Chesapeake Bay - Overview:
2008 Chesapeake Bay health remains poor
The overall health of Chesapeake Bay, assessed using water quality and biotic indicators, was poor in 2008, obtaining a grade of C-. As to be expected, health of the 15 individual reporting regions varied, ranging from B- (moderate-good) to F (very poor). The highest ranked region, for the second year in a row, was the Upper Western Shore, while the lowest ranked region this year was the Lower Western Shore (MD).
Little recovery after the impact of wet conditions in 2003
Chesapeake Bay health declined significantly in 2003 due to wet conditions washing excess sediment and nutrients into the Bay. Since this rapid decline, the Bay-wide health score has only modestly improved, increasing from 36% in 2003 to 43% in 2008-still much lower than the 55% the Bay scored in 2002, before the wet conditions.
Some regions improving, some worsening
While overall Bay health has remained poor and relatively unchanged in recent years, some individual regions have improved and some have worsened. The Upper Bay is a good example of a region showing improvements over the last 20 years, largely due to a resurgence of aquatic grasses. In contrast, the health of the Upper Eastern Shore has deteriorated greatly in the last four years, with a decline in aquatic grasses and benthic community condition. Loss of aquatic grasses in this region is perplexing considering the rapid resurgence in aquatic grasses observed in nearby regions.
Aquatic grasses continue to recover
Underwater aquatic grasses, which are a vital habitat for crabs and many fish, continued to recover in many regions of the Bay in 2008. While still well below the restoration goal, this improvement is encouraging after recent significant losses in 2006. In the Upper Bay this increase is primarily the result of continued expansion of freshwater grasses. In the Mid Bay, Lower Bay, and Lower Eastern Shore (Tangier) regions this is due to an expansion of eelgrass and/or widgeon grass. Unfortunately, the situation is the opposite in some areas, such as the Choptank River and the lower Potomac River, where aquatic grasses have been declining.
Health Index Map
This map shows the Bay Health Index for all reporting regions. You can also access individual reporting region summary pages by clicking on them, or mousing over for quick summaries.
2008 Bay health similar to 2007
Overall health was slightly better in 2008 compared to 2007, increasing from a score of 42% to 43%, which is rated moderate-poor. There were improved benthic community condition and aquatic grasses scores in certain regions, leading to reporting region scores that were higher in 2008 than in 2007. However, these improvements did not occur everywhere, with some regions of the Bay having decreased health, such as the Lower Western Shore (MD) and Lower Bay. The Patapsco and Back Rivers region declined this year, after increasing last year. The Upper Western Shore was the top-ranked region for the second year in a row, with a score of 64% or B-. Aquatic grasses, benthic community, and dissolved oxygen in this region continue to be very healthy. River flow, and therefore nutrients and sediment that affect Bay health were average this year, as they were in 2007. This was reflected in scores in 2008 that were similar to 2007 for most reporting regions.
This table shows the Water Quality Index, Biotic Index and the overall Bay Health Index for all reporting regions. Mouseover the index values to see the values of the component indicators/indices. You can also access individual reporting region summary pages by clicking on their name, or indicator details by clicking on their icons.
|Water Quality Index||43||53||56||45||37||40||45||42||35||43||35||31||29||20||16||31|
|Biotic Index||85||65||34||42||50||45||37||38||43||12||18||20||17||20||22||Insufficient Data|
|Bay Health Index||64||59||45||44||43||43||41||40||39||28||27||25||23||20||19||23*|
*Average of only four indicators
Listed in order of Bay Health Index from best to worst. You can access more detailed information on each reporting region by click on the region names.
|Upper Western Shore|
|Moderate-good ecosystem health--highest ranked region. Large improvement in benthic community condition and aquatic grasses in the past two years.|
|Moderate ecosystem health: Health improved significantly in the past five years, with rapid increase in aquatic grasses, phytoplankton community condition, and water clarity scores.|
|Moderate ecosystem health. Aquatic grasses continue to improve, with the highest score recorded in 15 years. In contrast, benthic community condition has declined over the past four years.|
|Moderate-poor ecosystem health. Highest score in the past five years due to improved water clarity and phytoplankton and benthic community condition.|
|Moderate-poor ecosystem health. Few signs of improving health after significant decline due to wet conditions in 2003.|
|Moderate poor ecosystem health. The overall health score only increased by 1% in 2008, compared to 2007. The bay-wide health score has only modestly improved over the past five years, increasing from 36% in 2003 to 43% in 2008. This is still much lower than the 55% the Bay scored in 2002, before the wet conditions in 2003.|
|Lower Eastern Shore (Tangier)|
|Moderate-poor ecosystem health. Best water clarity score in over 20 years of monitoring, but still degraded. Small recovery of aquatic grasses after losses in 2003 and 2006.|
|Moderate-poor ecosystem health. Best water clarity score in ten years. Aquatic grasses rapidly recovering after major loss in 2003.|
|Poor ecosystem health. Gradually recovering from impact of wet conditions in 2003. Recovery mostly due to a healthier phytoplankton community, but overall health is still degraded.|
|Poor ecosystem health. Aquatic grasses have rapidly declined in recent years, from 3,900 hectares in 2002 to 218 hectares in 2008.|
|Upper Eastern Shore|
|Poor ecosystem health—lowest score in 17 years. Recent decline in health due to loss of aquatic grasses and declining benthic community condition.|
|Poor ecosystem health. Health getting worse over the past five years, largely due to an overall decline of aquatic grasses and phytoplankton community condition.|
|Very poor ecosystem health. Most health indicators remained consistently poor over the past 20 years. Benthic community condition has declined in the 2000s compared to the late 1990s.|
|Patapsco and Back Rivers|
|Poor ecosystem health. Water quality scores over the past 20 years have been consistently poor, showing no signs of improving.|
|Lower Western Shore (MD)|
|Poor ecosystem health-lowest ranked region in the Bay. Benthic community condition has worsened over the past 15 years. Water clarity and chlorophyll a scores have remained poor.|
|Incomplete assessment.Two of the three biotic indicators do not have data at this time, leading to an incomplete assessment. Water quality score over the past 20 years has been consistently poor, showing no signs of improving.|
* Based on the average of four indicators, grade not provided.
Comparison of Bay Health Index scores for 2008 () compared to ()
|0 20 40 60 80 100|
|Upper Western Shore|
|Lower Eastern Shore (Tangier)|
|Upper Eastern Shore|
|Patapsco and Back Rivers|
|Lower Western Shore (MD)|
Overall Bay Trends GraphThe Bay Health Index (BHI) allows us for the first time to have an integrated view of the health of the Bay over the past 22 years. This long-term view of overall Bay health illustrates how similarly the water quality (dissolved oxygen, water clarity, and chlorophyll a) and biotic indicators (aquatic grasses, Benthic and Phytoplankton Index of Biotic Integrity) respond at a Baywide scale from year to year. This similarity illustrates the connection between the Bay's water quality and biological responses. For example, a period of high nutrient loads (e.g., during a wet year) leads to poor dissolved oxygen, which results in poor benthic conditions. These degraded conditions then contribute to an overall poor score. Throughout the 22-year period, the BHI is only about half way to the goal, which shows that we need to improve our efforts to restore the Bay. The other noticeable feature in the 22-year assessment is the variability of Bay health scores, and how this inter-annual variation corresponds to changes in rainfall or river discharge. During wet years the Bay's health deteriorates and during dry years it improves. This is particularly noticeable in the 2000 to 2003 period when successive dry years resulted in one of the highest BHI scores, 54, but the wet condition of 2003 resulted in a rapid decrease to one of the lowest on record, 36.
This graph is dynamic, you can: a) show and hide items by clicking them in the legend, b) select year range (click and drag), and c) export as an image.
The report card aims to inform citizens on the progress Chesapeake Bay is making toward becoming a healthy ecosystem. This year's report card shows that the health of the Bay improved slightly in 2007 when compared to 2006. While the overall health of the Bay and most regions of the Bay improved, the health of some regions of the Bay declined. This newsletter also explores some of the long-term changes in report card scores, making a connection between the scores and influencing factors such as land use and nutrient loads.
Getting to the source of the problem
It is well understood that excessive nitrogen, phosphorus, and sediments are major causes of Chesapeake Bay's poor health condition. To help reduce the amount of these pollutants entering the Bay, it is important to determine their sources, so that restoration efforts can be targeted for maximum effect. One of the tools used to estimate pollutant sources and loads and the effectiveness of best management practices (BMPs) is the Chesapeake Bay Watershed Model. This model estimates loads for a variety of land use types, based on factors such as BMP assumptions, average hydrology, vegetation cover, and point source nutrient loads. A simple assessment of the modeled nitrogen load estimates illustrates that the largest contributors are the Susquehanna, Potomac, and James Rivers, mainly due to the fact that these rivers have the largest watersheds. The main sources of nitrogen within each of the regions vary significantly. Agriculture is estimated to be the main source of nitrogen in the Eastern Shore regions, while point sources (wastewater) are the main factors in the James River and Patapsco and Back Rivers regions. The different primary nitrogen sources and the Bay health scores highlight the need for targeted implementation of best management practices. While the figure below provides a modeled estimate of nitrogen into each of the report card regions, it does not account for mixing or transport of nutrients from one region (e.g., the mainstem Bay) to another (e.g., a tributary such as the Patuxent River).
Estimated total nitrogen loads for 13 watersheds/regions in the Chesapeake Bay Watershed and the 2007 Bay Health Index for the 15 reporting regions.
Data: The Chesapeake Bay Watershed Model, Phase 4.3, 2007 Progress Run was used to estimate total nitrogen and phosphorus loads to Chesapeake Bay. Estimates for wastewater based on measured discharges; other categories based on average hydrology and current BMP efficiency assumptions. Does not include contributions from direct atmospheric deposition to tidal waters, tidal shoreline erosion, or the ocean.
Linking land use to Bay health
The Bay Health Index (BHI) provides a broad-level approach to assess the connection between land use and Bay condition. Land use within each of the watersheds is compared with the health of the adjacent waterway. In general, the higher the proportion of agricultural and developed land relative to forested land, the lower the BHI. This approach does not account for pollutants from other sources, such as coastal erosion or transport from adjacent waterways, but the strong correlation suggests that watershed activities in each region highly influence the BHI of the corresponding waterway. This relationship provides a useful framework from which the effects of land use change and best management practice (BMP) implementation can be viewed. Theoretically, if land use (% development and agriculture) stays the same, and the implementation of urban and agricultural best management practices is increased, then the health of the Bay will improve. Conversely, if BMPs were to decrease, then we can expect the health of the Bay to deteriorate. Additionally, if BMPs stay the same and land use (area % development and agriculture) changes, then the health of the Bay will also respond. This is an oversimplification of these relationships, but still serves as a good conceptual framework. An example of this oversimplification can be seen when looking at the effects of land use change from agriculture to developed land. Developed land (including urban run-off and partial treatment of human waste) within the Chesapeake watershed generates on average a total of 14.8 pounds of nitrogen per acre compared with the average agricultural rate of 11.71. Based on these numbers, a shift toward developed land at the expense of agricultural land will lead to increased nutrient loads unless urban BMPs can keep up with land use change — a factor not captured by the relationship shown.
The average Bay Health Index decreases with increasing conversion of forested lands to agriculture and urban development.
Estimated total nitrogen loads for 13 watersheds/regions in the Chesapeake Bay Watershed.
Data: Chesapeake Bay Watershed Model, Phase 4.3.
Best Management Practices
There are literally hundreds of Best Management Practices (BMPs) that target reduction of nutrient and sediment loads to Chesapeake Bay. These may be as simple as individuals fertilizing their lawn during the recommended time of the year (fall), to large and expensive engineering exercises such as upgrading municipal wastewater treatment plants. Here are some of the most important and some of the new BMPs being undertaken in agriculture and urban areas.
A. Cover crops - Non-harvested cereal cover crop specifically planted in fall for nutrient removal. Cereal cover crops reduce erosion and the leaching of nutrients to groundwater by maintaining a vegetative cover on cropland and holding nutrients within the root zone during the non-growing cash crop season (winter).
B. Riparian buffers - Up to 100-foot-wide buffer of grass, non-woody, or woody (forest) vegetation between crop and waterway. A 100-foot-wide strip of grass buffer can reduce sediment significantly. Fencing to exclude farm animals, although not a riparian buffer, can help slow the erosion of streamside soil.
C. Animal manure management - Animal farming uses directed flows to better contain waste products from animal houses. Lagoons, ponds, steel or concrete tanks, and storage sheds are used for the treatment and/or storage of wastes.
D. Septic upgrades - Septic denitrification represents the replacement of traditional septic systems with more advanced systems that have additional nitrogen removal capabilities. Septic connections/hookups represent the replacement of traditional septic systems with connection to and treatment at wastewater treatment plants.
E. Stormwater management control - Includes rain gardens (which direct flow from impervious surfaces to a vegetated area before the water reaches the storm drain), green roofs (which use the rainwater hitting the roof to feed plants), and riparian buffers. Filtering practices capture and temporarily store the water quality volume and pass it through a filter of sand, organic matter, and vegetation, promoting pollutant treatment and recharge.
F. Enhanced nutrient removal - Wastewater treatment plants are being upgraded to enhanced nutrient removal, which uses the most efficient removal process available, before the water is discharged into local waterways.