Analysis of Long-Term Variation of Phytoplankton Biovolume and Gelatinous Sheath Volume in Lake Biwa

Abstract

Chemical oxygen demand (COD) in Lake Biwa has not been improved during the past quarter century in spite of decreases in organic loadings from watershed and total phytoplankton biovolume. In addition, an increase in cyanobacteria has been observed in Lake Biwa. Most of cyanobacteria have a large volume of gelatinous sheath, which is usually called extracellular polysaccharides (EPS) and may play a significant role in COD in the lake. Therefore, we analyzed long-term variation of phytoplankton biovolume and EPS volume at Imazuoki, Nagahamaoki and Imazuokichuo-points in the northern basin of Lake Biwa from 1980 to 2009. The EPS volume in 2000-2009 increased approximately three times compared with that in 1980-1989 at Nagahamaoki-point, although the phytoplankton biovolume in 2000-2009 decreased to 85％ of that in 1980-1989. Furthermore, the ratio of EPS volume to the phytoplankton biovolume at Nagahamaoki-point reached 112 in 2000-2009 while that in 1980-1989 remained 31. At Imazuoki and Imazuokichuo-points, the ratio increased from 41 to 109 and from 40 to 120 during the same period, respectively. These results suggest that the large amount of EPS produced by phytoplankton could be one of the major sources of organic matter in Lake Biwa.

Effects of Algal Extracellular Polysaccharides on the Formation of Filamentous Manganese Oxide Particles in the Near-Bottom Layer of Lake Biwa

“…Regarding the long-term trend of the total biovolume of phytoplankton cells in the northern basin of Lake Biwa (0.5 m), research showed that the average total biovolume ranged from 1.5 to 1.8 mm 3 L −1 from 2000 to 2009, corresponding to 63% to 85% of the levels observed from 1980 to 1989 [ 33 ]. Although the total biovolume decreases, the total volume of mucilage sheaths surrounding the phytoplankton cells (16 to 21 mm 3 L −1 during 2000 and 2009) reaches more than twice the levels of 1980–1989 and 1990–1999, suggesting an increase in phytoplankton species with increasing sheath content.…”

“…In addition, 18-year data of the abundance of fi tous Mn particles observed at a depth of 90 m and the biovolume of phytoplankto m were used. The total biovolume was expressed as the sum of the biovolumes of ophyceae (cyanobacteria), Chlorophyceae (including Charophyceae; green algae) lariophyceae (diatoms), Chrysophyceae, Dinophyceae, and Cryptophyceae, whic calculated from the cellular or colony sizes, as described elsewhere (Kishimoto et al The biovolume data obtained from 2002 to 2009 at the Imazuoki-chuo point wer lished previously [32,33].…”

Effects of Algal Extracellular Polymeric Substances on the Formation of Filamentous Manganese Oxide Particles in the near-Bottom Layer of Lake Biwa

“…Regarding the long-term trend of the total biovolume of phytoplankton cells in the northern basin of Lake Biwa (0.5 m), research showed that the average total biovolume ranged from 1.5 to 1.8 mm 3 L -1 from 2000-2009, corresponding to 63% to 85% of the levels observed from 1980-1989 [33]. Although the total biovolume decreases, the total volume of EPS surrounding the phytoplankton cells (16 to 21 mm 3 L -1 during 2000 and 2009) reaches more than twice the levels of 1980-1989 and 1990-1999, suggesting the increase in phytoplankton species with increasing EPS content.…”

“…The total biovolume was expressed as the sum of the biovolumes of Cyanophyceae (cyanobacteria), Chlorophyceae (including Charophyceae; green algae), Bacillariophyceae (diatoms), Chrysophyceae, Dinophyceae, and Cryptophyceae, which were calculated from the cellular or colony sizes, as described elsewhere (Kishimoto et al 2013). The biovolume data obtained from 2002 to 2009 at the Imazuoki-chuo point were published previously [32,33].…”

Characterization and Dynamic Analysis of Dissolved Proteins in Lake Biwa Using Two-Dimensional Electrophoresis

“…It has been reported that the increase in refractory DOM may be attributed to the contribution of not only humic substances from soils around the rivers flowing into Lake Biwa but also algal DOM from phytoplankton in the lake. 3,[8][9][10][11][12][13][14] Furthermore, it has been clarified that humic substances might be released regularly from lake sediment. 15,16 However, few studies of the characteristics and contribution of algal DOM to refractory DOM in lake water have been done.…”