Boston Harbor water quality, 2013

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Boston Harbor Water Quality
2013 
Massachusetts Water Resources Authority 
Environmental Quality Department
Report 2014-11

Citation 
Taylor DI. 2014. Boston Harbor Water Quality 2013 . Boston: Massachusetts
Water Resources Authority. Report 2014-11. 7 pp.

Prepared by 
David I Taylor 
Massachusetts Water Resources Authority 
Environmental Quality Department 
100 First Avenue
Charlestown Navy Yard
Boston, MA 02129 
(617) 242-6000 
August 2014 
Environmental Quality 
Technical Report No. 2014-11

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TABLE OF CONTENTS 
EXECUTIVE SUMMARY……………………………………………………………… 1 
1. INTRODUCTION……………………………………………………………….. 1 
2. RESULTS………………………………………………………………………… 2 
2.1 WATER QUALITY……………………………………………………… 2 
2.1.1 Amounts and types of nutrients 2 
2.1.2 Amounts of phytoplankton 4 
2.1.3 Bottom-water DO 4 
2.1.4 Suspended particulate matter 5 
2.1.5 Transparency 6 
2.1.6 Pathogen indicators 6 
3. PHYSICAL CONDITIONS………………………………………………………7 
4. REFERENCES……………………………………………………………………7

1 
EXECUTIVE SUMMARY 
Significant improvements to the water quality of
Boston Harbor have been observed since the
early 1990’s. This report provides an overview
of water quality conditions in Boston Harbor
during 2013. Because the impacts of upstream
processes (including infrastructure projects by
the MWRA and others) are integrated by the
main body of the harbor, this report focuses on
this particular region of the harbor. 
• N and P concentrations during 2013
were the lowest since concentrations
were first measured in 1995. They were
much lower than during the years the
harbor received the discharges from the
Deer Island and/or Nut Island treatment
facilities. 
• Bottom-water dissolved oxygen DO
concentrations during 2013 were the
highest since monitoring started in 1994. 
• Enterococcus counts easily met the State
swimming standard, and were among
the lowest observed since 1996. River
inflows, and water temperatures and
salinity in the harbor were
approximately average for the period
1994-2013. 
• Phytoplankton biomass in the harbor
during summer 2013 (and measured as
concentrations of chl-a) was lower than
all years the harbor received the WWTF
discharges. Chl-a concentrations during
2013 were the second highest for the 13
summers since the discharges to the
harbor were ended. 
• TSS concentrations were the highest,
and water transparency the poorest
observed since monitoring was started.
The causes of these particular changes
are not known for certain, but sediment
resuspension or shoreline erosion was
likely the cause. 
Water quality in Boston Harbor has greatly
improved during the past 20 years, and apart
from the increased TSS and decreased
transparency, 
1.0 INTRODUCTION 
During the past 25 years the MWRA has
undertaken a series engineering projects to
better collect, treat and dispose of the
wastewater discharged from the City of
Boston and surrounding communities to the
harbor and its tributary rivers. These
projects have included the Boston Harbor
Project (Fig. 1, Taylor 2010), the combined 
Fig. 1. Deer Island wastewater treatment
facility with City of Boston in background. 
sewer overflow Control Plan (MWRA
2013), the TRAC pretreatment program, and
programs to decrease infiltration into the
sewer system. 
Over the same period MWRA has monitored
water quality in Boston Harbor in support of
these engineering projects. In this report we
document the harbor water quality during
2013. The report focuses on the main body
of the harbor, because water quality in this

2 
region integrates the impacts of pollutant
inputs from all sources. 
This report presents data collected by
MWRA at 12 harbor locations (Figure 2).
The data were collected as part of MWRA’s
Boston Harbor Water Quality Monitoring
(BHWQM) project. Most of the 12
locations have been sampled weekly or
every two weeks since 1994. The sampling
and analytical procedures used are described
in detail in Rex and Taylor (2000). 
Fig. 2. Boston Harbor showing the 12
sampling locations, and the Inner (IH) and
Outer Harbor (OH) regions of the harbor. 
All data in the report are averaged for either
the harbor as a whole, or for particular
regions of the harbor. The horizontal bars at
the top of each of the Figures shows the 13
years since the wastewater treatment facility
discharges to the harbor were discontinued
in September 2000. 
2.0 RESULTS 
2.1. WATER QUALITY 
2.1.1. Amounts and types of
nutrients 
The harbor’s total N (TN) and total P (TP)
concentrations in 2013 (18.2 μmol l -1 and
1.21 μmol l -1 , respectively), were the lowest
seen since the discharges to the harbor were
ended in 2000 (Figure 3). Total N refers to
dissolved inorganic N (DIN) + particulate
nitrogen (PN) + dissolved organic N (DON),
and DIN refers to NH4 + NO3+2. Total N:
total P concentration ratios during 2013
averaged 15.1:1. They fell within the range
seen since the discharges to the harbor were
discontinued, but were lower than during the
years the harbor received the wastewater
treatment facility discharges. 
Lowered concentrations of the 3 dissolved N
fractions (NH4, NO3+2, and DON) were
responsible for the low total N
concentrations during 2013; concentrations
of the particulate N (PN) fractions were
actually the second highest since the
discharges to the harbor were discontinued
(Fig. 4). 
Both the IH and the OH regions showed the
lowered TN concentrations during 2013
(Fig. 5). As in all years since monitoring
started in 1995, the IH showed greater TN
concentrations in 2013 than did the OH.

3 
Fig. 3. Annual average TN and TP
concentrations and TN:TP concentration
ratios, 1995-2013. 
Fig. 4. Annual average concentrations of
the four fractions making up total N (TN),
1995-2013 
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013 0
10
20
30
40
50 Post-diversion
AVERAGE TN CONC.
( μ MOL L -1 ) 
Total N 
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013 0.0
0.5
1.0
1.5
2.0
2.5
3.0 
Post-diversion
AVERAGE TP CONC.
( μ MOL L -1 ) 
Total P 
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013 0
5
10
15
20
25
30 
Post-diversion
ANNUAL AVERAGE MOLAR
TN:TP RATIO 
N:P 
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013 0
2
4
6
8
10 Post-diversion
AVERAGE NH 4 CONC.
( μ MOL L -1 ) 
AMMONIUM 
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013 0
2
4
6
8
10 Post-diversion
AVERAGE NO 3+2 CONC.
( μ MOL L -1 ) 
NITRATE + NITRITE 
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013 0
2
4
6
8
10 Post-diversion
AVERAGE PART. N CONC.
( μ MOL L -1 ) 
PARTICULATE N 
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013 0
5
10
15
20 Post-diversion
AVERAGE DON CONC.
( μ MOL L -1 ) 
DISSOLVED ORGANIC N

4 
Fig. 5. Annual average TN concentrations in the
Inner Harbor and Outer harbor, 1995-2013 
2.1.2. Amounts of phytoplankton 
Summer phytoplankton biomass (measured
as chlorophyll a) averaged 5.4 μg l -1 in 2013
(Fig. 6). 2013 chlorophyll concentrations
were again lower than during all years the
harbor received wastewater discharges, but
was relatively high compared to the other 12
years after the discharges to the harbor were 
Fig. 6. Summer average phytoplankton
biomass measured as chl-a, 1995-2013.
Summer = J, J, A, S. 
discontinued. Elevated concentrations in
both the IH and the OH regions were
responsible for the elevated 2013
concentrations (Fig. 7). 
Fig. 7. Comparison of summer chl-a in the
IH and OH, 1995-2013 
2.1.3. Bottom-water DO 
Minimum monthly average bottom-water
DO concentrations in 2013 (7.6 mg l -1 ) were
the highest since 1994 (Fig. 8). The harbor
appears to have shown a gradual increase in
bottom-water since 1994, and the elevated
2013 concentrations were a continuation of
this trend. Both in the IH and the OH, the
minimum monthly DO concentrations in
2013 easily met the State Std of 6 mg l -1
(Fig. 9). 
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014 0
10
20
30
40
50
OH 
AVERAGE TN CONC.
( μ MOL L -1 ) 
IH
Total N 
Post-diversion 
1994
1996
1998
2000
2002
2004
2006
2008
2010
2012
2014
0
2
4
6
8
2013 
Post-diversion 
2011
2009
2007
2005
2003
2001
1999
1997
1995
Annual average chl-a conc.
( μ g l -1 ) 
PHYTOPLANKTON BIOMASS
(summer) 
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014 0
1
2
3
4
5
6
7
8
OH 
AVERAGE CHL-A CONC.
( μ G L -1 ) 
IH
Phytoplankton biomass 
Post - diversion

5 
Fig. 8. Minimum monthly harbor-wide
average bottom-water DO concentrations,
1994-2013 
Fig. 9. Minimum monthly average bottom-
water DO concentrations observed in the
bottom-waters of the IH and OH 
2.1.4. Suspended particulate
material 
2013 TSS concentrations were by far the
highest observed since 1996 (Fig. 10). PC
concentrations, a measure of the organic
content of the TSS, were also elevated, but
concentrations were the highest since the not
to the same extent as TSS. PC 
Fig. 10. TSS, PC and PC as % TSS, 1996-
2013 
discharges to the harbor were discontinued,
but lower than during years the harbor
received wastewater discharges. PC
expressed as percent of TSS was the lowest
observed during the study. The elevated 
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014 4
5
6
7
8
9
10 
Post-diversion
Minimum monthly bottom-water
DO conc. ( MG L -1 ) 
Bottom-water DO 
Sta
std 
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014 3
4
5
6
7
8
9
OH 
Minimum monthly average bottom-water DO
( MG L -1 ) IH
BOTTOM-WATER DO 
Post - diversion
State
std 
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
0
1
2
3
4
5
6
7
8 
ANNUAL AVERAGE CONC. ( MG L -1 ) 
TSS 
Post-diversion 
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
0
10
20
30
40
50
60 
ANNUAL AVERAGE CONC. ( μ MOL L -1 ) PC 
Post-diversion 
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
0
5
10
15
20
25
30 
ANNUAL PC as % TSS 
PC as % TSS 
Post-diversion

6 
2013 TSS concentrations were evident both
in the IH and the OH (Fig. 11). 
2.1.5. Transparency 
Transparency in the harbor was the poorest
since 1996, but still relatively high for a
coastal bay or estuary (Fig. 12). Harbor
attenuation coefficients in 2013 averaged
0.62 m -1 . Note, the attenuation coefficients,
as reported, are reciprocal values, so the
higher the value, the more rapid the light
attenuation as it passes through the water. 
2.1.6. Pathogen indicator counts 
Enterococcus counts in 2013 were low, and
averaged 3 colonies 100 ml -1 (Fig. 13).
Counts in the IH were higher than in the
OH, as has been the case in all years since
1995. 2013 counts in the IH were the third
lowest since 1995 (Fig. 14). Counts in the
IH tend to vary more year to year than in the
OH. 
Fig. 11. Comparison of annual average TSS
concentrations in the IH and OH 
Fig. 12. Annual average attenuation
coefficients, 1997-2013 
Fig. 13. Average of the geometric mean 
Enterococcus counts by year, 1995-2013 
Fig. 14. Average geometric mean 
Enterococcus counts in the IH and OH 
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014 0
1
2
3
4
5
6
7 
Post-diversion 
OH 
AVERAGE TSS CONC.
( MG L -1 ) IH
Total suspended solids 
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9 
ANNUAL AVERAGE K ( M -1 ) 
TRANSPARENCY 
Post-diversion 
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013 0
2
4
6
8
10
12
14
16
18
20 Post-diversion
AVERAGE GEOMETRIC MEAN COUNTS
( COLONIES 100 ML -1 ) 
Enterococcus 
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014 0
2
4
6
8
10
12 
Post-diversion 
OH 
AVERAGE GEOMETRIC MEAN COUNTS
( COLONIES 1OO ML -1 ) 
IH
ENTEROCOCCUS

7 
3.0. 2013 PHYSICAL
CONDITIONS 
River flows during 2013 averaged 2.04 x10 6
m 3 d -1 , approximately average for the past
24 years (Fig. 15). Salinity averaged 30.1
psu, again approximately average for the
period 1994-2013 (Fig. 16). Salinity in the
IH in 2013 was lower than in the OH, as has
been the case in all years since 1994. 
Fig. 15. Annual average river inflows into
Boston Harbor. Data are sum of discharges
from Charles, Mystic, Neponset and
Weymouth-Weir rivers (data from USGS). 
Fig. 16. Comparison of annual average
salinity in the IH and OH, 1994-2013 
During all months except for October during
2013, the monthly average water
temperatures fell within the range seen
during other years since the discharges to
the harbor were discontinued (Fig. 17). 
Fig. 17. Average water temperatures by
month of year. Blues lines show data for
2001-2012. 
4.0. REFERENCES 
MWRA. 2013. Combined Sewer Overflow
Control Plan: Annual Progress Report 2012.
Massachusetts Water Resources Authority,
Boston. 
Rex A., Taylor D.I., 2000. Combined
Work/Quality Assurance Project Plan
(CW/QAPP) for Water Quality Monitoring and
Combined Sewer Overflow Receiving Water
Monitoring in Boston Harbor and Its Tributary
Rivers. Boston: Massachusetts Water Resources
Authority. Report 2000-ms-67. 48 p. 
Taylor D.I., 2010. The Boston Harbor Project,
and large decreases in loadings of
eutrophication-related materials to Boston
Harbor. Marine Pollution Bulletin 60: 609-619. 
1990
1992
1994
1996
1998
2000
2002
2004
2006
2008
2010
2012
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
2013
2011
2009
2007
2005
2003
2001
1999
1997
1995
1993
ANNUAL AVERAGE RIVER FLOWS
(x10 6 M 3 D -1 )
1991 
RIVER DISCHARGE 
Post-diversion 
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014 24
26
28
30
32
34 Post-diversion 
OH 
AVERAGE SALINITY
( PSU ) 
IH
Salinity 
1 2 3 4 5 6 7 8 9 10 11 12
-2
0
2
4
6
8
10
12
14
16
18
20
22
2013
D S N F M O M A A J J
MONTHLY AVERAGE TEMP.
( o C )
J 
WATER TEMPERATURE

Massachusetts Water Resources Authority
Charlestown Navy Yard
100 First Avenue
Boston, MA 02129
(617) 242-6000
www.mwra.com