Forecasting ‘Dead Zones’ to Help Protect Drinking Water

By Kevin Bunch, IJC

Cleveland, Ohio, depends on water from Lake Erie for its drinking supply, which can be affected by a hypoxic zone
Cleveland, Ohio, depends on water from Lake Erie for its drinking supply, which can be affected by a hypoxic zone. Credit: Rick Harris

A new tool in development should help water treatment plants in communities along Lake Erie prepare for when dead zones reach their shores.

Lake Erie is periodically affected by oxygen-poor hypoxic zones, also known as “dead zones” for how few things can survive in them. These zones form at the bottom layers of water in Erie’s central basin. Aside from being bad for aquatic life, hypoxic zones present a special challenge to water treatment facilities. The hypoxic zones can spread toward shorelines and temporarily impede operations for hours as treatment systems are set up to deal with the specific impacts of those conditions. The US National Oceanic and Atmospheric Administration, working with the Cooperative Institute for Great Lakes Research, hopes to lend a hand to water treatment plants with an experimental early warning system that would provide advance notice of potential hypoxic events.

Oxygen-deficient water often has a lower pH balance and may have higher concentrations of metals like manganese and iron, which can cause discoloration of treated water, according to Craig Stow, aquatic ecosystems modeling researcher at NOAA’s Great Lakes Environmental Research Laboratory. Water treatment plants can account for these water conditions, but operators need to know about those conditions to make the necessary treatment adjustments, and it takes time to retool their systems. Right now, they get alerted only when the hypoxic water has reached the intake.

“Hypoxic water can be treated, but it requires knowing hypoxic water is present to put those treatment adjustments in place,” Stow said. “Since these adjustments are more expensive to do or counter to normal treatment goals, you don’t want to be treating water all the time as if it were hypoxic.”

Hypoxic conditions typically occur in late summer, caused by long periods of high temperatures and stormwater events that wash fertilizer and manure off farms, and sewage from combined stormwater overflows into the lake. The nutrient input stimulates algal growth, and as that algae decomposes the aerobic bacteria feeding off it consumes oxygen, reducing the levels of dissolved oxygen in the water.

Lake Erie isn’t a static body – water is constantly being churned around, and occasionally this brings the hypoxic water from the bottom layers of the central basin near the shore and to the water intake pipes located near cities. By adapting an existing Lake Erie computer modeling framework used for other types of forecasts (like meteorology), Stow believes an effective early warning system can be developed to alert water managers that a hypoxic zone could be heading toward their intakes so that managers can adjust their treatment methods accordingly, possibly up to a few days in advance.

The project got underway in 2016. In the initial stages the warning system involved taking existing models focused on water temperature and other conditions and adding hypoxia to it, but chemical and biological components – like phytoplankton growth and phosphorus inputs – will be included later.

An additional goal of the project is to determine whether adding nutrient and biological components to the model will improve the accuracy of the hypoxia simulations over a purely physical model, according to Stow. A model that includes chemical and biological components may have additional applications, such as forecasting algal blooms, which would be helpful for water managers, anglers and boaters.

Seasonal changes through 2005 show how Lake Erie’s hypoxic (low-oxygen) zone develops in the central basin in July through September
Seasonal changes through 2005 show how Lake Erie’s hypoxic (low-oxygen) zone develops in the central basin in July through September. Credit: NOAA

NOAA researchers also are reaching out to groups with a stake in such a warning system. Water treatment and management agencies, Ohio Sea Grant and the Ohio Environmental Protection Agency are just some of those who could use the early warning system.

“The drinking water plant managers not only benefit from sharing operational information and research, but also by establishing lines of communication between water utilities and researchers that help identify common areas of interest,” Scott Moegling, water quality manager at Cleveland’s Division of Water, wrote in a NOAA blog post. “The end result, researchers providing products that can be immediately used by water utilities, is of obvious interest to the water treatment industry on Lake Erie.”

The current effort is focused on the US side of the lake. Stow said Canadian information isn’t available right now, but there have been discussions with Canadian agencies on collaboration efforts.

Ontario has been working along similar lines on its Lake Erie coastline, however.

Communities along the north shore of Lake Erie contend with the upwelling of hypoxic water, according to Todd Howell, Great Lakes ecologist with Ontario Ministry of the Environment and Climate Change. Fish kills have been reported that were linked to hypoxic water reaching the shoreline, and the ministry has conducted water quality monitoring that has confirmed that hypoxic water is reaching the coastline. Upwelling also can push nutrients like phosphorus from the lake bottom to the surface, giving algal blooms an additional food source in the summer.

Howell said the province has acquired and deployed a real-time sensor system offshore of Port Glasgow, located off the central basin of Lake Erie. The system is designed to detect low-oxygen water and upwelling, and was first deployed in late summer 2016.

“Our intent is to deploy the system annually over the May-to-November period,” Howell said.

The Ontario Great Lakes Intake Program has routinely monitored nutrient, chemical and chlorophyll characteristics and concentrations at water intakes along the north shore since 1976. While this has not been specifically developed to detect hypoxic water, the data it has collected suggests indirectly, through phosphorus detections, that there has been upwelling occurring around some central basin water intakes. A 2015 report prepared by Freshwater Research for the ministry recommends collecting more evidence of hypoxic events along the north shore.

Since receiving funding a year ago from the NOAA Center for Sponsored Coastal Ocean Research – which is studying hypoxic zones in the Gulf of Mexico and other waters – Stow said his team has an early version of their dissolved oxygen model online right now. The researchers are working on predicting hypoxic zones and watching to see how reality matches the model, by using profilers and sensor strings in the lake that measure oxygen and water temperature. Those will be retrieved in the fall to refine the model. Part of the project also includes studying how these hypoxic zones form in the first place.

Stow said the early warning system could be operational within the next few years, at which point it would be run by NOAA’s forecasting unit.

Kevin Bunch is a writer-communications specialist at the IJC’s US Section office in Washington, D.C.

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