The Boston Harbor Project, and large decreases in loadings of eutrophication-related materials to Boston Harbor

Marine Pollution Bulletin 60 (2010) 609–619

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Marine Pollution Bulletin journal homepage: www.elsevier.com/locate/marpolbul

The Boston Harbor Project, and large decreases in loadings of eutrophication-related materials to Boston Harbor David I. Taylor * Environmental Quality Department, Massachusetts Water Resources Authority, 100 First Avenue, Charlestown Navy Yard, Boston, MA 02129, USA

a r t i c l e

i n f o

Keywords: Wastewater Nutrients Loadings Eutrophication Boston Harbor

a b s t r a c t Boston Harbor, a bay–estuary in the north-east USA, has recently been the site of one of the largest wastewater infrastructure projects conducted in the USA, the Boston Harbor Project (BHP). The BHP, which was conducted from 1991 to 2000, ended over a century of direct wastewater treatment facility discharges to the harbor. The BHP caused the loadings of total nitrogen (TN), total phosphorus (TP), total suspended solids (TSS) and particulate organic carbon (POC) to the harbor, to decrease by between 80% and 90%. Approximately one-third of the decreases in TSS and POC loadings occurred between 1991 and 1992; the remaining two-thirds, between 1995 and 2000. For TN and TP, the bulk of the decreases occurred between 1997 or 1998, and 2000. Ó 2009 Elsevier Ltd. All rights reserved.

1. Introduction Eutrophication or organic enrichment (Nixon, 1995) caused by elevated inputs of reactive organic matter and/or nutrients (principally N and P), has been identified as a threat to coastal aquatic ecosystems worldwide (Scavia and Bricker, 2006; Schindler, 2006; Cloern, 2001). Many of the wastewater infrastructure projects conducted in the USA over the past 50 years have aimed to reduce the loadings of these materials to these systems (Conley et al., 2009). Many of the early projects focused on the removal of solids and reactive organic matter from the wastewater discharged to these systems (e.g. Albert, 1987; Brosnan and O’Shea, 1996). More recently, the projects have aimed to also remove nutrients, in certain cases P, and in others, N (e.g. Jaworski et al., 2007; Mallin et al., 2005). Certain of the projects have employed ocean outfalls to minimize the eutrophication-effects of the wastewater discharges (e.g. Smith et al., 1981). Boston Harbor, a bay–estuary in the north-east USA, has recently been the site of one of the largest wastewater infrastructure projects conducted in the USA, the Boston Harbor Project (BHP) (Breen et al., 1994; Brocard et al., 1994). Before the BHP the total loadings of total nitrogen (TN) and total phosphorus (TP) to the harbor were among the highest reported for bays or estuaries in the USA (Dettmann, 2001; Kelly, 1997). The two wastewater treatment facilities (WWTF’s) that at the time discharged to the harbor, and later became the focus of the BHP, contributed >90% of these elevated loadings (Alber and Chan, * Tel.: +1 617 788 49 52; fax: +1 617 788 48 88. E-mail address: [email protected] 0025-326X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.marpolbul.2009.10.006

1994). The harbor also showed symptoms of eutrophication that were typical of a highly-enriched, but well flushed bay (Diaz et al., 2008; Maciolek et al., 2006; Taylor, 2006; Giblin et al., 1997); the average hydraulic residence time of the harbor is 5–7 d (Stolzenbach and Adams, 1998). This paper documents the changes in the loadings of eutrophication-related materials to the harbor over the course of the BHP, to quantify the contribution of the BHP to the changes. The paper addresses only the loadings to the harbor. Diaz et al. (2008), Oviatt et al. (2007), Maciolek et al. (2006), Taylor (2006), Tucker et al. (2005), Giblin et al. (1997) and others, have documented the changes to the harbor itself.

2. Overview of the BHP The BHP involved five major construction milestones, which were completed between December 1991 and September 2000. Fig. 1 provides a schematic of the five milestones and the changes in the locations of the WWTF sludge and effluent discharges to the harbor over the course of the BHP. Based on these changes, the study could be partitioned into four loading periods (Periods I–IV). During Period I, which here represents the period before the BHP, the harbor received primary- (1°) treated effluent plus sludge generated by the 1°-treatment process, from two WWTF’s. The Deer Island (DI) WWTF discharged effluent and sludge to the North Harbor (Fig. 2). The Nut Island (NI) WWTF discharged effluent to the South Harbor and sludge to the North Harbor. The effluent discharges from the DI WWTF averaged 1.07  106 m3 d 1; from the NI WWTF, they averaged 0.47  106 m3 d 1. The North Harbor also received discharges from 46 combined sewer overflows (CSO’s).

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D.I. Taylor / Marine Pollution Bulletin 60 (2010) 609–619

Fig. 1. Schematic of the study period showing the changes in the locations of the WWTF sludge and effluent discharges, the approximate timing of the five construction milestones of the BHP, and the four loading periods (Periods I–IV).

In December 1991, the dumping of the sludge from the two facilities to the harbor was ended. This was the first construction milestone of the BHP, and also marked the start of Period II. On this date the sludge from both of the WWTF’s was redirected to a new sludge pelletization plant for conversion into fertilizer. The liquid pressate from the sludge was then returned to the NI WWTF for 1°-treatment, and then discharge from the NI WWTF outfalls. During Period II, which extended from 1 January 1992 to 26 April 1998, the harbor received discharges of effluent alone from the two WWTF’s, and at the same locations as in Period I. In July 1995 a new 1°-treatment facility was completed at the DI WWTF; this was the second milestone of the Project. The third milestone, the upgrade to secondary (2°) treatment at the DI WWTF, was started in July 1997, and completed in March 1998. Seven additional CSO’s that discharged to the harbor were eliminated during Period II. The fourth milestone of the BHP was completed on 26 April 1998, when the wastewater (+ sludge pressate) formerly treated at the NI WWTF was diverted through the upgraded DI WWTF for discharge to the mouth of the harbor. This ‘inter-island’ (or ‘I–I’) diversion marked the start of loading Period III. During this loading period, the harbor received WWTF discharges from the DI WWTF alone, and the effluent was 2°-treated. Two additional CSO’s were eliminated during Period III. The final milestone of the BHP was completed on 6 September 2000, when the now-combined and 2°-treated effluent from the DI WWTF was diverted 15-km offshore for diffusion into the bottom-waters of Massachusetts Bay. This ‘offshore’ (or ‘OFF’) diversion ended over a century of direct WWTF discharges to the harbor, and also marked the completion of the BHP. During the next 7 years, represented by Period IV, the effluent from the DI WWTF was discharged through an ocean outfall-diffuser system located on the seafloor of Massachusetts Bay, at a

water-depth of 30 m. The effluent discharged from the outfall during the summers entered the water-column of the bay below the seasonal pycnocline. A further 11 CSO’s were eliminated during Period IV. 3. Methods Loadings and inflows to the harbor were measured from the two WWTF’s, the four largest tributary rivers, and the non-point (NP) sources that discharged directly to the harbor, from 1990 to 2007. Emphasis was placed on the measurement of the flows/loadings from the WWTF’s and rivers; these being the sources responsible for by far the bulk of the loadings of eutrophication-related materials to the harbor (Alber and Chan, 1994). Effluent flows from the two WWTF’s were measured at the points of exit of the flows from the WWTF’s. 47% and 88% of the effluent discharged from the DI and the NI WWTF’s, and 100% of the sludge discharged from both facilities, were assumed to enter the harbor. Previous studies assumed entry of 100% of both the effluent and the sludge from both facilities to the harbor (e.g. Alber and Chan, 1994). The estimates of 47% and 88% were derived from particle dispersion modeling conducted before the BHP, by Signell and Buttman (1992). During the period after the completion of the project, 2% of the effluent discharged from the bay outfall was assumed to re-enter the harbor. This estimate, which is likely to be an over-estimate, was computed assuming the wastewater discharged from the bay outfall was dispersed equally through 360°, and that the proportion of the effluent entering the harbor was proportional to the contribution made by the mouth of the harbor, to the circumference of a circle centered on the bay outfall. Effluent flows from both WWTF’s were measured continuously. Flows from the DI WWTF were measured using magnetic flow

D.I. Taylor / Marine Pollution Bulletin 60 (2010) 609–619

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Fig. 2. Map of Boston Harbor showing the locations of WWTF and CSO discharges to the harbor before the BHP. Also shown are the locations at which the inflows and the loadings to the harbor were monitored during this study.

meters with an error of 0.2–1.4%. At the NI facility, flows were measured using Accusonic level indicators, with an error of 10–15%. At the DI WWTF, effluent nutrient concentrations were measured once per week; at the NI WWTF they were measured once per month. At both facilities, sludge nutrients concentrations were measured once per month. At both facilities, concentrations of total suspended solids (TSS) in effluent were measured once per day; sludge TSS concentrations

were measured once per week. Effluent particulate organic carbon (POC) concentrations were computed for both facilities assuming POC concentrations in 1°-treated effluent averaged 30.1 mg l 1, and in 2°-treated effluent, 3.6 mg l 1 (Butler et al., 1997). Sludge POC concentrations were assumed to be 0.73 times the measured TSS concentrations. TN-concentrations in the effluent and sludge were calculated by summing the measured concentrations of total Kjeldahl nitrogen

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LOADING PERIOD I

II

Sludge

1

III o

IV

o

2 I-I OFF

)

125

-1

( TON D

TSS LOADINGS

150

100 75 50 25 0

-1

)

100

( TON D

POC LOADINGS

120

80 60 40 20

WWTF SLUDGE NP SOURCES RIVERS WWTF EFFLUENT

0

)

30

-1

( TON D

TN LOADINGS

40

20 10 0

6

)

4

-1

3 2 1

2006

2004

2002

2000

1998

1996

1994

1992

0 1990

( TON D

TP LOADINGS

5

Fig. 3. Annual average total loadings of TSS, POC, TN and TP, partitioned by source, 1990–2007. Vertical arrows show the years the five construction milestones were either started or completed. Sludge = sludge dumping ended; 1° = completion of the new primary treatment facility at DI WWTF; 2° = start of the phase-in of secondary treatment at DI; I–I = completion of the inter-island diversion; OFF = completion of the diversion of the DI WWTF flows offshore.

(TKN) and nitrate + nitrite (NO3+2). Effluent and sludge concentrations of TKN were measured according to Clesceri et al. (1998, Method 4500-N); NO3+2 concentrations were measured using Method 353.2 (Clesceri et al., 1998). TP concentrations were measured using Method 365.1; TSS concentrations were measured using Method 160.3 (both methods from Clesceri et al., 1998). River flows to the harbor were obtained from USGS gauging stations (the USGS 8-digit gauging station ID’s are shown in Fig. 2). For the Charles, Mystic and Weymouth–Weir rivers, where the gauging

stations were located above the river–harbor junctions, the gauged flows were prorated by the fraction of the total area of each watershed served by each gauging station. For the Neponset River, where the gauge was located right at the river–harbor junctions, the gauged flows were the flows used to estimate the flows and loadings. For the Charles, Neponset and Mystic Rivers, the water samples for chemical analyses were collected at the river–harbor junctions, once per week, at 0.5 m depths. TN and TP concentrations were

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D.I. Taylor / Marine Pollution Bulletin 60 (2010) 609–619

LOADING PERIOD II

I

TSS:POC LOADINGS

1

o

IV

o

2 I-I OFF

5

-1

D )

3 6

( x 10 m

FRESHWATER INFLOWS

Sludge

III

4 3 2 1 0 3.0

WWTF SLUDGE NP SOURCES RIVERS WWTF EFFLUENT ALL SOURCES

2.5 2.0 1.5 1.0 0.5 0.0

15 10 5

2006

2004

2002

2000

1998

1996

1994

1992

0

1990

TN:TP LOADINGS

20

Fig. 4. Annual average total freshwater inflows and annual average TSS:POC and TN:TP loadings over the study period. The ratios of the loadings are for all loadings combined; the freshwater inflows are partitioned by source. Ratios are by weight.

measured on unfiltered samples, according to Solarzano and Sharp (1980a,b). Samples for TSS and chlorophyll analyses were filtered through nucleopore filters. TSS concentrations were determined according to Clesceri et al. (1998, Method 160.3). Chlorophyll concentrations were measured according to Holm-Hanson et al. (1965). River POC concentrations were calculated from the concentrations of chlorophyll measured in the rivers, assuming POC = chl + (1.94/0.17), r2 = 0.73 (this relationship was derived from concentrations of POC and chlorophyll measured in the Charles River, MWRA unpublished data). For the Weymouth–Weir River, the smallest of the rivers, concentrations of TSS, POC, TN and TP were assumed to be as for the Neponset River. Average CSO discharges to the harbor were estimated using the EPA SWMM Model 4.4, run using typical-year rainfall (roughly equivalent to 1992 rainfall), and the CSO infrastructure present each year (MWRA, unpublished data). CSO TN, TP and TSS concentrations were assumed to be 9310 mg m 3, 3080 mg m 3, and 120,000 mg m 3; these were the average concentrations measured in the CSO’s in 1997 (MWRA, unpublished data). CSO POC loadings were assumed to be 0.7 times the TSS-loadings.

The flows and the loadings from the non-CSO, non-point (NP) sources were estimated using ratios of the inputs from these sources relative to the inputs from the rivers (from Alber and Chan, 1994). The average monthly river flows/loadings measured during the current study were multiplied by these ratios to estimate the inputs from the non-CSO, non-point (NP) sources through the study. The specific ratios employed were 0.27:1 for freshwater inflows, and 0.20:1, 0.23:1, 0.61:1 and 0.27:1 for TSS, POC, TN and TP, respectively. 4. Results 4.1. Changes in loadings, and the major milestones of the BHP The annual average loadings of TSS, POC, TN and TP to the harbor, summed for all sources combined, decreased over the study (Fig. 3). The decreases coincided with the dates of completion of the various construction milestones of the BHP. The annual average TSS- and PC-loadings to the harbor decreased between 1991 and 1992, leveled off through 1994, and then declined again through 2001. The decreases between 1991 and 1992 coincided with, and

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Table 1 Comparison of the average (±1  SD) loadings of TSS, POC, TN and TP, and inflows of freshwater to Boston Harbor, during the four loading Periods. (n = 24 months for Period I, 76 months for Period II, 28 months for Period III, 88 months for Period IV). Source

Average values during Period

Difference between Periods I and IV

p (Mann–Whitney U test)

115( 89%) 71( 100%) 40( 100%) 4( 25%) 0(0%)

<0.05 <0.05 <0.05 <0.05

5+5 0.2 ± 0.1 0 4±3 1±1

87.5( 95%) 57( 100%) 28( 100%) 1( 20%) 1.5( 60%)

60.0 60.05 <0.05

20.0 ± 5.3 16.3 ± 3.0 0 2.6 ± 1.9 1.1 ± 0.8

4.2 ± 2.6 0.8 ± 0.2 0 2.4 ± 1.8 1.0 ± 0.8

19.6( 82%) 17.2( 96%) 1.6( 100%) 0.4( 14%) 0.4( 29%)

60.05 <0.05 <0.05

3.4 ± 0.77 3.2 ± 0.7 0 0.15 ± 0.11 0.05 ± 0.04

2.1 ± 0.4 1.9 ± 0.3 0 0.16 ± 0.12 0.06 ± 0.04

0.25 ± 0.1 0.05 ± 0.03 0 0.15 ± 0.09 0.05 ± 0.04

4.35( 95%) 3.85( 99%) 0.5( 100%) 0.00(0%) 0.0(0%)

60.05 60.05 <0.05

3.39 ± 1.88 1.02 ± 0.22 0 1.85 ± 1.33 0.52 ± 0.37

2.93 ± 1.66 0.70 ± 0.16 0 1.74 ± 1.20 0.49 ± 0.34

1.86 ± 1.19 0.03 ± 0.01 0 1.43 ± 0.99 0.40 ± 0.28

I

II

III

IV

TSS (ton d 1) Combined WWTF + river + NPS WWTF effluent WWTF sludge Rivers NP sources

128 ± 24 72 ± 21 40 ± 5 12 ± 8 4±2

74 ± 15 58 ± 8 0 11 ± 8 5±3

35 ± 18 15 ± 7 0 14 ± 10 6±4

13 ± 9 1±1 0 8±6 4±3

POC (ton d 1) Combined WWTF + river + NPS WWTF effluent WWTF sludge Rivers NP sources

92.5 ± 21 57 ± 21 28 ± 8 5±1 2.5 ± 1

55 ± 14 48 ± 12 0 5±2 2±1

15 ± 11 10 ± 5 0 4±2 1 ± 0.5

Total nitrogen (ton d 1) Combined WWTF + river + NPS WWTF effluent WWTF sludge Rivers NP sources

23.8 ± 5.3 18.0 ± 3.4 1.6 ± 0.6 2.8 ± 2.2 1.4 ± 0.9

25.8 ± 5.6 22.2 ± 4.1 0 2.5 ± 1.9 1.1 ± 0.8

Total phosphorus (ton d 1) Combined WWTF + river + NPS WWTF effluent WWTF sludge Rivers NP sources

4.6 ± 1.1 3.9 ± 0.9 0.5 ± 0.1 0.15 ± 0.11 0.05 ± 0.04

Freshwater inflows (106 m3 d 1) Combined WWTF + river + NPS WWTF effluent WWTF sludge Rivers NP sources

3.32 ± 1.78 0.99 ± 0.23 0.02 1.81 ± 1.06 0.50 ± 0.16

were caused by the ending of the sludge discharges in 1991 (Milestone 1). The decreases in the TSS- and POC-loadings between 1994/1995 and 2001 spanned the second through fifth milestones of the BHP. As can be seen in the figure, decreases in WWTF-effluent loadings were responsible for the decreases in the loadings during the midstudy. The start of the decreases in the TSS and POC loadings in 1994/1995 coincided with the completion of the new 1°-treatment facility at the DI WWTF. The annual average TN- and TP-loadings to the harbor remained elevated from 1990 to 1997 or 1998, and then declined through 2001. The start of the decrease in the TN loadings between 1998 and 1999 coincided with the diversion of the NI WWTF flows through the DI WWTF. The start of the decrease in the TP-loadings in 1997 coincided with the start of the phase-in of 2°-treatment at the DI WWTF. The decreases in the TN- and TP-loadings from 1997/1998 to 2001 were caused largely by decreases in the WWTF-effluent loadings to the harbor. Unlike for TSS and POC, the ending of the sludge discharges had little impact on the total loadings of TN and TP. For TN and TP, as for TSS and POC, the annual average loadings during the last 7 years of the study were a small fraction of the loadings during the years the harbor received the WWTF discharges. The harbor also experienced a decrease in total inflows of freshwater over the study (Fig. 4). The decrease was small compared to the decreases for TSS, POC, TN and TP, but was evident between 2000 and 2001. The difference was not as large as for the other variables, but during the last 7 years of the study the annual average inflows were consistently lower than during the years the harbor received the WWTF discharges. The average TSS:POC and TN:TP ratios of the loadings to the harbor increased over the study. The average TSS:POC loadings re-

1.46( 0.96( 0.02( 0.38( 0.10(

44%) 97%) 100%) 21%) 20%)

60.05 60.05 60.05

mained low from 1990 to 1998, increased between 1998 and 1999, and then remained elevated through 2007. For TN:TP, the average loadings increased from 1990 to 2000, increased more abruptly between 2000 and 2001, and then remained elevated through the end of the study. 4.2. Total changes, and the contributions of the WWTF loadings Table 1 compares the average loadings and inflows to the harbor, for all sources combined and partitioned by source, for each of the four loading periods. For all seven parameters, the average inputs during Period IV were significantly different from the averages during the baseline (Period I) (p < 0.05, Mann–Whitney Utest). For TSS and POC, the decreases in the loadings between the two periods totaled 115 ton d 1 (89%) and 87.5 ton d 1 (95%). Decreases in WWTF loadings were responsible for 111 ton d 1 (or 97%), and 69 ton d 1 (or 93%) of the respective decreases. For both parameters, the ending of the sludge discharges accounted for about one-third of the decreases; the decreases in the effluent loadings later in the project, accounted for the remaining twothirds. A background decrease in river inflows contributed 4 ton 1 or ca. 3% of the decrease in the TSS loadings. During Period IV, the average TN- and TP-loadings to the harbor were 19.6 ton d 1 (or 82%) and 4.35 ton d 1 (or 95%), lower than during Period I. Decreases in WWTF loadings accounted for 18.8 ton d 1 or 96%, and 4.3 ton d 1 or 100% of the respective decreases. For both nutrients, the decreases in the effluent loadings contributed 88% of the decreases. The decreases in the sludge loadings contributed 8% and 11%, respectively. The total inflows of freshwater to the harbor during Period IV were 1.46  106 m3 d 1 or 44% lower than during Period I. The ending of the WWTF discharges in 2000 accounted for

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D.I. Taylor / Marine Pollution Bulletin 60 (2010) 609–619

100

(TOND-1)

TSS LOADINGS

150

50 0

I

II

III

IV

I

II

III

IV

POC LOADINGS (TOND-1)

250 200 150 100 50 0

TN LOADINGS (TOND-1)

40 WWTF EFFLUENT

30

RIVERS

20

NP SOURCES 10 WWTF SLUDGE 0

I

II

III

IV

I

II

III

IV

6 4 2 0 4 3

3

-1

( X 10 M D )

2

6

FRESH WATER INFLOWS

TP LOADINGS (TOND-1)

8

1 0 --

I

--

II

--

III

--

IV

LOADING PERIOD Fig. 5. Comparison of the average TSS, POC, TN and TP loadings, and the average freshwater inflows between the four loading periods. The horizontal lines indicate the statistical significance of the differences in means between periods (tested using the Fisher’s LSD test). The averages with separate lines were significantly different from one another (p < 0.05).

0.98  106 m3 d 1 or 68% of the decrease. A background decrease in river inflows unrelated to the BHP, contributed an additional 0.38  106 m3 d 1 or 26% of the decrease. For only the river inflows and the river loadings of TSS, were the average inputs from sources other than the WWTF’s different between Periods I and IV. 4.3. Differences in loadings between the four loading periods Figs. 5 and 6 compare the average loadings and ratios of the loadings during the four loading periods. As can be seen from Fig. 5, the bulk of the decreases in the TSS and especially the POC

loadings occurred early in the study, and between Periods I and II, and to a lesser extent, between Periods II and III. For TN and, to a lesser extent for TP, the decreases occurred later in the study, and between Periods II and III, and especially between Periods III and IV. Most of the decreases in the total freshwater inflows to the harbor occurred between Periods III and IV and to some extent between Periods II and III. The bulk of the increase in the TSS:POC loadings occurred during the mid-study, and between Periods II and III. For the average TN:TP loadings, most of the increase occurred later in the study, and between Periods III and IV. The sizes

D.I. Taylor / Marine Pollution Bulletin 60 (2010) 609–619

TN : TP LOADINGS

TSS : POC LOADINGS

616

4 3 2 1 0

I

II

III

IV

ALL SOURCES

20 15 10 5 0 --

I

--

II

--

III

--

IV

LOADING PERIOD Fig. 6. Comparison of the average TSS:POC and TN:TP loadings between the four loading periods. Details as in Fig. 5.

and the combinations of the loadings received by the harbor were quite different during the four periods. The dominant sources of the inputs to the harbor also shifted over the course of the study. During Period I, the WWTF’s contributed most, and between 82% and 96% of the total TSS-, POC-, TNand TP-loadings to the harbor. They also contributed 31% of the total inflows of freshwater. During Period IV, the rivers + NP sources contributed 80% or more of the, in turn, much smaller total loadings of these materials to the harbor. They contributed 98% of the total freshwater inflows to the harbor. As can be seen from Fig. 5, the differences in the WWTF loadings were also largely responsible for the differences in the total loadings observed between periods. 4.4. Contributions by the different milestones Fig. 7 compares the contributions of each of the milestones of the BHP to the changes in the WWTF (sludge + effluent) loadings to the harbor. The first milestone, the ending of the sludge dumping, contributed 40% of the total decreases in the WWTF loadings of TSS and POC. It contributed 13% for TN and TP. The new 1°-treatment facility completed at the DI WWTF, accounted for 1.6% and 0.8% of the total decreases in the WWTF TSS- and POC-loadings, and 0.5% for TN and TP. The upgrade to 2°-treatment at the DI facility contributed 17% and 19% of the decreases in the WWTF loadings of POC and TP, and 5% and 8% for TSS and TN. The inter-island diversion contributed 15%, 23%, 19% and 28% to the decreases in the WWTF loadings of TSS, POC, TN and TP. The diversion of the DI WWTF discharges offshore contributed 31% and 19% of the decreases in the TSS and POC loadings, and 63% and 40% for TN and TP.

projects. Included in the figure for references are the loadings to Chesapeake Bay, Delaware Bay, Narragansett Bay, Ochlockonee Bay, and Tampa Bay. Note: the loadings for the Patuxent Estuary include only the loadings from the WWTF’s and from the Patuxent River. The loadings to the New River Estuary include only the WWTF loadings. Details of the wastewater projects associated with each of the systems are provided in Table 2. The loadings of TN and TP to Boston Harbor before the BHP were either the highest or second highest among the systems shown in Fig. 8. The pre-project loadings of TN to the harbor were 1.9  the equivalent loadings to the Potomac Estuary and Hillsborough Bay, and 10  the loadings to Kaneohe Bay. The TP loadings to the harbor before the BHP were 2.9  and 10  the equivalent loadings to the Potomac Estuary and Kaneohe Bay, respectively. The decreases in the loadings of TN and TP experienced by the harbor were also the greatest among the six systems that were subjected to wastewater projects, and for which pre- and postloading data were available. The decreases in the TN-loadings to the harbor were 8.5, 4.9 and 17.4 the decreases to the Potomac Estuary, Hillsborough Bay and Kaneohe Bay, respectively. The decreases in the TP-loadings to the harbor were 14.1 and 12.1 the decreases to the Potomac Estuary and to Kaneohe Bay. The fact that the decreases in the TN and TP loadings to the harbor were somewhat simultaneous and rapid was as for Kaneohe Bay, and probably also for the New River Estuary. They was however quite different from the decreases experienced by the Patuxent and Potomac estuaries. For both of these systems, the loadings of TP to the systems decreased first, and then a decade or more later, the loadings of TN decreased. The decreases in the TN- and TPloadings to the harbor spanned 3–4 years; they spanned 10 years and 10–15 years, respectively for the Potomac Estuary. 5.2. Changes within the harbor

5. Discussion 5.1. Comparisons with other systems Fig. 8 compares the changes in the total loadings of TN and TP experienced by Boston Harbor, with the changes in loadings experienced by five other bays and estuaries subjected to wastewater

Based on the changes that followed the smaller decreases in loadings experienced by Hillsborough Bay (Johanssen and Lewis, 1992), Kaneohe Bay (Smith et al., 1981), the New River Estuary (Mallin et al., 2005) and the Potomac Estuary (Jaworski et al., 2007), changes have likely also occurred in Boston Harbor. Much of the data collected in the harbor over the course of the BHP are

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D.I. Taylor / Marine Pollution Bulletin 60 (2010) 609–619 -2

100

TSS (%)

80

0

60

a

20000

40000

60000

80000

Ochlockonee Bay

40

16

Boston Harbor (before) b

20

Potomac Estuary (before)

c

0 o

1

o

2

I-I

OFF

c

Potomac Estuary (after)

-66,065 ( -82% )

12

Hillsborough Bay (after)

a

100

-9,749 ( -22% )

14

Hillsborough Bay (before)

b

Sludge

-13,505 ( -32% )

Narragansett Bay

a

10

Delaware Bay Boston Harbor (after)

80 a

POC (%)

-1

TN LOADINGS ( MG M Y )

60

8

Chesapeake Bay

d

Patuxent Estuary (before)

-6,124 ( -54% )

6

e

40

Kaneohe Bay (before)

d

20

f

Patuxent Estuary (after) 4

e

0 Sludge

o

1

o

2

I-I

OFF

-3,796 ( -57% )

Tampa Bay Kaneohe Bay (after)

g

2

New River Estuary (before)

g

-2,655 (wastewater data only)

New River Estuary (after)

100 -2

TN (%)

-1

TP LOADINGS ( MG M Y )

80 0

60 40

a

4000

8000

12000

16000

20000

17

Ochlockonee Bay

data not reported 16

Boston Harbor (before)

20 b

0

15

Potomac Estuary (before)

c

Sludge

o

1

o

2

I-I

OFF

14

Hillsborough Bay (before)

c

100

Potomac Estuary (after)

-14,600 ( -93% )

12

Hillsborough Bay (after)

b

data not reported 11

Narragansett Bay

a

80

-1,037 ( -19% )

data not reported 13

b

10

Delaware Bay

TP (%)

9

Boston Harbor (after)

60

a d

40

e

20

d f

0 Sludge

o

1

o

2

e

I-I

OFF g

MILESTONES

still being interpreted, but the analysis to date has identified a number of changes. The average concentrations of TN and TP, biomass of phytoplankton, and rates of 14C primary production in the water-column

7

Patuxent Estuary (before)

-803 ( -55% )

6

Kaneohe Bay (before) 5

Patuxent Estuary (after) 4

Tampa Bay 3

Kaneohe Bay (after)

-1,204 ( -79% )

2

New River Estuary (before) 1

g

Fig. 7. Percent contributions of the five construction milestones of the BHP to the total decreases in the WWTF loadings of TSS, POC, TN and TP to Boston Harbor.

8

Chesapeake Bay

-913 (wastewater data only)

New River Estuary (after)

Fig. 8. Comparison of the total loadings of TN and TP to Boston Harbor before and after the BHP, with the loadings to 10 other bays and estuaries. aNixon et al., 1996; b Jaworski et al., 2007; cJohanssen and Lewis, 1992; dTesta et al., 2008; eSmith et al., 1981; fGreening and Janicki, 2006; gMallin et al., 2005.

of the harbor have all decreased (Oviatt et al., 2007; Taylor, 2006). During summers, the concentrations of dissolved oxygen in the

Table 2 Comparison of the BHP and the wastewater infrastructure projects associated with Hillsborough Bay, Kaneohe Bay, New River Estuary, Patuxent Estuary, and the Potomac Estuary. System

Nature of infrastructure projects

Dates of projects

Sources

Boston Harbor

Termination of sludge dumping, upgrade to 2o-treatment, and diversion of WWTF discharges offshore Upgrade to tertiary (3o), or denitrification treatment of the largest WWTF

1991–2000

Present study

1970s

Upgrade to 2o treatment at the two largest WWTF’s Diversion of the upgraded discharges offshore Upgrade to 2o treatment of ca. 50% of WWTF discharges, and then diversion onto forested areas Upgrade to 3o (denitrification) treatment of remaining 50% of WWTF discharges Upgrade to 2o-treatment Upgrade to 3o-treatment Upgrade to advanced 2o-treatment at largest WWTF Upgrade to 3o-treatment at largest WWTF

Early 1970s 1997/1998 Mid-1990s

Johanssen and Lewis (1992) Smith et al. (1981)

Hillsborough Bay Kaneohe Bay New River Estuary

Patuxent Estuary Potomac Estuary

Mid-1990s 1970s Early 1990s 1970s Mid-1990s

Mallin et al. (2005)

Testa et al. (2008) Jaworski et al. (2007)

D.I. Taylor / Marine Pollution Bulletin 60 (2010) 609–619

CONSTRUCTION COSTS 6 ( x10 USD )

618

4000 COSTS

3000 2000 1000 0 a

b

c

d

e

f

150

unpublished data). The area of the harbor bottom covered by amphipod tube–mats has decreased, and the average depth of the redox potential discontinuity layer in the sediments has increased (Diaz et al., 2008). At certain locations in the North Harbor, the rates of oxygen uptake by the sediments, the rates of denitrification within the sediments, and the net fluxes of N and P from the sediments have decreased (Tucker et al., 2005; Giblin et al., 1997). The organic content of the surface sediments of the harbor has decreased (Tucker et al., 2005), as have the POC content and TSS:POC ratios of the particulate material in the harbor water-column (Taylor, 2006).

TSS

5.3. Construction costs per unit decreases in loadings

100

50

0 a

b

c

d

e

f

200 POC

50 0

3

-1

ton y )

100

6

( x10 USD per x10

COST PER UNIT DECREASE IN LOADINGS

150

a

b

c

d

e

f

2500

Fig. 9 compares the total construction costs, and the costs per unit decreases in WWTF loadings of TSS, POC, TN and TP, for six different construction milestones. The BHP is represented by the sixth scenario. The costs are for construction alone, and are in 2001 $USD. The total costs for the scenarios ranged from 728  106 $USD for the first scenario to 3693  106 $USD for the sixth scenario. The costs to decrease loadings per unit amount also differed among scenarios, depending on the material. For TSS and POC, the first scenario, the ending of the sludge discharges alone, provided the lowest costs per unit decreases. For all four materials, the second and third scenarios provided the highest unit costs; these scenarios included the new 1°-, or 1° + 2°-treatment facilities at the DI WWTF, but neither of the WWTF diversions. For TN and TP, the lowest unit costs were provided by the fourth and fifth milestones, that included 1°-treatment plus one or both of the diversions, but no 2°-treatment.

TN

2000

6. Disclaimer

1500

This paper represents the opinions and conclusions of the author and not necessarily those of the Massachusetts Water Resources Authority.

1000 500 0 a

b

c

d

e

Acknowledgements

f

10000 TP

8000 6000 4000 2000

e

BHP

d

Sludge + 1 o + I-I + OFF

c

Sludge + 1 o + I-I

b

Sludge + 1 o + 2 o

a

Sludge + 1o

Sludge

0

Grateful thanks are extended to K. Keay and W. Leo for reviewing early drafts of this paper. Thanks are also due to K. Coughlin for setting up and managing the river sampling, and for providing data management and QA/QC. L. Ducott, N. O’Neill, Keary Berger and others conducted the river monitoring. L. Ducott, N. O’Neill, and N. McSweeney provided laboratory QA/QC. D. Hersh, P. Ralston and others have managed the data.

f

Fig. 9. Total costs, and the costs per unit decreases in WWTF-loadings to Boston Harbor, for six different construction scenarios. The scenarios include combinations of the five construction milestones undertaken as part of the BHP.

bottom-waters of especially the deeper, more estuarine portions of the harbor, have increased (Taylor, 2006). The diversity of the benthic invertebrate communities of the harbor has increased (Maciolek et al., 2006), and the seagrass beds that once covered much of the harbor seafloor have shown early signs of recovery (Massachusetts Division of Marine Fisheries,

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