Impacts of long-term increase in silicon concentration on diatom blooms in Lake Kasumigaura, Japan

Abstract

-In the eutrophic Lake Kasumigaura in Japan, a trend of dissolved Si (DSi) concentration was detected over the last three decades, probably caused by the DSi release enhanced by an increase in sediment resuspension for the same period (Arai et al., Limnol., 13, 81-95, 2012). The present study described the long-term trends of the magnitude and seasonality of diatom blooms in the lake during 1981-2010 using the database and assessed the influencing factors for the trends by the numerical simulation of DSi and diatoms. The box model was developed based on the lake budgets (inflow, outflow, release and sedimentation) and the simple diatom growth model depending on DSi, temperature and light condition. As results, database analysis detected a long-term trend of increasing diatom abundance and a shift of blooming season from spring and autumn to the winter-spring period. Si could be regarded as a main nutrient factor limiting diatom growth by analyzing N:P:Si ratios. Our model simulation relatively well-reproduced the increasing trend and the shift of seasonality of DSi and diatoms, even though peaks of diatom blooms were underestimated in some years. Among input variables, the concentration of resuspended sediments radically increased. The model simulation with the input variables or parameters changed suggested as follows: (1) the recent DSi release from resuspended sediments enhanced diatom abundance and (2) the degradation of light condition caused by resuspension affected the shift of blooming season. These findings implicate the significance of the interactions between sediments and water to phytoplankton blooms.

Molecular biogeography of planktonic and benthic diatoms in the Yangtze River

“…Taxonomic compositions of riverine diatoms in the Yangtze River are markedly different from those in lakes [41] and oceans [13] because of the distinct differences in salinity and hydraulic conditions. For example, Actinocyclus spp.…”

“…, and Synedra spp. predominated in diatom communities in Lake Kasumigaura, Japan [41]. Moreover, Chaetocero s, followed by Fragilariopsis , Thalassiosira , and Corethron were reported to be the most abundant genera in the global oceans [13].…”

Regime shifts observed in Lake Kasumigaura, a large shallow lake in Japan: Analysis of a 40‐year limnological record

“…At the same time, high suspended solids (SS) concentrations and low chlorophyll a/SS ratios, were observed in R-III (Table 2). The increased T-Si in lake water was supported by laboratory experiments on Si release from suspended and bottom sediments (Arai et al 2012), and diatom dominance was predicted using a simple diatom growth model (Arai & Fukushima 2014). The high turbidity likely attributable to sediment resuspension (Fukushima et al 2005;Seki et al 2006;Terrel et al 2012).…”

“…The increased T‐Si in lake water was supported by laboratory experiments on Si release from suspended and bottom sediments (Arai et al . ), and diatom dominance was predicted using a simple diatom growth model (Arai & Fukushima ). The high turbidity likely attributable to sediment resuspension (Fukushima et al .…”

Decadal change in tripton concentration in a shallow lake

“…Changes in sediment resuspension rate [13], formation of calcite [14] and so on were suspected reasons for high turbidity [15]. Furthermore, this high turbidity probably affected silicon and phosphorus concentrations in lake water [16,17], and phytoplankton species composition [18,19], thus bringing about a regime shift in the ecosystem [20]. However, the changes in tripton during the last several decades have not been quantitatively assessed, and the reason(s) for variation in sediment resuspension have not been clarified.…”