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2022 Estuarine Nutrient Enrichment Status Report: Gateway NRA

Map of the Gateway National Recreation Area estuarine systems which are monitored for nutrient enrichment, and located in the Jamaica Bay Unit, New York.
Fig. 1: Map of the Gateway National Recreation Area estuarine area that is monitored for nutrient enrichment, and located in the Jamaica Bay Unit, New York.

Site Context

Gateway National Recreation Area (GATE) consists of 10,783 hectares of coastal uplands, freshwater ponds, marshes, bays, beaches, and mudflats (Fig. 1). Established in 1972, it is divided into three geographically separate units: Jamaica Bay, Staten Island, and Sandy Hook. The Jamaica Bay Unit encompasses almost all of island uplands and wetlands within Jamaica Bay. Thus, estuarine resources of GATE are fully contained within Jamaica Bay. The target population for estuarine monitoring includes 100% of these resources, approximately 4,615 ha, plus an additional 1,257 ha within Jamaica Bay but outside the park boundary.

The threat of nutrient enrichment is a primary management concern. Water quality monitoring follows Northeast Coastal and Barrier Network’s Protocol for Monitoring Estuarine Nutrient Enrichment (Kopp and Neckles, 2009). The protocol’s primary goal is to assess how estuarine natural resources are affected by changing nutrient inputs by determining the status and trends of response indicators within the monitored estuarine areas of each park.

Presented here are condition status summaries of three key response indicators:
1) bottom water dissolved oxygen (DO)
2) surface water chlorophyll-a
3) water column light attenuation (Kd)

Threshold values are used to determine “good”, “fair”, and “poor” condition categories (Table 1), which are consistent with those used by the US Environmental Protection Agency (USEPA) for national coastal condition reporting (USEPA 2001b, 2004) and thresholds used by National Oceanic and Atmospheric Association for the National Estuarine Eutrophication Assessment (Bricker et al. 1999).

Water clarity is expressed as Kd (m-1). Cutoff values of Kd have been calculated from the USEPA criteria for turbidity, using the thresholds for areas with significant submerged aquatic vegetation (SAV).

Table 1: Threshold values associated with each measured nutrient enrichment condition category.
Measure 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 < 0.92 m-1 0.92-1.61 m-1 > 1.61 m-1

Bottom Water Dissolved Oxygen

Bottom water DO concentration is an indirect indicator of nutrient load and direct indicator of estuarine water chemistry and organism health. Oxygen is consumed when microbial decomposers mineralize organic matter on and within estuarine sediments. When sediment organic matter increases due to nutrient over-enrichment it can cause an overgrowth of nuisance algae. The resulting heightened microbial decomposition can lower DO concentrations in bottom waters. It can also lead to increased extent and duration of bottom water anoxia and toxic sulfide concentrations. Nutrient enrichment can, ultimately, impact fauna diversity and abundance and shift species dominance.
Bar chart of bottom dissolved oxygen concentration (mg/L) condition categories by percent of total estuarine area at Gateway National Recreation Area.
Fig. 2: Bottom water dissolved oxygen concentration (mg/L) condition categories by percent of total estuarine area at Gateway National Recreation Area.
During the 2022 summer index period, GATE park-wide average bottom water dissolved oxygen concentration was good within 58.0% of the sampled estuarine area, fair within 41.0%, and poor within 1.0% (Fig. 2). 2022 conditions were consistent with all previous index periods where there has been a majority of the area in good condition and a smaller portion in fair condition, except for 2008, when there was a majority in fair condition. 2022 and 2020 displayed a lesser majority in good condition compared to the previous five years. All years except for 2003 and 2014 have shown some percentage in poor condition.

Surface Water Chlorophyll-a

Nutrient enrichment often stimulates phytoplankton production, leading to population growth. Phytoplankton growth is often nutrient-limited. Trends of increasing biomass can suggest increasing nutrient load. Surface water chlorophyll-a concentration is an indicator of phytoplankton population growth, nutrient enrichment, and overall water quality.

Bar chart of surface chlorophyll-a concentration (μg/L) condition categories by percent of total estuarine area at Gateway National Recreation Area.
Fig. 3: Surface water chlorophyll-a concentration (μg/L) condition categories by percent of total estuarine area at Gateway National Recreation Area.
During the 2022 summer index period, GATE park-wide average surface water chlorophyll-a concentration was fair within 59.2% of the sampled estuarine area, and poor within 40.8% (Fig. 3). 2022 conditions show a decrease in poor condition areas compared to the previous five years. The 2022 period is one of four (2010, 2016, 2020, and 2022) where there were no areas in good condition.

Water Column Light Attenuation

Submerged aquatic vegetation (SAV) provide important ecosystem services. SAV productivity and distribution depend on light. Light attenuation through the water column is dependent on concentrations of phytoplankton, which can correlate with nutrient enrichment, and suspended inorganic and dissolved organic matter. Regardless of current SAV presence, NCBN continues to monitor this critical SAV parameter, as it provides information relevant to the overall estuarine eutrophication status.
Light attenuation, represented by coefficient Kd (m-1), condition categories by percent of total estuarine area at Gateway National Recreation Area.
Fig. 4: Water column light attenuation, represented by coefficient Kd (m-1), condition categories by percent of total estuarine area at Gateway National Recreation Area.
During the 2022 summer index period, GATE park-wide average water column light attenuation (Kd) was good within 15.4% of the sampled estuarine area, fair within 73.6%, and poor within 11.0% (Fig. 4). 2022 conditions show an increase in good and fair condition areas and a decrease in poor condition areas, as compared to the previous index period.

Conclusion

In 2022, Gateway National Recreation Area saw a positive trend in all three response variables: bottom water dissolved oxygen, surface water chlorophyll-a and water column light attenuation (Kd), compared to the previous year.

The majority of sampled area for bottom water dissolved oxygen concentration was in good condition. Historically, bottom water DO levels have been good for most of the GATE sample system. For surface water chlorophyll-a, the majority of the area was in fair condition. Observations, however, showed a decrease in poor condition area. Water column light attenuation was fair throughout the majority of the sampled estuarine area. GATE saw a decline in poor condition area in 2022, and an increase in good condition area.

Conditions of surface water chlorophyll-a and water column light attenuation at Gateway National Recreation Area in 2022 indicate that the estuarine system remains nutrient over-enriched.
Scientist holds water quality sensor and dangles cord over the edge of a boat.
Park staff collects water quality data in one of the monitored estuaries.

NPS Photo / Michaela Compo

References

Part of a series of articles titled NCBN Yearly Status Reports | Estuaries.

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Gateway National Recreation Area

Last updated: September 5, 2024