FAUNAL MORTALITY AT A GULF COAST AQUACULTURE SITE...CARELESS DREDGE SPOIL RELEASE OR “NATURAL SEDIMENTATION”? PLM-XRD ANSWERS THE QUESTION!

Aquaculture is now a profitable and widespread practice in all coastal areas of the United States and throughout the world. Not unexpected, successful operation of such “farms” may be threatened by other activities located in their proximity. An example is the recent allegation that substantial damage to an oyster farm in Mississippi Sound occurred during enlargement of an offshore bird sanctuary by the State of Alabama. Over 600 yards³ of mud was dredged from the bottom of the Sound and “piped” one mile northward to expand an existing bird sanctuary. A multi-million dollar damage suit was filed by the farm operators alleging that improper control during the piping operation resulted in massive spillage and uncontrolled mud release. Diurnal tides and storm events were then responsible for carrying the mud northward some 3.5 miles as “bottom and suspended sediment load” to the farm site where resuspended mud smothered and caused destruction of planted oyster spat.

The defense, however, provided data that confirmed that distinct differences were present in the clay and heavy mineral suite of sediments at the oyster farm versus the dredge site. The presence of minerals such as garnet, hornblende, and epidote at the dredge site reflect derivation for these sediments from adjacent Mobile Bay. These sediments themselves reflect erosion from “Appalachian Orogen” crystalline source rocks exposed in the Mobile Bay watershed. The sediment contaminating the oyster farm lack these minerals and were derived from recent upland Coastal Plain strata that are being discharged from the mouth of a river located less than 1,000 feet from the aquaculture site! Consideration of this evidence provided by the defense resulted in acceptance by the plaintiff of a “modest” out-of-court settlement, concluding the litigation.