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Will Grand River’s ‘dead zone’ revive?

On­go­ing up­grades of Water­loo Re­gion’s waste­water treat­ment plant on the Grand River in Kitchener has re­sulted in many im­prove­ments to the wa­ter.

KITCHENER — More than seven years since Waterloo Region made major upgrades at the Kitchener wastewater treatment plant online, Patty Gillis is still looking for any sign of mussel life near the plant.

It’s a recovering area, and she’s hopeful.

The mussel “dead zone,” as the Environment Canada researcher calls it, is a seven-and-a-half kilometre section of the Grand River between the Kitchener wastewater treatment plant and the fork where the Speed and Grand Rivers meet. Between those two places, practically no mussels can be found.

The plant’s ongoing upgrades have resulted in many improvements: more oxygen in the water; fewer excess nutrients like ammonia and phosphorus washed into the river; and the return of healthier native fish. But Gillis still doesn’t know if the mussel population is recovering.

Freshwater mussels are considered a sign of a healthy waterway. They also

filter toxins out of the water.

Gillis remembers discovering the dead zone in 2012, when she and her team were trying to determine how effluent from Kitchener wastewater treatment plant affected wild mussels over the long term.

To do this, they searched the river in 100-metre sections to find mussels to study.

At first, Gillis wasn’t worried when they didn’t find any within the first few hundred metres. Mussels tend to be patchy, she says.

“So we kept looking,” says Gillis. “And we went out over a number of days, which turned into a number of weeks, and we were slowly working our way downstream from the Kitchener plant, downstream many kilometres.”

Gillis says her team searched six weeks before finding a single live mussel downstream from the plant.

Experts at the Grand River Conservation Authority had raised concerns about high nutrient levels in the river downstream from the Kitchener wastewater treatment plant in the early 2000s. Ammonia, which naturally occurs in human waste, was particularly alarming.

Ammonia is toxic. Even in relatively low concentrations it’s known to damage fish gills and kidneys over time and impede development and survival of fish larvae and young hatchlings. In high enough concentrations it kills organisms, according to Environment Canada.

“There were definitely times where the ammonia levels were toxic in the river in the early 2000s,” said Sandra Cooke, formerly senior water quality supervisor for the conservation authority.

Additionally, once released into the river, bacteria transform ammonia into nitrate. This process uses much of the water’s oxygen, decreasing the amount available to the mussels and fish that need it.

From the excess nitrate grow more algae and plants which release oxygen during the day, but take up oxygen at night, creating major daily swings in available oxygen. This is a stressful environment for the river’s animals, and only those species that can handle environments with low oxygen survive, slashing diversity.

The last major upgrade to the Kitchener wastewater treatment plant had been in 1975, said Trevor Brown, the manager of engineering and wastewater programs at the Region of Waterloo.

Region staff advised to plan for major upgrades in 2007, with the goal of improving the river’s health. Construction started in 2010 and hasn’t stopped. In the last decade, the region spent over $250 million on the Kitchener plant’s upgrades alone.

Increasing the nitrifying capacity of the plant was a major component of the upgrades. This means that the oxygensucking process of transforming ammonia into nitrate would be finished before entering the river.

Before the upgrades, the Kitchener wastewater treatment plant regularly released effluent with ammonia levels between 15 and 35 mg/L.

Currently the Ministry of Environment Conservation and Parks enforces a limit of 0.5mg/L.

Once the nitrification upgrades were running in the late summer of 2012, the ammonia levels in Kitchener’s effluent decreased dramatically to just over 5mg/L and now regularly sit below 0.2mg/L, according to Brown.

While the wastewater upgrades were targeting ammonia, an unforeseen positive side-effect was the decrease in levels of pharmaceutical estrogen entering the river, as people had flushed birth-control pills and other medications down their toilets. The estrogen was feminizing almost all the fish downstream of the plant. After the upgrades, these levels went from 100 per cent of fish studied to upstream levels. Meanwhile, fish abundance greatly improved.

Gillis returns to this section of the river every two years to look for any sign the mussels are recolonizing, now that ammonia levels have almost disappeared and the fish that the mussels depend on to host their young have returned.

She still hasn’t found them. This year she is scheduled to look again but complications caused by the global pandemic might get in the way.

Even so, she’s optimistic. Fresh water mussels are very slow growing and hard to find even in the best of conditions, says Gillis. Mussel larvae start off microscopic in size, and young mussels can be half the size of a pinky fingernail while they burrow among sand and gravel.

“I’m hoping with time we’ll know that those upgrades changed the water quality enough — lowered the ammonia, lowered the nitrogen, took away the feminization in the fish, and all those things together made the water quality better so that mussels can repopulate,” said Gillis.

Mussels are sentinel species, she said.

They tell a lot about a river’s health because they filter all the chemicals, metals and pharmaceuticals that come to them from upstream, and they can’t leave if their section of the river becomes toxic.

Gillis says if mussels are protected, much of the whole river ecosystem will be as well.