CHAPTER THREE 

 ECOLOGICAL PROCESSES IN DELTA MARSHES 



In the previous chapter, I 

 considered marsh changes across spatial 

 gradients and also those temporal changes 

 that are measured in hundreds or thousands 

 of years. But within any fairly 



homogeneous patch of marsh, many complex 

 interacting processes occur and reoccur in 

 cycles that are measured in days and 

 seasons. In order to understand the 

 marsh ecosystem, it is necessary to 

 understand how these processes operate and 

 how they interact. However, it is not 

 clear how best to study them. One can 

 analyze the individual components of the 

 systan and from these attempt to 

 reconstruct the whole. Or conversely, it 

 is possible to examine the system from a 

 "macroscopic" point of view, almost as an 

 independent organism which acts as an 

 integrated individual. Both approaches 

 have their strengths and weaknesses. The 

 latter "systems" approach has been 

 emphasized in Mississippi delta marshes in 

 studies supported by the Louisiana Sea 

 Grant program, and I will draw heavily on 

 them in this chapter. In addition, much 

 excellent research has also focused on 

 individual species, especially fish, 

 mammals, and birds. Without these 



studies it would not have been possible to 

 draw as complete a picture as we now have. 



In the systems approach one often 

 relies heavily on ecosystem models which 

 conceptually organize and simplify the 

 ecosystem under study. Although more 

 sophisticated, quantitative models of 

 delta marshes have been published (Day 

 et al. 1973; Hopkinson and Day 1977; 

 Costanza et al. 1983), I will use a simple 

 conceptual model to focus the reader's 

 attention on the most important coiTiponents 

 and processes in the marsh ecosystem. 

 Each of these will then be considered 

 further. This model (Figure 40) 



emphasizes the importance of (1) primary 

 production and its control, (2) 

 decomposition, detritus, and the role of 

 micro-organi sns, (3) the benthos, (4) the 

 food chain to vertebrates - fish, water- 

 fowl, and fur animals, and (5) nutrient 

 cycles. 



Throughout this discussion the role 

 of hydrology will be emphasized. This 

 property makes wetlands unique. Nearly 

 everything that happens in wetlands is 

 influenced by the flooding properties of 

 the site. Some of these - flooding 

 dynamics, chemical and physical properties 

 of the substrate, vegetation zones - have 

 already been considered. In addition, 

 each of the five groups of processes 

 emphasized in Figure 40 is influenced by 

 hydrology. The extent of hydrology's 

 influence should become increasingly clear 

 in the following discussion. 



PRIMARY PRODUCTION 



It is convenient to consider marsh 

 plants in four different groups. (1) The 

 most extensively studied are the emergent 

 vascular plants, most of them grasses 

 which are responsible for most inarsh 

 photosynthesis. (2) Almost always 



associated with the emergent plants on the 

 mud surface, and especially on the lower 

 parts of the vascular plant stems, is an 

 active community of epiphytic filamentous 

 algae and diatoms along with many 

 microscopic consumers. (3) The benthic 

 algal community in marsh ponds, almost 

 always submerged, is a rich surface 

 coating of diatoms and other unicellular 

 green and blue-green algae. (4) Finally, 

 in many marsh ponds submerged macrophytes 

 such as Ruppia maritima , Eleocharis 



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