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.

The Chesapeake Bay Estuary

According to the US Fish and Wildlife Service, the Chesapeake Bay is the largest of 130 estuaries in the United States. Like all estuaries it is an incredibly complex ecosystem that we are only beginning to understand. Estuaries are productive ecosystems and habitats. The type of habitat is determined by geology, salinity and climate. The Chesapeake Bay serves as a nursery ground for the fish and shellfish industry and protects the coast from storm surges and filters pollution. The estuary filters water that is carrying nutrients and contaminants from the surrounding watershed. The nutrients in proper balance bring fertility, but excess nutrient contamination to the Chesapeake Bay has caused degradation in the habitat. As a result, US EPA has taken control of the situation (despite NOAA’s and the National Estuarine Research Reserve System mission to protect and study US costal estuaries) and has developed a new federally mandated TMDL (total maximum daily load) to try to restore the natural balance in the estuary by controlling nutrients in the local waters. The TMDL allocates a pollution budget among the states which will decrease over time.

About half of the Chesapeake's water volume comes from salt water from the Atlantic Ocean the rest is fresh water from more than 50 rivers and innumerable smaller tributaries within the enormous 64,000-square-mile watershed. As would be expected of this mix of fresh and salt water, the Bay's salinity gradually increases as you move from north to south and will change with rainfall and climate influences. Because salt water is heavier than fresh water, estuaries like Chesapeake Bay contain two layers: a saltier layer that lies on the bottom and a freshwater layer above. Mixing occurs where the two layers meet. Further mixing takes place as a result of wind, tides, temperature changes and rainfall.

Due to the coriolis force (earth’s rotation), one side in the estuary is saltier than the other side. In the Chesapeake Bay this rotation causes salt water accumulate on the Eastern Shore of Maryland, so water tends to be saltier on the eastern side of the Bay at any latitude. Overall, however, the proportions of fresh and salt water in the Bay depend largely on the amount of rainfall that flows out of the Chesapeake's major rivers. During a wet year, the entire Bay will be somewhat fresher than normal, and conversely, a dry year will result in higher-than-average salinities. Salinity is one of the most important physical features in determining what lives in a particular part of the Bay, so plant and animal populations in the Bay differ north to south, west to east, and from year to year. Temperature and bottom sediment also determine the distribution and abundance of organisms.

Estuaries are classified by both geologic events that created them and water circulation. The Chesapeake Bay is a coastal plain estuary also called a drowned river valley. The Chesapeake Bay (and all coastal plain estuaries) was formed at the end of the last ice age. As the glaciers melted and receded, sea level rose and flooded the low lying river valleys. The deep water channel in the Chesapeake Bay is the ancient river bed of the lower Susquehanna. The Chesapeake Bay watershed is characterized by rapidly flowing rivers discharging to the bay where tidal currents are weak. This creates the most stratified or least mixed type of estuary (as classified by water circulation) - a salt-wedge. Fresh water, which is less dense than salt water floats on top of the salt water as it is pushed out to sea by the rivers. A sharp boundary with limited mixing is characteristic of salt wedge estuaries. The location of the wedge boundary varies with weather and tidal conditions.

Estuaries are fragile ecosystems that are very susceptible to disturbances both natural and those created by man. In the United States the ecology of estuaries has been severely damaged by man. Diverting fresh water from tributaries for irrigation and drinking water supplies changes flow, quantity of fresh water entering the estuary, and impacts the balance within the ecology. Excess nutrients and sediment from sewage treatment plants, farm fields and animal pastures, urban and suburban run off from roads and landscaping can cause eutrophication. As the ecosystem of estuaries declines, species die out, coastlines experience excessive erosion by wind, tidal action and ice. It is going to take knowledge, effort and resources (wealth in all forms) to restore the Chesapeake Bay.

Solution to Pollution is Dilution

When I worked at the US EPA in the 1970’s there was a sign on the wall of the adjacent office that said, “The Solution to Pollution is Dilution.” There was both truth and cynicism in that sign. At the time we were determining the likely contaminates in a waste stream and the levels of those contaminants that would be acceptable based on the potential impact to life. The guiding principal of toxicology is that there is a relationship between a toxic reaction (the response) and the amount of poison received (the dose). An important assumption in this relationship is that there is almost always a dose below which no response occurs or can be measured. So if the concentration of the contaminant was low enough there would be no toxic reaction.

In addition, there is another factor that has been observed for generations and studied in the recent decades. The planet is able to filter and heal itself from limited amounts of pollution. There have been numerous studies of groundwater and surface water systems that have documented this. In Dutchess County New York and North Carolina studies documented that the most important factor in septic regulation is controlling nitrogen pollution from septic systems was average density. Both studies demonstrated that density of on-site waste disposal should not exceed one unit per 2-3 acres for an average size house (and household) to ensure water quality. Adequate dilution, soil filtration and time are necessary to ensure sustainable water quality. These studies were performed on nitrate concentrations as a proxy to achieve adequate dilution and natural attenuation of all contaminants.

Historically, horizontal and vertical setbacks for septic systems were developed without consideration of the dilution for wastewater components like nitrate, pharmaceutical residue, caffeine and other substances we humans consume, process or produce. The overall regional density of septic systems was examined to ensure that groundwater resources would not be overwhelmed by the total load of contaminants. The density recommendations were developed based on the nitrate concentration in traditional septic wastewater. Nitrate was used as a proxy because all humans produce about 10 pounds of nitrate per year, it does not easily break down and there is a drinking water standard and an inexpensive analytical test. Dilution was really the goal here.

An estuary is a coastal area where freshwater from rivers and streams mix with saltwater from the ocean. Estuaries are protected from the full force of the ocean by mudflats, sandspits and barrier islands. One of the least appreciated functions of estuaries is to help control pollution. Water from upland areas often carries sediment and pollutants. The marshy land and plants in estuaries filter these pollutants out of the water. The plants in estuaries help prevent shoreline erosion. Estuaries also protect inland areas from flooding and storm surges. When a storm hits, estuaries often absorb water from the storm before it can reach upland areas. The Chesapeake Bay is an estuary. Right now we are engaged in a major effort to reduce the nitrogen, phosphorus, and sediment pollution that enters the estuary through its tributaries in an attempt to restore the estuary to some arbitrary historic state.

The Chesapeake Bay and its tidal waters are impaired by the release of excess nitrogen, phosphorus and sediment. These pollutants are released from waste water treatment plants, from agricultural operations, urban and suburban runoff, wastewater facilities, air pollution and other sources, including septic systems that enter the tributaries and Chesapeake Bay. These pollutants cause algae blooms that consume oxygen and create dead zones where fish and shellfish cannot survive, block sunlight that is needed for underwater grasses, and smother aquatic life on the bottom. Over the past quarter century the excess nutrient contamination to the Chesapeake Bay has decreased, primarily because of regulation of wastewater treatment plants and improved farm practices, but the Bay’s waters remain seriously degraded.

The “strict pollution diet” that EPA is imposing on the six Chesapeake Bay Watershed states only addresses nitrogen, phosphorus and sediment it does not address other contaminants that have been noted in the tributary waters by the US Geological Survey. The USGS began looking into skin lesions on bass in the southern branch of the Potomac River. Some fish had bacterial lesions, some fungal lesions, and some fish had parasite. The USGS concluded that there was no specific cause of the lesions and that the fish appeared to be immunosupressed so that any pathogen in the water could attack the fish. A series of studies were performed over a period of years and it was discovered that the bass suffering from lesions were intersexed. This prompted further sampling of the river that identified higher concentrations of wastewater chemicals near the wastewater plants. Pesticides currently used in agriculture were detected at all locations sampled and traces of estrogenic endocrine-disrupting chemicals were found at all locations examined though their source is not yet known. Though they cannot identify a single chemical or group of chemicals responsible, USGS have embarked on further study to gain greater understanding of the implications to the earth’s ecosystem.