Long-term light environment variability in Lake Biwa and Lake Kasumigaura, Japan: modeling approach

Abstract

Light environment variability was investigated in the two Japanese lakes Biwa and Kasumigaura, which offer a broad range of optical conditions in the water bodies due to their diverse morphometries and limnological characteristics. To elucidate their light environments, Secchi depths (SDs) were related to long-term monitored datasets of concentrations of optically active substances (OASs) using two approaches based on statistical and mechanistic models. A good estimate for the nonphytoplanktonic suspended solids (NPSS) concentration gained using a monthly factor d (which represents the phytoplanktonic portion in total suspended solids) from a longterm analysis was utilized to develop robust models. Using the mechanistic model, the contribution of each OAS to the SD can be understood and investigated in more detail than possible with a statistical approach, but the statistical model yields better results in terms of SD prediction. Based on the results of an analysis of the contribution of each OAS to the SD, it was clear that NPSS was the component that exerted the most influence on the light environments in the two lakes; in this respect, this study agrees with other studies that show the importance of suspended inorganic particles as the main contributor to the SD in inland waters. Using ANOVA, we analyzed how specific inherent optical properties may have changed spatially and temporally, and the results indicated that the temporal (monthly) effect was primarily responsible for the loss of accuracy in the models. In addition, the ANOVA analysis suggested that grouping the data improved the predictive performances of the statistical models. Finally, we concluded that combining the two models yields the most reliable results in terms of SD prediction and determining the contribution of each OAS to the SD at present.

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

“…; Terrel et al . ). Although many hypotheses relating to biotic and/or abiotic factors were proposed for the increased sediment resuspension, no definitive conclusion currently exists (Fukushima et al .…”

“…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). Although many hypotheses relating to biotic and/or abiotic factors were proposed for the increased sediment resuspension, no definitive conclusion currently exists (Fukushima et al 2005).…”

Development of photosynthetic carbon fixation model using multi-excitation wavelength fast repetition rate fluorometry in Lake Biwa

“…We used previously measured, average values of limnetic sites from each basin, 1.03 and 2.28, for a CDOM (320) for the North Basin and the South Basin, and 0.017 for S [ 85 , 92 ] ( S4B Appendix ). a NAP was estimated as a NAP = a NAP (440) exp(-S(λ-440)) [ 93 ]. We used 0.264 for a NAP (440) and 0.004 for S as typical values for the area ( S4C Appendix ).…”

Development of photosynthetic carbon fixation model using multi-excitation wavelength fast repetition rate fluorometry in Lake Biwa

“…We used previously measured, average values of limnetic sites from each basin, 1.03 and 2.28, for a CDOM ( 320) for the North Basin and the South Basin, and 0.017 for S [77,81] (S4 Appendix B). a NAP was estimated as a NAP = a NAP (440) EXP(-S (λ-440)) [82]. We used 0.264 for a NAP (440) and 0.004 for S as typical values for the area (S4 Appendix C).…”