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Many coastal national parks hold estuaries, where salt water meets fresh. Those waters suffer from nutrient enrichment — excess nutrients, largely from human activities, that degrade water quality. The parks of the National Park Service's Northeast Coastal and Barrier Network depend on healthy estuaries and near-shore ecosystems, and the network checks them every summer.
2022 status at Gateway National Recreation Area: over-enriched.
| Indicator | Park-wide condition |
|---|---|
| Bottom-water dissolved oxygen | Good |
| Surface-water chlorophyll-a | Fair |
| Light attenuation (water clarity) | Fair |
The estuarine area of Gateway National Recreation Area monitored for nutrient enrichment, in the Jamaica Bay Unit, New York. NPS.
The park
Gateway National Recreation Area, established in 1972, covers 10,783 hectares of coastal uplands, freshwater ponds, marshes, bays, beaches and mudflats in three separate units: Jamaica Bay, Staten Island and Sandy Hook. The Jamaica Bay Unit includes nearly all the island uplands and wetlands in the bay, so all of the park's estuarine resources lie within Jamaica Bay. Monitoring covers all of them, about 4,615 hectares, plus another 1,257 hectares of the bay outside the park.
Nutrient enrichment is a primary management concern. Following the network's monitoring protocol, three indicators are rated against thresholds consistent with the U.S. Environmental Protection Agency's national coastal reporting and NOAA's National Estuarine Eutrophication Assessment:
| Indicator | Good | Fair | Poor |
|---|---|---|---|
| Chlorophyll-a | < 5 µg/L | 5–20 µg/L | 20 µg/L |
| Dissolved oxygen | 5 mg/L | 2–5 mg/L | < 2 mg/L |
| Light attenuation (Kd) | < 0.92 m⁻¹ | 0.92–1.61 m⁻¹ | 1.61 m⁻¹ |
The light-attenuation cutoffs come from EPA turbidity criteria for areas with significant underwater grasses.
Dissolved oxygen: mostly good
Oxygen near the bottom is an indirect sign of nutrient load and a direct measure of water chemistry and the health of living things. When excess nutrients feed nuisance algae, decomposing organic matter in the sediment uses up oxygen, which can lead to longer and wider stretches of oxygen-free bottom water and toxic sulfides — and ultimately change which animals live there and in what numbers.
In summer 2022, bottom-water oxygen was good in 58.0% of the sampled area, fair in 41.0% and poor in 1.0%. As in every previous year except 2008, when most of the area was fair, the majority was in good condition — though in 2022 and 2020 that majority was smaller than in the five years before. Every year except 2003 and 2014 has had some area in poor condition.
Bottom-water dissolved oxygen by condition category, share of estuarine area. NPS.
Chlorophyll-a: fair to poor
Nutrients often fuel phytoplankton growth, so surface chlorophyll-a is a measure of phytoplankton, nutrient enrichment and overall water quality. In 2022 it was fair in 59.2% of the area and poor in 40.8%, with less area in poor condition than in the previous five years. As in 2010, 2016 and 2020, no area was in good condition.
Surface-water chlorophyll-a by condition category. NPS.
Water clarity: mostly fair
Underwater grasses provide important ecosystem services and depend on light, which is dimmed by phytoplankton — often tied to nutrients — and by suspended and dissolved matter. The network measures clarity whether or not grasses are present, because it reflects overall eutrophication. In 2022 light attenuation was good in 15.4% of the area, fair in 73.6% and poor in 11.0% — more good and fair and less poor than in the previous monitoring period.
Water column light attenuation (Kd) by condition category. NPS.
Conclusion
All three indicators improved in 2022 compared with the year before: most of the area had good bottom-water oxygen, as it historically has; poor chlorophyll conditions shrank; and water clarity improved. Even so, chlorophyll-a and water clarity show that Jamaica Bay's estuarine system remains over-enriched with nutrients.
Collecting water quality data in one of the monitored estuaries. NPS Photo / Michaela Compo.
Sources
- National Park Service, Northeast Coastal and Barrier Network: "2022 Estuarine Nutrient Enrichment Status Report: Gateway NRA," following Kopp and Neckles (2009) and citing Bricker and others (1999) and the U.S. Environmental Protection Agency (2001, 2003). The report names NOAA the "National Oceanic and Atmospheric Association"; the correct name is used here.
En estas publicacionesGateway National Recreation AreaNCBN Yearly Status Reports | Estuaries
Licencia: CC0 1.0 (dominio público) · Adaptado de www.nps.gov
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