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Nitrogen Management Strategies & Tools

Sub-pages: Nitrogen Management Origins | 1999 TMDL Recommendations | 2007 Model General Bylaw | Septic System Maintenance |

History of the Buzzards Bay NEP's Nitrogen Management Strategy

In 1990, the Buzzards Bay NEP, a participant in the U.S. Environmental Protection Agency's National Estuary Program, developed a Total Maximum Daily Loads (TMDLs¹) strategy to manage anthropogenic nitrogen inputs to coastal embayments in Buzzards Bay. This strategy was contained in the 1991 Buzzards Bay Comprehensive Conservation and Management Plan. The proposed approach was based on relating empirical information about water quality and living resources (like eelgrass) to different measures of nitrogen loading. While the 1991 CCMP recognized that embayment-specific models were desirable for setting nitrogen loading limits, these were viewed as too expensive and difficult to apply to 30 Buzzards bay embayments in a timely way. The BBNEP's methodology provided a quick yardstick to measure watershed loadings and establish watershed limits. One of its most important drawback was that it was a on-size fits all approach that did not accommodate the loading pathways and hydrological features of each embayment.

In 1992, the Buzzards Bay NEP established, in partnership with the citizens group the Coalition for Buzzards Bay, a water quality monitoring program to evaluate nitrogen loading impacts in Buzzards Bay. The purpose of this monitoring program was to not only document water quality conditions and trends in Buzzards Bay embayments, but to also evaluate the appropriateness of the specific nitrogen loading limits recommended in the 1991 CCMP. The data also proved useful in building public support for nitrogen action. This program continues to this day.

DEP's Massachusetts Estuaries Project

Background

Overview of Program
Oceancscience.net web site (primary host)
Overview of Program
DEP site

Overview of Program
UMass Dartmouth SMAST web site

DEP Fact Sheet
Covers TMDL issues

DEP's list of estuaries
Schedule subject to change

MEP 2001 Pilot Project documents
Has the original planned schedule.

Multi-town collaboration
DEP web page with links

Nitrogen Management Tools
A Cape Cod Commission Report

Restoring Estuaries
A DEP Links page

BB Estuary Reports

West Falmouth Harbor
Completed

Phinneys Harbor / Back River complex
Completed

Wareham River Estuary Complex
Anticipated Jan. 2009

New Bedford Inner Harbor
Anticipated Nov. 2008

Slocums and Little River Complex
Anticipated Nov. 2008

The data collected in this citizen-based water quality monitoring program has proved useful to both managers and the public and has prompted action to manage both point and non-point pollution sources alike. However, it was not until the late 1990s that the BBNEP used the data to revise the original CCMP loading limit recommendations. The 1999 report below represents that undertaking. While the data in the report supports the fundamentals of the Buzzards Bay NEP's management approach such as calculating mass loadings to land, and tailoring TMDLs to bay volume and flushing, it also suggested that the recommended limits are too high, and in some cases need to be reduced by one half.

About 2001, the Buzzards Bay NEP's methodology for establishing nitrogen loading limits was superseded by the DEP's Massachusetts Estuaries Project (MEP) model. This new approach identified threshold loading targets based on a similar nitrogen loading approach, but where existing water quality was compared to loading and a predictive water quality model. This improved approach was what was originally envisioned in the original CCMP, and the BBNEP fully supports the efforts of the MEP program.

When the MEP established, its goal was to develop TMDLs for 89 embayments in Massachusetts. Originally this work was scheduled to be complete by 2010, but delays in completion of studies and budget shortfalls have slowed progress on the effort.

The MEP's nitrogen loading methodologies are quite similar to that of the BBNEP's and both loading models use similar assumptions. The BBNEP recommended approach in 1991 was to use parcel data to calculate loading for embayments, and the BBNEP did this for the Buttermilk Bay overlay district in 1991, but GIS parcel coverages were not readily available in the 1990s, so most of the BBNEP's initial watershed analyses were based on an evaluation of MassGIS land use data. The MEP's parcel loading spreadsheets are more comprehensive in that every Assessor's office parcel area is assigned an area for impervious, lawn, natural landscapes, and so forth. these areas are multiplied times loading coefficients. The Buzzards Bay NEP's GIS spreadsheets use principally MassGIS land use areas, with residential units calculated from US Census GIS coverage, parcel data, or other information as desired.

Because most watershed nitrogen loads are dominated by septic systems, the most important element of any nitrogen loading model is to correctly estimate the number of septic systems in the watershed, and beyond that, estimating the number of individuals using those septic systems. The Buzzards Bay NEP's approach was simply to assume per capita wastewater discharge to groundwater was 2.7 kg (5.94 lb). To calculate annual loadings the BBNEP would then use US census statistics and GIS coverages to get average occupancy for the watershed being studied. One disadvantage of this process was that it failed to capture high summer seasonal use which occurred in some Cape Cod coastal areas.

The MEP took a very different approach to the problem by examining annual water use based on municipal water records. The advantage of this process is that it better captured seasonal increased occupancy. The disadvantage of this approach was that it was confounded by the fact that water use during the summer may double at at any particular residence because of lawn and garden irrigation, and consumption for filling pools.

Another issue that arises with water use data is that an assumed wastewater concentration must be adopted. Actual septic system loading is calculated by flow times concentration. In reviewing household wastewater studies, the BBNEP recognized that wastewater nitrogen concentrations from residences with similar occupancies can vary dramatically with water use. That is to say, wastewater nitrogen concentrations will be much higher in homes constructed with low flow devices (toilets and showers) or where water conservation is practiced.

The annual per capita loading rate adopted by the BBNEP (2.7 kg) was based on a review of studies of human waste and wastewater. The value adopted was also comparable to the assumed 35 ppm and 56 gpd per capita discharge assumed by the Cape Cod Commission in their loading models in the 1990s. Today per capita water use discharge to septic systems is generally assumed to be much less than 56 gpd and groundwater effluent concentrations assumed to be higher than 35 ppm. In the MEP loading models, wastewater concentrations are assumed much lower (26.25 ppm), but septic discharge to ground water much higher perhaps 70 or 80 gallons per day for loadings per capita loadings comparable to BBNEP assumed loadings of 2.7 Kg per year.

Below we provide the BBNEP's loading spreadsheets here to evaluate both sites and watersheds. The BBNEP's nitrogen loading calculators can also help evaluate and guide land use decisions until better information is available through the MEP in the coming years. Town's can also consider our nitrogen model bylaws to implement MEP recommended loading limits.

Comments about this page should be directed to Joe Costa.

BBNEP 2000 Proposed Water Quality Standards

In 1999 and 2000, the Buzzards Bay NEP proposed the water quality standards in the table below to DEP (see 1999 and 2000 papers below) based on best professional judgment. These standards were proposed as surrogate measures of nitrogen loading, corresponding to the proposed TMALs for nitrogen identified for waters designated ORW, SA, and SB categories as proposed in our original nitrogen strategy. The table was developed empirically based on the correlations between loadings and water quality response shown in the figures in the 2000 paper. Thus they represent the lowest value possible before dropping into the next lower category of "good" "fair" and "poor." In this sense they are not necessarily the ideal value for that category. The ideal goals for Buzzards Bay embayment water quality remain closer to the Eutrophication Index values shown in the table. All these values are based on mean summertime concentrations when critical conditions are most likely to occur. See Costa et al. (1999) for definition of eelgrass to habitat ratio.

In the end, DEP and the Massachusetts Estuaries Project adopted a similar approach to establish TMDLs for Massachusetts embayments, but instead of using the simplified tiered strategy proposed by the BBNEP in the early 1990s, new, more sophisticated embayment-specific modeling methods that had become available are now being used that incorporate flushing, loading, and other factors that defines each embayments response to nitrogen loading and specific target total nitrogen and chlorophyll concentration, and eelgrass cover goals goals.

2009 Updates to the BBNEP nitrogen loading spreadsheets

Because of the level of effort needed to develop parcel level data nitrogen loading spreadsheets, many managers and consultants still use the BBNEP nitrogen loading spreadsheets as a good first approximation of nitrogen loading. To ensure that these spreadsheets are consistent with the assumed nitrogen loadings adopted by the MEP, the Buzzards Bay NEP has has revised a number of the loading coefficients to better match the MEP loading model assumptions. The table below shows these latest changes. Our spreadsheets now include a date in the file name to assist in identifying our most recent loading spreadsheets.

table being prepared

	Excellent	"Good to Excellent "	"Fair "	"Eutrophic "
Parameter	100 pts Eutrophication Index	ORW	SA	SB
Eutrophication Index	100	65	50	40
Alt. Eutrophication Index (no 02)	100	65	45	30
Total N (ppm)	0.28	0.43	0.54	0.65
Chl a (g/l)	3.	5.0	7.0	9
Secchi depth (m)	3.0	1.9	1.5	1.3
Eelgrass to core habitat ratio	Not incl., but perhaps 1.2	0.8	0.5	0.3