Chesapeake Bay - Overview:

Synopsis

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Chesapeake Bay health declined in 2010
Based on water quality and biotic indicators, the overall health of Chesapeake Bay declined for the first time in four years, by 4%. The overall grade declined from C in 2009 to C‒ in 2010, which indicates moderately poor health. Only two reporting regions (James River and York River) had improved grades in 2010, three were unchanged, and nine declined. The highest-ranked region in previous years, the Upper Western Shore, decreased to fourth highest. The Upper Bay (C+) became the top-ranked region in 2010.


Potomac River health declines in 2010 following high winter flow
The Potomac River region's overall health score decreased from 49% in 2009 to 34% in 2010, changing the overall grade from a C to a D. This decline in score may be related to several factors, including high streamflow in late winter and early spring.

While total streamflow to Chesapeake Bay was within the normal range during the 2010 water year (October 2009–September 2010), Potomac River daily flow was frequently higher than average, especially during late winter. 

Two major storm events—January 27 and March 15, 2010—contributed to this high flow. The streamflow pattern was unique because it is unusual to have two very high flow events so close together, and because these conditions were followed by prolonged periods of lower than average flow in late spring and summer.

Left: 2010 Potomac River streamflow compared to the long-term average. Two storm events contributed a large amount of nutrients and sediments to the river. Data: USGS; normal range is 25–75%.

Right: High-flow event in Great Falls Park along the Potomac River in March 2010.


 

A large percentage of the phosphorus and sediment loading in a year can result from just one or two high flow events. The high winter flow in the Potomac likely contributed an above average amount of nitrogen, phosphorus, and sediment to the estuary in early 2010. Four of the six water quality and biotic indicator scores decreased sharply this year, possibly as a result of increased winter loads followed by decreased summer loads. The phytoplankton community score was the lowest in 14 years, the chlorophyll a score was the lowest since monitoring began in 1986, and the water clarity and benthic community scores declined following multiple years of improvement. More information is available at /ecocheck/report-cards/chesapeake-bay/2010/summaries/potomac_river/.

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.

 

Region Rankings

2010 Bay health declines from 2009
Overall health was worse in 2010 compared to 2009, decreasing from a score of 46% to 42% which is rated a C-, or moderately poor. Overall declines were seen in two water quality indicators: chlorophyll a and water clarity. Overall dissolved oxygen remained steady in 2010. Overall distribution of aquatic grasses across the Bay was about the same in 2010 as in 2009. However, this is 5% less than the 2008 score. Benthic community condition decreased slightly and phytoplankton community condition increased slightly. The decline in 2010 overall Bay health likely reflects increased streamflow (and therefore nutrients and sediment) during winter 2010, followed by very low streamflow during late spring and summer 2010.

Only two reporting regions (James River and York River) had improved grades in 2010, three were unchanged, and nine declined. The highest-ranked region in previous years, the Upper Western Shore, decreased to fourth highest. The Upper Bay (C+) became the top-ranked region in 2010.

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		51	40	54	45	35	40	41	37	39	50	36	33	26	18	19		26
Biotic Index		62	60	44	48	50	44	43	46	29	16	28	24	21	15	8		Insufficient Data
Bay Health Index		57	50	49	47	43	42	42	41	34	33	32	29	24	16	13		19*

 *Average of only four indicators

Excel Spreadsheet

Region Summaries

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.

Comparison

Comparison of Bay Health Index scores for 2010 () compared to

20122011200920082007200620052004200320022001200019991998199719961995199419931992199119901989198819871986

()

	Score (%)
	0               20               40               60               80              100

Upper Bay
Lower Bay
James River
Upper Western Shore
Rappahannock River
Overall Bay
Mid Bay
Lower Eastern Shore (Tangier)
Potomac River
Choptank River
York River
Upper Eastern Shore
Patuxent River
Elizabeth River
Patapsco and Back Rivers
Lower Western Shore (MD)

Trends

Overall Bay Trends Graph

The Bay Health Index (BHI) allows us for the first time to have an integrated view of the health of the Bay over the past 24 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. In 2010, water quality indicators declined more than biotic indicators. This is a slight mismatch that needs further investigation.

Throughout the 24-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 newly finalized Chesapeake Bay Total Maximum Daily Load (TMDL) and Watershed Implementation Plans (WIPs) are tools that can help restore the Bay. The other noticeable feature in the 24-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.

Excel Spreadsheet

Background

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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.

Agricultural BMPs

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.

Urban BMPs

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.