Assateague Island's Bays in 2022: Still Over-Enriched With Nutrients

At a glance

2022 status: over-enriched.

Coastal parks' estuaries, where salt water meets fresh, suffer from nutrient enrichment, mostly from human activity, which harms water quality. The parks of the National Park Service's Northeast Coastal and Barrier Network depend on healthy estuaries and near-shore ecosystems. The data are in the NPS DataStore, and an interactive dashboard covers this and other parks.

Figure 1. The estuarine area of Assateague Island National Seashore monitored for nutrient enrichment, in Maryland and Virginia. NPS.

The setting

Assateague Island National Seashore is a 60-km barrier island off the Delmarva Peninsula; its northern two-thirds are in Maryland and its southern third in Virginia. It is one of two coastal parks in the region with a highly developed water-quality monitoring program, run with many federal and state partners. The park boundary takes in Park Service lands, the U.S. Fish and Wildlife Service's Chincoteague National Wildlife Refuge and Maryland's Assateague State Park, and Sinepuxent Bay and Maryland's part of Chincoteague Bay are managed as a National Estuary Program estuary — so the park's interest extends across the coastal bays. About 37,319 hectares of estuary are monitored, 6,867 of them inside the park.

Nutrient enrichment is a primary management concern. Monitoring follows the network's protocol (Kopp and Neckles, 2009) and tracks three response indicators, with thresholds consistent with those of the U.S. Environmental Protection Agency and NOAA:

Dissolved oxygen: good

Bottom-water oxygen reflects both nutrient load and the health of estuarine life. When excess nutrients feed nuisance algae, more organic matter settles; microbes decomposing it use up oxygen, and bottom water can lose oxygen entirely and build up toxic sulfides, changing which animals live there.

Figure 2. Bottom-water dissolved oxygen condition by percent of the sampled estuary. NPS.

In summer 2022, oxygen was good in 98.8% of the sampled area and poor in 1.2% — consistent with past years, in which most of the area has been good.

Chlorophyll-a: mostly fair

Nutrients spur the growth of phytoplankton, so rising chlorophyll-a can signal rising nutrient loads.

Figure 3. Surface chlorophyll-a condition by percent of the sampled estuary. NPS.

In 2022, chlorophyll-a was good in 33.3% of the area, fair in 65.0% and poor in 1.7% — like earlier years, mostly fair, though the good area grew.

Water clarity: improving

Submerged aquatic vegetation (SAV), which provides important ecosystem services, depends on light, and light through the water depends on phytoplankton and on suspended and dissolved matter. The network keeps tracking it whether or not SAV is present, because it says much about the estuary's condition.

Figure 4. Water-column light attenuation condition by percent of the sampled estuary. NPS.

In 2022, clarity was good in 16.2% of the area, fair in 43.4% and poor in 40.4% — better than before, breaking a run of mostly poor clarity from 2005 to 2020. Only 2010, 2014, 2020 and 2022 have had any area in good condition.

Conclusion

Oxygen was good across most of the estuary, as it has been historically; chlorophyll-a was mostly fair, as in past years; and water clarity improved. But the chlorophyll-a and clarity readings show that the estuary remains over-enriched with nutrients.

Figure 5. Park staff collecting dissolved oxygen and other water-quality data in a monitored salt pond. NPS / Michaela Compo.

Sources

Based on "2022 Estuarine Nutrient Enrichment Status Report: Assateague Island NS," Northeast Coastal and Barrier Network, National Park Service; a work of the United States government in the public domain. It cites Kopp and Neckles (2009), the U.S. EPA (2001, 2003, 2004) and Bricker and others (1999).