Atmospheric deposition estimates prior to the period of NADP wet deposition estimates (<1982)  use the model of Bowen and Valiela (2001) (N deposition = Year * 0.026 - 39.4).  From 1982 to 2014, we use wet deposition estimates from NADP, and the model of Bowen and Valiela to derive estimates of dry deposition and DON deposition (where DON is 0.24 of total deposition, and wet and dry deposition are each 50% of the remainder). Wet deposition data came from the NADP Lexington, MA site for 1982 to 2008 and from the NADP Franklin, MA site for 2009 to 2014 (the site at Lexington MA was discontinued in 2010).

Gross imports in food = Population in Ipswich * 4.8 kg/person/year.

Fertilizer inputs are from Ruddy et al. 2004 and Battaglin (county level data from 1945 to 2001), scaled to proportion of Ipswich in Middlesex and Essex county MA.  Fertilizer estimates for prior to 1945 assumethe decay function derived from Vadeboucour et al. 2010. Due to missing county level data, N inputs to the watershed cannot be updated for 2009 to 2014.

Human waste N export is assumed to occur for population on sewer systems (all waste water treatment plants are outside the basin boundaries).  Proportion of the population on sewer systems is based on data from Claessens et al. 2006.

Net Food N inputs are Gross imports - Sewered Exports.

Riverine N exports are based on the PIE LTER long term nitrogen database.  The USGS Load Estimator program LOADEST was applied to the monthly grab sample data over the perriod of record to predict daily nitrogen flux from 1993 to 2008. For 2009 to 2014, riverine N exports are estimated  as the annual flow-weighted mean multiplied by total yearly discharge.

Runoff is derived from th USGS gage at Ipswich period of record from 1934 to present.

N in water diversions uses net interbasin transfers of water from Claessens et al. 2006, and assumes concentration as at the mouth of watershed used to calculate riverine N exports.

Bowen, J.L. and Valiela, I. 2001. The ecological effects of urbanization of coastal watersheds:Historical increases in nitrogen loads and eutrophication of Waquoit Bay estuaries. Canadien Journal of Fisheries and Aquatic Sciences. 58, 1489-1500.

Claessens, L., C. Hopkinson, E. Rastetter, and J. Vallino. 2006. Effect of historical changes in land use and climate on the water budget of an urbanizing watershed. Water Resources Research 42:W03426.