NITROGEN IN THE CHESAPEAKE BAY:
A RETROSPECTIVE
Nitrogen pollution has been a primary cause of a degraded Chesapeake Bay ecosystem for over a century. However, resource management
response to excess nitrogen only began in the 1970s with the Clean Water Act. Since then, Bay monitoring programs have measured the amount
of nitrogen coming from human activities on land (urban, suburban, rural, and industrial) and from natural cycling in the water column. This
newsletter summarizes monitoring data and describes nitrogen trends in both the non‒tidal and tidal areas of the Chesapeake Bay.
Human response to nitrogen loading in the
Chesapeake Bay: How far have we come?
1300
BAY EUTROPHICATION
Estuar
y Scien
ce Ex
plorat
ion & E
xploita
tion
Population
13,000
Degradation begins from early human population growth
(Europeans settle in the Chesapeake area around 1650).
Large‒scale land clearing for timber and agriculture begins (1820s).
Extensive use of natural fertilizer begins (1835;
(using bird guano from South America).
1600
1800
Population
1 million
HUMAN RESPONSES
Virginia lawmakers make a law in order to prevent overfishing
in the Rappahannock River (1680).
States begin outlawing commercial hunting (1820s).
1900
Increasing scientific studies of human impacts
on the bay (1925−).
2002
30,000
Largest amount of
aquatic grasses
recorded (2002)
since monitoring
began (1984).
20,000
2005
Date
2000
1995
0
1990
10,000
1985
Hectares
40,000
Restor
ation S
cience
Largest hypoxic zone
(1993) in the bay
mainstem during period
of record (1985–2009).
Eutrop
hicatio
n Scien
ce
Extensive use of chemical
fertilizers begins (1950).
Dramatic decline in
aquatic grasses due to
excess sediment and
nutrients (1970s).
Population
4.5 million
1950
Population
7 million
2000
Population
15.8 million
Municipal and
industrial
wastewater
Urban and
suburban
lands
20%
42%
Agriculture
(manure and
fertilizer)
16%
22%
Atmospheric
deposition
Resurgence of aquatic grasses in low salinity
zones of the bay is correlated with
decreasing nutrient loads (2010).
Accou
ntabil
ity
While nitrogen trends in the bay improve,
water clarity remains poor.
Bay nitrogen sources, 2007
Baltimore is first city in U.S. to use
wastewater treatment facility (1920).
Clean Water Act passed, limiting the type and
amount of nutrients to the Bay. It also
provided for municipal sewage treatment
plants (1972).
Chesapeake Bay Commission created (1980).
Chesapeake Bay Program
created (1983).
Goals set to reduce nitrogen (1987).
1 million acres of farmland are under
nutrient management plans (1994).
Blue Plains WWTP (biggest in watershed) begins
BNR for half of its flow (1996).
Chesapeake 2000 sets goal of reducing pollution
enough to take the bay off the EPA’s impaired
waters list.
2002 Farm Bill passed,
funding agricultural subsidies.
2004 Chesapeake Bay
Restoration Fund (MD) for
WWTP upgrades to ENR.
Bay‒wide report card
introduced (2006).
EPA proposes draft nitrogen
Total Maximum Daily Load
(TMDL) for Chesapeake
Bay (2010).
Future:
Ecosystem Response
BNR = biological nutrient removal
ENR = enhanced nutrient removal
WWTP = wastewater treatment plant
Figure 1. Tracking Chesapeake Bay ecosystem health in relation to nitrogen and human milestones over time documents some resource management
success, in spite of the continued challenge of population growth. Blue text represents phases for Chesapeake Bay science.
Connecting nitrogen trends in the Bay and its watershed
Trends in the bay
The US Geological Survey (USGS), US EPA Chesapeake Bay Program, and state agencies measure nitrogen and streamflow at many
locations in the Chesapeake Bay watershed. This information is used to evaluate management actions for nutrient reduction. Nitrogen
concentration varies each year due to both human‒related and natural factors. Human activities include agricultural and suburban
fertilizer application as well as implementation of management practices. Natural factors include variation in weather (precipitation)
and transportation times of nitrogen in streams and groundwater.
Nitrogen concentration at individual locations varies within years mostly due to rainfall and resulting streamflow, as seen at a
Potomac River site near Washington DC (Figure 2). Results for the same Potomac site over a 24-year period show a slight decrease in
nitrogen from 1984 to 2007 (Figure 3). Of the 34 sites tested for trends
in the non‒tidal network, the majority have statistically significant
improving or no significant trends in non-flow-adjusted total nitrogen
concentrations (Figure 4). It should be noted that while the improving
trends are statistically significant, in many cases, the amount of change
has not been enough to meet nutrient reduction goals. This is not
surprising considering only 50% of the sites show improving trends. As
a result, there is still a large amount of nitrogen making its way into the
Chesapeake Bay.
Significant nitrogen concentration trends are present for most of the Chesapeake Bay mainstem since monitoring began in the
mid-1980s, except in the Upper Bay (Figure 5). There are some signs of improving nitrogen trends in the middle and lower mainstem,
although many of these trends show a switch from degrading or no nitrogen concentration trends to improving nitrogen concentration
trends (Figures 6 and 7).
A closer look at data from specific tributary and mainstem locations reveals both improving and degrading nitrogen concentration
trends. In the upper tidal Potomac River, a resurgence in aquatic grasses may be related to improving nitrogen concentrations, as well
as decreased point source nitrogen loads by a recently upgraded wastewater treatment plant. Most monitoring stations in the lower
Chesapeake Bay mainstem show improving nitrogen trends, although the source of these trends is unclear, since the tributaries flowing
into the lower Bay have degrading or no trends in nitrogen concentrations. It could be the influence
of ocean water coming into the Bay and mixing with Bay waters.
At other stations across the tidal portion of the Bay, monitoring reveals degrading total nitrogen
trends. Nitrogen concentrations are degrading in the upper Patuxent River (since the early to mid
2000s). Additional degrading trends are found in the middle of Virginia’s Rappahannock River, and
at most of the monitoring stations in the lower York River, perhaps due to increasing total nitrogen
point source loads. These degrading nitrogen concentrations may reflect increasing or additional
pressures from human activities or biological processes.
Dept of Nat. Resources; Laura Fabian
Trends in the watershed
Water quality is collected by automatic data logger platforms and
researchers throughout the Chesapeake Bay watershed. Water
samples are taken back to the lab for nitrogen analysis.
Total nitrogen concentrations in non‒tidal
Chesapeake Bay (rivers and streams)
C. Wicks
0
25
50 Miles
0
40
81 Kilometers
25
50 Kilometers
2.5
2.0
The mainstem Bay shows decreasing
nitrogen concentrations (indicated
by the green arrows and inverted
U shapes), which coincide to
decreasing nitrogen concentrations
in the Susquehanna River watershed.
However, the shape of the trend,
as an inverted U, indicates that
nitrogen has just started to decrease
after either increasing, or staying the
same, for many years. The trends in
the tidal Rappahannock and York
River follow the degrading or no
trend nitrogen concentrations seen
in the watershed.
1.5
1.0
0.5
0.0
Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sept Oct
Date
Figure 2. Non-flow-adjusted nitrogen concentrations on
the Potomac River at Great Falls, MD, shows variability
from month to month.
Long-term non-flow-adjusted
total nitrogen concentration
Potomac
watershed
Potomac River Site
01646580
Fishing Bay
James
watershed
Tangier Sound
Rappahannock
River
Pocomoke River
8
6
4
Improving nitrogen
trend
2
1993
Date
1998
2003
2007
Figure 3. The long-term, non-flow-adjusted concentration
data for the same site show a slight decrease in nitrogen
from 1984 to 2007.
No trend found
in the data
Figure 4. Map of non-flow-adjusted total nitrogen concentration trends in
the non‒tidal Chesapeake Bay watershed. Approximately half of the sites
are shown to be improving.
0.4
0.3
0.2
0.1
0
Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sept
Date
Figure 6. Monthly averages for the mainstem tidal site,
CB7.4, for the 2003 water year. One year of data is not
enough to see a trend due to the variability in the data.
Long-term total nitrogen concentration
Mobjack Bay
James River
Non‒linear improving
due to decreasing loads
Degrading nitrogen
trend
0.5
York River
0.9
0.8
Lower
Eastern
Shore
watershed
10
Concentration (mg l‒1)
Nanticoke River
Nitrogen is declining in the Bay
where nitrogen is declining in
the watershed
1989
Total nitrogen concentration, water year 2003
0.6
Non‒linear degrading
due to increasing loads
No trend found in
the data
Degrading trends due
to increasing loads
Improving trends due
to decreasing loads
Figure 5. Total nitrogen concentration trends in the tidal portions of Chesapeake Bay. MD
and VA tributaries data are from 1985 through 2009 while the VA mainstem Bay data are
from 1988 through 2009. The difference in date ranges may have influenced the observed
trends. Note: No non‒linear trends available for VA tributaries.
Concentration (mg l‒1)
Concentration (mg l‒1)
0
31 Miles
Potomac River
3.5
Concentration (mg l‒1)
15.5
A researcher measures water
quality parameters on the tidal
portion of the Rhode River.
Choptank River
3.0
0
1984
0
Susquehanna
watershed
Non-flow-adjusted total nitrogen concentration,
water year 2003
4.0
12
Total nitrogen concentration trends in tidal Chesapeake Bay
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
1987
1992
1997
Date
2002
2007
2011
Figure 7. The data for tidal site, CB7.4, over the entire
period of record show an initial increase in nitrogen
followed by a reversal of this trend.
Point source nitrogen = Managed pollution
Over the last 25 years, the model of the annual load of total
nitrogen to the Bay shows a decrease (Figure 8). However, the
model of point source nitrogen shows a continued contribution
of about 20% of the nitrogen that ends up in the Chesapeake Bay.
Wastewater treatment plants are an example of point source
pollution. In the late 1980s, technological advancements for
“cleaning” the water of nitrogen before it enters local waters were
introduced. The latest improvements, called Enhanced Nutrient
Removal (ENR), remove more than 90% of pollutants and reduce
nitrogen concentrations to 3 mg L‒1 (ppm). Although advanced methods for controlling nitrogen inputs
to the bay are well understood, there is a lag time between
Blue Plains BNR
Full Operation
20
60
15
40
10
20
5
0
1990
1995
>5000 less
1000–5000 less
0–1000 less
0–1000 more
Minor WWTPs
Watershed population 25
Total nitrogen
80
1985
Change in total nitrogen (lbs day‒1)
from late 1980s to 2006
2000
2005 2010 2025
Susquehanna
watershed
Population (millions)
Total point source nitrogen
(millions lbs yr-1)
100
the development of the technology and its implementation
at wastewater treatment plants due to the time required for
implementation and at least in part to a lack of public funding.
As a result, many such facilities are still waiting to be upgraded,
which may partly explain the increase in total nitrogen in Figure 9.
Potomac
watershed
0
Lower Eastern
Shore
watershed
Figure 8. Total nitrogen loads delivered per year to Chesapeake Bay
(modeled) and projected population growth. BNR=Biological Nitrogen
Removal; Data: Chesapeake Bay Program.
DCWASA
York watershed
Employees adjust machinery (left) and test nitrification
tanks (right) at wastewater treatment plants.
Newsletter design and layout:
Emily Nauman, EcoCheck
Jane Hawkey, IAN‒UMCES
Heath Kelsey, EcoCheck
Caroline Wicks, EcoCheck
0
25
50 Miles
0
40
81 Kilometers
Figure 9. This map shows the modeled change in total nitrogen at major wastewater
treatment plants (WWTPs) in the Chesapeake Bay. There is an overall decrease in nitrogen
from WWTPs to local waters but many facilities can still be improved.
This newsletter was produced with help from the Tidal Monitoring and Analysis Workgroup (TMAW) of the
Chesapeake Bay Program, as well as USGS, Maryland Department of Natural Resources, and Old Dominion
University. We would like to thank Katie Foreman, Mike Lane, Mike Langland, Joel Blomquist, Renee Karrh, and Bill
Romano for data and review.
For more information: http://www.chesapeakebay.net/nutr1.htm
Published:
August 2010
www.eco-check.org
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