An Ecological Characterization Study 



of the 

 Chenier Plain Coastal Ecosystem 

 of Louisiana and Texas 



1.0 The Ecological Characterization 

 Process 



1.1 INTRODUCTION 



An ecological system, or ecosystem, is composed 

 of plants and animals which interact with one another 

 and with their habitat or physical environment. Man 

 is^part of the ecosystem and his actions influence or 

 respond to the various components and processes of 

 the system. Only when man understands how ecosys- 

 tems function will he be able to effectively manage 

 his natural resources and prudently guide develop- 

 ments generated by social and economic demands. 



An ecological characterization study describes 

 tlie important components and processes of an eco- 

 system and provides an understanding of their inter- 

 relationships by synthesizing and integrating exist- 

 ing physical, biological, and socioeconomic infor- 

 mation. The main purpose is to provide an informa- 

 tion base to aid in evaluating human impacts on 

 the ecosystem and to provide an ecological frame- 

 work for guiding resource management and coastal 

 planning. 



1.2 CHENIER PLAIN ECOLOGICAL 

 CHARACTERIZATION 



The Chenier Plain (fig. 1-1) in southwestern 

 Louisiana and southeastern Texas is a relatively large 

 coastal ecosystem created by 5,000 years of sediment 

 deposition from the Mississippi River. This ecosystem 

 was selected for study because of its biological 

 diversity, valuable fish and wildlife resources, and its 

 proximity to actual and proposed oil and gas pro- 

 duction activities. 



1.2.1 APPROACH OF THE STUDY 



In this study the Chenier Plain is modeled and 

 described at four levels of ecological organization 

 (fig. 1-2). Major processes which operate at each 

 level are identified (fig. 1-3). This facilitates an 

 understanding of their relationsliips by minimizing 

 problems associated with differences in scale and 

 duration between physical and biological events. 



Discussions about components and processes 

 and their interrelationships are often supplemented 

 by the use of graphic models and symbols (fig. 14). 

 A circle represents an external driving force, such 

 as solar energy. A dashed line encloses a system of 

 interest (A). Arrows represent a flow of energy in 

 tlie direction indicated. The energy may take many 

 fonns; between biotic compartments it is usually a 

 flow of organic matter (food), such as when a predator 

 eats its prey (B). 



Often energy transfer is much more subtle. For 

 instance, tides or inorganic nutrients are energy 

 sources that do work or allow work to be done on 

 the recipient. This energy flow is also shown by arrows. 



A consumer, pictured as a hexagon (B), is an 

 organism or system that consumes more organic 

 matter than it produces. According to the second law 

 of thermodynamics, because no process is totally 

 efficient, some of the energy involved in any process 

 is changed into a nonusable form (the Law of Energy 

 Degradation). Respiration of living organisms demon- 

 strates this; part of the organic energy they metabolize 

 is converted to waste heat. Symbolically this is repre- 

 sented by a heat sink such as that shown for the 

 consumer (C). This energy "loss" is universal and is 

 implied for every process occurring in an ecosystem, 

 but for simplicity's sake it is not shown in the system 

 diagrams in this study. 



A common symbolofgeneralutility is the storage 

 bin (D), which symbolizes the storage or standing 

 stock of a commodity. It is implied in the producer 

 and consumer modules and is generally used for 

 nonUving materials. Thus when plants die, the dead 

 tissue accumulates in a litter compartment. 



Three other common symbols are used to denote 

 functional groups. The bullet (E) is the symbol for 

 producers of organic matter, plants such as emergent 

 grasses, trees, or phytoplankton. Producers convert 

 the sun's energy to organic matter (F). 



Production is controlled by avaUabUity of 

 nutrients, shading (e.g., turbidity for phytoplankton) 

 or by other limiting factors. A "work gate" (G) 

 shows this as in the control of phytosynthesis by 

 nutrients and turbidity (H). Interactions that control 

 the flow of energy are shown by (I). 



