Scientists expect the Chesapeake Bay to see a slightly smaller than average dead zone this summer, due to reduced rainfall and less nutrient-rich runoff flowing into the Bay from the Susquehanna River this spring.
Dead zones are areas of little to no dissolved oxygen that form when nutrient-fueled algae blooms die and decompose. Resulting low-oxygen conditions can suffocate marine life. The latest forecast predicts an early-summer no-oxygen zone of 0.27 cubic miles, a mid-summer low-oxygen zone of 1.37 cubic miles and a late-summer no-oxygen zone of 0.28 cubic miles. This forecast, funded by the National Ocean and Atmospheric Administration (NOAA), is based on models developed at the University of Maryland Center for Environmental Science and the University of Michigan.
Nutrient pollution and weather patterns influence dead zone size. According to the U.S. Geological Survey (USGS), 58 million pounds of nitrogen entered the Bay in the spring of 2015, which is 29 percent lower than last spring’s nitrogen loadings.
Researchers with the Maryland Department of Natural Resources (DNR) and the Virginia Department of Environmental Quality (DEQ) will measure oxygen levels in the Bay over the next few months. While the final dead zone measurement will not take place until October, bimonthly updates on Bay oxygen levels are available through DNR’s Eyes on the Bay.
During summer months, Chesapeake Bay waters become home to a range of bacteria. One of the most talked-about bacteria is Vibrio, which occurs naturally in warm estuarine waters and can infect those who eat contaminated shellfish or swim with open wounds in contaminated waters. But illness can be avoided. Learn about the bacteria—and how to avoid infection—with this list of five Vibrio facts.
Image courtesy CDC/Wikimedia Commons
1. Vibrio is a naturally occurring bacteria. There are more than 80 species of Vibrio, which occur naturally in brackish and saltwater. Not all species can infect humans, but two strains that can have raised concern in the Bay watershed: Vibrio vulnificus and Vibrio parahaemolyticus. The bacteria are carried on the shells and in the bodies of microscopic animals called copepods.
2. The presence of Vibrio in surface waters is affected by water temperature, salinity and chlorophyll. Because Vibrio prefers warm waters, it is not found in the Bay during winter months. Instead, it is common in the summer and early fall. When water temperatures are warm, algae blooms form, fed by nutrients in the water. These blooms feed the copepods that carry the Vibrio bacteria. When the copepods die, Vibrio bacteria are shed into the water. As climate change increases the temperature of the Bay, both algae blooms and Vibrio could persist later in the season.
3. Vibrio infections can occur in people who eat raw or undercooked shellfish or who swim with open wounds or punctures in contaminated waters. While infections are rare, they do take place and can be particularly dangerous for people with compromised immune systems. The ingestion of Vibrio can cause vomiting, diarrhea and abdominal pain, and in some cases can infect the bloodstream. If an open wound or puncture comes into contact with the bacteria, the area around the wound can experience swelling, redness, pain, blistering and ulceration of the skin.
4. Infection can be avoided. To avoid Vibrio infection, follow these tips:
5. Vibrio symptoms can start 12 to 72 hours after exposure. If you think you’ve been infected with Vibrio, seek medical attention. Make sure to let your doctor know that you have eaten raw or undercooked shellfish or crabs or have come into contact with brackish or saltwater.
The R/V Rachel Carson is docked on Solomons Island. At 81 feet long, the red and blue research vessel stands out against the deadrise workboats that share the Patuxent River marina. Her mission today is to lead researchers from the University of Maryland Center for Environmental Science (UMCES) to the Chesapeake Bay’s dead zone.
Every summer, this so-called “dead zone” forms in the main stem of the Bay. The area of low-oxygen water is created by bacteria as they feed on algae blooms growing in nutrient-rich water. The dead zone persists through the warm summer months because the Bay is stratified into two layers: a surface layer of lighter, fresher water that mixes with the atmosphere, and a bottom layer of denser, saltier water, where oxygen depletion persists. These layers won’t mix until the cooler temperatures of autumn allow the surface waters to sink.
To find the dead zone, Director of Marine Operations and Rachel Carson Captain Michael H. Hulme takes us to one of the deep troughs that run down the center of the Bay. Geologic remnants of the ancient Susquehanna River, these troughs can reach up to 174 feet deep in an estuary whose average depth is just 21 feet. Hulme anchors offshore of Calvert Cliffs State Park.
The boat is equipped with a dynamic positioning system, which holds it in place regardless of wind or waves. This allows the captain to step away from the helm and offer his hands on deck. “Being able to hover over that [specific] latitude and longitude is what makes the Rachel Carson so unique,” said Hulme. It’s also one of the reasons the vessel is so useful to scientists, who often return to the same sampling site again and again over time.
UMCES Senior Faculty Research Assistant David Loewensteiner drops a CTD overboard. The oceanography instrument takes eight measurements per second, tracking conductivity, temperature and depth as it is lowered through the water. Connected to the ship with a cable, the CTD sends data to a laptop in the boat’s dry lab. We measure 2.04 mg/L of dissolved oxygen in surface water, and just 0.33 mg/L at 98 feet deep. Critters need concentrations of 5 mg/L or more to thrive; these are “classic dead zone” conditions.
Dead zones are bad for the Bay. Like animals on land, underwater critters need oxygen to survive. In a dead zone, immobile shellfish suffocate and those fish that can swim are displaced into more hospitable waters. “If you were a self-respecting fish and oxygen was [low], what would you do?” asked Bill Dennison, Vice President for Science Applications and Professor at UMCES. “Swim away.”
First reported in the 1930s, the appearance of the dead zone in the Bay is linked to our actions on land: as we replace forests with cities, suburbs and farms, we increase the amount of nutrients entering rivers and streams. This fuels the growth of algae blooms that lead to dead zones. “Hypoxia [or low-oxygen conditions] is driven by what we do on the watershed,” said UMCES Assistant Professor Jeremy Testa. “The Bay is naturally set up to generate hypoxia because of that [stratification] feature. That said… when there were no people here, there was not much hypoxia.”
While it is our actions on land that created the dead zone, it is our actions on land that can make the dead zone go away. Research has shown that certain pollution-reducing practices—like upgrading wastewater treatment plants, lowering vehicle and power plant emissions and reducing runoff from farmland—can improve the health of local rivers and streams. Scientists have also traced a decline in the duration of the dead zone from five months to four, which suggests that conservation practices gaining traction across the watershed could have very real benefits for the entire Bay.
To view more photos, visit the Chesapeake Bay Program Flickr page.
Images by E. Guy Stephens/Southern Maryland Photography. Captions by Catherine Krikstan.
Scientists expect the Chesapeake Bay to see an above-average dead zone this summer, due to the excess nitrogen that flowed into the Bay from the Potomac and Susquehanna rivers this spring.
Dead zones, or areas of little to no dissolved oxygen, form when nutrient-fueled algae blooms die and decompose. The latest dead zone forecast predicts an early-summer oxygen-free zone of 0.51 cubic miles, a mid-summer low-oxygen zone of 1.97 cubic miles and a late-summer oxygen-free zone of 0.32 cubic miles. This forecast was funded by the National Oceanic and Atmospheric Administration (NOAA) and is based on models developed at the University of Maryland Center for Environmental Science (UMCES) and the University of Michigan.
Dead zone size depends on nutrient pollution and weather patterns. According to the U.S. Geological Survey (USGS), 44,000 metric tons of nitrogen entered the Bay in the spring of 2014. This is 20 percent higher than last spring’s nitrogen loadings, and will influence algae growth and dead zone formation this summer.
Researchers with the Maryland Department of Natural Resources (DNR) and the Virginia Department of Environmental Quality (DEQ) will measure oxygen levels in the Bay over the next few months. While a final dead zone measurement is not expected until October, DNR biologists measured a larger-than-average low-oxygen zone on their June monitoring cruise, confirming the dead zone forecast.
The duration of the Chesapeake Bay’s annual “dead zone” has declined over time, according to research published last month in the scientific journal “Limnology and Oceanography.”
First reported in the 1930s, the Bay’s dead zone, or conditions of low dissolved oxygen also known as hypoxia, results from excess nutrients, which fuel the growth of algae blooms. As these blooms die, bacteria decompose the dead algae. This decomposition process removes oxygen from the surrounding waters faster than it can be replenished, suffocating marine life. While intensified agriculture and development continue to push nutrients into rivers and streams, research by Yuntao Zhou and others shows the duration of the Bay’s dead zone decreased from five months to four months between 1985 and 2010, and the end of the hypoxic season moved up from October to September. This could suggest that efforts to manage nutrient loads—through upgrades to wastewater treatment plants, cuts to vehicle and power plant emissions and reductions to runoff from farmland—are working.
This same research showed no change in the average onset of the Bay’s dead zone or for its average volume, whose peak has moved from late to early July. In other words, while the duration of the Bay’s dead zone has declined, its size and severity have not.
While Zhou points out that nutrient pollution is the foremost factor that fuels the development of our dead zone, his research also shows that weather patterns can act as an additional driver. Northeasterly winds, for instance, can create conditions that reinforce the separation between the Bay’s fresh and saltwater, leading to larger hypoxic volumes.
The Chesapeake Bay’s dead zone measured near average in size this past summer, coming close to scientists’ June prediction of a smaller than average hypoxic zone in the nation’s largest estuary.
Dead zones, or areas of little to no dissolved oxygen, form when nutrient-fueled algae blooms die. The bacteria that aid in algae bloom decomposition suck up oxygen from the surrounding waters. The resulting hypoxic or anoxic conditions can suffocate marine life, shrinking the habitat available for fish, crabs and other critters.
Each summer, the Maryland Department of Natural Resources (DNR) and the Virginia Department of Environmental Quality (DEQ) collect water samples to measure the hypoxic volume of the Bay. Since 1983, this number has ranged from 15.3 to 33.1 percent. In 2013, it measured 22.1 percent: 5.6 percent higher than the previous year and just above the 21.9 percent average.
Dead zones are impacting the distribution and abundance of fish that live and feed near the bottom of the Chesapeake Bay, according to new research from the Virginia Institute of Marine Science (VIMS).
Dead zones, or areas of little to no dissolved oxygen, form when nutrient-fed algae blooms die and decompose, and are most pronounced in the deep waters of the Bay’s mainstem during warm summer months. During a decade-long study of the bottom-feeding fish that inhabit this portion of the Bay’s water column, scientists noticed drastic declines in species richness, diversity and catch rate as dead zones restricted habitat and displaced the fish toward more hospitable waters.
So-called “demersal” fish—which include Atlantic croaker, white perch, spot, striped bass and summer flounder—avoid dead zones because a lack of oxygen can place stress on their respiratory and metabolic systems. While the fish often return to their former habitat when oxygen levels improve, dead zones can also wreak havoc on their forage grounds, stressing or killing the bottom-dwelling invertebrates the fish need for food.
“Once oxygen levels go up, we do see the average catch rate go up,” said Andre Buchheister, Ph.D. student and author of the VIMS study. “That’s a good sign. It indicates that once those waters are re-oxygenated, it’s possible for fish to move back in. But the availability of food is compromised, and studies have shown that the productivity of benthic biomass—or the critters that live in and on the bottom of the Bay—is stressed.”
The impact that demersal fish displacement could have on Bay fisheries is unclear, Buchheister said. Commercial fishermen who work outside of the mainstem might not be affected. But recreational anglers searching for striped bass could struggle if their forced move out of cool, deep waters is shown to contribute to poor health among the population.
In June, a forecast from researchers at the University of Maryland Center for Environmental Science (UMCES) and the University of Michigan predicted a smaller than average dead zone for the coming summer, thanks to lower than average nutrient loads that entered the Bay last spring. But to return the Bay’s mainstem to its former health, “one or two good summers won’t make that much of a difference,” said Buchheister. Instead, benthic habitat must be rebuilt, as long-term improvements boost Bay health from the bottom up.
Images courtesy Virginia Institute of Marine Science (VIMS)
Dead zones, or areas of little to no dissolved oxygen, form when nutrient-fueled algae blooms die. As bacteria help these blooms decompose, they suck up oxygen from the surrounding waters. The resulting hypoxic or anoxic conditions can suffocate marine life.
The Chesapeake Bay Program tracks dissolved oxygen as an indicator of water quality and Bay health.
The latest NOAA-funded forecast from researchers at the University of Maryland Center for Environmental Science (UMCES) and the University of Michigan predicts an average summer hypoxic zone of 1.108 cubic miles, lower than last year’s mid-summer hypoxic zone of 1.45 cubic miles.
This predicted improvement should result from the lower than average nutrient loads that entered the Bay this spring. According to the U.S. Geological Survey (USGS), 36,600 metric tons of nutrients entered the estuary from the Potomac and Susquehanna rivers, which is 30 percent lower than average.
The Bay’s dead zones are measured at regular intervals each year by the Maryland Department of Natural Resources (DNR) and the Virginia Department of Environmental Quality. While the final dead zone measurement will not take place until October, DNR biologists measured better than average dissolved oxygen on its June monitoring cruise, confirming the dead zone forecast.