748-9326/8/1/014039.
To browse a cross-site database of stream chemistry data, visit
The Pacific Northwest Research Station—headquartered in Portland,
Oregon—generates and communicates scientific knowledge
that helps people make informed choices about natural resources
the environment. The station has 11 laboratories and centers
located in Alaska, Washington, and Oregon and about 390 employees.