Nitrogen Management Strategies & Tools
In brief, 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 (TMDLs) equivalent 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.
The BBNEP methodology compared watershed nitrogen loading estimates (using the accepted methods of the time) to observations of ecosystem response. By the mid 1990s, as new scientific information became available, and as the NEP began evaluating results of the volunteer water quality monitoring program, we began modifying some of our nitrogen loading model assumptions, such as adding nitrogen contributions from natural landscapes. In 1999, we also recommended more stringent loading limits based on our approach (see our 1999 TMDL page).
In 2001, the Department of Environmental Protection established the Massachusetts Estuaries Project with the goal of developing nitrogen TMDLs for 89 embayments in Massachusetts. The MEP approach is based on nitrogen loading model linked to an embayment specific circulation modeling that could predict total nitrogen concentrations based on different loading scenarios (an ecosystem response model). The MEP methodology supersedes the tiered loading limit strategy proposed by the BBNEP in 1991 for setting loading limits standards for coastal embayments, and fulfils one of the key goals of the Buzzards Bay CCMP: to identify embayment specific nitrogen loading limits based on sound science. The focus of the Buzzards Bay NEP now is to assist municipalities in complying with these recommended nitrogen loading limits.
The nitrogen loading methodologies used in the MEP loading model are quite similar to that of the loading assumptions used by the BBNEP and Cape Cod Commission in the 1990s in their loading models. However, the MEP also updated key loading coefficients based on new studies and information. The MEP’s parcel loading spreadsheets are also more comprehensive in that every Assessor’s office parcel area is also assigned an area for impervious, lawn, natural landscapes, water use, and so forth. These areas and water use are multiplied times various loading coefficients.
To approximate the MEP loading model, the Buzzards Bay NEP’s GIS and parcel analysis spreadsheets have been updated to use all MEP loading coefficients. The exception is septic system loadings, which in the BBNEP loading spreadsheets are calculated either by assumed per capita loadings times occupancy, or if available, MEP reported water use times the MEP wastewater loading coefficients. Generally the MEP uses parcel specific water use data in their loading model.
2009 Updates to the BBNEP nitrogen loading spreadsheets
Because of the level of effort needed to develop parcel level data nitrogen loading spreadsheets for an entire watershed, 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 as consistent as practical with the assumed nitrogen loadings adopted by the MEP for the “rainbow tables” in their reports (watershed loading summary tables in Section IV of their reports), the Buzzards Bay NEP has revised all our loading coefficients to closely match the MEP loading model. One important difference between our loading model spreadsheets and the MEP’s calculations of septic system loading is that the MEP typically adds actual water use of all parcels for subwatersheds, whereas the spreadsheets here can employ either the average watershed residential water use values published by the MEP, or assumed per capita loadings times census occupancy rates (population divided by occupied + vacant units). These approaches are useful because parcel level water use data is not always readily available to planners when calculating loading.
|Old BBNEP rate||MEP Loading Coefficient||The BBNEP has adopted the MEP loading rates in this table.|
|Category||MassGIS land Use #||(kg/ha unless spec.)||(lb/ac unless spec.)||(kg/ha unless spec.)||(lb/ac unless spec.)||comments|
|21 or 23||18.6||16.6||22.93
|Updated. Up until 2010, the MEP used in their TMDL watershed nitrogen analyses an annual nitrogen application rate of 31 pounds per acre with 66% leaching, for a net loading rate of MEP uses a loading rate of 20.46 lbs/acre. In 2011, MEP draft reports now use 6.2 lbs per acre based on 2005. 2006, and 2009 studies by Demoranville and others (see especially Demoranville (2006) Cranberry Bog Management Practices which is the principal study including nitrogen in pump water nitrogen concentrations, and this Demoranville PowerPoint presentationpresentation which identifies the 6.4 lbs per acre and 8.6 lbs per acre as the effective nitrogen loading rate for non-flow through and flow-through bogs respectively (slide on page 33). Additional insights from this research are contained in Phosphorus Studies in Massachusetts, Phosphorus dynamics in cranberry production systems, DeMoranville, C., B. Howes, D. Schlezinger, and D. White. 2009. Cranberry phosphorus management: How changes in practice can reduce output in drainage water. Acta Horticulturae 810:633-640), the White Island Pond Phosphorus TMDL and this Law Review article. The focus of most of the Demoranville studies was to evaluate phosphorus loading from pumped surface water discharges from non-flow-through bogs, although nitrogen was also measured. Because phosphorus does not travel appreciably in Massachusetts soils, groundwater nitrogen discharges were not directly measured in these studies. Thus, the 6.2 lbs per acre used in the MEP TMDL studies may potentially underestimate actual watershed nitrogen loads from the non-flow cranberry bogs studied. There are also still many flow through bogs in the region, so a higher loading rates would be justified for those parcels with these type of cranberry bog systems, although the Demoranville study suggests far lower loading rates for flow-through bogs than used in previous MEP TMDL studies.|
|cropland, various (except Pasture)||1||20.0||17.8||10.20||9.10||MEP assumes 30.33 lb/ac application and 30% leaching|
|Pasture||2||10.0||8.9||5.00||4.46||MEP assumes 4.46 lb/ac application and 100% leaching|
|Nurseries||inc in 21, or 36||10.1||9.1||5.00||4.46||Nurseries use fertilizer, and this value may be too low for some properties. However, nurseries occupy negligible amounts of land area in any watershed, so this loading term generally has negligible impact on loading.|
|Fertilized Lawns, per 5,000 sq, ft lawn||use parcel data||3.4 per lawn||3.0 per lawn||1.21 per lawn||1.08 per lawn||The original BBNEP loading rate was 3 lbs per lawn effective leaching rate based on assumptions from the early 1990s. Based on interviews on Cape Cod studies, MEP assumed only 5.40 lbs of N were applied annually to each 5,000 sq ft lawn with 20% leaching to groundwater. These are the values to the left. The MEP also assumes 1/2 of lawns are fertilized, but this assumption is built into the loading rate above. See additional information on our nitrogen loading assumptions page.|
|Lawn fertilizer per acre, effective based on use||na||29.3||26.1||10.54||9.41||As noted above, the MEP’s lawn assumptions result in a loading rate of 9.41 lbs/ac (10.5 Kg/ha). Text and loading spreadsheets by the MEP note that they assume only 1/2 of all lawns are fertilized. Previously we had halved the values to the left, but after reviewing recent MEP loading spreadsheets, the assumption of half the lawns are fertilized is built into the 1.08 lbs per lawn noted above. In the MEP loading model, lawns are a larger nitrogen source per unit area than roof runoff but less than road area.|
|Golf Courses||7||29.3||26.1||26.70||23.83||MEP uses different rates for greens, fairways, and roughs. The value shown is the average rate for several courses based on total fertilizer use divided by total acres of green, fairway, and rough, but fertilizer rates can vary slightly from course to course, and may vary among various MEP models. See additional information on our nitrogen loading assumptions page.|
|Spectator Recreation||8||29.3||26.1||29.29||26.14||Playing fields, parks, etc.|
|Impervious, road run off||18, and sewered 16 and roads||15.8||14.1||15.13||13.5||MEP assumes impervious recharge is 90% of annual precipitation (site specific, this example 44.4) x 1.5 ppm N. (see note 1). Value may vary slightly depending on actual regional long term watershed precipitation averages used in the model.|
|Impervious, roof run off||na||7.3||6.5||7.57||6.76||Same assumption as for roads, except nitrogen concentration assumed to be 0.75. Value may vary slightly depending on actual regional long-term watershed precipitation averages.|
|Deposition on embayments and FW ponds||20||7.3||6.5||10.9||9.73||The BBNEP ignored atmospheric deposition on freshwater ponds, presuming that little reached coastal waters, or treating it like other natural landscapes, thus the original BBNEP value is for embayment deposition. The MEP uses an atmospheric N concentration of 1.08 for both. The per acre loading value may vary slightly depending on actual regional long-term watershed precipitation averages used in the model. In only one published TMDL report (Slocums River available at Oceanscience.net) did the MEP also lump vegetated wetland area into the water body surface area calculation. This was a significant deviation from their standard model because there are 648 acres of water body surface area in this watershed but 6,178 acres of wetlands plus open water.|
|Natural Landscapes||3,4||0.17||0.15||0.5||0.45||Originally the BBNEP ignored this contribution, then in the 1990s we adopted the values shown. The BBNEP also assumed either natural landscape contributions or no contributions from wetlands. The MEP estimate (for wetlands and forested uplands) assumes 27.25 in. annual recharge and 0.072 ppm N, but varies slightly with actual regional long term watershed precipitation averages. In all studies, except the Slocums River study, the MEP included vegetated wetlands as natural landscapes. In the Slocums River they asserted “are nearly saturated with nitrogen and are exporting nearly the same nitrogen loads as are being added to them by precipitation” and assigned them the same high rate of nitrogen loading as direct precipitation on the estuary and ponds.|
|4||6.5||10.9||9.73||0.45||In all published MEP TMDL studies, except the Slocums River study, the MEP included vegetated wetlands as natural landscapes. In the Slocums River report, available at the OceanScience.net website, the MEP stated that the wetlands “are nearly saturated with nitrogen and are exporting nearly the same nitrogen loads as are being added to them by precipitation” and assigned them the same high rate of nitrogen loading as direct precipitation on the estuary and ponds.|
|1/2 acre lot, 3 person occupancy||23.9||21.3||22.1||19.7||This example is comparable to the MEP estimates for the Wareham River estuary watershed (draft report has been provided to town officials), where 15.26 lbs per septic unit was used for the entire watershed, which has an estimated Census occupancy of 2.48 persons per unit. This total includes, average lawn, roof, and driveway size, but does not add natural landscapes). Actual values can vary appreciably among watersheds because the MEP bases the watershed loading coefficient on municipal water use records. For comparison, the BBNEP formerly used 5.86 pounds per person. Go to our nitrogen loading assumptions page to see examples of actual MEP residential wastewater loading rates.|
|Notes: 1) Annual precipitation decreases by several inches moving west to east across the Buzzards Bay watershed.|
Loading and Land Use Spreadsheets
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.
Single Parcel Spreadsheet: Calculate your N-loading footprint with this single parcel loading spreadsheet
Excel Spreadsheet “n-subdivision.xls”: Calculate nitrogen loading from a subdivision with this spreadsheet
(right click to save to your hard disk)
Interactive Nitrogen Calculators
We have created a webpage with Interactive calculators so that town officials, managers, engineers, and the public can quickly estimate and validate nitrogen loading contributions from various sources. Go to our Interactive Nitrogen Calculators. When the page opens, you may have to tell your web browser to allow scripts to run on that page. These calculators are just spreadsheets where you can enter data, and then even save on your own computer.
MEP septic loading estimates as compared to other approaches
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 used to simply be based on assuming a per capita wastewater discharge to groundwater was 2.7 kg (5.94 lb). To calculate annual loadings, the BBNEP would use GIS town parcel data and either US census statistics or town statistics to get average annual occupancy for the watershed being studied. One disadvantage of using US Census data alone is that it fails to capture high summer seasonal occupancy use which occurs in many coastal village areas. If it was assumed that summer populations tripled in the summer in a watershed, average annual occupancy could be estimated with a simple formula (= .75 year-round + .25 seasonal populations, for example).
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 could be confounded by higher than expected water use in some watersheds during the summer may double at any particular residence because of lawn and garden irrigation, or by water consumption for filling swimming 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.
Despite the various limitations of both approaches, a combined approach using comparisons of US Census block level GIS information, together with use of municipal water use accounting for outliers, will likely remains the best approach for estimating wastewater loadings in any particular watershed.
Noteworthy early BBNEP Correspondence on Nitrogen:
July 1990: To DEP on application of BBNEP’s Nitrogen management strategy to a sewage treatment facility (in Marion).
June 1993: Issue Paper provided to DEP: Can Title 5 Protect Coastal Embayments?
This paper contributed in part to the adoption of the 440 gpd per acre dosage limit for septic systems in N sensitive areas.
Costa, J. E., B. L. Howes, A. Giblin, and I. Valiela. 1992. Monitoring Nitrogen and indicators of nitrogen to support management action in Buzzards Bay, p. 497-529. In McKenzie et al.(eds) Ecological Indicators, Elsevier, London
A brochure on land use options to manage nitrogen inputs to coastal waters for property owners and town officials.
This is a 216 KB reduced resolution version for the web as a PDF file. If you want the 1 MB version, so you can print and hand out a high-resolution double-sided copy, just send us an email.
Citizen Water Quality Monitoring Program.
In collaboration with the Buzzards Bay Coalition, the Buzzards Bay NEP funded and designed a citizen-based water quality monitoring program to evaluate the impacts of nitrogen loading to coastal waters. Visit our page with the information contained in the joint Project-Coalition Report.
Download 1994 Quality Assurance Plan
[File QAPPCITZ.EXE when run unzips into QAPPCITZ.doc MS Word file]
BBNEP’s 1994 draft report “Use of a Geographic Information System to estimate nitrogen loading to coastal watersheds,”
Buzzards Bay Watershed and Subwatershed
The Buzzards Bay basin delineation shown here represents the updated jurisdictional boundary of the Buzzards Bay National Estuary Program as defined in the Buzzards Bay Comprehensive Conservation and Management Plan adopted by the Commonwealth of Massachusetts and the US EPA in 1992. It differs from the Buzzards Bay jurisdictional boundary adopted by some other programs within the Commonwealth, which omits Cape Cod in the Buzzards Bay “watershed” for various political or regulatory reasons. For more information on changes in the watershed and subwatershed boundaries, go to our Buzzards Bay Watershed and Subwatershed Information page.