Potomac Environmental Research and Education Center

Gunston Cove Ecosystem Study

PEREC’s long term study of Gunston Cove is an internationally recognized case study for ecosystems recovery

In 1984, PEREC began a long-term study of Gunston Cove (A multidecadal report was published in 2020). The study aimed to gain a greater understanding of the ecological conditions of the watershed. The rapid development of Fairfax county led to concerns about the effect of urban runoff, coming from the Accotink and Pohick watershed. Futhermore, there was concern about the effects of the run off from the Potomac Wastewater Treatment Plant. As Gunston Cove is located near the Mason Neck Wildlife Refuge (an area that is home to Bald Eagles), there was a great need for the study. Several goals were established, which includes:

  1. Determining the abundance of major groups of aquatic organisms
  2. Compare those aquatic community to other, typical, freshwater ecosystems
  3. Determine how biological communities and environmental parameters vary by location (i.e. cove, river, inlet stream), season, and depth
  4. Determine specific effects of plant effluent on the chemistry and biology of the Cove where possible

For over a quarter century, the same stations at Gunston Cove have been tested. Each year, conclusions are draw regarding the present ecological status of the area, and recommendations for future needs are made to Fairfax County. For more background information, take a look at the introduction from the 1984 Gunston Cove Report.

Summary of Results

Gunston Cove is an area located downriver from the Noman M. Cole Jr. Pollution Control Plant. In the late 1970s, Fairfax County made efforts to reduce the nutrient load that was passed from the wastewater treatment plant into the Potomac, which empties into the Chesapeake Bay.

P= Phosphorus N= Nitrogen Flow= The amount of water passed through the plant As you can see, Phosphorus drops dramatically in the early 1980s, while Nitrogen levels decrease in the mid 2000s.
P= Phosphorus;   N= Nitrogen;   Flow= The amount of water passed through the plant
As you can see, Phosphorus drops dramatically in the early 1980s, while Nitrogen levels decrease in the mid 2000s.

Since then, careful monitoring of the area has revealed that many of these proactive changes have had a positive effect on the ecosystem of Gunston Cove.  In the early 1980s, phosphorus removal practices were instituted at the wastewater treatment plant, and since then there has been a dramatic reduction in phosphorus. In the past several years, nitrogen has also begun to decrease.

A direct result of the phosphorus removal practices has been an increase in the amount of submerged aquatic vegetation (SAV). These plants are habitats for fishes and the organisms they consume. The increase in SAV is also linked to an increase in the number of banded killifish and sunfish. This is because SAV provide safe areas to spawn and cover for fry. Before the increase in SAV, white perch was the dominant fish found in the Gunston Cove studies. However, as SAV began to provide habitats, the overall diversity of the fish population increased.

There has also been a significant decline in chlorine and ammonia from the plant, which has allowed fish to recolonize the tidal Pohick Creek. This area is used as a spawning grown by species such as chad, and the improvement of water quality has contributed to positive changes in the Chesapeake Bay.

For specific information about each year, view the reports below.

An Ecological Study of Gunston Cove 2022 Final ReportDownload

Past Reports