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2.2.14 



ENVIRONMENTAL HYDROCARBON MEASUREMENTS 

 IN ECOSYSTEM STUDIES 



Dr. Mahlon C. Kennicutt II 



Geochcmical and Environmental Research Group 



Texas A&M University 



Ten South Graham Road 



College Station, TX 77840 



The measurement of various chemical parameters are often only seen in a support mode for biologically driven 

 programs. In fact these measurements are often invaluable factors in interpreting and modeling ecosystems and 

 their response to man's activities. In particular the direct measurement of an innate property closely associated 

 with the process of interest is most directly applicable and unambiguous, i.e., hydrocarbons and OCS oil and gas 

 activities. The use of hydrocarbon measurements and the ultimate program objectives can be addressed on the 

 basis of four conceptual approaches. Environmental hydrocarbon measurements can be used (1) to assess 

 baseline values, (2) as tracers of inputs, (3) to establish temporal variations and trends, and (4) as supporting 

 ancillary data. These concepts are summarized and potential benefits are discussed. 



Probably the most direct approach for hydrocarbon measurements is the "baseline concept". In simplest terms 

 the natural and/or presently occurring hydrocarbon levels are measured in an inventory-like mode. This 

 approach attempts to define natural or existing background concentrations in various pools (sediments, tissue, 

 water, etc.) and areal variability is defined. This approach documents existing contamination and aids in 

 differentiating contaminant processes, both those of interest and contributions from other sources. The data base 

 produced is also necessary in order to recognize future man-related perturbations over and above natural 

 variations. This approach is particularly important in the northern Gulf of Mexico for two reasons. First, the 

 Gulf has a long history of man-related activities and no pristine or pre-drilling data for a given area may exist. 

 Secondly, natural seepage, an important process in the northern Gulf of Mexico, tends to contaminate with the 

 same petroleum potentially released by OCS activities. 



The "tracer" concept relies upon unique fingerprints that can be used unambiguously to recognize inputs derived 

 from multiple sources, i.e., terrigenous (land) versus plankton (water column). These studies lend clues to 

 processes affecting a given area and provide a basis to assess the fate, and ultimately the effect, of by-products 

 of various activities. The "tracer" concept can be pursued at many levels of detail depending on project goals. 



Time dependent variations have become recognized as a significant feature of continental shelves, thus 

 hydrocarbons can be used to assess "trends". These studies determine the cyclic or episodic nature of inputs and 

 suggests the time-scale and magnitude of variability within a system. The physical-chemical environment can be 

 quite variable and it is important to determine if man's activity could accentuate or moderate cyclic or episodic 

 events or vice versa. 



In a more support-oriented mode, hydrocarbon measurements can be determined as "ancillary" data. It is 

 important to provide a chemical framework not only to support the biological interpretations but also in 

 evaluating the relationship between biological variability and definable chemical environment changes. This 

 also provides a broader framework to compare a given study area with existing environmental data bases to 

 determine the severity of contamination or pristineness in relation to world wide pollutant trends. 



These approaches to hydrocarbon data provide significant input and information to ecosystem studies. Program 

 and sampling design for the assessment of hydrocarbon sources, fates, and distributions must be considered in 

 light of the ultimate program's goals. The Gulf of Mexico northern continental shelf long-term monitoring effort 

 would benefit from all four hydrocarbon approaches and hydrocarbons are seen as an integral and important 

 component of any ecological study to be proposed. 



