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The amount of dissolved oxygen (DO) – a good thing – has been steadily improving in all three sections of the river. Because the MD Anacostia (Section 1) receives oxygen-rich water from two large tributaries -- the Northwest and the Northeast Branches - DO tends to be higher there than in the DC portion (Section 2&3).
The large drop in dissolved oxygen in 2012 is likely due to the less intense rainfall events that year compared to 2011. Less stream flow input to the tidal Anacostia added less dissolved oxygen.
DC Water (formerly DC WASA) broke ground in October 2011 on the $2.6 billion Clean Rivers Project (CSO Long Term Control Plan) to control sewer overflows. The Anacostia River will see benefits from the project starting in 2018. The project reduces combined sewer overflows by 98 percent at completion in 2022. Both DC sections will then see significant improvement in DO levels because sewage contains significant amount of organic matter that sucks up oxygen in the water when it decomposes.
Many Anacostia watershed residents know of the Combined Sewer Overflow problems in DC. The sewer system in DC is designed to overflow into the river when a rain event exceeds approximately a half inch. However, contrary to public perception, downstream DC water is cleaner than the upstream MD water in the Anacostia in terms of fecal bacteria. There are possible two reasons to account this: (1) the tidal action washes the mouth of the Anacostia with much cleaner Potomac River water, and (2) there is large amount of fecal matter input from Maryland. Washington Suburban Sanitary Commission (WSSC) in Maryland and DC Water are working to repair sewer leaks and implement remediation projects to reduce sewer overflows. However, we still have to deal with a large portion of fecal matter from wildlife.
According to a study conducted by AWS and Charles Hagedorn of Virginia Tech University, funded in part by Chesapeake Bay Trust (CBT), approximately 70 percent of fecal bacteria from Maryland is attributed to wildlife1. Feces excreted on impervious surfaces is washed away by rainfall and is carried into streams. Though the largest source of fecal bacteria may be wildlife, its transport to the river is caused by the impervious surfaces we have created. In natural settings, wildlife feces tend to decompose on site and most rainwater drains into the ground.
All river sections show steady improvement over the years with the District portions improving faster. In 2012, all sections had much better scores due to fewer intense rainfall events that year. Fewer intense rainfall events brings less fecal matter to the river.
Water clarity indicators (Secchi Disk Depth tests) have been low for all sections in all years for which data is available. In almost all cases, the score was below 50 percent. In the graph above, the trend line (not the scatter plots) is the average value of scores for the past five years. This method clearly illustrates the trend.
In recent years water clarity is declining. In the Lower DC Anacostia (Section 3) the best average score was in 1995. Since then the average has been steadily declining. In Maryland and Upper DC (Sections 1 and 2) the best average score was in 2001. Since then, the average is declining though there seems to be improvement in the past three years in Section 2. We need to obtain more data to see if the possible improvement in Section 2 continues or not. Perhaps relating to the water clarity decline, Submerged Aquatic Vegetation (SAV) disappeared from the Anacostia River in 2003. (See the trend analysis for SAV for details.)
In order to solve this grave issue, stringent regulations on stormwater runoff should be implemented because the increased peak stream flows resulting from flashy stormwater runoff from increased impervious surfaces have been eroding the streambanks and scouring streambeds, making the water cloudy. According to a study conducted for the Total Maximum Daily Loads (TMDL) for sediment, about 73 percent of sediment is coming from streambank erosion. The study was conducted for suspended sediment particles in the water. When heavier particles of sediment are taken into consideration, it is safe to say that more than 73 percent of sediment is coming from streambank erosion.
Scores for Chlorophyll(a) are improving.
The better score in Maryland (Section 1) does not mean that there are no excessive nutrients coming from Maryland. Because Chlorophyll(a) is a green pigment in plants, algae, and cyanobacteria, it does not accurately reflect the nutrient amounts in water. There is a lag time between discharge of nutrients and their uptake by plants, etc.
In the free-flowing tributaries of the Anacostia, discharged nutrients travel to the tidal Anacostia. Because the tidal river moves slowly, there is plenty of time for microalgae to take up nutrients. Thanks also to the ample sunlight for photosynthesis in the tidal Anacostia, the DC portions of the river (Section 2 and Section 3) tend to have higher Chlorophyll (a) values, resulting in lower scores. Both upstream and downstream communities need to stop nutrients runoff (fertilizer, for example) from properties.
Chlorophyll is the green pigments of plants that converts sunlight into organic compounds during photosynthesis. There are seven known types of chlorophyll; Chlorophyll(a) and Chlorophyll(b) are the two most common forms. Chlorophyll(a) is used as a measure of microalgae biomass, which is controlled by factors such as water temperature, light, and nutrient availability. Too much algae leads to large algal blooms that can reduce water clarity. Also, once an algae bloom dies, it depletes water of oxygen.
Submerged Aquatic Vegetation (SAV) are plants that cannot withstand excessive drying and therefore live with their leaves at or below the water surface. Such vegetation constitutes an important habitat for young fish and other aquatic organisms.
SAV data source: http://web.vims.edu/bio/sav/index.html
AWS's goal for submerged aquatic vegetation (SAV) in the Anacostia is 20 acres, a goal identified in the Anacostia Watershed Restoration Indicators and Targets for Period 2001-2010 by scientists at Metropolitan Washington Council of Governments (COG). Because there has been no SAV observed in the Anacostia since 2003, the score has been zero (0) for over a decade.
As soon as the degradation of water clarity in the Lower DC Anacostia (Section 3) was observed in 1995, the acreage of SAV started to decline.
While there is no SAV in the tidal Anacostia, it is known that there is SAV in non-tidal tributaries to the Anacostia River.
AWS is not certain why SAV was present in the past --particularly in the 1980s and 1990s when the water clarity seemed worse than or equal to the current clarity. However, we have several hypotheses:
· The nature of the cloudiness of the water was different. There are many factors that make the water cloudy. Recent cloudiness may be complex combination of sediment particles due to erosion, decaying organic matter from sewage, algae bloom, etc. while past cloudiness may have mainly come from sediment particles.
· The river was monitored less often in the 1980s and 1990s. The water quality data may then be less reliable during the time period.
· The SAV may have suffered in the 1980s and 1990s, but may still have been reducing pollution.
· The overall nature of pollution may have changed. In more recent years, numerous types of pollutants including chemicals such as pharmaceuticals, pesticides, herbicides, and heavy metals on top of water cloudiness may have helped eliminate the plants.
Stormwater runoff has been steadily increasing as long as stream discharge (flow) data has been available.
AWS is expecting that this trend will change and start to show improvement, though it will take time due to the vast areas of impervious surfaces that must be retrofitted with water-infiltrating green infrastructure to measurably reduce runoff.
It will be instructive to monitor differences in rates of runoff reductions in the Anacostia’s Northeast and Northwest Branches where different standards and practices exist. The Northeast Branch is mainly in Prince George's County while the Northwest Branch flows largely through Montgomery County.
While new development throughout Maryland is required to treat runoff from a 1-year/24-hour storm (approx. 2.7 inches), the key to reduce stormwater runoff and restore the Anacostia is runoff reduction for existing development. Montgomery County regulations now require that redevelopment projects treat 2.6" of rain. However, Prince George's County only requires treating 0.5 inches until 2016 and just 0.75 inches beyond that.