| Summary: | 碩士 === 國立臺灣大學 === 海洋研究所 === 87 === Abstract
Nitrogen and phosphorus are very important elements in the biogeochemical cycle. The exported nitrogen and phosphorus compounds from rivers have strong impact on the coastal marine ecosystem. Although rivers in Oceania islands are small, the total number is large. Consequently, the study of the distribution of nitrogen and phosphorus species in on of these rivers is helpful to the understanding of the importance of nutrient fluxes supplied by these rivers.
Kao (1995) first studied the nitrogen and phosphorus species in Lanyang Hsi by investigating the temporal and spatial distribution of nitrate and phosphate. There are still other species, such as ammonia, dissolved organic phosphorus and particular species, which have not been studied. Ammonia is a very important species in the nitrogen cycle, because it is preferentially taken up by phytoplankton and it is the first product of remineralization of organic nitrogen. However, analysis of ammonia in nature water has lots of problems. Since the indophenol blue method is the most common by used analytical method for determination of ammonia in natural water; this study explored some basic problems of indophenol blue method. From this study, the author found that the high buffer capacity observed during analysis of sea water is due to the complex formation between magnesium ion and citrate. While using o-phenylphenol to replace phenol for fresh water samples, the author found very low buffer capacity because of the low concentration of o-phenylphenol used in the procedure, which is in turn limited by its low solubility in water.
To investigate the temporal and spatial variability of nitrogen and phosphorus species in the Lanyang Hsi watershed, the author measured the following nitrogen and phosphorus species: dissolved inorganic nitrogen (nitrate, nitrite, ammonia), particular nitrogen, phosphate, dissolved organic phosphorus, particular inorganic phosphorus and particular organic phosphorus. The Lanyang Hsi watershed could be divided into three different types of regions: the agriculture-dominated, the non-disturbed and the city-dominated. According to observations of this study, nitrate is the most important nitrogen species, which accounts for about 60~80% in Lanyang Hsi. Ammonia is not negligible, for it accounts for about 4~19%. Dissolved organic phosphorus is a rather important phosphorus species, which accounts for 30~70%. The upstream plantations are strong sources of nitrate. The municipal areas near the river mouth are important sources of ammonia, phosphate and dissolved organic phosphorus. Distribution of nitrate in the river water shows it as nearly conservative, but distribution of phosphate exhibits evidence of its removal during the transport.
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