Mostly good news about water quality

Can we improve the water quality of our lakes and rivers? It turns out that there are things we can do, and they’re working.

Reviving dead zones in the Thames

Tower Bridge in London
The Tower Bridge spans the Thames in London. The water quality of the river has improved over the last 60 years due to better sewage treatment and monitoring. Shutterstock image.

The River Thames, which flows through London and supplies much of its drinking water, is no longer biologically dead. In 1959, its low oxygen concentrations caused the British Natural History Museum to declare it incapable of sustaining marine life. That motivated better sewage treatment and monitoring of water quality. Those efforts are paying off: now wildlife such as seahorses and sharks live in the Thames.

However, pollution isn’t the only danger to wildlife habitats in the Thames, as the temperature of the water is rising due to climate change. In addition, the nitrate concentrations are higher. And microplastics not only pose a danger to riverine wildlife, but eventually make their way to the ocean.

Tequila splitfin returns to Río Teuchitlán

The tequila splitfin, a small fish in Mexico’s Río Teuchitlán, was extinct in its native habitat. Pollution, human activity, and nonnative species had combined to eliminate it from the wild. But the fish had been a valuable part of the local ecosystem, helping to control the mosquitoes that spread dengue fever. Conservationists sought the help of local people to restore the fish to the river. The conservationists bred tequila splitfin from aquarium stock. Once they understood the potential ecological and health benefits, a group of local people, mostly children, began to collect garbage, clean the river, and remove invasive plants. Cattle are no longer permitted to drink in some areas. All that has improved the water quality, making it possible to reintroduce the tequila splitfin.

Water quality in Minnesota

Closer to home, the Minnesota Pollution Control Agency (MPCA) has removed 12 lakes from its list of impaired waters due to reductions in the mercury concentrations. That result surprised scientists, as global emissions of mercury have increased. However, mercury emissions in Minnesota are about half what they were in 2005. And in the Upper Midwest as a whole they’ve been reduced by 75% during that time. These results suggest that local sources of mercury are more important than scientists had realized.

Mercury is harmful, particularly to children, because it’s a neurotoxin. As a heavy metal, it accumulates in the food chain—people eat big fish, which ate smaller fish, which ate plants.

The main sources of mercury emissions are coal-fired power plants. Many of these have either closed or converted to burning natural gas. Those remaining have had to meet stricter emissions standards since 2015.

Another source of mercury is garbage incineration. Banning mercury from products that end up in landfills has also lowered mercury emissions from garbage incineration.

Tree leaves have small pores that absorb elemental mercury from the air. When the leaves fall, bacteria break them down, releasing the mercury, which can then find its way into streams and lakes. This is yet another reason for sweeping the streets in the fall to capture the leaves to prevent them from polluting the water.

In the Twin Cities metro area, we use 300,000 tons of salt every year to keep our roads clear of ice. Unfortunately, the chlorides in salt are toxic to fish and aquatic birds. MPCA has developed strategies for smart salting to reduce the amount of salt that ends up in streams and lakes. In the long term, though, it’s likely that we’ll be using different deicing chemicals that aren’t so hard on the environment.