The Study Of Nitrogen Biogeochemistry In The Coastal Zone Of The Qi'ao Island, Pearl Piver Estuary

Temporal and spatial variation characteristics of nutrients and chlorophyll-a in the coastal water of the Qi'ao island is investigated in 4 April, 11 August, 3 September, 23 September, 16 November, 13 December, respectively. By means of the N2 flux method, denitrification rates of six sediment samples are measured using a continuous in flow-through system in order to study the effect of various factors on denitrification in the area. Based on the survey results of nutrients and denitrification, nitrogen biogeochemistry cycle in the area is studied preliminary. The results are as follows:(1) The concentration of TIN inside mangrove zone is higher than that in nearby mangrove zone, and the concentration of TIN in coastal water west to Qi'ao island is higher than that in south to Qi'ao. NO3--N is the main form of nitrogen in surveyed waters, which accounts for about four fifths of DIN. The concentration of phosphorous varies little. The concentration of silicate is relative higher at summer and autumn, and lower at spring ad winter. The content of chlorophyll-a in Qi'ao island coastal zone of Pearl River Estuary is higher than those in Hangzhou bay, Beihai bay and Bohai bay. This is related to high content of nutrients, which is favor of grow of phytoplankton.(2) There exists good the relationship chlorophyll-a and TIN in April and September. There exists less the relationship between chlorophyll-a and phosphorus, silicate.(3) The N/Si in coastal water of th Qi'ao is higher than those in tropical and subtropical large rivers, but in the same level with those of seriously polluted and eutrophicated rivers. The survey area characterized as high concentration of nutrients and high N/P ratio is affected greatly by authropogenic processes.(4) The denitrification rate in the coastal zone of Qi'ao island is vary greatlytemporally and spatially. It depends on temperature, the concentration of NO3-, organic carbon and bioturbation in the overlying water and types of sediment. Denitrification rate is not limited by absolute concentrate of NO3-, rather than the availability of NO3-. The effect of macrophyte on denitrification rate in coastal zone of Qi'ao island is in the first order, the next is temperature and availability of NO3-, whereas the effect of organic carbon is very small. Because of the effect of macrophyte, the denitrification rate of Q0411-5 is two times of Q0411-3. Taking A NO3- as the availability of NO3-, when â–³NO3- double increaseed of one time, denitrification rate will elevated with a factor of 1.24. The effect of temperature on dinitrificaiton rate in the area is not investigated.