John R. Proni
Atlantic Oceanogr. and Meteorol. Labs., Ocean Acoust. Div., 4301 Rickenbacker Causeway, Miami, FL 33149
Acoustical methods such as backscatter and Doppler current measurements are gaining substantial acceptance in both point source and nonpoint source oceanic pollution studies. Using acoustical backscattered energy, chemical and biological samplers are guided to oceanic water column regions of higher contaminant concentration. In typical discharge operations, e.g., dredged material, sewage effluents, oil-well blowouts, after-discharge backscatter levels are initially at least three to four orders of magnitude above normal background backscatter levels and are available for tracking of plumes and guidance of sampling operations. Additionally, acoustical backscatter may also be used to map naturally occurring surfaces within the oceanic water column along which both discharged material and naturally recurring particulates may accumulate. Thus nonacoustical sampling may continue to be guided indirectly far beyond the time or distance at which plume concentration levels may be considered to have diminished to average water column background levels. Furthermore, such surfaces may be loci of increased probability of exposure to contaminants for plankton, larvae, and juvenile fish and as such should be closely studied. Acoustical detection of incursions of discharged material along sub-oceanic surfaces for both negatively and positively buoyant plumes will be illustrated using sewage sludge discharges and secondarily treated wastewater effluent discharges. Preferential accumulation surfaces present: (1) at the boundary region of Hudson/Raritan River water and continental shelf water and (2) within Chesapeake Bay, detected through backscatter and transverse Doppler, measurements will be shown.