Distinguishing Ambient And Anthropogenic Sediments At SensitiveCoastal Ocean Sites

Abstract

2 Jacksonville District, US Army Corps of Engineers, USA Abstract Often during dredging, beach renourishment, or other coastal engineering activities, questions arise as to whether those activities are causing unintended, unexpected, deleterious environmental impacts. A typical question arising during dredged material disposal operations in a coastal zone, is whether any of the discharged dredged material is being transported out of the designated disposal site to a sensitive coastal ocean site of concern. In Florida (USA), and in the Caribbean, a sensitive coastal ocean site of concern is typically a coral reef location. In dredging operations in Ft Pierce Florida, local citizens expressed concern about a muck- like substance, observed covering a coral site, and wondered if it originated from the designated dredged-material disposal site, Proni (l). To address this concern a long term monitoring program has been undertaken to determine the following: 1) what other potential sources, besides the discharged dredged material, of the muck- like material may exist, Trefry (2), 2) what are the biological, chemical and sedimentary characteristics of the material, 3) do any of the other potential sources of material have similar characteristics, 4) do oceanographic and meteorological conditions favor the transport of dredged material from the disposal site to coastal site(s) of concern and, 5) what is the chronological history of the appearance of muck-like material at the site of concern? In this paper a discussion of results obtained to date is presented. Potential other sources of the material are identified and discussed, which include upwelled Atlantic ocean water, flood control releases from canals and bays, and dredging site transport (in contrast to transport from the dredged-material disposal site). Oceanic current observations are presented together with a discussion of potential sediment transport pathways. Potential effects of meteorological phenomena on coastal sediments are also discussed. Statistical cluster analysis of biological parameters suggests an ability to distinguish dredging site related organisms from coastal shelf organisms.