Below the Surface of Monitoring: Dissolved Oxygen

Water chemistry is sort of like a finely balanced seesaw. When one side goes up, the person riding on it goes up with it in a sort of direct relationship. Meanwhile, the other goes down, in an indirect relationship due to its opposite reaction. When it comes to dissolved oxygen, which measures the concentration of oxygen gas in a liquid, water temperature is its trusty friend on the other side. However, the effects of warming waters on dissolved oxygen in the Chesapeake Bay watershed are no game.

Algal bloom in the Tred Avon River, tributary of the Chesapeake Bay

At higher temperatures, dissolved oxygen is lower because adding more energy, such as heat, allows gas to escape the liquid easier. Furthermore, increased biological activity, promoted by an increase in energy availability, sucks oxygen out of the water during decay. Both of these processes are key to the phenomenon known as stratification, in which lighter, warmer freshwater overlays heavier, colder seawater. When the lower layer of water is cut off from an oxygen supply and decomposition continues to compound the oxygen depletion, a condition called anoxia is created.

Anoxic waters depleted of oxygen, called dead zones, jeopardize the survival of aquatic life. Water temperature isn’t the only parameter that has severe effects on the realized niche of all living things. As discussed in last week’s parameter blog post, lower dissolved oxygen limits the niche for aquatic organisms, especially those like fish that rely solely on dissolved oxygen to breathe. But why are these waters becoming so rapidly depleted of oxygen from just a little warming?

Well there’s more to the story—anoxia is accelerated by excess nutrient pollution in water from nitrogen fertilizer, which comes from agricultural or wastewater runoff. Algal blooms flourish in fresh, salt, and brackish waters, inciting mass decomposition events. In California, sea lions who became sick from unusually toxic algal blooms have forced them to act more aggressively and bite passersby. As an endangered species, their sickness puts them under threat of bycatches and having to be put down for public safety.

Floating algal mats in Maryland’s coastal bays

The dissolved oxygen crisis in the Bay is one that harms animals, habitats, and humans alike. In addition to the global economic stress caused by failing fisheries due to destabilized fish stocks, anoxic waters have been a cause and effect of environmental injustices related to land ownership.

In areas like Tappahanock, just up the Rappahannock River from the sites highlighted in this blog, multinational corporations are purchasing land parcels for agriculture and logging in order to monopolize on a global scale. This encroachment poses a threat to the long history of “communal and reciprocal” culture cultivated by Black communities in the waterscape. Black coastal labor communities date back to the 1860’s, when freed Black citizens were drawn to the Chesapeake region to find jobs in shipbuilding and fisheries. These regions became cultural and economic centers that still thrive today. Traditional chanteys, which are rhythmic work songs, are rooted in African tradition and were used to control the pace of net hauling.

Stingray Point, Virginia on the shore of the Rappahannock River

In addition to the nutrient pollution caused by agriculture, soil deterioration from deforestation and the ever-growing urban sprawl across the Chesapeake Bay watershed have plagued tributaries. But rather than causing a call to action to reduce capitalist commodification of the watershed, anoxia has been used to justify further possession of precious land in order to assert control. In the words of Global Environmental Justice expect J.T. Roane, “these processes threaten the system with large oxygen-depleted zones that impact survivability in these waters and justify future settler intervention as the solution to the social and ecological crises of rural landscapes.”

Although anoxia is a critical condition that requires immediate attention for conservationists worldwide, these histories are a good reminder that centralized control is not always the best conservation solution. Justified by the need for swift conservation action, exploitative land-grabbing perpetuates cycles of injustice. Caution is necessary in conservation as to not take power away from community-driven systems that are fortified by reciprocity and care.

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