Liu Mingliang

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.

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.

Chlorophyll-a concentration estimation with field spectra of summer water-body in Lake Qiandao

Based on the in situ data collected in August 2010,hyperspectral data models estimating summer chlorophyll-a concentration in Lake Qiandao are presented.A large quantity of hyperspectral reflectance data and water quality data of the typical area of the lake were obtained.Hyperspectral data were measured using ASD FieldSpec3,and were calculated for water-leaving radiance and reflectance of water.Different methods including band ratio model,the first derivative model,three-band-model and BP neural network model were used to estimate chlorophyll-a concentration.Results showed that single band reflectance model gave the worst estimation on chlorophyll-a concentration.Band ratio model with the ratio of reflectance 596 nm/489 nm and the first derivative model of reflectance near 545 nm gave better results with high determination coefficients of 0.782 and 0.590,respectively.By comparison,the three-band-model had higher estimation precision(coefficient of 0.838) than the band ratio model and the first derivative model.BP neural network model performed best with a high determination coefficient of 0.942.The root mean square error between measured and estimated chlorophyll-a concentrations using the four models was 0.89,1.98,0.71 and 0.63 μg/L,respectively.Therefore,three-band-model and BP neural network model was recommended to estimate chlorophyll-a concentration with remote sensing data for large area of Lake Qiandao in the summer.

Thermodynamics and stratification in Xin'anjiang Reservoir(Lake Qiandao)

利用2012年1—12月在新安江水库（千岛湖）6个点位的每月一次的水温及其他环境因子的周年观测资料，分析了水库水温逐月变化、季节变化、垂直分布及温跃层的形成与变化，探讨了温跃层特征量（温跃层深度、厚度、强度）与表层水温、水体透明度的关系．新安江水库表层和中层水温与气温存在显著的线性相关，又以表层水温线性关系最好，而下层水温与气温没有显著相关性，说明下层水温受气温的影响很小，全年处于相对恒温状态．水库表层和中层水温逐月变化明显，呈现夏季最高、春秋季次之、冬季最低的变化趋势，其中中层水温最高值出现的季节较表层水温明显后延，下层水温没有明显的逐月变化和季节变化．水温垂直分布显示，4个季节均存在不同程度的温跃层和温度分层现象，其中水深最深的大坝前水温分层最明显．小金山、三潭岛和大坝前3个典型点位从春季的4月份到冬季的2月份温跃层深度由1．61±0．47m逐渐增加至39．37±5．35m，而温跃层厚度和强度则在夏季最高、冬季最低，温跃层随着季节的变化呈现增强-稳定-减弱-消失的周期变化．温跃层深度与水体透明度存在显著正相关，与表层水温存在显著负相关，并基于透明度和表层水温建立温跃层深度的多元线性回归模型．

Characteristics of spectral absorption,fluorescence and remote sensing algorithms of chromophoric dissolved organic matter in winter,Lake Taihu

Based on two investigations with 100 sampling sites in Lake Taihu in January,2006 and 2007,the characteristics of spectral absorption and fluorescence,spatial distribution,and the retrieval model of chromophoric dissolved organic matter(CDOM) were studied.The ranges and mean values of CDOM absorption coefficient at 355nm a(355),fluorescence normalized Fn(355) and dissolved organic carbon(DOC) concentration were 1.83-7.34,3.37±1.01 m-1;9.79-29.18,13.4±3.37 N.FL.U;and 4.61-10.45,6.37±1.24 mg/L,respectively.Significant positive correlations between a(355) and DOC,a(355) and Fn(355) were found.Spatially,two surveys have shown that the higher values of a(355),Fn(355),DOC concentration were found in Meiliang Bay and lower values were found in East Lake Taihu and Gonghu Bay.Overall,a(355),Fn(355),and DOC concentration were significantly higher in two transects in northern lake regions than those in other transects in southern lake regions.The results showed that BP neural network model was superior to a single band model and the first order differential model for CDOM absorption estimation.The relative root mean square error(RRMSE) and mean relative error(MRE) of BP neural network model were 14.9% and 11.7%,respectively,based on an independent validation dataset including 25 samples.Thus,BP neural network model could be better used to estimate CDOM absorption in Lake Taihu.