Thursday, July 19, 2012

Less Rain Means a Cleaner Bay

Rainfall has been below normal. In the Washington Metropolitan area Virginia, Maryland and the District of Columbia are dependent on the flows of the Potomac River and the Occoquan for their water supply. Potomac River basin has been abnormally dry this year with the eastern shore of Maryland in a moderate drought and river flows below normal. Although the recent rainfall has eased drought in some areas, not enough rain has fallen to raise watershed stream flow to normal levels. Temperatures have been abnormally high and there appears little chance for precipitation in the near term.  But for now, the Interstate Commission on the Potomac River Basin, ICPRB, reports that from a water supply perspective, there is sufficient flow in the Potomac River to meet both the Washington metropolitan area’s water needs and the environmental water flow needs without augmenting river flows by releasing water from the upstream reservoirs. So we can enjoy the clearer flows of the river with little worry or need to conserve water for now.

The ICPRB allocates and manages the water resources of the Potomac River through the management of the jointly owned Jennings Randolph and Little Seneca reservoirs, the Potomac River Low Flow Allocation Agreement and the Water Supply Coordination Agreement adopted in 1982 which designated the ICPRB as responsible for allocating water resources during times of low flow and assist in managing water withdrawals at other times. The ICPRB limits water withdrawals by the local water utilities coordinating Fairfax Water’s utilization of the Occoquan and Potomac and limiting total withdrawals from the Potomac if necessary. In the event that the Potomac River flow at Little Falls is below 700‐million gallons per day the ICPRB releases water from Jennings Randolph and Little Seneca reservoirs to make up the flow and ensure that the saline and freshwater balance necessary to maintain the oxygen levels for oysters, clams and crab populations is maintained. The reservoirs ensure in-stream flows to meet minimum aquatic habitat requirements and the drinking water needs of the region.  

The July 5th Water Supply Outlook from the ICPRB reports that both groundwater and stream flow remain adequate for the short term, but are below normal as rainfall has been below normal for much of the early spring and June. Jennings Randolph (the big reservoir) is full and we are not going to run out of water this year. The good news is that nitrogen and phosphorus contamination in the Chesapeake Bay could fall to the lowest levels since the droughts of a decade ago. The nitrogen and phosphorus contamination in the Bay is correlated with rainfall as seen below and we can enjoy this little preview of what a cleaner Bay might look like.
From the Chesapeake Bay Program 2012

Since the 1970’s large algae blooms have formed in both the Potomac and Upper Bay portions of the Chesapeake Bay watershed each summer. Larger than normal blooms occurred in the upper Chesapeake Bay and its tributaries during August and September 2000 and 2011. These blooms were probably the result of greater than normal amounts of freshwater and nutrients entering the Bay in those years, but there are still factors that need to be studied.  The dead zones form in summers when higher temperatures reduce the oxygen holding capacity of the water, the air is still and especially in years of heavy rains that carry excess nutrient pollution from cities and farms. The excess nutrient pollution combined with mild weather encourages the explosive growth of phytoplankton, which is a group of single-celled algae. While the phytoplankton produces oxygen during photosynthesis, when there is excessive growth of algae the light is chocked out and the algae die and fall below the interface between the warmer fresh water and fall into the colder sea water. The phytoplankton is decomposed by bacteria, which consumes the already depleted oxygen in the lower salt level, leaving dead oysters, clams, fish and crabs in their wake. Thus, the name- dead zone.

In a wedge estuary such as Chesapeake Bay the layers of fresh and salt water are not typically well mixed, there are still several sources of dissolved oxygen. The most important is the atmosphere. At sea level, air contains about 21% oxygen, while the Bay’s waters contain only a small fraction of a percent. This large difference between the amount of oxygen results in oxygen naturally dissolving into the water. This process is further enhanced by the wind, which mixes the surface of the water. Recent heavy wind storms may have increased oxygen levels in various water layers. ICPRB staff scientists will be working with Maryland and West Virginia natural resources scientists to survey algae blooms in the upper Potomac watershed. Researchers will visit numerous sites along the Potomac, its South Branch up to Moorefield, W.Va., the Cacapon River, and the lower Shenandoah River. The summer-long assessment will document the types and extent of algal blooms in this section of the watershed.

While the recent storm brought much damage, the powerful winds that took down trees also served to mix the waters of the Potomac. The waters of the Bay appear clearer than they have in recent years. While drought does improve nitrogen, phosphorus and sediment levels in the Bay in the short run, the cost of drought can be high (agricultural losses and water restrictions) and ultimately droughts end and the rains will come.  The Chesapeake Bay Foundation still judges the Bay to be “dangerously out of balance” despite progress made in the health of the Bay in the past 30 years and this year’s clear waters and healthy shad run. As the Washington Post Reported recently, the District’s 45 miles of Potomac watershed streams and rivers is so tainted with bacteria from the combined sewer overflows that the city prohibits swimming. The waters of the Potomac are the primary drinking water supply for the region they should be clean enough to be safe for swimming and recreation.  The Watershed Implementation Plans from the six states and Washington DC and the $2.6 billion sewage treatment plant upgrade for Washington DC under the Chesapeake Bay TMDL will further improve the waters of the Potomac and the Bay in the next decades. The Maryland, Virginia and the District estimates that it will cost more than $30 billion for them to meet the mandates of the Chesapeake Bay TMDL pollution diet over the next 13 years. Water is not free, it’s just we do not often see many of the costs associated with it. We need to see and understand all the cost of guaranteeing 24/7 access to clean abundant water.  

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