Suitable habitat for native fishes in many Great Plains streams has been significantly reduced by the pumping of ground water from the High Plains aquifer – and scientists analyzing the water loss say ecological futures for these fishes are "bleak."
their study have been published in the journalEcohydrology.
alluvial aquifers, which can be replenished seasonally with rain and snow,
these regional aquifers were filled by melting glaciers during the last Ice
Age, the researchers say. When that water is gone, it won't come back – at
least, until another Ice Age comes along.
a finite resource that is not being recharged," says Jeffrey Falke, a
post-doctoral researcher at Oregon
and lead author on the study. "That water has been there for thousands of
years, and it is rapidly being depleted. Already, streams that used to run
year-round are becoming seasonal, and refuge habitats for native fishes are
drying up and becoming increasingly fragmented."
his colleagues, all scientists from Colorado
where he earned his Ph.D., spent three years studying the Arikaree
River in eastern Colorado. They conducted monthly
low-altitude flights over the river to map refuge pool habitats and connectivity,
and compared it to historical data.
conclude that during the next 35 years – under the most optimistic of
circumstances – only 57 percent of the current refuge pools would remain – and
almost all of those would be isolated in a single mile-long stretch of the Arikaree River. Water levels today already are
significantly lower than they were 40 and 50 years ago.
their study focused on the Arikaree, other dryland streams in the western Great
Plains – comprised of eastern Colorado,
western Nebraska and western Kansas – face the same fate, the researchers
that the draining of the regional aquifers lowers the ground water input to
alluvial aquifers through which the rivers flow, creating the reduction in
streamflow. He and his colleagues estimate that it would require a 75-percent
reduction in the rate of ground water pumping to maintain current water table
levels and refuge pools, which is "not economically or politically
feasible," the authors note in the study.
streams in the Great Plains host several warm-water native fish species that
have adapted over time to harsh conditions, according to Falke, who is with the
Department of Fisheries and Wildlife at Oregon State
minnows, orange-throat darters and other species can withstand water
temperatures reaching 90 degrees, as well as low levels of dissolved oxygen,
but the increasing fragmentation of their habitats may impede their life cycle,
limiting the ability of the fish to recolonize.
"The Arikaree River and most dryland streams are
shallow, with a sandy bottom, and often silty," Falke notes. "The
water can be waist-deep, and when parts of the river dry up from the pumping of
ground water, it is these deeper areas that become refuge pools. But they are
becoming scarcer, and farther apart each year."
that the changing hydrology of the system has implications beyond the native
fishes. The aquifer-fed stream influences the entire riparian area, where
cottonwood trees form their own ecosystem and ground water-dependent grasses
support the grazing of livestock and other animals.
regional aquifers is done almost entirely for agriculture, Falke says, with
about 90 percent of the irrigation aimed at corn production, with some alfalfa
impact goes well beyond the Arikaree
River," Falke explains.
"Declines in streamflow are widespread across the western Great Plains,
including all 11 headwaters of the Republican River.
Ultimately, the species inhabiting these drainages will decline in range and
abundance, and become more imperiled as ground water levels decline and climate