Seasonal And Diel Variation Of Nutrients And Chlorophyll A Concentration In The Qiongdong

The Qiongdong was located in the Southwestern edge of Northern South China Sea continental shelf and the west of Nanhai Warm Current. The Qiongdong was a famous upwelling area in China, with a high concentration of nutrient, formed the qinglan and seven states fisheries. And it belongs to subtropical monsoon region, its climate change was mainly controlled by the east Asian monsoon, the summer prevailing warm and moist southwest monsoon, the winter prevailing dry and cold northeast monsoon.Moreover, the Qiongdong was near the eastern coastal hainan island influenced by human activities and a series of intermittent water exchange significantly. These unique geographical environment,climate and hydrological conditions have an important influence on the spatial and temporal distribution of nutrient and chlorophyll a. The spatial distribution of nutrients and Chlorophyll a and their controlling factors indicated by the dissolved inorganic nitrogen(DIN= NO3-+NO2-), phosphate(PO43-), silicate(SiO32-) and Chlorophyll a were studied on the basis of two cruises in the Qiongdong sea during the winter of 2012(opening of the south China sea voyage) and the summer of 2013(guangdong ocean university open voyage). The article research conclusions were as follows:1. The spatial distribution of nutrients structure and its controlling factors indicated by the dissolved inorganic nitrogen(DIN=NO3-+NO2-), phosphate(PO43-), silicate(SiO32-)were studied on the basis of two cruises in the Qiongdong sea during the winter of 2012 and the summer of 2013. The results indicated that during winter the high DIN, SiO32- and DIN/P, Si/P appeared in the north of survey sea. The nutrient concentration and ratio in the other stations were low and distributed smoothly. The reason for the phenomenon might be that the nutrient in the northern of survey sea were affected by Guangdong coastal current with high DIN, SiO32- and low PO43-. In the summer, the distribution of DIN and PO43-was similar to winter with a uniform distribution, while that of SiO32-and Si/DIN, Si/P was high in nearshore and low in the offshore. This was because of the nearshore was affected by Hainan runoff with low DIN, PO43- and high SiO32-. It was also influenced by the high biomass and enhanced stratification in the nearshore.2. The spatial distribution of Chlorophyll a was studied on the basis of two cruises in the Qiongdong sea during the winter of 2012 and the summer of 2013. The results indicated that during winter the high Chlorophyll a appeared in the northeast of survey sea.The Chlorophyll a in the other stations was low and distributed smoothly. The reason forthe phenomenon might be that the Chlorophyll a in the northeast of survey sea was affected by Guangdong coastal current with a high nutrient concentration, which promoting the growth of phytoplankton. In the summer, The Chlorophyll a was high in nearshore and low in the offshore. This was because of the nearshore was affected by Hainan runoff with a high nutrient concentration, which promoting the growth of phytoplankton. The Chlorophyll a in summer was higher than the winter significantly. This was because of the Hainan runoff with more nutrient than Guangdong coastal current, and the photosynthesis of phytoplankton in summer strengthen than winter.3. Further analysis of the nutrients limitation for phytoplankton growth showed that in surface water there was a obviously Si limiting in winter, the relative frequency(%) of silicon is 58.83%. Similarly, it showed a coupling of N and Si limiting in summer. This might be related with the Biological needs, Seasonal river runoff, Guangdong coastal current and stratification, the limiting factor from Si change to Si and N.4. The distribution and controlling factors of diel variation of nutrients and Chl-a were studied on the basis of 2 continuously measuring stations during the summer(August) in2013. The results indicated that the nutrients concentration in the surface was close to that in the middle at S1 and S2, and the concentration on the bottom at S1 was higher than that in the surface and middle. This could be related with the thermocline which weakened the transportation of nutrients upward. The diel variation of silicate, nitrate, and phosphate on the bottom of nearshore station S1 appeared a semidiurnal period, but not at offshore station S2, suggesting that nutrients at nearshore station S1 was influenced by the tidies more obviously. Moreover, the Chl-a level at S2 displayed vertical stratification, and low Chl-a level at S1 at night reflected the feeding of planktonic animal. Our results suggests that the Chl-a and nutrients at S1 and at S2 were controlled by the thermocline, tidies,bioglogical effect and light. The tides are more obvious at S1, and the Chl-a was also affected by the feeding of planktonic animal. It is because Chl-a and nutrients are controlled by many environmental factors, making Chl-a unrelated to nutrients.