A model for predicting the levels of oxygen in water, developed by West Virginia University researcher Omar Abdul-Aziz, gives citizen scientists nationwide a tool for taking action on stream pollution.
“I have been looking at water quality data for 20 years,” said Abdul-Aziz, an associate professor at the Benjamin M. Statler College of Engineering and Mineral Resources. “I can tell you that a big percentage of streams in the United States are polluted. Urban streams are getting dumpster runoff, stormwater carrying lawn fertilizers and trash. Wastewater plants aren’t necessarily treating for the dissolved organic carbon, nutrients and pharmaceuticals we’re putting into our sewage.”
Abdul-Aziz’s model relies on only water temperature and pH, a measure of acidity, to give an accurate measure of the health of any freshwater stream in the contiguous United States as represented by the amount of oxygen dissolved in the water. Oxygen is fundamental to stream health, and his model is significant because it predicts how much oxygen is in the water of any given stream at any location or time, based on a small amount of easily obtainable data.
“Once we know the oxygen levels in these streams, we can take interventional measures such as stream restoration, and we can use green engineering solutions like increasing watershed and streamside vegetation,” he said.
Abdul-Aziz presented the model in a paper co-authored with WVU doctoral student Aron Gebreslase and published in Water Resources Research.
Developed with support from a $500,000 National Science Foundation CAREER award, Abdul-Aziz’s model incorporates water quality information collected from 86 monitoring stations across 32 states between 1998 and 2015. That large data set encompasses temperate, continental, arid and Mediterranean climates, as well as land covers and uses as diverse as forests, grazing lands and parking lots.
The information the model provides can help determine how the Environmental Protection Agency classifies a stream and whether the EPA will permit a project that affects a particular stream.
“This tool is going to help the EPA implement the Clean Water Act, which for non-urban streams requires that ‘dissolved oxygen’ — the amount of oxygen in water — be at no less than five milligrams per liter,” Abdul-Azis said. “Dissolved oxygen is important because, if the level of oxygen in those streams goes below that five milligram cutoff, it starts to become hard for fish and other aquatic animals to breathe and the stream is typically considered impaired.”
Designation of a stream as impaired can impede project permitting by the EPA, which has emphasized the critical roles streams play in providing clean drinking water, protecting against floods and erosion, resupplying groundwater, reducing pollution and facilitating economic activities such as agriculture, manufacturing and outdoor recreation.
“The tool is a simple mathematical model that uses only water temperature and pH to predict oxygen in the water,” Abdul-Aziz said. “People can plug in their temperature, which is readily available data, and their pH — or if they don’t have pH, I also offer a model with just temperature. Then they can see how water quality will change under different scenarios for climate, that is, temperature and changing land use.”
Many factors beyond water temperature and pH, contribute to the health of a stream. Sunlight, atmospheric pressure, flowrate, width, depth, the roughness of the streambed and steepness of the banks, the area’s flora and fauna, and whether the land is urbanized, agricultural, or industrial are factors, but their measurements aren’t required for the tool to be accurate. Water temperature is the decisive data point for making predictions, ideally supplemented with pH levels.
“The higher the temperature, the less oxygen in the water,” Abdul-Aziz explained. “It’s the same thing that happens to us on a hot day. When there’s less oxygen in the air it can be hard to breathe.”
High water temperatures make it harder for oxygen to dissolve in water. Higher temperatures also promote the decomposition and oxidation of organic matter and increase microbial respiration, processes which use up oxygen.
When insufficient oxygen leads to the death of aquatic life, “the issues for humans range from food shortages to health hazards,” he said. “Dissolved oxygen is a central indicator for the overall stream water quality and ecosystem health.”
The tool is fully scalable, so it works for any freshwater stream in the U.S., except for some streams in the mountainous west that experience significant geothermal effects, like those in Yellowstone National Park. It can be used to understand conditions in the past, get a current understanding of a stream’s health or predict the future using water temperature estimates to evaluate how different climate change scenarios would affect aquatic ecosystems.
“With agriculture, logging, mining and chemical processing plants, most of our country’s populated areas now have contaminated streams, and this model allows people to do something about that,” Abdul-Aziz said.
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