August 16, 2022
Enlarge / Satellite photo of an algal bloom in western Lake Erie, July 28, 2015.

Midsummer is the time for forecasts of the size of this year’s “dead zones” and algal blooms in major lakes and bays. Will the Gulf of Mexico dead zone be the size of New Jersey, or only as big as Connecticut? Will Lake Erie’s bloom blossom to a human health crisis, or just devastate the coastal economy?

We are scientists who each have spent almost 50 years figuring out what causes dead zones and what it will take to resuscitate them and reduce risks of toxic blooms of algae. Researchers can forecast these phenomena quite well and have calculated the nitrogen and phosphorus pollution cuts needed to reduce them.

These targets are now written into formal government commitments to clean up Lake Erie, the Gulf, and the Chesapeake Bay. Farmers and land owners nationwide received $30 billion to support conservation, including practices designed to reduce water pollution, from 2005 to 2015, and are scheduled to receive $60 billion more between 2019 and 2028.

But these efforts have fallen short, mainly because controls on nutrient pollution from agriculture are weak and ineffective. In our view, there is no shortage of solutions to this problem. What’s needed is technological innovation and stronger political will.

The Gulf of Mexico hypoxic (dead) zone in 2021, which measured 6,334 square miles (16,400 square kilometers). Lower values represent less dissolved oxygen in the water.
Enlarge / The Gulf of Mexico hypoxic (dead) zone in 2021, which measured 6,334 square miles (16,400 square kilometers). Lower values represent less dissolved oxygen in the water.

Problems return to Lake Erie

State and federal agencies have known since the 1970s that overloading lakes and bays with nutrients generates huge blooms of algae. When the algae die and decompose, they deplete oxygen in the water, creating dead zones that can’t support aquatic life. But in each of these “big three” water bodies, efforts to curb nutrient pollution have been slow and halting.

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The US, Canada, and cities around Lake Erie started working to reduce phosphorus pollution in the lake from domestic and industrial wastes in 1972. Water quality quickly improved, dead zones shrank and harmful algal blooms became less frequent.

But the scourges of low-oxygen waters and sometimes-toxic algae reappeared in the mid-1990s. This time, the source was mostly runoff from farm soils saturated with phosphorus from repeated applications of fertilizer and manure. Climate change made matters worse: Warmer waters hold less oxygen and cause faster growth of algae.

Phosphorus loads to Lake Erie, 1967-2001. Non-point sources are wide areas without a distinct discharge point, such as farm fields.

Phosphorus loads to Lake Erie, 1967-2001. Non-point sources are wide areas without a distinct discharge point, such as farm fields.

Slow progress in the Chesapeake Bay

Nitrogen and phosphorus reach the Chesapeake Bay from sources including wastewater treatment plants; air pollution emitters, such as factories and cars; and runoff from urban, suburban, and agricultural lands. In 1987 the federal government and states around the bay agreed to reduce these flows by 40 percent by the year 2000 to restore water quality. But this effort relied on voluntary action and failed to make much progress.

In 2010 the states and the US Environmental Protection Agency entered a legally binding commitment, to reduce pollutant loads below prescribed maximum levels needed to restore water quality. If the states make inadequate progress, the EPA can limit or rescind their permitting authority, and the states may lose federal funding.

Nitrogen and phosphorus pollution has been reduced primarily by tightening permit requirements and upgrading wastewater treatment plants. Air pollution controls for power plants and vehicles have also reduced nitrogen reaching the bay. Water quality has improved, and the yearly dead zone has shrunk modestly.

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But with the commitment’s 2025 deadline nearing, nitrogen loads have been reduced by less than 50 percent of the targeted amounts, phosphorus by less than 64 percent. Most of the remaining pollution comes from farm runoff and urban stormwater. Intensifying agriculture in rural areas and sprawl in urban areas are counteracting other cleanup efforts.