QUANTITATIVE STUDY ON LONG-TERM VARIATION OF PHYTOPLANKTON IN JIAOZHOU BAY

This paper studies quantitative variation of phytoplankton (chlorophyll-a) based on long-term observational by data during May 1991 to Nov. 2002 in Jiaozhou Bay that is a semi-enclosed bay surrounded by Qingdao City with average water depth of 7m and 2—3km wide mouth to the South Yellow Sea. Water samples were taken from of the surface and bottom in 5L water-sampling bottles at ten observation stations in quarterly cruise (Feb., May, Aug., and Nov.) every year. Each 500ml sample was filtered in vacuum through cellulose acetate membrane. Chlorophyll-a was determined using spectrophotometer method. To calculate the chlorophyll-a value, formula of Jeffery and Humphery (1975) was used. The results showed that the high chlorophyll-a values appeared mainly in the northwestern and northeastern parts nearshore area, and the lower were found in the middle and southern parts of Jiaozhou Bay. Chlorophyll-a value was higher inside the bay than outside the bay. It was similar in this respect to the horizontal distribution of nutrients (NO 3-N; NH 4-N; PO 4-P and SiO 3-Si) in Jiaozhou Bay. An obvious seasonal variation of chlorophyll-a was found. The peak of chlorophyll-a value frequently occurred in winter and summer, with the mean of (4.72±3.15)mg/m 3 and (4.33±2.57)mg/m 3, respectively. In spring, the mean of chlorophyll-a was (2.78±2.43)mg/m 3. The lowest occurred in autumn, only (1.95±0.80)mg/m 3. Annual mean content of chlorophyll-a from 2.09mg/m 3 to 5.70mg/m 3, mean of (3.47±1.19)mg/m 3. Annual fluctuation of chlorophyll-a value was obvious in 1980s to 1990s. Because of the phytoplankton standing stock was limited by a number of factors including the availability of nutrients and certain trace substances, light, temperature, water column stability etc. Man-induced fluxes of waste water had a significant effect on the variation of chlorophyll-a value. The composition of chlorophyll-a contents of different-sized phytoplankton showed that the mean percentage of microphytoplankton (20μm) was 35.8%; the nanophytoplankton (2—20μm) and picophytoplankton (2μm) were 51.3% and 12.9%, respectively, showing the order as nano- micro- pico-. Pattern of the distribution changed with season. In winter, the pico- portion contributed the smallest amount to the phytoplakton standing stock among other seasons because Synechococcus, the main component of the picophytoplankton in the Bay, its abundance is constrained by temperature and nutrients. The nanophytoplankton dominates the contribution over other two.