What will fish communities of the North Carolina Piedmont look like in the future?
“Many factors could affect this,” says U.S. Forest Service research hydrologist Peter Caldwell. “Water withdrawals could be one of the most important.”
Water withdrawn from rivers may eventually flow out of kitchen faucets. Many municipalities get drinking water from rivers and streams.
Caldwell recently contributed to a modeling study that projected fish species richness under different future scenarios of water withdrawals, land cover, and climate in the NC Piedmont.
“In some areas, withdrawals of 25 percent of natural flow could cause more than three species to disappear,” says Caldwell. Across the region, an average of one species would be lost.
In 2013, the NC Ecological Flows Science Advisory Board reached a similar conclusion – leaving 80 percent or more of a river’s water should protect ecological integrity under typical conditions. “Our findings support this conclusion,” says Caldwell, who served on the advisory board.
The current study is novel – few research studies explore fish communities of an entire ecoregion, partly because of the difficulty in acquiring consistent data.
“We used fish data collected by the NC Division of Water Resources,” says Caldwell. “The division has a specific, consistent protocol. It’s a great resource – a long-term dataset, with excellent spatial coverage across the Piedmont.”
In addition to the fish data, Caldwell and his colleagues modeled streamflow across the 385 sampling sites. The researchers then constructed flow-ecology models.
The researchers used the Water Supply Stress Index (WaSSI) to predict streamflow characteristics, such as the maximum amount and variability of streamflow. They also predicted the amount of streamflow originating on parking lots and other impervious surfaces. Streamflow characteristics, as well as the river basin each site was located in, were then used to predict fish species richness.
River basins include land around the river as well as all of the streams and creeks that drain into the river. The researchers studied seven Piedmont river basins: the Broad, Cape Fear, Catawba, Neuse, Roanoke, Tar, and Yadkin.
The NC Piedmont is growing quickly. NC has one of the highest rates of population growth in the U.S., and much of the growth has occurred in Charlotte, Durham, Raleigh and Winston-Salem. The need for water grows with the population. Population growth also brings increased development and more impervious cover.
The study suggests that climate change and increases in impervious cover may not affect fish species richness across the region as a whole.
However, the scientists also evaluated 886 smaller watersheds, known as twelve-digit Hydrological Unit Code or HUC catchments. Each of these smaller watersheds drains about 40 square miles.
“At these finer scales, climate change and more impervious cover could certainly affect fish in individual watersheds,” says Caldwell.
In some of the smaller watersheds, increases in impervious cover could cause more than three fish species to disappear.
“Others have said that when impervious cover reaches 10 percent, you see impacts on biological communities,” says Caldwell. “We found similar evidence that fish species richness declines when the amount of water in the stream from impervious surfaces exceeds 10 to 20 percent.”
The study also highlights the potential of WaSSI. “WaSSI is very well suited for regional ecological studies,” says Caldwell. “WaSSI has great potential for exploring the effect of streamflow changes on fish communities across broad regions.” WaSSI is also fairly easy to use, and as Caldwell and others found in 2015, it generally performs as well as more complex models.
Water managers can use the modeling approach to identify areas of concern or hotspots where changes in streamflow could threaten fish communities. Identifying such hotspots will help managers make informed decisions about water conservation.
The Southeast Climate Science Center funded the study.
For more information, email Peter Caldwell at firstname.lastname@example.org.