A new study finds that hypoxic dead zones occur in urban streams.
Hypoxic dead zones, which occur when dissolved oxygen levels in water drop so low that fish and other aquatic animals living there suffocate, are well-documented problems in many coastal waters. Now, a new Duke University-led study reveals they also occur in freshwater urban streams.
“We were surprised to find these dead zones are happening in our own backyards, not just in rivers and coastal waters downstream of major point sources of nutrient pollution,” said study leader Joanna Blaszczak, a 2018 doctoral graduate of Duke’s Nicholas School of the Environment.
Blaszczak and her colleagues published their peer-reviewed study Dec. 3 in the journal Limnology & Oceanography. To conduct the study, they measured dissolved oxygen concentrations, light levels, water chemistry and stream flow in six streams draining urban watersheds in Durham and Raleigh, N.C., from 2015 to 2017. They used the data to model the growth of algae and oxygen-consuming bacteria in the streams and examine the frequency at which dissolved oxygen concentrations dropped below two milligrams per liter -- the danger point for fish and other aquatic organisms.
“Streams draining developed areas are subject to intense, erosive storm flows when roads and stormwater pipes rapidly route runoff into streams during storms, without allowing the water to infiltrate into the soil,” Blaszczak said.
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