Welcome to Below the Surface of Monitoring, a series in which we dive deep into the nuances of the Alliance’s Water Quality Monitoring program. Follow along as we take the numbers off of the data sheet and out into the world!

Beneath the surface of the Chesapeake Bay’s water is a surprising symphony, unable to be heard by the human ear. However, with the help of hydrophone, the elusive rhythm of an eelgrass exhibition was revealed, providing an unexpected intersection of music and conservation. By amplifying the rhythms created by bubbles produced by eelgrass, scientists were able to quantify the process of photosynthesis as the plants convert greenhouse gasses to essential oxygen necessary for survival of aquatic life in the Bay. All in all, eelgrass accounts for 10% of the ocean’s ability to store carbon.

Aquatic grass floating in shallow water

Eelgrass growing in intertidal mudflats

But as you might guess, these crucial keystone species are a primary victim of our modern water quality plight. For one, they are affected by water temperature, unable to survive in waters warmer than 86ºF. But more crucially, these grasses are subject to risk with changes in water clarity, which measures how much light penetrates water from top to bottom. Turbidity, which is measured in meters by a Secchi disk or turbidity tube by RiverTrends monitors, is the cloudiness of water itself. When increased sediment, plankton, and dissolved organic material pollutes a body of water, less light is able to reach the depths of the water column, preventing maximum eelgrass growth. Decreased water clarity, and increased turbidity, is expedited by large storm events that increase high-sediment land runoff into tributaries.

Two people standing on a dock, holding a black and white disk over water

RiverTrends monitor using a Secchi disk to measure turbidity

Not only does global warming further limit the available habitats for eelgrass, but also increases the negative effects of turbidity, since warmer waters mean that even more light is necessary for these temperamental plants to survive. In the Chesapeake, this “habitat squeeze” has reduced eelgrass cover by 50% in twenty years. Today, eelgrass beds live at a depth 5 inches shallower than before, since there is no longer enough light to survive any deeper. It is now rare to find eelgrass communities deeper than 3 feet, making deeper northern habitats inhabitable.

Water clarity is instrumental in determining the health of the Chesapeake Bay, and has an unquantifiable impact. For one, aquatic organisms rely on light for photosynthesis, especially at depths. When light is limited, food chains are affected from the bottom-up. In addition, some fauna rely on light to see prey and navigate. A decrease in low food-chain plant populations affects fish, crabs, and waterfowl that use the grass as both habitat and food source. Along the Swedish coast, scientists have attributed the release of carbon and nitrogen into waters to eelgrass meadow surface area loss, which is a direct cause of sediment erosion. It was estimated that eelgrass loss caused 24 megagrams of carbon and 2.6 megagrams of nitrogen per acre and an economic deficit of $57,000 per acre. Nitrogen storage provides an essential ecosystem service since its sequestration mitigates eutrophication, which is the cause of harmful algal blooms.

A wide landscape shot of grass along a body of water

Seagrass bed in St. Martin River, Maryland

The loss of eelgrass in the Bay has real economic and recreational consequences, affecting 20 million residents. Blue crab fisheries are estimated to have lost a year or more of catch based solely on eelgrass cover loss. In total, it is estimated that $1-2 billion is lost per year in the Bay alone with their population decline. This crisis is only going to be accelerated by climate change. For example, take Harford County, Maryland, located next to the Susquehanna Flats where crucial eelgrass populations neutralize acidity. In this county alone, more accurate climate-adjusted rainfall differs from expected rainfall by 2.3 inches. This means that the chance for a 1-in-100 year storm is actually likely to occur every ten years. Increased storm severity in precious eelgrass habitats like the Susquehanna flats will expedite their endangerment and increase economic losses for the Bay economy.

Eelgrass is only a cog in the conservation crisis wheel that plagues the Chesapeake Bay. Accelerated by climate change, water quality continues to prove to have unexpected effects on the livelihoods of aquatic organisms and coastal communities alike. It is only through the mobilization of community scientists and programs like RiverTrends that water quality’s vast impact can be fully revealed, informing conservation initiatives to save the Bay and save our blue planet.

Learn more about our water quality monitoring efforts

By Kate Marston, Water Quality Monitoring Intern, Alliance for the Chesapeake Bay