Zhang Yunlin

Effect of sediment resuspension on underwater light field in shallow lakes in the middle and lower reaches of the Yangtze River: A case study in Longgan Lake and Taihu Lake

Based on three continuous in situ underwater light field measurement under different wind waves conditions in Longgan Lake, Meiliang Bay of Taihu Lake in July 2003 and littoral zone near TLLER in July 2004, respectively, the effects of sediment resuspension caused by wind waves on PAR diffuse attenuation, absorption coefficients and euphotic depths are analyzed. In Longgan Lake, PAR diffuse attenuation coefficients during small, middle and large wind waves were 1.74, 2.02 and 2.45 m−1, respectively, and the corresponding PAR spectral diffuse attenuations ranged from 0.98 to 2.97, 1.34 to 3.95 and 1.80 to 5.40 m−1, respectively. In Meiliang Bay, PAR diffuse attenuation coefficients were 2.63, 3.72, 4.37 m−1 during small, middle and large wind waves. PAR diffuse attenuation coefficients increased by 41% and 66% from small to middle, large wind waves, respectively. Absorption coefficients integrated over the range of PAR of CDOM, phytoplankton were 0.26, 0.28 m−1; 0.76, 0.49 m−1, respectively during middle and large wind waves. Absorption coefficients integrated over the range of PAR of non-algal particulate matter and total suspended particulate matter increased from 0.94 to 1.73 m−1, and from 1.70 to 2.22 m−1, respectively during middle and large wind waves. Relative contributions of absorption coefficients of non-algal particulate matter to total absorption coefficient integrated over the range of PAR were 44.14%, 65.05%, respectively, during middle and large wind waves. PAR euphotic depths decreased by 0.40, 0.19, 0.20 m from middle to large wind waves in Longganhu Lake, Meliang Bay and littoral zone near TLLER. Significant correlations were found between transparency, PAR diffuse attenuation coefficients, euphotic depths and total suspended particulate matter, wind velocity, wave height. Most significant correlations were found between transparency, PAR diffuse attenuation coefficients, euphotic depths and inorganic suspended particulate matter but low correlations for chlorophyll a, dissolved organic carbon. Increase of total suspended particulate matter, especially inorganic suspended particulate matter caused by wind waves was the dominant factor affecting underwater light field in shallow lakes in the middle and lower reaches of the Yangtze River based on observations at three stations.

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

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.

Wind-wave affected phosphate loading variations and their relationship to redox condition in Lake Taihu

Variation of wind speed and the physico-chemical parameters, such as dissolved phosphate, ferrous and manganese in lake water were observed on site. Together with the chemistry analysis and simulated experiment in lab, the change of phosphate concentration in lake water was analyzed. The variation of ferrous/phosphate ratio explained that along with the enhancement of wind-wave effect and the oxidation ability of lake water, the effects of co-precipitation and removal of dissolved phosphate and iron in the lake water were reinforced. The ferrous/phosphate ratio in pore water was less than 2.0, demonstrating that the dissolved phosphate can be released into the overlying water. But, in the lake water, the stability of phosphate was controlled by the water dynamics. The phosphate release experiment showed that molecular release was only part of the whole and the direct discharge of phosphate in the pore water was also a part. The mineralization and biological process of suspended particulates in the water may be another important reason for the whole phosphate loadings.

Characterization of absorption and three-dimensional excitation-emission matrix spectra of chromophoric dissolved organic matter at the river inflow and the open area in Lake Taihu

Using absorption and three-dimensional excitation-emission matrix spectra (3DEEMs), concentration and source of chromophoric dissolved organic matter (CDOM) were studied at the river inlet and open water area of the Lake Taihu in summer of 2007. Significantly spatial difference was recorded for CDOM absorption coefficient at the areas (ANOVA, P0.001), with the highest value in the river inflows of Dapu and Caoqiao and with the lowest value in East Lake Taihu and Xukou Bay. CDOM absorption coefficients are significantly correlated with dissolved organic carbon (DOC) and with chemical oxygen demand (COD) concentrations. Four EEMs peaks were identified in every samples, including a humic acid fluorescence peak (C) in visible range, a humic acid fluorescence peak in UV range (A) and two protein-like fluorescence peaks (B and D). Strong humic acid fluorescence was identified in the samples from the river inflows, with a significant spatial difference from humic acid fluorescence (Peaks A and C) at the river inlet and the open lake area (ANOVA, P0.05). However, there was no significant decrease for protein-like fluorescence (Peaks B and D) from the river inlet to the open area due to the dilution of lake water, showing that the dilution effect is increasing from internal source of phytoplankton degradation to protein-like fluorescence. The ratio of peak B over peak C (r(B/C)) was lower than 1 with the average value of 0.62±0.14, but was larger than 1 at sample 12 with the average value of 1.12±0.13. The r(B/C) can be preliminary used to distinguish the composition and source of CDOM. Significantly positive correlations were found between CDOM absorption coefficient and the fluorescence intensities of peaks A, C, D, but no significant correlation found with peak B.

Spectral absorption properties of chromophoric dissolved organic matter and particulate matter in Yunnan Plateau lakes

The Yunnan Plateau lakes with different lake types, located in Yunnan Province in southwestern China, are one of the five densest lake areas in China. The lakes, which are generally distributed at elevations from 1200m to 4000m above sea level, receive high intensity UV-B radiation. In this study, the spectral absorption properties of chromophoric dissolved organic matter(CDOM) and particulate matter are studied based on a wide investigation including 34 lakes in the Yunnan Plateau. The study will be helpful in the understanding of the ultraviolet radiation attenuation and the effects of increased UV-B radiation on lake ecosystems. A wide range of variability in CDOM absorption was found among the Yunnan Plateau lakes. CDOM absorption coefficient generally corresponded to the nutrient level with a significantly positive linear correlation between aCDOM(320) and total nitrogen concentration. Exponential model with constant parameters of background items could give the most approximate estimation of CDOM absorption spectra. A marked phytoplankton absorption peak around 675nm was only observed in Qiluhu, Tinghu and Xinyunhu with very high chlorophyll a concentration. High contribution of CDOM to the total absorption was found during the wavelength range lower than 600 nm especially in the ultraviolet range lower than 400nm. The contribution of CDOM to the total absorption was significantly higher in UVR range (350-400nm) than in PAR range (400-700nm) (ANOVA, P0.001). For the clear lake water with secchi disc: SD≥1.0, the contribution of CDOM absorption to the diffuse attenuation of ultraviolet radiation would increase, and CDOM absorption, with a large probability, would determine the attenuation depth of ultraviolet radiation.

Effect on the growth of Microcystis aeruginosa by the simulated continuous UV-B radiation

An experiment that Microcystis aeruginosa was exposed to short-term(0-24h) simulated UV-B radiation was carried out to determine the effect of increased UV-B radiation on the phytoplankton growth in lakes,especially lakes in the mountain and plateau.By measuring the biomass,physiological and ultrastructural indices,the response of M.aeruginosa to UV-B radiation was analyzed.When the UV-B radiation exposure time reached to 1h,the M.aeruginosa began to die,but the protein concentration increased and chlorophyll-a concentration remained stable.When the UV-B radiation exposure time was less than 4h,the activity of superoxide dismutase(SOD) enzyme remained high,the cell membrane was in good condition,and the number of thylokoids and cyanophycin granules remained stable.When the UV-B radiation exposure time was more than 4h,chlorophyll-a concentration and the activity of SOD enzyme of M.aeruginosa started to rapidly drop.The UV-B continuous radiation exposure time reaching to 4h was the maximum resistance of M.aeruginosa.An experiment that Microcystis aeruginosa was exposed to short-term(0-24h) simulated UV-B radiation was carried out to determine the effect of increased UV-B radiation on the phytoplankton growth in lakes,especially lakes in the mountain and plateau.By measuring the biomass,physiological and ultrastructural indices,the response of M.aeruginosa to UV-B radiation was analyzed.When the UV-B radiation exposure time reached to 1h,the M.aeruginosa began to die,but the protein concentration increased and chlorophyll-a concentration remained stable.When the UV-B radiation exposure time was less than 4h,the activity of superoxide dismutase(SOD) enzyme remained high,the cell membrane was in good condition,and the number of thylokoids and cyanophycin granules remained stable.When the UV-B radiation exposure time was more than 4h,chlorophyll-a concentration and the activity of SOD enzyme of M.aeruginosa started to rapidly drop.The UV-B continuous radiation exposure time reaching to 4h was the maximum resistance of M.aeruginosa.

Response of water quality to the catchment development and protection in Tianmuhu Reservoir,China

Based on the 9-year monthly monitoring data,the response of water quality to the economic development activities and the protection countermeasures in catchment and water body of Tianmuhu Reservoir,a meso-eutrophic reservoir with an area of 12 km2located in southeastern of China,was studied.The result showed that the high-density big-head carp(Hypophthalmichthys nobilis) cultivation benefited the algal bloom in the growth season of phytoplankton.Fishery adjustment,with decrease the bighead carp biomass and increase the silver carp(Hypophthalmichthys molitrix) to big-head carp ratio,significantly decreased the peak value of summer phytoplankton biomass.While when the biomass decreased to relative low value,such as 15 mg/L,the control ability of fishery to phytoplankton became weak.The influence of nutrient condition and climate factor became more important to the growth of phytoplankton.Agricultural and tourism development dramatically enhanced the nutrients runoff to the reservoir,especially the tea-farming in the steep slopes strongly increase the spring nitrogen concentration in the reservoir.Low rainfall could significantly decrease the nitrogen concentration in the water on the seasonal scale.This study suggests fishery adjustment,strictly controlling agriculture and tourism development,decreasing the fertilizer application,and expanding the wetland buffer area in the catchment,are the fundamental countermeasures for the water protection in the reservoirs located at southern China like Tianmuhu Reservoir.

Calculation and retrieval of euphotic depth of Lake Taihu by remote sensing

The euphotic zone is defined as the layer where net phytoplankton production is positive. Therefore, determination of the euphotic depth is useful for estimating primary production. The TM data on 2007-01-07 and 2006-08-01, accompanied by real-time water quality parameters including concentrations of tripton and chlorophyll-a (Chl.a) in Lake Taihu, were used to develop quantitative retrieval models of tripton and Chl.a. Euphotic depth was calculated using the model developed in Lake Taihu based on the concentrations of tripton and Chl.a. The euphotic depth ranged from 0.27 to 2.28m (mean 0.56±0.22m) in winter depth from 0.21 to 2.03m (mean 0.98±0.24m) in the summer. In the winter, the euphotic depths showed spatial distributions which were ordered as : the south of Lake Taihu the west coast of Lake Taihu the lake center Xukou Bay Gonghu Bay Meiliang Bay East Lake Taihu Zhushan Bay. In summer, the order changed as follows: the west coast of Lake Taihu Meiliang Bay East Lake Taihu the lake center Gonghu Bay Zhushan Bay the south of Lake Taihu. Seasonally, the euphotic depth was significantly shallower in summer than in winter; however, seasonal variation differed among areas of the lake. Euphotic depths in Meiliang Bay, Gonghu Bay, the west coast of Lake Taihu, the lake center, Xukou Bay and the south of Lake Taihu were higher in the summer than in the winter, but no marked seasonal variations were found in Zhushan Bay and East Lake Taihu.

Spatial pattern of euphotic depth and estimation of phytoplankton primary production in Lake Taihu in autumn 2004

Based on the underwater photosynthetically active radiation (PAR) profile measurement and the concentrations of the optically active substances, the spatial patter and affecting factors of euphotic depth in Lake Taihu are discussed. Phytoplankton primary production (PPeu) of all the lakes in autumn 2004 is estimated using the vertically generalized production model (VGPM) based on measured surface chlorophyll-a (Chl.a) concentration, euphotic depth, water temperature, PAR at the water surface, photoperiod and water depth. Euphotic depth ranges from 0.37 to 5.27m with a mean value of 1.52 ± 1.06 m. The higher euphotic depth appears in the macrophyte-dominated lake regions such as East Lake Taihu, Xukou Bay and water area between Xishan and Dongshan Islands. In contrast, the lower euphotic depth is found in algal-dominated lake region such as Meiliang Bay and the southwestern open water. The regression analyses show that euphotic depth is mainly controlled by nonpigment particle matter, next to phytoplankton and chromophoric dissolved organic matter (CDOM). Nonpigment particle matter can explain 96.7% variation of euphotic depth. The ranges of Chl.a concentration and estimated PPeu are 1.21-53.59μg/L, 77.4-2484.9mg/(m·d), respectively. The estimated daily mean PPeu distribution coincides closely with that of Chl.a concentration. Higher Chl.a and PPeu values are recorded in Meiliang Bay and lower values are found in Xukou Bay or southwestern open water. There is a good correlation between VGPM PPeu * 中国科学院知识创新工程方向性项目(KZCX2-YW-419)、国家自然科学基金项目(40730529, 40671138)和江苏省自然科学 基金项目(BK2006580)联合资助. 2007-05-28 收稿; 2007-09-17 收修改稿. 张运林, 男, 1976 年生, 博士, 副研究员; E-mail: ylzhang@niglas.ac.cn. 张运林等: 太湖秋季真光层深度空间分布及浮游植物初级生产力的估算 381 and primary production from the empirical model (PPem) (r = 0.79, p < 0.0001). Daily mean PPeu and PPem of all the lakes are 694.5 ± 492.0, 719.8 ± 315.4mg/(m·d), respectively. Although the ranges of the two methods differ, the mean values are very close. PPeu more accurately captures spatial variation by considering the effect of euphotic depth, water temperature, surface PAR and photoperiod on PP.

Optical Measurements of Primary Production in Meiliang Bay, Taihu Lake

According to the study of the pimary production and light in Meiliang Bay Taihu Lake in May, October, December of 1998, August of 1999 and July, September of 2001, the anthors found that the greatest primary production was at the depth of 0. 2cm, the relationship between primary production(P) and the concentration of Chla was; P = 0. 012-0. 028 [Chla] (n= 30). On the basis of the relationship between light spectrum and concentration of Chla, as well as the relationship between primary production and light intensity, the relationship between primary production and light spectrum was found and validated. Further analysis revealed that the Kd of light spectrum at the blue end and at the red end was greater than that of green, the lowest was at 550 nm.