Thursday, July 4, 2013

The Chesapeake Bay Gets a C- Overall Health is Improving

For the past seven years the University of Maryland Center for Environmental Science has issued a report card for the Chesapeake Bay, evaluating the environmental health of the estuary. In the past the grade was based on three water quality indicators and three biotic indicators, which had then been averaged into an overall Bay Health Index and grade. This year the method was changed.  Total nitrogen and total phosphorus load (important indicators form the U.S. Environmental Protection Agency (EPA) mandated Chesapeake Bay total maximum daily load of those nutrients) were added and phytoplankton (whose growth in excess is a major contributing factor to the summer dead zone) was eliminated. In addition, each of what are now seven indicators is weighted equally in measuring the health of the Chesapeake Bay. Part of the reason for the change was the data collected under the EPA mandate does not include phytoplankton. According to the scientists and their grading scale we got a “C”. The overall health of Chesapeake Bay improved from 2011 to 2012. In 2011 the overall grade was a 40%, and now is 47%.
From 2012 Chesapeake Bay Report Card

One drawback of the annual reporting framework is the lack of context- an indication of whether Bay health is improving or getting worse. Now with this change in the grading method looking back is more important than ever. This year, Professor Bill Dennis and the other researcher of the University of Maryland Center for Environmental Science have graded all 15 reporting regions of the Chesapeake Bay for the years 1986 to 2011 to look for trends in the data using a consistent methodology. Four out of the fifteen regions had a significantly improving trend. The four reporting regions with significantly improving trends were the Upper Western Shore, Upper Bay, James River and Elizabeth River. One region, the York River, showed a slightly improving trend, although it was not statistically significant. Unfortunately, the MidBay with moderate ecosystem health (its overall grade is a C) is the onlyregion with a declining health trend since 1986 that seemed to be driven by declinesin benthic community and aquatic grasses despite improvements in water clarityand total nitrogen load.  

The organisms that live at the bottom of the Chesapeake Bay and its streams and rivers like clams, worms, oysters and mussels are examples of benthic organisms. Scientists believe that the health of the benthic community organisms provide a good snapshot of environmental conditions in the Bay and its streams and rivers. Most benthic creatures are fairly stationary and reflect pollution or unhealthy water conditions in particular locations. Benthic communities are exposed to many stressors, including low oxygen levels caused by excess growth of phytoplankton, excess sediment and chemical contaminants. Some reasons that the benthic community would be poor are:
  • In summer, high temperatures and nutrient pollution often lead to low-oxygen areas at the bottom of the Bay and its rivers.
  • Excess sediment suspended in the water can block sunlight from reaching bay grasses growing at the bottom. When sediment finally settles, it can bury oyster bars and other benthic species.
  • Many chemical contaminants that are not part of the Chesapeake Bay pollution diet concentrate and bind to bottom sediments, remaining there for years. Benthic species become contaminated when they feed and live in these toxic sediments.
  • Heavy spring rains particularly those associated with flash floods are generally responsible for high nutrient runoff and earlier and larger dead zones in the mid Bay’s tidal waters. This usually results in greater degradation in the benthic community. The 2012 dead zone was the 2nd smallest since 1985 and has been followed by the prediction that the 2013 dead zone will be smaller than average this summer. Professor Bill Dennis of the University of Maryland Center for Environmental Science attributes this smaller dead zone to the cool and relatively dry spring followed by late arriving rains. Yet even with this good news, the mid bay region has deteriorated. 

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