Structure, Function And Services Of Estuarine Wetland Ecosystem: A Case Study In Yangtze Estuary

Estuarine wetland ecosystem is an ecotone where the fresh water meets the salt, and the land connects to the sea. It has unique structure and function to all the other ecosystems. But with the drastic population growth and fast urbanization development in the estuarine region, severe human disturbances were induced on the estuarine wetland, such as nutrient over-enrichment of estuarine water, wetland reclamation. On the other hand, it arose the tremendous requirements for ecosystem services, which may benefit the society. Linking the study from ecosystem structure and function to services of the estuarine wetland can be more important in such situation.This paper took Yangtze estuarine wetland ecosystem as a case study. Salt marsh and waders(Charadriiformes) were chosen as typical producer and consumer of the ecosystem. The estuarine and coastal dynamic processes and human disturbances were took as the context of the study. After studying the characteristics of ecosystem structure, function and services, "what is the linkage between structure, function and services of the estuarine wetland ecosystem" is the central question that the paper aimed to answer. Some questions about the structure and function that had not been solved validly before were also discussed. Major conclusions of the study are:1. Structure and function characteristic of the producer(1)Elevation variation determined the variation of the salt marsh structure and production. Along the elevation gradient from lower to higher, environmental stress on the salt marsh faded out gradually and salt marsh production went up. According to the height, above- and under-ground biomass allocation, Phragmites australis and Spartina alterniflora could be the win-win competitors to Scirpus mariqueter for above- and under-ground competition. The competitive displacement between the dominant species Phragmites australis ( or Spartina alterniflora} and Scirpus mariqueter did not show the characteristics of resource ratio hypothesis which put forward by Tilman(1982,1988), but lie on the upward growth of elevation. But the nutrients over-enrichment of the estuarine water may make things different. Especially in last 50 years, the sediment input to the estuary by river inflow had reduced dramatically. If the sediment input could not compensate the subsidence caused by nutrients over-enrichment, the elevation might decline, which might lead tothe change of salt marsh structure and function entirely.(2)Dominant salt marsh species had ties in habitat forming, and Scirpus mariqueter had some characteristics of "keystone engineer". Scirpus mariqueter could significantly slow down the water flow and trap the sediments, which led to the sediment accretion, elevation upward growth, and in turn the variation itself. Scirpus mariqueter modified the elevation, which provide the zonation chance for Phragmites australis and Spartina alterniflora and lead to the competitive displacement. At the same time, due to such function that Scirpus mariqueter carried out, sediment input to Phragmites australis and Spartina alterniflora zone and sediment accretion there declined significantly. Thus the Phragmites australis and Spartina alterniflora could maintain a tremendous distribution zone, and would not be displaced fast by other species, which distributed in the area on upper zone.(3) Different spatial distribution patterns of under-ground components led to the competitive coexistence of Scirpus mariqueter and Scirpus triqueter. Recently Sun et al. (2003) had concluded that Scirpus triqueter was the best above-ground and under-ground competitor to Scirpus mariqueter, which lead to the invasion success and clones maintaining of Scirpus triquete in Scirpus mariqueter zone. But current research had proved that Scirpus mariqueter could be the best under-ground competitor and Scirpus triqueter could be the best above-ground competitor at the edge of Scirpus triqueter tussoks which surrounded by Scirpus mariqueter. The Scirpus triqueter rhizomes distributed in upper stratum, which...