The Source Of Sedimentation Organic Matter From The Seaweed Bed In Gouqi Island

Seaweed bed is a multifunctional complex ecosystem in coastal area on land or sea in the rocky reef. One of the typical coastal life habitats for seaweed bed is supported by the macroalgae biocenosis. One of the most productive habitats in the world in seaweed bed can provide a variety of invertebrate and fish habitat space and avoid enemy places and provide feeding, laying eggs. The seaweed bed has a unique ecological value and resource potential, together with mangrove, forest coral reef, tidal flats and other habitat constitute nearshore Marine ecosystems. As one of important content in the study of the global carbon cycle, the seaweed bed of matter exchange frequently between the surrounding ecosystems. The seaweed bed of SOM as the primary productivity of biomass carrier flow, have the basic attributes of functional properties of primary productivity. The material energy flow in seaweed bed can be achieved by the rocky reef of water power caused by the transport. At present, many problems about the source, distribution and migration of SOM in seaweed bed require a large number of detailed studies.The SOM is to realize the important material basis of ecosystem service function in seaweed bed. The representative area are selected according to the distribution characteristics of the seaweed bed in Gouqi Island, and considering the surrounding waters natural dynamic environment of the waves and human activities can affect the composition and distribution of SOM. The SOM and other samples were collected in July 2014, October 2014 and May 2015 based on three cycle stages of the macroalgae life history: seeding and growing period during August to Mar of next year; mature and flourishing period during April to May; recession and apoptosis period during June to July. The samples of elements（C and N） and stable isotope(δ¹³C and δ¹⁵N) were determined, and particle size analysis for SOM. The sources of SOM were analyzed by these parameters as indicators. The macroalgae contribution to the SOM was estimated by combining with stable carbon isotope in the sediment samples. Understand the source, distribution characteristics, main controlling factors of SOM and the macroalgae contribution, the main results were show as following:The content of TOC and TN in the sediment have the time difference, it is the highest levels in July, the range of 2.34³.75% and 0.38⁰.63%, the time variation trend is: July>May>October. Particle size analysis for SOM showed that, greater than 63 microns fraction of the macroalgae body clastic percentage have the time difference, it is the highest levels in July, the range of 15.42³1.78%, and they have no significant difference in October and in May the following year（P>0.05）. Three times C/N ratio of SOM are smaller than 8, the results show that the SOM is a typical marine source. The TOC, TN and particle size of time difference were due to anniversary of the life history characteristics of macroalgae. The SOM was composed of a large number of algae body clastic in the macroalgae apoptosis period in July. The TOC and TN of SOM has significant correlation with sediment particle size in seaweed bed from Gouqi Island, this is similar to other estuarine wetland sediments. Through the calculation of SOM C/N, the macroalgae contribution to the SOM showed as the following trend at different times: July>May>October.In order to study the source of SOM in the rocky reef seaweed bed, on the basis of the chemical indexes（C/N） and stable isotope composition(δ¹³C and δ¹⁵N), the source and change of SOM was analyzed by using carbon and nitrogen stable isotope The SOM of C/N values are in the range of 5.86-6.63 in July, 5.97⁶.91 in October and 5.37⁶.17 in May the following year, and the results show that the SOM is a typical marine source. The depth of the water on the gradient of the δ¹³C for SOM range from-20.28‰ to-17.56‰ in July, there is a significant difference among them（P<0.05）. The δ¹³C of SOM are in the range of-22.28‰^-21.69‰ in October,-21.39‰^-20.99‰ in May the following year, they have no significant difference during the two seasons（P>0.05）. The δ¹³C of SOM has time variation characteristics, and has space variation characteristics in July. According to the relationship between δ¹³C, δ¹⁵N and C/N, most of the SOM was from the phytoplankton and macroalgae on seaweed bed in July, and the SOM mainly came from the contribution of phytoplankton in October and in May the following year. At the same time, the contribution from the macroalgae was calculated by the stable carbon isotopic mass balance hybrid model, the macroalgae contributed up to 66.67% for SOM on seaweed bed in July. The macroalgae crumbs in the SOM percentage has significant effects by the ocean dynamic environment.