Many coastal parks hold estuaries, where salt water meets fresh. Their water quality suffers from nutrient enrichment, largely caused by human activities, and the parks of the Northeast Coastal and Barrier Network depend on healthy waters to sustain complex estuary and near-shore ecosystems. This 2022 status report covers Colonial National Historical Park in Virginia. Its overall verdict: over-enriched.
| 2022 condition | Thoroughfare | Tidal creeks |
|---|---|---|
| Dissolved oxygen | good | good |
| Chlorophyll-a | poor | poor |
| Light attenuation | poor | poor |
Figure 1. The estuarine areas at Colonial National Historical Park monitored for nutrient enrichment, around Jamestown, Virginia. Credit: National Park Service.
Where the monitoring happens
Colonial National Historical Park has two main parts, the Yorktown and Jamestown Units, joined by the narrow Colonial Parkway. Its estuary monitoring is divided into two areas:
- Tidal creeks — every estuarine resource inside the park boundary, including small creeks draining park wetlands, the spots where the parkway crosses tidal creeks, and a few places where the boundary does not follow a creek shoreline exactly.
- Jamestown Island/Thoroughfare — estuarine waters outside Park Service ownership in Sandy Bay, Back River and the Thorofare.
The James and York Rivers are left out: they are major systems outside the park, and trying to monitor them would badly dilute the effort in the park and at Jamestown. In all, about 293 hectares of estuary are monitored, including all the estuarine waters inside the park.
How condition is judged
The report tracks three indicators, with thresholds consistent with those of the U.S. Environmental Protection Agency's national coastal condition reports and the National Oceanic and Atmospheric Administration's National Estuarine Eutrophication Assessment. The clarity thresholds come from EPA turbidity criteria for areas with significant underwater grasses.
| 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 |
Bottom-water oxygen: good
Oxygen near the bottom reflects nutrient load indirectly and the water's chemistry and the health of its animals directly. When nutrient over-enrichment fuels algae and adds organic matter to the sediment, microbes decomposing it use up oxygen. That can lower bottom oxygen, extend the area and duration of oxygen-free water and toxic sulfides, and in the end change which animals live there and in what numbers.
In the summer 2022 index period, bottom oxygen was good across 99.7% of the sampled area and fair across 0.3%. It was good across all of the Thoroughfare, and good across 98.9% of the tidal creeks and fair across 1.1% — in both cases in line with earlier years.
Figure 2. Bottom-water dissolved oxygen condition across the park's estuarine area, 2022. Credit: National Park Service.
Figure 3. Bottom-water dissolved oxygen condition in the Thoroughfare and tidal creeks. Credit: National Park Service.
Chlorophyll-a: poor
Extra nutrients often spur the growth of phytoplankton, whose growth is usually limited by nutrients, so rising biomass can signal a rising nutrient load. Surface chlorophyll-a measures phytoplankton growth, nutrient enrichment and overall water quality.
Park-wide in 2022, chlorophyll-a was fair across 14.0% of the sampled area and poor across 86.0%. In the Thoroughfare it was fair across 15.4% and poor across 84.6%; in the tidal creeks, fair across 9.4% and poor across 90.6%. Both showed more area in poor condition than in the previous five index periods.
Figure 4. Surface-water chlorophyll-a condition across the park's estuarine area, 2022. Credit: National Park Service.
Figure 5. Surface-water chlorophyll-a condition in the Thoroughfare and tidal creeks. Credit: National Park Service.
Water clarity: poor
Underwater grasses provide important ecosystem services and need light to grow and spread. How much light the water absorbs depends on phytoplankton, which can track nutrient enrichment, and on suspended and dissolved matter. The network measures it whether or not grasses are present, because it helps show an estuary's overall nutrient status.
In 2022, light attenuation was poor across 100% of the sampled area, and across all of both the Thoroughfare and the tidal creeks — as in every earlier index period, except for a small fair area in the tidal creeks in 2014.
Figure 6. Water-column light attenuation (Kd) across the park's estuarine area, 2022. Credit: National Park Service.
Figure 7. Water-column light attenuation (Kd) in the Thoroughfare and tidal creeks. Credit: National Park Service.
Conclusion
In 2022, both the Thoroughfare and the tidal creeks had most of their area in poor condition for chlorophyll-a and water clarity. Both have historically been poor for chlorophyll-a, while bottom oxygen has stayed good across most of both since 2008. Chlorophyll-a and water clarity show that the park's monitored estuary remains over-enriched with nutrients.
The data behind this report are on the NPS DataStore, and an interactive water quality dashboard shows them alongside other parks'.
Park staff collecting water quality data in one of the monitored estuaries. Credit: National Park Service / Michaela Compo.
Sources
Based on "2022 Estuarine Nutrient Enrichment Status Report: Colonial NHP," published by the National Park Service, Northeast Coastal and Barrier Network; rewritten in hubnx's own words.
- The report cites EPA (2001, 2004) and Bricker and others (1999). It names the National Oceanic and Atmospheric "Association"; the agency is the National Oceanic and Atmospheric Administration.
In these publicationsColonial National Historical ParkNCBN Yearly Status Reports | Estuaries
Licence: CC0 1.0 (public domain) · Adapted from www.nps.gov
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