While a decrease of water certainly isn’t good, an increase of precipitation is not good for water quality either

Lake Erie, one of the give Great Lakes in the United States (U.S.), in 2011, when the lake received record-breaking nutrient loads, resulting in an extensive algae bloom. Image credit: Tom Archer

While increased rainfall would generally be thought of as good, especially in this time of drought, it is not so – increased precipitation could pollute waterways, clogging them with excess nitrogen, and raising the likelihood of severe water quality impairments, according to a new study conducted by research scientist, Eva Sinha and Anna Michalak of the Carnegie Institution for Science and Venkatramani Balaji of Princeton University, published in the journal, Science.

As rainfall and other precipitation washes nutrients from various human activities such as agriculture into rivers and lakes, when these nutrients overload waterways, a process known as eutrophication, the results can be potentially dangerous.

In these cases, hazardous algae that produce toxins can develop, alongside perilous low-oxygen dead zones. And over the past few years, dead zones and algae blooms have been the focus of extensive news coverage.

A huge algae bloom off the Atlantic coast, U.S. in 2015. Image credit: NASA

Algae blooms in Lake Okeechobee in Florida, U.S. in 2016. This is only the blooms upstream, and downstream, water discharge led to more blooms. Image credit: NASA

In their study, Sinha and Michalak used predictive models to forecast how climate change affects eutrophication.

“In the 1970s, we discovered human-caused eutrophication and took steps to reverse its course,” Tom Torgersen, director of the National Science Foundation’s Water, Sustainability and Climate programme, which founded the research, said. “As this paper shows, however, even seemingly minor climate variations can result in a return to the eutrophication of the past. It will take more research to create better management strategies just to stay even.”

In an earlier research study, both Sinha and Michalak observed that while land use and management does control the supply of nitrogen to the water, it is the precipitation that controls how much of the nitrogen that flows from the land and into waterways. They also noted that the amount of precipitation is a determining factor in the nitrogen runoff that happens during annually.

Using these factors and insight, they have managed to predict how any changes to precipitation in the future caused by climate change will, in and of themselves, affect nitrogen runoff and in turn, increase the chances of water quality impairment.

They used the projections from 21 separate models and examined three possible future scenarios. Both researchers found that if the trends in greenhouse gas emissions continues at its current rate, the resulting changes in climate would alter the precipitation patterns and increase nutrient pollution by 20 per cent by 2100.

A large algae bloom off the Pacific Northwest coast of the U.S. in 2014. Image credit: NASA

But offsetting the increased amount of nitrogen that is being washed into waterways would be an enormous task, as it needs a reduction of a third in overall nitrogen inputs, such as fertiliser use.

“Our findings demonstrate that it is imperative that water quality management strategies account for the effect of future precipitation changes in nitrogen loading,” Michalak said.

Although their findings are specific to the United States (U.S.), both Sinha and Michalak have also identified China, India, and Southeast Asia as areas at a high risk for large increases in nitrogen pollution due to increased precipitation.

“These are regions that more than half the world’s population calls home, so severe water quality impairments could have serious effects,” Sinha explained.