The Boston Harbor Project, and large decreases in loadings of eutrophication-related materials to Boston Harbor
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, 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.
Section snippets
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
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
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 were caused by the ending of the sludge discharges in
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 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
Disclaimer
This paper represents the opinions and conclusions of the author and not necessarily those of the Massachusetts Water Resources Authority.
Acknowledgements
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.
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