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Strong bottom-up effects on phytoplankton community casued by a rainfall during spring and summer in Sagami Bay, Japan

Tue, 01 Jan 2008 00:00:00 GMT

Title: Strong bottom-up effects on phytoplankton community casued by a rainfall during spring and summer in Sagami Bay, Japan Authors: Seung Ho Baek; Tomohiko Kikuchi; Myung-Soo Han; Kim, Hyun-cheol; Shinji Shinmode Abstract: To assess the consequences of bottom-up effects onphytoplankton community composition during the rainy season, phytoplankton levels and environmental factors were monitored daily from 12 April to 22 July 2003 in Sagami Bay, Japan. The relevant environmental factorswere analyzed using cross-correlation analyses. Based on time-series analysis, lowsurface salinity conditions lasting 0 or 2 days after heavy rainfalls resulted in significant nutrient loading, such as dissolved inorganic nitrogen (DIN), into the coastal area. Also, Chlorophyll-a (Chl-a) concentration frequently increased 2 and 6 days after rainfall. Based on the high total Chl-a concentration, the time was divided into three periods, from1 to 11May (Period A), 26May to 9 June (Period B) and 30 June to 22 July (Period C). The phytoplankton assemblages during Period A were dominated by two dinoflagellates, Ceratium furca and Ceratiumfusus. Prior to these species blooming, the heterotrophic dinoflagellate Noctiluca scintillans was dominant. During Period B, the phytoplankton communities were dominated primarily by the diatoms Rhizosolenia delicatula, Hemiaulus sinensis and Navicula spp. Finally, Cerataulina dentata, Rhizosolenia spp., Lauderia borealis and Neodelphineis pelagica were dominant during Period C. After increases in phytoplankton abundance, available nitrogen (N) and phosphorous (P) were consumed and exhausted, which were considered a potential cause of the shift in the dominant organisms from large diatoms to pico- and nano-plankton in the low Chl-a environment. In particular, silicate (Si) was not a major limiting factor for phytoplankton production, since the Si:DIN and Si:P ratios clearly demonstrated that there were no any potential stoichiometric Si limitations, and almost all silicate concentrationswere N2.0 μMduring this study. Our results reveal that nutrient sources supplied by river discharge are a main cue for strong bottom？up effects on algal bloom succession during the early

Phytoplankton growth stimulation and nutrient puls by natural rainfall during spring and summer in Sagami Bay, Japan

Tue, 01 Jan 2008 00:00:00 GMT

Title: Phytoplankton growth stimulation and nutrient puls by natural rainfall during spring and summer in Sagami Bay, Japan Authors: 한명수; 시모데신지; 키쿠치토모히코; Kim, Hyun-cheol; 백승호 Abstract: To assess the consequences of high-nutrient freshwater input on the phytoplankton community structure during the rainy season, the phytoplankton levels were monitored daily together with environmental factor variables from 12 April to 23 July 2003 in Sagami Bay, Japan. The low salinity conditions lasting 2-3 days after heavy rainfalls resulted in a significant loading of nutrients, such as dissolved inorganic nitrogen (DIN), into the coastal area. Also, a few days after the decrease in salinity, increases in Chlorophyll-a (Chl-a) concentration were frequently observed. Based on the high values of total Chl-a concentration, the time was divided into three periods, which were from 1 to 11 May (Period A), from 26 May to 9 June (Period B) and from 30 June to 22 July (Period C). The phytoplankton assemblages during Period A were dominated by two dinoflagellates, Ceratium furca and Ceratium fusus. Prior to the blooming of these species, the heterotrophic dinoflagellate Noctiluca scintillans was dominant. During Period B, the phytoplankton communities were dominated primarily by the diatoms Rhizosolenia delicatula, Hemiaulus sinensis and Navicula spp. Finally, Cerataulina dentate, Rhizosolenia spp., Lauderia borealis and Neodelphineis pelagica were the dominant species during Period C. The increase in their phytoplankton abundances had consumed and exhausted the available nitrogen (N) and phosphorous (P), as the two main nutrient levels measured during almost all of the high Chl-a periods were low enough to indicate N and P limitation. In addition, this may have also been the cause of a shift in the dominant organisms from high diatoms to pico- and nano-plankton in the low Chl-a environment. In particular, silicate (Si) was not a major limiting factor for phytoplankton production, since the plots of the Si: DIN and Si: P ratios clearly demonstrated that there were not any potential stoichiometric limitations created by Si, and almost all silicate concentrations were > 2.0

Relationship between the Changjiang Diluted Water and SeaWiFS chlorophyll-a during summer

Tue, 01 Jan 2008 00:00:00 GMT

Title: Relationship between the Changjiang Diluted Water and SeaWiFS chlorophyll-a during summer Authors: Hisashi Yamaguchi; Kim, Hyun-cheol; Jianrong Zhu; Joji Ishizaka; Sang-Woo Kim; Sinjae Yoo Abstract: Satellite chlorophyll-a distribution was analyzed with statistical analysis, K-means clustering. And proper satellite chlorophyll concentration to indicate the Changjiang Diluted Water (CDW) was found. During 1998-2006, the distribution of CDW controlled by the Changjiang summer freshwater discharge showed significant interannual variations. The Sea-viewing Wide field-of-view Sensor (SeaWiFS) chlorophyll-a showed that interannual variations of the spatial distribution of high satellite chlorophyll-a (>0.9-0.4 mg m-3) was well corresponded with distribution of low salinity CDW (<30-32), and that interannual variation of the CDW area was associated with the interannual variation of the Changjiang summer freshwater discharge. Correlation analysis between the high satellite chlorophyll-a and summer freshwater discharge showed that the area of relatively-high-satellite chlorophyll in August showed best correlation (R2≈ 0.85, P<0.0001) with SFD in July. The second good correlation (R2≈ 0.79, P<0.001) was shown between the area and SFD in August. The third (R2≈ 0.58, P<0.02) was between the area in September and SFD in July. Correlation analysis indicated that low salinity, high satellite chlorophyll-a CDW spread further in the East China Sea after 1 to 2 months time lag of the discharge.

The Changjiang Diluted Water (CDW) detection by satellite chlorophyll-a

Tue, 01 Jan 2008 00:00:00 GMT

Title: The Changjiang Diluted Water (CDW) detection by satellite chlorophyll-a Authors: Jianrong Zhu; Kim, Hyun-cheol; Joji Ishizaka; Sinjae Yoo; Byong-Kwon Park; Im Sang Oh Abstract: It is known that the Changjiang Diluted Water (CDW), which mixed Changjiang summer freshwater discharge and Kuroshio Surface Water and/or Taiwan Warm Water, spreads eastwards over the broad area of the East China Sea and reaches as far as Jeju Island to Tsushima Strait. It is expected that the distribution of CDW is controlled by the Changjiang summer freshwater discharge and showed significant interannual variations. Here we analyzed the Sea-viewing Wide field-of-view Sensor (SeaWiFS) chlorophyll-a during 1998-2006 and showed that interannual variations of the spatial distribution of high satellite chlorophyll-a (>0.9-0.4 mg m-3) was well corresponded with distribution of low salinity CDW (<30-32) and that interannual variation of the CDW area was associated with the interannual variation of the Changjiang summer freshwater discharge. In order to decide criteria of the higher satellite chlorophyll-a area showing CDW, we used K-means clustering method to distinguished the concentration. Correlation analysis between the high satellite chlorophyll-a and summer freshwater discharge indicated that low salinity, high satellite chlorophyll-a CDW spread in the East China Sea after 1 to 2 months time lag of the discharge. Satellite chlorophyll-a is a good indicator of the low salinity CDW in the East China Sea