2020 Dead Zone Update

Overall, the total volume of the 2020 Dead Zone in the Chesapeake Bay was the second lowest since 1985 and was estimated to be considerably lower than in the Last several years. The “Dead Zone” of the Chesapeake Bay refers to a volume of hypoxic water that is characterized by dissolved oxygen concentrations less than 2 mg/L, which is too low for aquatic organisms such as fish and blue crabs to thrive.

If your will recall, in mid-June, the EPA Chesapeake Bay Program, United States Geological Survey, University of Maryland Center for Environmental Science and University of Michigan scientists released their prediction for slightly smaller than average 2020 Dead Zone. This prediction was based on slightly less than average water and nitrogen flows into the bay from January – May 2020. The actual Dead Zone was smaller than they predicted.

At various times each summer the Maryland Department of Natural Resources measures the dissolved oxygen in the Maryland portion of the Chesapeake Bay main stem and the size of the Dead Zone. While the Virginia Institute of Marine Science (VIMS), Anchor QEA and collaborators at UMCES, operate a real-time three-dimensional hypoxia forecast model using input of that predicts daily dissolved oxygen concentrations throughout the Bay (www.vims.edu/hypoxia) using the National Weather Service wind monitoring data.

"The average hypoxic volume of the eight 2020 summer cruiseswas 0.63 cubic miles, compared to a historical summer average from 1985-2019 of0.84 cubic miles. During 2020, every cruise except the one in late July hadbetter than average oxygen conditions for its time period. The most recentmonitoring cruise conducted in September found no hypoxic waters in theMaryland mainstem of the Chesapeake Bay. "The September cruise normally occurs mid-month but was delayed a week due to several days of high winds which, along with cool September temperatures, contributed to the increase in oxygen in the deeper bay waters. Similarly, no hypoxia was observed in Virginia Chesapeake Bay mainstem waters in September. 

Crabs, fish, oysters, and other creatures in the Chesapeake Bay require oxygen to survive. Scientists and natural resource managers study the volume and duration of bay hypoxia to determine possible impacts to bay life. Each year from May to September, the Maryland Department of Natural Resources computes these volumes from data collected by Maryland and Virginia monitoring teams during twice-monthly monitoring cruises. Data collection is funded by these states and the Environmental Protection Agency’s Chesapeake Bay Program. Bay hypoxia monitoring continues throughout the year.

From the VMIS 2020 Bay Report Card:

“Springtime nitrogen inflows in 2020 were 17% below the long-term average, resulting in the prediction that the amount of hypoxia would similarly be slightly less than average... cool windy weather helped mix and aerate Bay water in the spring, resulting in hypoxia beginning later than in previous years. As summer arrived, weak winds and very high temperatures allowed hypoxia to increase considerably, resulting in a very large dead zone in late July... In 2020, hypoxia decreased quickly in early August in response to Hurricane Isaias; however, hypoxia returned in early September until stronger winds and cooler temperatures prevailed, ending hypoxia in the mainstem of the Bay earlier than in previous years. Overall, the total amount of hypoxia in 2020 was estimated to be considerably lower than in the recent past, with hypoxia both starting later and ending earlier, as was also seen in periodic ship based observations of dissolved oxygen.”

Despite the fact that the rain fall was above average in the region, and an extended heat wave struck the area in July the hypoxia was below average. This could be an indication that the Chesapeake Bay pollution diet is working, or an indication that the large number of storm that passed through the region bringing strong winds and cooler temperature were the controlling factor.

2020 Dead Zone Summer Update

The “Dead Zone” of the Chesapeake Bay refers to a volume of hypoxic water that is characterized by dissolved oxygen concentrations less than 2 mg/L, which is too low for aquatic organisms such as fish and blue crabs to thrive. Within the hypoxic area life of the bay dies and a “Dead Zone” forms. The Chesapeake Bay experiences hypoxic conditions every year, with the severity varying from year to year, depending on nutrient and freshwater flows into the bay, wind, and temperature.

In mid-June, the EPA Chesapeake Bay Program, United States Geological Survey, University of Maryland Center for Environmental Science and University of Michigan scientists released their prediction for slightly smaller than average 2020 Dead Zone. This prediction was based on slightly less than average water and nitrogen flows into the bay from January – May 2020.

At various times each summer the Maryland Department of Natural Resources measures the dissolved oxygen in the Maryland portion of the Chesapeake Bay main stem and the size of the Dead Zone. While the Virginia Institute of Marine Science (VIMS), Anchor QEA and collaborators at UMCES, operate a real-time three-dimensional hypoxia forecast model using input of that predicts daily dissolved oxygen concentrations throughout the Bay (www.vims.edu/hypoxia) using the National Weather Service wind monitoring data.

The peak of oxygen depletion typically occurs in July or August. Water temperatures are highest during these months and the days are longest accelerating the growth of phytoplankton that ultimately consumes all the dissolved oxygen. The dead zone is typically gone by late fall. Cooler air temperatures at that time of year chill the surface waters, while the deeper water remains warm and allows more mixing of the layers during storms. Cooler water also will hold more oxygen. The size and shape of the dead zone is variable from month to month during the summer.

From VIMS

This year our region experienced a long heat wave in July. The hot and still conditions were ideal for promoting hypoxia and resulted in an expanding Dead Zone throughout the month. Warmer waters hold less oxygen, and warmer surface waters can create a barrier to oxygen mixing into deep waters of the bay.

From VIMS

Hypoxia started later in the summer than in other recent years, peaked in late July, and decreased quickly with the passing of Hurricane Isais whose winds stirred up the Chesapeake Bay near the beginning of August. The outlook for the rest of the season changed with the increase in tropical storm activity impacting our area. Isais was followed by Laura. .

In the fall of each year, the Virginia Institute of Marine Science and Anchor QEA release a retrospective seasonal analysis of the severity of hypoxia in the Chesapeake Bay. The Annual Chesapeake Bay Hypoxia Report Card summarizes dissolved oxygen concentrations in the Bay as estimated by the team's 3-D, real-time hypoxia forecast model. We should see that report in two to three months. The modeling team also generates the same dissolved oxygen statistics for previous years for comparative purposes you can look at the past few years below.

In 2019, hypoxia decreased quickly in late August and early September due to the winds of Hurricane Dorian; however, the Dead Zone returned with the high temperatures in late September and early October until strong winds mixed the Bay water and ended the Dead Zone in the mainstem of the Bay for the year. Overall, the total amount of hypoxia in 2019 was estimated to be on the high end of the normal range for 1985 to 2018, and higher than in the recent past (see above); and as in 2018, hypoxia also lasted longer than in other recent years.

The Chesapeake Bay Gets a C- Overall Health is Improving

For the past seven years the University of Maryland Center for Environmental Science has issued a report card for the Chesapeake Bay, evaluating the environmental health of the estuary. In the past the grade was based on three water quality indicators and three biotic indicators, which had then been averaged into an overall Bay Health Index and grade. This year the method was changed.  Total nitrogen and total phosphorus load (important indicators form the U.S. Environmental Protection Agency (EPA) mandated Chesapeake Bay total maximum daily load of those nutrients) were added and phytoplankton (whose growth in excess is a major contributing factor to the summer dead zone) was eliminated. In addition, each of what are now seven indicators is weighted equally in measuring the health of the Chesapeake Bay. Part of the reason for the change was the data collected under the EPA mandate does not include phytoplankton. According to the scientists and their grading scale we got a “C”. The overall health of Chesapeake Bay improved from 2011 to 2012. In 2011 the overall grade was a 40%, and now is 47%.

From 2012 Chesapeake Bay Report Card

One drawback of the annual reporting framework is the lack of context- an indication of whether Bay health is improving or getting worse. Now with this change in the grading method looking back is more important than ever. This year, Professor Bill Dennis and the other researcher of the University of Maryland Center for Environmental Science have graded all 15 reporting regions of the Chesapeake Bay for the years 1986 to 2011 to look for trends in the data using a consistent methodology. Four out of the fifteen regions had a significantly improving trend. The four reporting regions with significantly improving trends were the Upper Western Shore, Upper Bay, James River and Elizabeth River. One region, the York River, showed a slightly improving trend, although it was not statistically significant. Unfortunately, the MidBay with moderate ecosystem health (its overall grade is a C) is the onlyregion with a declining health trend since 1986 that seemed to be driven by declinesin benthic community and aquatic grasses despite improvements in water clarityand total nitrogen load.  

The organisms that live at the bottom of the Chesapeake Bay and its streams and rivers like clams, worms, oysters and mussels are examples of benthic organisms. Scientists believe that the health of the benthic community organisms provide a good snapshot of environmental conditions in the Bay and its streams and rivers. Most benthic creatures are fairly stationary and reflect pollution or unhealthy water conditions in particular locations. Benthic communities are exposed to many stressors, including low oxygen levels caused by excess growth of phytoplankton, excess sediment and chemical contaminants. Some reasons that the benthic community would be poor are:

• In summer, high temperatures and nutrient pollution often lead to low-oxygen areas at the bottom of the Bay and its rivers.
• Excess sediment suspended in the water can block sunlight from reaching bay grasses growing at the bottom. When sediment finally settles, it can bury oyster bars and other benthic species.
• Many chemical contaminants that are not part of the Chesapeake Bay pollution diet concentrate and bind to bottom sediments, remaining there for years. Benthic species become contaminated when they feed and live in these toxic sediments.
• Heavy spring rains particularly those associated with flash floods are generally responsible for high nutrient runoff and earlier and larger dead zones in the mid Bay’s tidal waters. This usually results in greater degradation in the benthic community. The 2012 dead zone was the 2nd smallest since 1985 and has been followed by the prediction that the 2013 dead zone will be smaller than average this summer. Professor Bill Dennis of the University of Maryland Center for Environmental Science attributes this smaller dead zone to the cool and relatively dry spring followed by late arriving rains. Yet even with this good news, the mid bay region has deteriorated. 
  

2013 Dead Zone

The NOAA-funded forecast, for the Chesapeake Bay, calls for a smaller than average dead zone in the nation's largest estuary this summer. Professor Bill Dennis of the University of Maryland Center for Environmental Science attributes this smaller dead zone to the cool and relatively dry spring followed by late arriving rains. The spring load of nutrients into the bay was light and locked in a lighter load of nutrients in the water layers within the Chesapeake Bay for the summer. The forecast is based to a large extent on the quantity and timing of rainfall in the Chesapeake Bay watershed, but the overall health of the Chesapeake Bay is also a contributing factor. So, there is hope that this forecast also reflects that the overall condition of the bay may be improving.

Dead zones have become a yearly occurrence in the Chesapeake Bay and other estuaries. Dead zones form in summers when higher temperatures reduce the oxygen holding capacity of the water, the air is still and especially in years of heavy rains that carry excess nutrient pollution from cities and farms. The excess nutrient pollution combined with mild weather encourages the explosive growth of phytoplankton, which is a single-celled algae. While the phytoplankton produces oxygen during photosynthesis, when there is excessive growth of algae the light is chocked out and the algae die and fall from the warmer fresh water into the colder sea water. The phytoplankton is decomposed by bacteria, which consumes the already depleted oxygen in the lower salt level, leaving dead oysters, clams, fish and crabs in their wake.

In a wedge estuary such as Chesapeake Bay where the layers of fresh and salt water are not well mixed, there are several sources of dissolved oxygen. The most important is the atmosphere. At sea level, air contains about 21% oxygen, while the Bay’s waters contain only a small fraction of a percent. This large difference between the amount of oxygen results in oxygen naturally dissolving into the water. This process is further enhanced by the wind, which mixes the surface of the water. Scientists are still studying the impact of the winds in delivering oxygen to various water layers. The other important sources of oxygen in the water are phytoplankton and aquatic grasses which produce oxygen during photosynthesis, but when they die consume oxygen during decomposition by bacteria. Finally, dissolved oxygen flows into the Bay with the water coming from streams, rivers, and the Atlantic Ocean.

From USGS

Stream flow into the Chesapeake Bay is currently at “normal” levels after a relatively dry early spring. Overall, data from the U.S. Geological Survey, USGS, shows that the dry years of 2000-2004 are behind us and we may be entering a wet period. The Chesapeake Bay Program in partnership with USGS, monitors stream flow, nutrients and sediment in the rivers throughout the Chesapeake Bay watershed. There are 85 sites in the network; currently being monitored; however, only 31 of these sites have enough long-term data to be used to forecast trends. In the mid-1980s, the Chesapeake Bay Program (CBP), a partnership between the Commonwealths of Pennsylvania and Virginia, the State of Maryland, the District of Columbia, the Federal Government, and the Chesapeake Bay Commission, began efforts to reduce nutrients and sediments in the bay. Improvement in water-quality conditions in the bay has been slower than promised; however, and the U.S. Environmental Protection Agency, EPA, stepped in to put the entire region on a pollution diet. The Chesapeake Bay pollution diet, the Total Maximum Daily Load (TMDL) was mandated by the EPA to the six Chesapeake Bay Watershed states and the District of the Columbia. TMDLs for nitrogen, phosphorus and sediment were assigned by the EPA to each segment of the Chesapeake Bay Watershed in all six Chesapeake Bay watershed states.

Dead zones have become common summer events caused by man, human waste, and the waste and excess nutrients from agriculture necessary to feed us and ornamental gardens to please us. It has be predicted by Researchers from Texas A&M University that the Gulf of Mexico dead zone currently estimated at 3,300 square miles will exceed the typical summer average of 5,600 square miles. The scientists are predicting more than 9,400 square miles of dead zone in the coastal waters of the estuary due to the heavy rains in the upper  Mississippi that flooded fields and towns during the spring carrying with the flood waters the excess nutrients from farms, yards, septic systems and sewage treatment plants in its wake. The Gulf of Mexico Dead Zone is not expected to peak until late August.

From IAN UMCES source of nitrogen pollution in Chesapeake