| Wetlands, together with marines, and forests are known as three of the world’s major ecosystems. The coastal wetland in Jiaozhou Bay plays an important role in purifying environment, maintenance of biodiversity, disaster mitigation, and in protecting coastlines erosion. The reed (Phragmites australis) community, as the principal community type in the estuary wetland of Dagu River, has significant effect on primary production and biogeochemical cycling in the ecosystem. Manila clam (Ruditapes philippinarum) in the Jiaozhou Bay wetlands is not only an important fisheries species, but also acts a critical role in the material cycling of the ecosystem.In the present study, the Dagu River estuary wetland and the shallow water region of Jiaozhou Bay were concerned, and selected Manila clams and reeds as two typical animal and plant species respectively. Data was collected by monthly surveys from May2009to Jun.2010in Jiaozhou Bay wetland (excerpt for Feb. and Apr.2010) and monthly surveys between Apr. and Nov.2009in Dagu River estuary wetland. The biological and ecological stoichiometry characteristics of Manila clams and reeds, as well as their ecological effects on the ecosystem were analyzed and assessed to make preliminary exploration of restoration technologies for the degraded wetland ecosystem. The main results are summarized as follows:1) The clam shells grew19.64mm annually, similar to other relative studies. Dry weight of the soft body and fatness was higher in August2009and June2010, and the density of the clam reduced gradually within the study period. Low biomass was detected in winter and spring, while it was high in summer and autumn (2318.52±124.75to3343.37±277.37g·m-2). Water temperature was the main factor affecting the mortality of clam, and the relationship between growth rate and water temperature was against to that with salinity; the clam growth was also closely related to breeding activity and clam density.2) The variation trend of carbon content in shell was similar to that in entire clam, which tended to be higher in summer and autumn. Carbon content of flesh showed opposite variation trend to that of shell in most months. Nitrogen content of shell and flesh showed obvious seasonal changes, which were lower in spring and summer. Total nitrogen content of clam ranged from0.50±0.003to0.76±0.10mmol-g-1with a decreasing tendency except a high value in March2010. Phosphorus content of clam exhibited large fluctuations, while phosphorus content of shell displayed a lagged variation compared with that of flesh. Carbon and nitrogen contents were slightly affected by shell length, width or height. Elemental contents were closely related to the reproduction cycle3) The average height of reed showed significant correlation with density of reed (P<0.01). During the main growth season periods, the aboveground biomass of reed showed generally increasing tendency, reaching at maximum point in October and exhibited evident monthly variations, ranging from between37.59±13.94to7033.02±967.37g-m-2for dry weight. Biomass of leaves, stem and sheath of reed increased generally from April to October. Aboveground biomass of non-photosynthetic organs made a larger contribution to the changes of total aboveground biomass. Preliminary study showed that rainfall had great positive effects on growth of aboveground biomass of reed in the wetlands of Daguhe Estuary.4) The leaves, sheaths, stems, ground carbon element content of reed changes in similar pattern, with higher quantity in spring and autumn, and lower in summer. Nitrogen content of the aboveground components reduced gradually Phosphorus content fluctuated in leaf, sheaths, and stems. The carbon content in underground root was higher in spring and autumn and lower summer; the nitrogen content initially decreased then increased, lowest in July. Considering the underground components, the phosphorus content increased gradually along with sampling month, and carbon and nitrogen content exhibited larger variation in fibrous roots. Along with the process of growth, development and wilt of reeds, the carbon accumulated gradually from leaf to stem.5) The annual harvest of fresh clams was2.5×105t in the bay, the annual removal of carbon, nitrogen, and phosphorus elements through fishing and natural morality of the clams totaled3.16×104t,1449.6t, and149.1t respectively. The annual removal of carbon, nitrogen, and total phosphorus through reed harvest were3.99×104tC·a--1(i.e.1.39×105tCO2·a-1),627.88t N·a-1and104.05t P·a-1, respectively. The storage of carbon, nitrogen and phosphorus in wetland soil amounted to1757.06t C·a-1,55.82t N·a-1and139.58t P·a-1. Compared with other studies, the reed in estuary wetland of Dagu River is stronger in the capability of carbon sequestration. Reed’s retention capacity of nitrogen was significantly higher than that of phosphorus, and exhibited obvious difference compared with its carbon sequestration capacity. The contribution of soil in phosphorus removal cannot be ignored.6) Based on the analysis of biological and ecological stoichiometry characteristics of Manila clams and reeds as well as their ecological effects on the ecosystem, preliminary exploration of restoration technologies for the degraded wetland ecosystem was made. It could be concluded as a combination of "polyculture of Manila clam and kelp" and reed planting. |
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