Temporal-spatial variations of euphotic depth of typical lake regions in Lake Taihu and its ecological environmental significance

Abstract

By using the data of underwater irradiance measured in the different lake regions of Lake Taihu during 1998-2004 and total suspended solids (TSS), wind speeds of the total 13 stations in typical lake regions during 1993-2003, this paper analyzes the factors of influencing on PAR (photosynthetically available radiation) attenuation, euphotic depth, and presents the temporal and spatial variations of euphotic depth of typical lake regions in Lake Taihu, and the spectral distributions of euphotic depth at station 2. The results show that the concentration of TSS is the most important factor impacting PAR attenuation, followed by chlorophyll a; chromophoric dissolved organic matter (CDOM) has little impact on the PAR euphotic depth. During 1993-2003, the mean yearly PAR euphotic depths of the typical lake regions ranged from 1.04 to 1.95 m with a mean value of 1.35±0.23 m. The PAR euphotic depth fell into 3 spatial zone types: Type I, the lowest, including the lake center and the inflows of rivers; Type II, intermediate, including Meiliang Bay, Wulihu Lake and Gonghu Bay; Type III, the greatest, including the East Lake Taihu; corresponding mean depths were approximately 1.1, 1.4, 2.0 m, respectively. The seasonal variations of euphotic depths were not quite the same in different lake regions. In the lake center, the mean values of PAR euphotic depth in summer and autumn were significantly greater than those in winter and spring; in the Meiliang Bay, winter means were significantly greater than in the other three seasons; in the East Lake Taihu, winter means were significantly less than in the other three seasons. However, no distinct seasonal change was recorded in the Wulihu Lake, Gonghu Bay and the inflows of rivers. The spectral distributions of euphotic depth present a minimal value at the blue light wave band of 400 nm, and a peak at the green light wave band of around 580 nm. In 1998 and 1999, based on the seasonal many-day continuous measurements, the PAR euphotic depths at station 2 were recorded 2.00±0.21, 2.52±0.45, 1.58±0.24, 2.00 ±0.15 m in spring, summer, autumn and winter, respectively. The peak value of 440 nm absorbed by phytoplankton corresponded to a euphotic depth of only 0.81-1.47 m (mean 1.07±0.29 m), which was much lower than the mean PAR euphotic depth of 1.98±0.41 m.

Spatial Distribution of Diffuse Attenuation of Photosynthetic Active Radiation and Its Main Regulating Factors in Inland Waters of Northeast China

“…The GIs of all the sample points were calculated and the results (Table 2) showed that the highest GIs were obtained by comparing between TSM and Kd(PAR). These results indicated that TSM had a higher contribution to Kd(PAR) than Chl-a and CDOM, which is consistent with previous studies in Lake Taihu in China [7,12] and UK marine waters [10]. Furthermore, in order to assess the difference of the relationships across various waters, lakes with more than 10 sampling points were also selected to calculate GIs individually.…”

“…The average of the data can eliminate the error to some extent and result in a stable performance. The slope of the linear model between K d (PAR) and TSM in the current study was slightly higher than results in [7] (slope = 0.0626, intercept = 1.6068) and [12] (slope = 0.0563, intercept = 1.52). Considered that our research covered a larger number of lakes than those earlier studies, such a difference was acceptable.…”

“…K d (PAR) was determined by applying the exponential regression model which utilizes Equation (1) [33], provided that the water column was homogeneous. The results were accepted only if the coefficient of determination (R 2 ) was no less than 0.95 [7] and the number of depth points was no less than 4. In Equation (1), the PAR(Z) represents the PAR value at depth Z and PAR(0 − ) represents the PAR value just beneath the surface of the water.…”

“…Therefore, a linear regression analysis was performed to establish the quantitative relationship between K d (PAR) and the concentration of the OACs. In some researches the regression analysis was also used to identify the dominant factor of K d (PAR) [2,7] so it can also be used to validate the result of GIs analysis in this paper. In order to further evaluate the applicability of the predicting model, we first used the leave-one-out cross validation (LOO-CV) method and then accessed the model's spatial transferability.…”

Spatial patterns of diatom diversity and community structure in ancient Lake Ohrid

“…and pH were measured in situ with Hanna Ò HI98129 Combo tester. Additional physical and chemical characteristics ( Zhang et al (2006). The samples for the analyses of the water chemistry were also collected with 1L Ruttner sampler.…”