Atmospheric nitrogen deposition to the Mullica River-Great Bay Estuary

Measurements of nitrate and ammonium in precipitation and associated with aerosols were conducted at Rutgers University Marine Field Station in Tuckerton, New Jersey from March 2004 to March 2005 to characterize atmospheric nitrogen deposition to the Mullica River-Great Bay Estuary. The arithmetic means of nitrate and ammonium concentrations for precipitation samples were 2.3 mg L−1 and 0.42 mg L−1, respectively. Nitrate and ammonium concentrations in aerosol samples averaged 3.7 μg m−3 and 1.6 μg m−3, respectively. Wet deposition rates appeared to vary with season; the highest rate of inorganic nitrogen deposition (nitrate + ammonium) occurred in the spring with an average value of 1.33 kg-N ha−2 month−1. On an annual basis, the total (wet and dry) direct atmospheric deposition fluxes into the Mullica River-Great Bay Estuary were 7.08 kg-N ha−2 year−1 for nitrate and 4.44 kg-N ha−2 year−1 for ammonium. The total atmospheric inorganic nitrogen directly deposited to the Mullica River-Great Bay Estuary was estimated to be 4.79 × 104 kg-N year−1, and the total atmospheric inorganic nitrogen deposited to the Mullica River watershed was estimated to be 1.69 × 106 kg-N year−1. Only a fraction of the nitrogen deposited on the watershed will actually reach the estuary; most of the nitrogen will be retained in the watershed due to utilization and denitrification during transport. The amount of N reaching the Mullica River-Great Bay Estuary indirectly is estimated to be 5.07 × 104 kg-N year−1, approximately 97% is retained within the watershed. This atmospheric nitrogen deposition may stimulate phytoplankton productivity in the Mullica River-Great Bay ecosystem.