Habitat

Underwater Grasses

2023 D+

2020 C-

2018 C-

Underwater grasses, also referred to as submerged aquatic vegetation (SAV), are an ideal indicator of overall water health. Because they are highly sensitive to pollution and usually thrive in pristine conditions, they typically serve as the “canary in the coal mine” for a lot of Chesapeake Bay tributaries. Serving as habitat for yellow perch, crayfish, and a host of other wildlife, as well as producing ample amounts of dissolved oxygen, these habitats are vital to ensuring the Potomac River’s health.

Underwater grasses have suffered in the past due to high amounts of sediment pollution and poor water clarity, often a result of irresponsible deforestation or poor sediment management practices. Despite recent successes in reducing polluted runoff in rural and urban areas alike, underwater grasses are still having a difficult time expanding to acreage levels seen in the past. A goal of 3,581 hectares of underwater grasses (roughly the size of five Rock Creek Parks!) was set for the Potomac River watershed to reach healthy levels of underwater grasses. Unfortunately, as of 2020, the Potomac was only 33% of the way to reaching this goal with surveys measuring 2,855 hectares of SAV recorded across the watershed. Reductions in runoff and sediment pollution, as well as continued improvements in urban BMPs are important indicators to watch, which may signal improved conditions for SAV coverage across the watershed.

Streamside Forest Buffers

2023 D+

2020 F

2018 F

Forest buffers (also called riparian buffers) along local streams and waterways are one of the best defenses against polluted runoff and excess sediment. When planted along the banks of a stream, trees reduce erosion by holding sediment in place with their root systems. Trees absorb rainwater and slow down incoming runoff, filtering it before it reaches a waterway. In recent years, states in the Potomac River watershed have fallen short in the creation of new forest buffers. In 2020, however, shoreline trees and plants doubled across the watershed when compared to 2018 and 2019, meeting 36 percent of the annual goal of 207 miles of forested buffers planted. Looking into the future, it’s essential that WV, MD, and VA continue to expand the amount of forest buffers planted as polluted runoff from rural and urban areas of the watershed still poses a serious issue.

Stream Water Quality (Non-tidal)

2023 B

2020 B

2018 C

The Potomac River flows with freshwater from its headwaters in West Virginia, Virginia, and Maryland down through the Potomac Gorge. Downstream of Chain Bridge, adjacent to McLean, Virginia, the Potomac is considered tidal as it experiences periodic rising and falling of water levels.

Upstream water quality is often assessed using macroinvertebrates: small bugs that live in streams and are highly sensitive to pollution, making them ideal indicators of stream health. Many macroinvertebrates live in streams for several years, making them effective indicators of long-term changes in stream health, as opposed to water quality measures which may change radically from season to season, or due to short-term temporal changes (e.g., flood). In short, the presence or absence of sensitive macroinvertebrate species provide valuable insights into stream health and stability.

The Interstate Commission on the Potomac River Basin (ICPRB) collects and calculates the health of non-tidal streams in the Potomac River watershed every six years using a method referred to as the “Chessie BIBI” or a biotic integrity for stream macroinvertebrates. As of the last assessment 50% of non-tidal streams in the Potomac River watershed were considered healthy. With approximately half of non-tidal streams considered healthy, the region is 71% towards meeting our goal for non-tidal water quality.

Tidal Water Quality

2023 D+

2020 D+

2018 C

The Potomac River transitions to a tidal river starting at Chain Bridge (adjacent to McLean, Virginia) where it flows downstream through Washington, DC and then another 100 miles to the mouth of the Chesapeake Bay. The tidal Potomac experiences the periodic ebb and flow of tides and mixes with brackish waters, with higher salinity levels closer to the Bay. It’s in these waters, that bottlenose dolphins from the Atlantic Ocean migrate into the Bay and the Potomac each May to birth and raise their calves.

Tidal water quality, for the purposes of this report, consists of a combined assessment of dissolved oxygen (DO), water clarity, and chlorophyll a (or algal biomass). Dissolved oxygen in waterways is essential for aquatic organisms’ survival and can fluctuate throughout the year, decreasing in warmer weather. Underwater grasses and other aquatic plants help to increase the amounts of dissolved oxygen as they release oxygen into the water through photosynthesis. Dissolved oxygen trends in the tidal Potomac River have been slowly improving with an average DO concentration of 80 percent over the past 20 years.

Water clarity is a measure of how clear or cloudy a body of water is. Suspended sediment, plankton, particulate matter, and other factors contribute to water clarity conditions. Clear waters are crucial to the health of a river ecosystem because aquatic plants need sunlight to grow and thrive. Similar to dissolved oxygen, water clarity has slowly improved over the past few decades, most likely due to an increase in best land management practices and a reduction in sediment runoff.

Algal biomass has become increasingly important to monitor in recent years as the occurrence of harmful algal blooms has increased. Chlorophyll a is a key indicator of the presence or absence of algal blooms and can indicate excessive nutrients in the watershed. Large quantities of algae are the primary cause of dead zones present in the Chesapeake Bay during summer months. In the Potomac River, chlorophyll a conditions have remained poor as excessive amounts of algal biomass are recorded in the watershed. In 2020, Potomac chlorophyll a levels registered a score of 14%, indicating “very poor” conditions according to the University of Maryland Center for Environmental Science (UMCES). As a result, monitoring of harmful algae has increased in certain spots across the watershed where humans and pets may be at most risk.

Indicators for habitat aim to establish the baseline health of various ecosystems that exist throughout the entire Potomac River watershed and compare them to existing conditions. Both tidal and non-tidal water quality assessments are closely monitored and scored by local, state, and Chesapeake Bay program agencies on a frequent basis to track overall Potomac River and Bay health status and trends. Scores for tidal water quality were determined based on Bay reports from the University of Maryland Center for Environmental Sciences and are presented in percentages of restoration goals. Non-tidal water quality uses Chessie BIBI scores for HUC12 sub-watersheds and is determined at six-year intervals. The score for this report reflects Chessie BIBI Stream Index scores from the interval 2012-2017.

The density of underwater grasses across the tidal Potomac river are calculated each year through aerial surveys conducted by the Virginia Institute of Marine Science (VIMS). The grade is presented in percentage of restoration goal, with a total restoration goal for the Potomac watershed of 8,581 hectares.

Forest buffers are measured in miles planted per year and require accurate and consistent reporting from multiple organizations and agencies to gain a full accounting of total trees planted each year. Due to inaccurate or inconsistent reporting, the forest buffer grade for this report is based on best available data from the US EPA Chesapeake Bay Program and reporting states and organizations.

Data for the “Habitat” indicator was sourced from the Chesapeake Bay Program, University of Maryland Center for Environmental Studies, the Interstate Commission on the Potomac River Basin, the Virginia Institute of Marine Science (VIMS), and Chesapeake Progress.