The large dead zone in the northern Chesapeake is the product of a chain reaction that began with months of heavy rain. Hot weather and calm winds this summer only helped build the monster in the Chesapeake in 2019. Besides the dead zone, there was an extreme drop in salinity that is only just beginning to reverse.
Nobody really likes to say it, but the health of the bay relies a lot on the weather. That’s why it’s critical to reduce the amount of nutrients spread across farm fields or released from overwhelmed sewage treatment plants.
The multistate bay pollution “diet” still has a 2025 deadline.
All of those ecological imbalances add stress on species already challenged by poor water quality.
Since flooding rains began in the late spring of 2018, the ecosystem has been stressed.
The dead zone occurs every summer, trapped in the bay’s waters from around the Bay Bridge south to the mouth of the Potomac. It’s largest down the bay’s middle, but it can also flow into deeper channels of the Choptank, Potomac and other tributaries.
The dead zone begins with winter and spring rain, washing fertilizers and sewage into waterways. Those nutrients feed algae blooms that slurp up sunlight from aquatic grasses growing at the bottom. The blooms decomposition process also uses up oxygen stored in the water.
As ugly as the dead zone is, low salinity from heavy rains is also a big problem. North of the Bay Bridge, there have been reports of oysters killed by low salinity. And around much of the bay, water has only recently become salty enough to plant oyster larvae on wild oyster beds. The unusually fresh water has also allowed invasive blue catfish, which feast on oysters and juvenile crabs to gain a stronger foothold.
Grasses had to weather a surge of rainwater that scoured some beds. Bay-wide grass surveys this summer suggest saltwater grasses are still struggling.