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Bay Grasses Decline to Lowest Levels in More than a Quarter Century

Bay grassesUnderwater grasses in the Chesapeake Bay declined last year to the lowest levels in more than a quarter century, in part because of storms in 2011 that flushed runoff pollution into the estuary, according to scientists with the Chesapeake Bay Program. Global warming is also cooking a temperature-sensitive species of grass in the southern Bay.

Bay grasses declined 21 percent, to 48,191 acres, between 2011 and 2012, Dr. Robert Orth, an aquatic vegetation expert and Professor of Marine Science at the Virginia Institute of Marine Science, said during a press conference this morning.

Chesapeake Bay Foundation President Will Baker said the decline is a sobering reminder that extreme weather can set back recovery of the Bay. He said it is also a reminder that we need to focus on the elements we can control, especially reducing pollution to the Bay.

“In 2012, underwater grasses suffered a one-two punch,” Baker said. “Extreme heat in 2010 led to a significant decline in grasses in the lower Bay in 2011. And 2011 was a very wet year, beginning with heavy spring rains and ending with Hurricane Irene and Tropical Storm Lee, creating poor conditions for growth in 2012.”

An accurate picture of the Bay’s health is more complex than just the grass numbers, with improvements recently in other areas. The Chesapeake last year experienced the smallest low-oxygen “dead zone” since 1985. Oysters are showing improved resiliency, and striped bass are at significantly higher levels now than during the 1970s and early 1980s.

Dr. Orth and Lee Karrh, Senior Biologist at the Maryland Department of Natural Resources and chair of the Chesapeake Bay Program’s Submerged Aquatic Vegetation Work Group, said the solution to the recent problems with the Bay grasses is for regional governments to reduce pollution to meet EPA pollution limits for the estuary. These limits (also called the Bay “Total Maximum Daily Load” or TMDL) require the implementation of state plans to reduce pollution that are a blueprint for saving the Bay.

“The TMDL is the elephant in the room,” said Dr. Orth. “And how to deal with (the EPA pollution limits) on a local basis is what everyone is talking about.”

Karrh agreed. “The best thing we can do is to improve water quality,” to restore the Bay’s grasses, he said.

According to the Bay Program scientists, a species of aquatic vegetation common in the southern bay -– eelgrass -– is being killed by warming Bay waters caused by climate change. Eelgrass requires relatively cool waters to survive.

Grasses in the lower and middle Bay were subjected to excessively warm waters in the summer of 2010. Poor water clarity –- caused in part by algal blooms likely fed by nitrogen and phosphorus pollution -- since then has kept the grasses from rebounding, according to the Bay Program scientists.

Grasses in two other areas of the Bay showed notable resilience. In the far northern part of the Bay, the grass beds at the mouth of the Susquehanna River remained robust and dense, although they also declined somewhat, according to the Bay Program scientists. In Virginia, grasses in the James River continued to increase.

The Bay Program yesterday unveiled new online maps that people can use to track how underwater grasses have changed in abundance and location over the last three decades. To view it, click here.

By Tom Pelton Chesapeake Bay Foundation

(Photo from Chesapeake Bay Program)

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