Modeling biomass and nutrient dynamics in seagrass meadows (Thalassia hemprichii)

• Main Authors: Ruei-Jiuan Tsao, 曹瑞娟
• Other Authors: Chia-Shun Yu
• Format: Others
• Language: zh-TW
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/z4djy8

碩士 === 國立中山大學 === 海洋環境及工程學系研究所 === 95 === This study refers to developed ecological model abroad, and established the seagrass model with MATLAB compiler. I also took the seagrass meadows in south Taiwan-Nanwan for my studying case, and simulated the dynamic effect of seagrass and epiphyte biomass, as well as nutrient, and attempted to go on probing into the cause with northeast monsoon and typhoon. The simulating site of this study was Nanwan, which is located at Hengchun Peninsula, the southern tip of Taiwan. The dominant species in this area is Thalassia hemprichii. South Taiwan is situated at a tropical climate, and the variation of air temperature is small. Additionally, Kurshio embranchment cause the variation of water temperature smaller, about 24 (℃) to 30 (℃).The northeastern monsoonal winds, formed downhill winds, are extremely forceful from October to April, so the wind speed is greater during this period than the rest of the year. In South Taiwan, dry-wet season is clearly. The dry season is from November to April, and the wet season is from May to October. The main rainfall comes from southwest monsoon, especially summer typhoon (June to September). The wind speed is raised abruptly by typhoon and makes water agitate, which not only cause the mortality raising but also the sediment turbulence. By Lin’s research (2005), the growing area of seagrass meadow in Nanwan is a half-closed tidal pool where human makes huge effect and there is a lot of drainage of house and inn sewage. Furthermore, these seagrasses in Nanwan would be exposed to air during the period of poor tide and the emerged period is the longest of these three areas -Nanwan, Dakwan and Wanliton. The seasonal dynamic of seagrass, which is located in the high site of intertidal zone, is obvious, and the biomass is larger in summer than in winter; but that is not obvious in the low site and tidal pool. By the seasonal condition and some specially climate condition mentioned above, the analysis of simulate cases would be go on. Comparing of the modeling result and real measurement, the seasonal changing situation mostly match up. No matter high site (emerged and dried) or low site, there is the maximum of seagrass biomass (including above ground, below ground, or shoot density) in summer, and the minimum in winter. Typhoon causes the biomass losing abruptly in summer. R/S ratio (below-ground biomass division above-ground biomass) is bigger in winter than in summer. On one hand the inside nitrogen redistribution is larger in summer, because the larger growth rate occurs in summer, and the more nutrient is supplied from roots, on the other the redistribution is smaller in winter cause the less nutrient is supplied from roots. Epiphyte biomass has the maximum in summer, when the nutrient concentration of water is larger. In the section of the difference between low and high site seagrass, it is apparent that the high site seagrass would be exposed to air and dried by northeast monsoon. Although typhoon comes up, its influence is not so strong as northeast monsoon at high site. The maximum biomass still occurs in summer, and it is presumed that the living environment of high site seagrass is with more pressure by nature. The above-ground biomass of high site seagrass is smaller than low site, but the below-ground biomass is much lager at high site. Besides, shoot density is larger at high site. The biomass of epiphyte is larger at low site just opposite to shoot density. It is supposed that high site seagrass is emerged to air and limited by environment factors so above-ground biomass would be reduced and store up the sustenance to below-ground biomass. It is conjectured that the main factor with shoot density is affected by light density and below-ground biomass. In shallow water, the seagrass at high site could accept more light energy, moreover the below-ground biomass is sufficient and the recruitment rate is large, thus there are more shoots at high site. Epiphytes are also limited by water depth and wind, and the biomass of epiphyte at high site is smaller than at low site.