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Chesapeake Bay’s Dead Zone Shows Mixed Results in 2024

Oxygen-Starved Waters Create an Unpredictable ‘Dead Zone’ in the Bay

The Chesapeake Bay’s dead zone, an area marked by dangerously low oxygen levels, was once again in the spotlight this summer. Scientists report that the 2024 dead zone was, on the whole, near average. However, a deeper look reveals that the year’s oxygen-starved waters were a mixed bag of better and worse-than-usual conditions. This fluctuation has left many wondering if progress is being made in the Bay’s long battle for healthier waters or if more work is still needed.

This year’s dead zone started early, with conditions in June that were worse than usual. But by August, those very conditions dramatically improved. Still, the variation in conditions has raised questions about how much progress has actually been made in improving the health of the Bay.

Dead Zones: An Indicator of the Bay’s Health

The dead zone is a critical measure of the Chesapeake Bay’s overall ecosystem health. It forms when excess nutrients, primarily nitrogen and phosphorus, run off from land and fuel harmful algae blooms. As these algae die off and sink to the Bay’s bottom, bacteria break them down, consuming the oxygen in the water and creating hypoxic—or low-oxygen—conditions.

Chesapeake Bay dead zone

Marine life in the Bay, including fish, crabs, and shellfish, depends on oxygen to survive. So, any drop in oxygen levels puts immense stress on these creatures. Hypoxic conditions typically begin at 2 parts per million (ppm) of oxygen, with anything above 6 ppm considered healthy for most aquatic species. The extent of hypoxia each summer depends on a variety of factors, from nutrient levels to weather patterns.

In recent years, efforts to cut down on nutrient pollution have shown some success. The goal has been to shrink the size of the dead zone, and indeed, the average area of oxygen-starved water has decreased somewhat. However, weather patterns still play a major role in the intensity and duration of these low-oxygen conditions.

The 2024 Dead Zone: Mixed Signals from Scientists

The summer of 2024 saw early signs of an unusually large dead zone. In June, oxygen-starved conditions spread across a larger portion of the Bay, with scientists estimating that 20% of the Bay and its tidal tributaries experienced low oxygen levels. This made it the largest dead zone since 2019, when a quarter of the Bay’s waters were impacted by hypoxia.

However, these worst conditions occurred earlier in the season than usual, and were followed by a sudden shift. In early August, the remnants of Hurricane Debby swept through the region, mixing the oxygen-rich surface waters with the low-oxygen bottom waters and improving conditions dramatically. This shift was particularly notable, as it marked the earliest turnaround in hypoxic conditions in years.

According to scientists from the Virginia Institute of Marine Science (VIMS), 2024’s conditions were slightly worse than average. Their estimates showed that hypoxia affected 20% of the Bay at its peak in mid-June. However, by early August, most of the dead zone had dissipated, with the hypoxic conditions only persisting for 96 days. This was the shortest duration of hypoxia since 2017.

On the other hand, the Maryland Department of Natural Resources (DNR) reported slightly better-than-average conditions. They found larger-than-usual hypoxic areas in June, but also noted that conditions in late June and July improved significantly. The DNR also observed the most favorable oxygen levels in early August in nearly 40 years of monitoring.

Yet, even as conditions appeared to improve, the Bay’s hypoxic areas flared up again in late August and September. This resurgence of low oxygen levels added a level of uncertainty, with scientists unsure whether the brief improvements signified true progress or were simply a temporary shift caused by weather events like Hurricane Debby.

What This Means for the Bay’s Long-Term Health

The findings from the 2024 dead zone highlight just how complicated the health of the Chesapeake Bay is. While the nutrient reduction efforts made by local governments have brought some positive results, the variability in weather patterns, particularly during spring and summer, continues to make it difficult to predict what each year will bring.

Wetter-than-usual conditions, particularly in spring, can lead to an increase in nutrient runoff. This, in turn, fuels the algae blooms that create low-oxygen conditions in the Bay’s deeper waters. On top of that, temperature and wind conditions also play significant roles in determining how large and how long-lasting the dead zone will be each year.

Scientists are still working to understand these variables and their interactions fully. While they have made significant strides in improving the Bay’s water quality, progress remains slow and uncertain. For the Bay’s struggling marine life, the fluctuating dead zone conditions underscore the need for continued monitoring, research, and efforts to cut down on nutrient pollution.

Despite the seemingly contradictory findings from this year’s report, it’s clear that the state of the Bay’s dead zone will continue to be an important measure of its overall health. And while conditions in 2024 may have been “near average,” the complexities of the ecosystem ensure that the fight to restore the Bay is far from over.

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