Recirculating sea water benthic chamber for the study of the biogeochemistry of petroleum components at the sediment water interface

Abstract

The experimental benthic chamber was designed to conduct both laboratory and in situ investigations on the transport and degradation of petroleum type hydrocarbons at the sediment water interface, and to investigate the sediment/ water/organism interactions. In its basic form, it consists of a rectangular flume constructed of stainless steel tube, a windowed observation chamber, a variable velocity pumping system and its associated controls, battery packs, and interconnecting cables. The base of the observation chamber is a removable assembly, allowing the user to select either a closed rectangular box for laboratory use, or a mud grab bottom sampler configuration for in situ evaluation. For in situ use, the mud grab doors are opened, the device lowered until it contacts and settles into the bottom. The side walls of the mud grab, its jaws, and the observation chamber walls effectively seal the assembly into a closed recirculating sea water system that uses the bottom sediment as the controlled sample. Hydrocarbon, oxygen, or other materials may be used to spike the recirculating sea water or bottom sediment. Several instrumentation ports have been provided to allow monitoring of the internal system chemistry. The self-contained power pack is pressure compensated with gaseous carbon dioxide, providing a non-explosive atmosphere within the battery box compartment as well as the pump drive motor package. A five day, on-the-bottom, operational test indicated that the battery system would provide sufficient reserve power to operate the device for an extrapolated minimum of 10 days without serious degradation of the internal water flow within the system. On completion of the bottom program, the mud grab doors are pneumatically closed, retaining the sea water and sediment sample as a complete ecological test system that can be returned to the surface for additional evaluation.