2022 Estuarine Nutrient Enrichment Status Report: Colonial NHP

2022 Status : over-enriched explore our interactive data viewer

Quick dive

Many of our coastal parks are home to dynamic estuaries, where saltwater meets freshwater. These waters also experience the detrimental effects of estuarine nutrient enrichment, largely from human activities, that impact water quality. The Northeast Coastal and Barrier Network (NCBN) parks depend on high-quality aquatic resources to sustain complex estuarine and near- shore ecosystems.

Condition of majority of sampled area, by strata.
Note: Surface water chlorophyll-a and water column light attenuation conditions at Colonial NHP indicate that estuarine area within the strata remains nutrient over-enriched.  

	Thoroughfare	Tidal Creeks
Dissolved oxygen	Good	Good
Chlorophyll-a	Poor	Poor
Light attenuation	Poor	Poor

Additional Resources

The data referenced in this brief is available here. Our water quality dashboard provides an interactive visualizer for this data and that of our other parks.

Fig. 1: Map of the Colonial National Historical Park estuarine areas that are monitored for nutrient enrichment, and located in Jamestown, Virginia.

Site Context

Colonial National Historical Park (COLO) consists of two significant land holdings, the Yorktown and Jamestown Units. These are connected by a narrow traffic corridor, the Colonial Parkway. COLO estuarine sampling area is divided into two strata. The first, a tidal creek stratum, includes all estuarine resources falling inside park boundaries. This includes small tidal creeks that drain off park wetlands, the small regions of park ownership where the Colonial Parkway overpasses tidal creeks, and a few additional areas where the park boundary does not precisely coincide with a tidal creek shoreline. The second, Jamestown Island/Thoroughfare stratum, includes non-NPS estuarine resources in Sandy Bay, Back River and The Thorofare. The sample area is defined to exclude the non-NPS estuarine resources associated with the James River or York River. These are major systems outside COLO boundaries and attempting to monitor them in any meaningful fashion would severely dilute NPS efforts within the park and at Jamestown. Between both strata, approximately 293 ha of estuary are monitored, including 100% of the estuarine resources that fall within the park boundary.

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 (K_d)

The condition of the status indicators is presented for the entire monitored area, providing a parkwide condition and for each individual stratum (Fig. 1):
1) Thoroughfare (TH)
2) tidal creeks (TC)

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 K_d (m^-1). Cutoff values of K_d 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.

Fig. 2: Bottom water dissolved oxygen concentration (mg/L) condition categories by percent of total estuarine area in 2022 at Colonial National Historical Park.

Park-wide

During the 2022 summer index period, COLO park-wide average bottom water dissolved oxygen concentration was good within 99.7% of the sampled estuarine area, and the remaining 0.3% was fair (Fig. 2).

Fig. 3: Bottom water dissolved oxygen concentration (mg/L) condition categories by percent of total estuarine area of Thoroughfare and tidal creeks strata, Colonial National Historical Park.

Thoroughfare

Average bottom water DO concentration was good within 100% of the TH stratum (Fig. 3). 2022 conditions were consistent with previous index periods, where a majority of the estuarine area has been in good condition.

Tidal Creeks

Average bottom water DO concentration was good within 98.9% of the TC stratum, and fair within 1.1% (Fig. 3). 2022 conditions were consistent with previous index periods, when a large majority of the estuarine area has been in good condition and some proportion in fair 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.

Fig. 4: Surface water chlorophyll-a concentration (μg/L) condition categories by percent of total estuarine area in 2022 at Colonial National Historical Park.

Park-wide

During the 2022 summer index period, COLO park-wide average surface water chlorophyll-a concentration was fair within 14.0% of the sampled estuarine area, and poor within 86.0% (Fig. 4).

Fig. 5: Surface water chlorophyll-a (μg/L) concentration condition categories by percent of total estuarine area of Thoroughfare and tidal creeks strata, Colonial National Historical Park.

Thoroughfare

Average surface water chlorophyll-a concentration was fair within 15.4% of the TH stratum (Fig. 5). The remaining 84.6% was poor. 2022 conditions showed an increase in poor condition in comparison to the past five index periods.

Tidal Creeks

Average surface water chlorophyll-a concentration was fair within 9.4% of the TC stratum, and poor within 90.6% (Fig. 5). 2022 conditions showed an increase in poor condition in comparison to the past five index periods.

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 influenced by 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.

Fig. 6: Water column light attenuation, represented by coefficient Kd (m-1), condition categories by percent of total estuarine area in 2022 at Colonial National Historical Park.

Park-wide

During the 2022 summer index period, COLO park-wide water column light attenuation (K_d) was poor within 100% of the sampled estuarine area (Fig. 6).

Fig. 7: Water column light attenuation, represented by coefficient Kd (m-1), condition categories by percent of total estuarine area of Throughfare and tidal creeks strata, Colonial National Historical Park.

Thoroughfare

Average water column light attenuation was poor condition within 100% of the TH stratum (Fig. 7). 2022 conditions were consistent with all previous index periods, where 100% of the stratum has been in poor condition.

Tidal Creeks

Average water column light attenuation was poor within 100% of the TC stratum (Fig. 7). 2022 conditions were consistent with all previous index periods, where 100% of the stratum has been in poor condition, except for in 2014 when there was a small percentage in fair condition.

Conclusion

In 2022, Colonial National Historical Park saw varying conditions of bottom dissolved oxygen and surface water chlorophyll-a, and overwhelmingly poor water column light attenuation (K_d) throughout the Thoroughfare and tidal creeks strata. Both strata had a majority of the sampled estuarine area in poor condition for both surface water chlorophyll-a concentration and water column light attenuation condition.

Historically, both Thoroughfare and tidal creeks strata have been in poor condition in terms of surface water chlorophyll-a. Bottom water dissolved oxygen concentrations have maintained good condition in the majority of both strata since 2008.

Surface water chlorophyll-a and water column light attenuation conditions at Colonial National Historical Park, however, indicate that estuarine area within the strata remains nutrient over-enriched.

Park staff collects water quality data in one of the monitored estuaries.

NPS Photo / Michaela Compo

References

Click to expand

Bricker, S.B., C.G. Clement, D.E. Pirhalla, S.P. Orlando, and D.R.G. Farrow. 1999. National estuarine eutrophication assessment: effects of nutrient enrichment in the nation’s estuaries. NOAA, National Ocean Service, Special projects Office and the National Centers for Coastal Ocean Science, Silver Spring, MD. 71pp.

Kopp, B. S. and H.A. Neckles. 2009. A Protocol for Monitoring Estuarine Nutrient Enrichment in Coastal Parks of the National Park Service Northeast Region. Natural Resource Report NPS/NCBN/NRR—2009/110. National Park Service, Fort Collins, Colorado.

U.S. EPA. 2001. National coastal assessment: field operations manual. U.S. Environmental Protection Agency, Office of Research and Development, National Health and Environmental Effects Research Laboratory, Gulf Ecology Division, Gulf Breeze, FL. EPA 620/R-01/003.

U.S. EPA: 2003. Ambient Water Quality Criteria for Dissolved Oxygen, Water Clarity and Chlorophyll a for the Chesapeake Bay and Its Tidal Tributaries, EPA-903/R-03/002, United States Environmental Protection Agency, Region III Chesapeake Bay Program Office, Annapolis, MD; Region III Water Protection Div., Philadelphia, PA, and Office Water, Office of Science and Technology, Washington, D.C.