Record rainfall degrades Chesapeake Bay’s waters, but not as much as scientists thought

The Chesapeake Bay, the nation’s largest estuary, is a little less healthy than it used to be.

Record rainfall upset the salinity balance and caused more pollutants to run off into the water, but newly-released results aren’t as bad as scientists expected.

More than one-third of the bay and its tidal tributaries met clean water standards for clarity, oxygen and algae growth between 2016 and 2018, according to the Chesapeake Bay Program. The goal is to reach 100% dissolved oxygen in the water.

Newly-released measurements taken during the three-year period indicate 38% of the bay has sufficient oxygenation. That rating is down from 42% at last count.

“When we say 38% … when you look at the bay as a whole, 38% of the bay has enough oxygen for the fish now. Thankfully, most of that oxygen is in the upper part of the bay waters. There, we are doing OK. It’s the lower part of the waters, the deeper waters, where we don’t have enough oxygen,” said Scott Phillips, Chesapeake Bay program coordinator for the U.S. Geological Survey.

While the score is lower than the record-high 42% from the previous reporting period, it is the fifth-highest estimate of water quality standards attainment since 1985, the Chesapeake Bay Program said. The Chesapeake Bay Program said for Chesapeake Bay and its tidal tributaries to function as a healthy ecosystem, water quality must improved in 62% of the bay.

In 2018, Phillips said the Washington-Baltimore region received 60 inches of rain, up significantly from the average 40 inches for the year.

“We had a record amount of rainfall in 2018 which washed more pollution into the bay. So, we thought our water quality indicators were actually going to be worse than just a 4% drop,” Phillips said.

The focus is to try and reduce the amount of suburban and agricultural runoff. However, during years with heavy rain, scientists expect more rain will mean more runoff into Chesapeake Bay.

Water quality is influenced by nitrogen, phosphorus and sediment. Algae blooms that lead to low-oxygen dead zones in the Chesapeake Bay’s deep waters are fueled by nitrogen and phosphorus. Dead zones are where no aquatic life can survive. Sediment keeps sunlight from reaching underwater grasses where shellfish live.

Phillips said 2019 was also a particularly wet year, indicating the bay’s health score may not increase in the immediate future.

The changes in the bay’s water quality affects its ecosystem, and of course, those living in it.

“A 4% difference is not going to have a large impact in the amount of fish we can catch, the or the amount of crabs we can harvest,” he said.

With a rush of freshwater, though, the balance of saltwater in the bay was disturbed.

“And so in some cases, oysters, which require a certain amount of salt, died off. Crabs moved to different parts of the bay because they like certain salt levels. So it really affected where the fish and crabs were located, versus if they survived the lower dissolved oxygen conditions,” he said.


Megan Cloherty

WTOP Investigative Reporter Megan Cloherty primarily covers breaking news, crime and courts.

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