Chesapeake Bay - Overview:
Improved health of Chesapeake Bay in 2009
The overall health of Chesapeake Bay, assessed using water quality and biotic indicators, was the best it has been since 2002. The overall grade improved from Câ€’ in 2008 to C in 2009. Eight reporting regions had improved grades in 2009, four were unchanged, and two had slightly worse grades. The highest ranked region, for the third year in a row, was the Upper Western Shore (Bâ€’), while the lowest ranked region this year was the Patapsco and Back Rivers (F).
2009 precipitation pattern provides insights about Bay health
The unique precipitation (rain, snow, and ice) pattern seen in 2009 provides insights into the relative roles of nutrient and sediment inputs, which affect Bay health, from the Susquehanna River versus the smaller tributaries in Maryland and Virginia. Pennsylvania and New York received relatively low amounts of precipitation in 2009, while tributaries adjacent to the Bay received unusually high levels of precipitation (see figure). This most likely led to decreased inputs from the Susquehanna River and higher inputs from the tributaries in Maryland and Virginia. The mainstem portion of the Bay tends to be more strongly influenced by flow from the Susquehanna than from other tributaries, and in 2009 the Mid Bay (D+ in 2008; C in 2009) and Lower Bay (C- in 2008; C in 2009) mainstem regions appeared to respond positively to the decreased Susquehanna flow. The improvements in 2009 overall Bay health likely reflect the improvements in the Mid and Lower Bay scores, which are the Bay’s two largest reporting regions.
In the 2009 Summer Review, EcoCheck reported that the streamflow also followed these patterns, with a higher-than-average proportion of streamflow coming from the Maryland and Virginia tributaries compared to the Susquehanna River. Furthermore, the total nitrogen and sediment loads to the Bay were lower in 2009 than in recent years. The total non-flow-adjusted loads of nitrogen and sediments decreased from 2008 to 2009, adding to the improved health of the Bay in 2009. All of these data indicate that the health of the Bay improved in 2009 due to decreased nitrogen and sediment overall but particularly due to the lower-than-average amount from the Susquehanna River.
2009 Susquehanna River flow was lower than normal on average for the year. Specifically, the spring months—Feb, March, April, and May—were lower than normal, which affect summer conditions in the Bay. This is one of the reasons the mainstem Bay scores increased this year.
Figure: Estimated annual total nitrogen and sediment loads to Chesapeake Bay. Note the different beginning years of monitoring. Data: US Geological Survey.
Water clarity improves in 2009
An encouraging sign for the Bay’s health was an improvement in water clarity. Following a long-term trend of declining water clarity throughout the Bay, the last two to three years have seen improvement, especially in the average increase in Bay-wide water clarity of 12% in 2009. The water clarity improvements were most dramatic in the middle regions of the Bay, including the mainstem, Choptank, Potomac, and Rappahannock Rivers. However, the reporting regions with chronically poor water clarity, the Patapsco and Back Rivers, Lower Western Shore of Maryland, York River, and Elizabeth River, still had poor water clarity.
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.
2009 Bay health improves from 2008
Overall health was slightly better in 2009 compared to 2008, increasing from a score of 43% to 47% which is rated a C, or moderate. The Upper Western Shore was the top-ranked region for the third year in a row, with a score of B-, or 61%. The Patapsco and Back Rivers were the lowest ranked region this year, with a score of F, or 19%. Overall improvements were seen in all three water quality indicators (chlorophyll a, dissolved oxygen, and water clarity) as well as in benthic community condition. Overall distribution of aquatic grasses across the Bay was the same in 2009 as in 2008. The improvements in 2009 overall Bay health likely reflect reduced nutrient and sediment loads from the Susquehanna River (providing half of the freshwater flows to the Bay in average years), whose watershed received less precipitation than average in 2009.
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||42||52||39||49||52||45||48||47||52||47||43||32||33||26||15||25|
|Biotic Index||79||66||64||48||44||47||44||44||34||21||24||27||14||21||23||Insufficient Data|
|Bay Health Index||61||59||51||49||48||46||46||45||43||34||34||30||24||23||19||19*|
*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 for third year in a row. Very good dissolved oxygen. Aquatic grasses remained steady at healthy levels despite poor water clarity.|
|Moderate ecosystem health: Overall health is the same as last year. Aquatic grasses remained steady at healthy levels after several years of improvement.|
|Moderate ecosystem health. Large improvements in water clarity and benthic and phytoplankton community condition led to highest overall health score in eight years.|
|Moderate ecosystem health. Continued improvement in overall health due to improvements in water clarity and aquatic grasses. Declines in dissolved oxygen and phytoplankton.|
|Lower Eastern Shore (Tangier)|
|Moderate ecosystem health. Water clarity score is the highest since first year of monitoring in 1986, although still considered poor. Aquatic grasses score increased for the second year in a row.|
|Moderate ecosystem health. The overall health score increased by 3% in 2009, compared to 2008. This is the best bay-wide health score since 2002, before the wet conditions that caused the scores to decline from 55% in 2002 to 36% in 2003. This year's improvement is in keeping with the gradual recovery of the Bay from the wet conditions in 2003.|
|Moderate ecosystem health. Improvement in overall health. Aquatic grasses, dissolved oxygen, chlorophyll a, and water clarity scores all showed improvement this year.|
|Moderate ecosystem health. Slight improvement in overall health due to improvements in chlorophyll a, water clarity, and benthic and phytoplankton community conditions.|
|Moderate-poor ecosystem health. Aquatic grasses continue to improve, however, chlorophyll a scores declined by 11%. This region hovers around the border of moderate to moderate-poor health.|
|Poor ecosystem health. Overall health improved slightly, but is still poor. Improvements in water clarity, and benthic and phytoplankton community conditions. |
|Upper Eastern Shore|
|Poor ecosystem health. While still poor, the overall health of this region improved for the first time in five years. The scores for all six indicators showed improvement.|
|Poor ecosystem health. Overall health is slightly better for second year in a row. Water quality indicators continue to be poor, while benthic community condition improved significantly.|
|Poor ecosystem health. No improvement in overall health of this region despite a slight improvement in dissolved oxygen. Most health indicators remain consistently poor.|
|Lower Western Shore (MD)|
|Poor ecosystem health. Improved dissolved oxygen and chlorophyll a conditions. Although benthic community condition improved, overall biotic health continues to be poor.|
|Patapsco and Back Rivers|
|Very poor ecosystem health - lowest ranked region in the Bay. Continued decline of dissolved oxygen, chlorophyll a, and water clarity scores. Biotic indicators are slowly improving.|
|Incomplete assessment.Two of the three biotic indicators do not have data at this time, leading to an incomplete assessment. Water quality indicators show no sign of improvement. Phytoplankton community condition continues to be very poor with a 0% for three years in a row.|
* Based on the average of four indicators, grade not provided.
Comparison of Bay Health Index scores for 2009 () compared to ()
|0 20 40 60 80 100|
|Upper Western Shore|
|Lower Eastern Shore (Tangier)|
|Upper Eastern Shore|
|Lower Western Shore (MD)|
|Patapsco and Back Rivers|
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 23 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 23-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 23-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.