Ecosystem processes of the northwestern Gulf of Mexico. Part 2, Material transport and ecosystem dynamics : draft

Abstract

Energy-related activities have an increasing impact on the marine ecosystems of the Texas-Louisiana continental shelf, traditionally one of the richest fishing grounds in the nation. This proposal is part of a comprehensive plan of study designed to determine the impact of energy-related activities on marine processes in this area. A four-year program is envisioned. For convenience, the research program—Ecosystem Processes of the Northwestern Gulf of Mexico—has been divided into two parts: Part 1-Currents and Hydrography, Part 2-Material Transport and Ecosystem Dynamics. Parts 1 and 2 of this proposal will be separately submitted to the U.S. Energy Research and Development Administration. Since the factors driving the processes of the northwestern Mexico ecosystem are poorly understood, the initial effort will be directed toward answering the following question: What is the strength and influence of the various driving forces affecting the shelf ecosystem? Effluents from the land and estuaries, inputs from the deep waters of the Gulf, benthic-neritic interaction on the shelf, atmospheric-neritic interactions, trans-shelf transport. Both parts of the proposal describe a first-year plan of work. Results of this work will guide continuing studies for the second, third and fourth years. ... The work of Part 2 during the first year will focus on biological, biochemical and sedimentological aspects, to which geochemical and more geological studies will be added as the work progresses in subsequent years of the study. The first-year objectives will stress measurement of the flux of imported material onto the shelf across the terrestrial, atmospheric and oceanic boundaries and the flux of regenerated material from the sediments; the role of the inorganic and organic nutrient fluxes on the processes of the northwestern Gulf; the seasonal response of the various trophic levels to these inputs. Several geographic areas affected by representative combinations of driving forces will be chosen and comprehensively studied to determine the material pathways and transfer rates characteristic of different parts of the shelf. Initial studies will investigate the ecosystem dynamics off Port Aransas, Tx., a relatively unperturbed area, and off the Mississippi River delta, an area dominated by freshwater runoff. Nitrogen will be used as the primary tracer because (1) it is frequently a limiting nutrient in the sea, (2) its diverse chemical species initiate the food chain by different processes, and (3) good analytical techniques are available. Information on the activity of other elements (C, P, Si) in the ecosystem will be gathered to supplement the nitrogen measurements. The purpose of the study of ecosystem processes in the northwestern Gulf is to enable a determination—by subsequent monitoring of community structure, physiological rates, directional flows and transfer efficiencies—of the impact of energy-related activities on marine processes in this area.