Graduation Year

2004

Document Type

Dissertation

Degree

Ph.D.

Degree Granting Department

Civil Engineering

Major Professor

Poor, Noreen D.

Keywords

atmospheric deposition, estuary, eutrophication, micrometeorology, modeling

Abstract

An ammonia emissions inventory discovered that 90% of the ammonia emitted from Pinellas, Hillsborough, and Polk counties, originated from the latter two counties. This finding is significant and suggests that a substantial portion of the ammonia deposited to Tampa Bay is transported with easterly air masses. Ammonia and ammonium concentrations at the coastal Gandy Bridge site were seasonally and diurnally consistent, but the rural Sydney site showed greater variability. It was determined that wind direction was the most influential parameter affecting the Gandy Bridge site, which supports the hypothesis that an advection of ammonia from the east is a major source of ammonia to the estuary. Sequential sampling of ammonium in wet deposition at the Gandy Bridge site confirmed that between 35% and 60% of the ammonium (CNH4) in rainfall is deposited to Tampa Bay during the initial 20% of precipitation (D) according to a power law CNH4=aD-b.

Ammonium concentrations were predicted with an aqueous-phase accumulation model and a relationship between I, rainfall intensity in mm min-1 and (beta), scavenging rate in min-1 was shown as (beta) = 0.08I0.66. This algorithm will facilitate future modeling studies that explore the relationship between the wet deposition of ammonium and ammonia reduction strategies in Tampa Bay. The NOAA Buoy model accurately predicts sensible heat flux, and is an effective tool for estimating the offshore air/water exchange rates of ammonia over Tampa Bay. If near-shore vs. offshore meteorological measurements are used, the model under-predicts flux parameters by as much as 30% in the summer season. The model was "calibrated" to correct this deficiency. Bi-directional ammonia flux measurements during the fall and winter seasons resulted in an average flux rate of 96.2 (mu)g-NH3 m-2 d-1, indicating a net transfer from air to water.

During the 2003 summer season, an average ammonia flux rate of -117.9 (mu)g-NH3 m-2 d-1 and a 32% reduction in the annual ammonia dry deposition rate to Tampa Bay was calculated. Wet deposition likely contributes to ammonia reemission from the estuary. These results indicate that volatilization of ammonia reduces the nitrogen burden available for biological synthesis in Tampa Bay.

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