The % Score for dissolved oxygen (DO) has been steadily improving for all 3 sections. Because the MD Anacostia (Section 1) receives oxygen-rich water from 2 large tributaries -- the Northwest and the Northeast Branches -- the % Score of DO tends to be higher than in the DC sections.
The recent drop in % Score in DC may be because the data in 2008 through 2010 includes real-time monitoring data collected by District Department of the Environment (DDOE). Real-time data include values collected during overnight hours but traditional "grab sampling" data were collected during business hours. Overnight DO values are lower than those during daytime because there is no oxygen supply from aquatic plants that release oxygen into water by photosynthesis. Aquatic plants and algae actually consume oxygen in the water all the time and the oxygen consumption by them overcomes the production during night time.
The MD Anacostia does not have this real-time monitoring data, and thus samples only reflect daytime DO levels.
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 benefit from the project starting in 2018, when the project reduces combined sewer overflows by 98%. Both DC sections will then see significant improvement in DO levels because sewage includes a 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 half an 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 2 reasons to account this: (1) the tidal action washes the mouth of the Anacostia with much cleaner Potomac River water, or (2) there is large amount of fecal matter input from Maryland. Washington Suburban Sanitary Commition (WSSC) in Maryland and DC Water are working hard to repair sewer leaks and implement remediation projects to reduce sewer overflows.
According a study conducted by AWS and Charles Hagedorn of Virginia Tech University, funded in part by Chesapeake Bay Trust (CBT), approximately 70% of fecal bacteria from Maryland is attributed to wildlife. All 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, the cause is human activity -- we humans created the impervious surface.
All sections show steady improvement over the years. Downstream sections (Upper and Lower DC) show faster improvement rate.
The % Score of Secchi Disk Depth has been low for all sections, in all years for which data is available. In almost all cases, the % Score was lower than 50%.
In the graph above, a reading on the trend line (not the plot scattered) is an average value of the % Score for the past 5 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 steadily declining. Perhaps not coincidentally, 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 problem, 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% of sediment is coming from streambank erosion. The study was conducted for suspendable sediment in the water. When heavier particles of sediment were taken into consideration, it is safe to say that more than 73% of sediment must have come from streambank erosion.
The % Score for Chlorophyll (a) shows improvement over time. The data for the Upper DC Anacostia (Section 2) was not sufficient to conduct a trend analysis.
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 directly reflect the nutrients amount in water. There is a lag time between discharge of nutrients and uptake of those nutrients by plants, etc.
In free-flowing tributaries of the Anacostia, discharged nutrients travel to the tidal Anacostia. Because the river moves so slowly, there is plenty of time for microalgae to take up nutrients. Thanks also to the ample sunlight in the tidal Anacostia, the DC portions of the river (Section 2 and Section 3) tend to have higher Chlorophyll (a) values, resulting lower % Scores.
Both upstream and downstream communites need to stop nutrients runoff from our properties.
*The green pigments of plants. There are seven known types of chlorophyll; Chlorophyll a and Chlorophyll b are the two most common forms. It allows plants to convert sunlight into organic compounds during photosynthesis. Chlorophyll (a) is used as a measure of microalgae biomass, which is controlled by factors such as water temperature and 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 waters of oxygen.
SAV data was obtained from this website: http://web.vims.edu/bio/sav/index.html
AWS's goal for submerged aquatic vegetation (SAV) is 20 acres; this metric was set in the Anacostia Watershed Restoration Indicators and Targets for Period 2001-2010 by scientists at Metropolitan Washington Council of Governments (COG).
Because since the year 2003 there has been no SAV observed in the Anacostia, the % Score -- calculated with the formula of (observes SAV acres)/(20 acres)*100 -- has been 0 (zero) since 2003.
As soon as the degradation of Water Clarity in the MD Anacostia (Section 3) was observed in 1995, the acreage of SAV started to decline.
AWS is not certain why SAV was present in the past --particularly in the 1980s and 1990s when the % Score of Water Clarity seemed worse than or equal to the current clarity. However, we have several hypotheses:
** Vegetation 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.
Click here to download a printable version of the 2011 State of the Anacostia River.