A new study from North Carolina State University researchers finds that the conversion of forests to urban development or agriculture near streams can have harmful effects on water quality downstream, presenting both health concerns and raising the cost of water treatment.
Using a model called the Soil and Water Assessment Tool, researchers mapped out the current and projected future effects of four land-use scenarios at 15 water intake locations across the Middle Chattahoochee watershed in Georgia and Alabama.
By combining a series of potential socioeconomic outcomes and climate change models reaching out to 2070, researchers examined several potential land use change scenarios to predict their effects on water quality. The research is published in the journal PLOS Water.
Katherine Martin, associate professor in the NC State University College of Natural Resources and co-author of a paper on the study, said that in models where forest cover was converted to other land uses, water quality suffered.
Fig 1. Middle Chattahoochee study area with the 2011 NLCD showing point source, calibration gage, and drinking water intake facility locations.
"In terms of aspects of water quality that we have long-term data on, two of the biggest are nitrogen levels and the amount of sediment in the water. Looking at those two, in places where we're losing forest cover, we see both of those increasing," she said. "Those are both detrimental to the quality of drinking water, and they require more filtration."
Part of the issue, Martin said, is the relatively high level of fertilizer used in large-scale agriculture. Urban development results in large areas of impermeable surfaces, where rainwater cannot soak into the ground and instead runs off into rivers and streams. This causes the water to carry more sediment into those waterways than it would if it had been absorbed into the ground.
Increased filtration has several knock-on effects, Martin said. Not only is it potentially harmful for aquatic life, but it also increases the cost of managing water treatment plants. For facilities that do not serve large populations, this can lead to large per-capita price increases that end up being passed on to residents.
These areas are also more likely to see increased development, due to their abundance of open land. The study suggests that more attention should be paid to where development might have serious effects on water quality for people living nearby, Martin said.
"Agriculture and urban development are beneficial, and this study does not say otherwise," she said. "What we are seeing is that there are trade-offs when we lose forest cover, and we need to open up the conversation about those."
