Home | Overview | Regions | Indicators | Watershed Stream Health | Methods | FAQ | Get Involved | Hi-Res Images

Chesapeake Bay - Frequently Asked Questions:

General

What is the Chesapeake Bay annual ecosystem health report card?
The report card is a scientifically robust and geographically detailed annual assessment of Chesapeake Bay ecosystem health. The report card combines multiple indicators (regarding water quality and habitat) of ecosystem health into a single score for 15 regions the Bay.

When is the report card released?
The report card is expected to be released annually in early to mid April.

How does the report card score ecosystem health?
Currently, this report card rates Chesapeake Bay health as defined by progress of six indicators toward established scientifically derived ecological thresholds or goals. A low report card score therefore means that the area of interest rarely meets the ecological threshold levels. A high score means that the area often meets the threshold levels.

How many indicators does the report card include?
There are three water quality indicators (chlorophyll a, dissolved oxygen, and water clarity) and three biotic indicators (aquatic grasses, Benthic Index of Biotic Integrity, and Phytoplankton Index of Biotic Integrity). Other indicators, especially those related to fish and shellfish, will be added to the report card in the future as suitable data becomes available.

How were the report card indicators chosen?
Indicators for the Chesapeake Bay report card were chosen so that they would relate to the management objectives established in the Chesapeake 2000 Agreement, represent key ecological processes, and fulfill practical requirements such as data availability and geographic coverage.

Does the report card address human health issues?
No - Indicators used in the report card have been chosen to measure the health of the Bay's ecosystem and not how healthy the Bay is for human use, such as swimming and fish consumption.

What do the grades mean?
A: All water quality and biological health indicators meet desired levels. Quality of water in these locations tends to be very good, most often leading to very good habitat conditions for fish and shellfish.

B: Most water quality and biological health indicators meet desired levels. Quality of water in these locations tends to be good, often leading to good habitat conditions for fish and shellfish.

C: There is a mix of good and poor levels of water quality and biological health indicators. Quality of water in these locations tends to be fair, leading to fair habitat conditions for fish and shellfish.

D: Some or few water quality and biological health indicators meet desired levels. Quality of water in these locations tends to be poor, often leading to poor habitat conditions for fish and shellfish.

F: Very few or no water quality and biological health indicators meet desired levels. Quality of water in these locations tends to be very poor, most often leading to very poor habitat conditions for fish and shellfish.

What are the factors that affect the grades on a long-term basis?
There are several factors that affect the grades on a multi-year scale. The amount of rainfall in the area can influence how much nutrients and sediment enter the Bay. For example, in 2002 the bay scored a 55% because there were several years of low rainfall. But after the wet conditions of 2003, the health of the Bay deteriorated to a 36%, and has not recovered quickly. Another factor affecting the bay's health on a multi-year basis is the amount of restoration and best management practices that are occurring throughout the bay watershed. For example, stormwater retention ponds and wastewater treament plant upgrades help to keep the bay clean, but it can take multiple years to implement and measure the benefits of these practices.

2006

What were the conditions affecting Bay health in 2006?
The amount of nutrients and sediment deposited into Chesapeake Bay is strongly related to river flow rates and hence weather conditions. Although total flow rates were near normal in 2006, the year was characterized by a dry spring period and an early summer rain event in June caused by tropical storm Alberto. These extreme conditions led to varying impacts to the Bay's ecosystem health.

What is the overall health of Chesapeake Bay in 2006?
The overall health score for Chesapeake Bay in 2006 is 39* out of a possible 100. This score shows that overall health can be considered poor. However, the health of the Bay varies from region to region, with some regions having relatively good health, such as the Upper Bay, while other regions have very poor health, such as the Patapsco and Back Rivers.
*A slightly revised score from the report last year due to an updated, more comprehensive assessment of some indicators. 2006's reported BHI score was 37%.

Why is the Upper Bay so healthy?
Despite being close to the mouth of the Susquehanna River, the Upper Bay had the highest report card score in the Bay (55). Relatively good conditions in this area may be due to high flushing rates, rapidly pushing sediments and nutrients into more southern regions of the Bay. Ecosystem indicators leading to the high score in this region include low chlorophyll a values, a healthy benthic community and more aquatic grasses relative to the restoration goal than any other region of the Bay.

Why is the Patapsco and Back Rivers region so unhealthy?
The Patapsco and Back Rivers region had the lowest water quality score in the Bay because water clarity and chlorophyll a levels never met thresholds levels at any time. Additionally, the region only achieved 11% towards the aquatic grasses restoration goal. The low score was mainly due to the large population living on a watershed that drains into a relatively small river.

How healthy were aquatic grasses in 2006?
There was a decrease of aquatic grasses in 2006 throughout most regions of the Bay. Reasons for the loss are varied and dependent on region of the Bay. Loss in the Lower Bay, including the Maryland portion of Tangier Sound, was due to high water temperatures in late 2005. Dry spring conditions may have contributed to loss of freshwater species due to salinity stress followed by poor water clarity resulting from the June rain event.

Is the Bay's water clarity getting worse?
Yes - Long-term (~20 year) analysis of mid-channel water clarity indicates that the Bay is getting worse. While processes leading to reduced water clarity include sediment resuspension, shoreline erosion and sediment loads from rivers, the exact cause for the trend in reduced clarity still needs to be determined.

What factors lead to low dissolved oxygen levels during the summer?
Low summer-time dissolved oxygen in the mainstem of the Bay is controlled primarily by the quantity of nutrients flowing out of the Susquehanna River during the preceding spring. The excess nutrients lead to blooms of phytoplankton that settle to the bottom of the bay when they die. Bacteria decompose the dead phytoplankton, a process which consumes dissolved oxygen. During summer water temperatures increase and this enhances the rate of decomposition and subsequent reduction in dissolved oxygen levels. During summer factors such as wind and river flow also play an important role in affecting dissolved oxygen levels.

What was the volume of anoxic (oxygen depleted) water in 2006?
Each spring the Chesapeake Bay Program forecasts the amount of oxygen depleted water expected within the Bay over the summer. As predicted, the volume of oxygen-deprived water last summer was better than average, despite the potential effects of the late summer rain event.