Date of Award

5-2005

Document Type

Thesis

Degree Name

Master of Arts (MA)

College/School

College of Science and Mathematics

Department/Program

Earth and Environmental Studies

Thesis Sponsor/Dissertation Chair/Project Chair

Yuan Gao

Committee Member

Michael J. Kennish

Committee Member

Harbans Singh

Committee Member

Duke Ophori

Abstract

To characterize atmospheric nitrogen deposition and its potential impact on the Mullica River-Great Bay Estuary, atmospheric sampling was conducted at Rutgers University Marine Field Station in Tuckerton, New Jersey from March 2004 to March 2005. A total of 52 precipitation samples were collected on an event basis using a MIC wet-only automatic precipitation sampler. A total of 23 aerosol samples were also taken during this period of time with a high-volume aerosol sampler. Chemical analysis was performed using a Dionex Ion Chromatograph to determine the concentrations of nitrate and ammonium in precipitation and associated with aerosols. Nitrate concentrations for precipitation samples ranged from 0.53 to 9.2 mg L-1 , with an average value of 2.3 mg L-1. Ammonium concentrations for precipitation samples ranged from 0.013 to 1.6 mg L-1, with an average value of 0.42 mg L-1. The nitrate-to-ammonium ratio is 5.5 in precipitation, similar to the values obtained for the Chesapeake Bay and Barnegat Bay, suggesting a regional signature of atmospheric inorganic nitrogen. The pH of each precipitation sample was measured and the average monthly value was 4.3, indicating an acidic nature. High nitrate and ammonium concentrations were related to low pH values. Nitrate and ammonium concentrations in aerosol samples ranged from 1.5 to 9.7 ug m-3 and 0.34 to 3.6 ug m-3 , respectively, and the average concentrations were 3.7 ug m-3for nitrate and 1.6 ug m-3 for ammonium.

Atmospheric deposition fluxes of nitrate and ammonium were then calculated using simple wet and dry atmospheric deposition models with incorporation of the in situ concentration data. The results indicate that wet deposition rates vary with season; the highest rate was seen in the spring with an average value of 0.42 g m-2 month-1, accounting for ~ 42% of the total wet deposition. Total dry deposition increased approximately 20-30% per month in the spring suggesting that the formation of nitrate and ammonium in the atmosphere could be promoted by increased air temperature and solar radiation intensity. Back trajectory analysis was used to identify possible sources of nitrogen to this estuary and to determine if the origins of the air masses influence the seasonal variation of nitrogen species. During a high wet deposition event occurring in the spring, air masses had an inland origin while for a low wet deposition event, which occurred during the fall, the air masses had more of a marine origin.

The annual wet deposition flux for nitrate and ammonium are 2.7 g m-2 year-1 and 0.49 g m-2 year-1, respectively. The annual dry deposition flux is roughly estimated to be 0.38 g m-2 year-1 for nitrate and 0.087 g m-2 year-1 for ammonium. In order to estimate the annual dry deposition, it was assumed that there was no seasonal change for the remainder of the year since dry deposition was only directly measured in the spring so there are uncertainties related to these values. Overall, the total direct atmospheric deposition fluxes into the Mullica River-Great Bay Estuary are 3.1 g m-2 yr-1 for nitrate and 0.58 g m-2 yr-1 for ammonium. Nitrate deposition is the dominant fraction, accounting for ~ 84% of the total inorganic nitrogen deposition to this estuary. These annual fluxes were then used to calculate the total nitrogen deposition to the water surface and watershed of this estuary. The total atmospheric inorganic nitrogen directly deposited to the Mullica River-Great Bay Estuary is estimated to be 15 x 107 g year-1 and the total atmospheric nitrogen deposited to the Mullica River watershed is estimated to be 5.5 x 109 g year-1.

Remotely sensed ocean color data was used to investigate the relationship between the atmospheric nitrogen input to this estuary and chlorophyll a, an indicator of plant biomass. The satellite images suggest that atmospheric nitrogen deposition could influence chlorophyll a concentrations for the Mullica River-Great Bay Estuary. When there was a high atmospheric nitrogen deposition event, chlorophyll a concentrations eventually increased in response and vice versa. Other sources of nitrogen, including runoff from the Mullica River, may also influence these chlorophyll a concentrations. Combining this atmospheric nitrogen data with the water column nutrient data that is being collected at the Jacques Cousteau National Estuarine Research Reserve will assist in generating nutrient budgets to better manage the coastal resources of the Mullica River-Great Bay Estuary.

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