[Spatial Variation Characteristics and Remote Sensing Retrieval of Total Suspended Matter in Surface Water of the Yangtze River].

Total suspended matter(TSM) is an important parameter that describes optical characteristics and water pollution level. Remote sensing was used to obtain suspended matter concentrations in the planar water body, which can monitor and analyze the reliability of turbidity and pollution levels. In this study, a semi-empirical model of suspended matter along the Yangtze River mainstream(from Chongqing to Shanghai) was constructed based on the field measured hyperspectral data and suspended matter concentration and its components, with reference to MODIS(1-4 band), Landsat 8(1-5 band), Sentinel 2(2-6 band), HJ-B1(1-4 band), and other commonly used band ranges. The results show that:① Turbidity and TSM of the Yangtze River mainstream increased from Chongqing to Shanghai during the dry season, whereas the proportion of OSM to TSM(OSM/TSM) decreased from Chongqing to Shanghai. ② The spectral properties of chlorophyll-a were not obvious; however, it showed a bimodal spectral characteristic of suspended matter concentration. Due to the low concentration of suspended matter in the water(<114.68 mg·L-1), the first peak value was significantly higher than the second peak. However, peak reflection and position had an obvious "red shift" phenomenon in the direction of the wavelength. ③ The reflectance values of the Yangtze River mainstream were most sensitive to the concentration of suspended matter in the 600-710 nm and 475-550 nm bands. Most of these fall in the green and red band of MODI, Landsat 8, Sentinel 2, and HJ-1B satellites. Therefore, the commonly used satellites have a band setting to detect the inversion of turbidity degree index of the Yangtze River main stream water body. The Sentinel 2 satellite band is most suitable for the inversion of suspended matter concentration in the Yangtze River mainstream. The mean absolute percentage error(MAPE) and root mean square error(RMSE) of the optimal exponential model were 10.23 mg·L-1 and 23%, respectively.

Correction: Analysis of the Antennal Transcriptome and Insights into Olfactory Genes in Hyphantria cunea (Drury).

[This corrects the article DOI: 10.1371/journal.pone.0164729.].

[Response of Chromophoric Dissolved Organic Matter Composition to Different Hydrological Scenarios in Large Eutrophic Lake Taihu].

Chromophoric dissolved organic matter (CDOM) is a fraction of dissolved organic matter that can strongly absorb light in the ultraviolet and blue regions and plays an important role in the biogeochemical cycling of carbon, nitrogen, and phosphorus. Unraveling the sources, optical composition, and corresponding spatial variabilities of CDOM can improve our understanding of carbon, nitrogen, and phosphorus cycling in lakes and lake water quality management. CDOM spectral absorption and fluorescent excitation-emission matrices were measured to investigate the compositional dynamics of CDOM under different hydrological scenarios. Our results showed that the mean value of dissolved organic carbon (DOC) concentration of (8.11±1.26) mg·L-1 in the rainy season was significantly higher than that in the dry season (3.53±1.19) mg·L-1 (t-test, P<0.01), whereas the mean spectral slope S275-295 of (20.89±1.90) µm-1 in the dry season was significantly greater than that in the rainy season (19.09±1.81) µm-1 (t-test, P<0.001). Three fluorescent components were identified using parallel factor analysis, and we further found that the dynamics of the three CDOM components were strongly influenced by hydrological conditions. Fluorescence intensity (Fmax) of the terrestrial humic-rich component C2 increased with increasing water levels and rainfall. Significant negative relationships were found between all three fluorescent components and dissolved oxygen (P<0.01), suggesting that all three components served as important substrates for microbial processing. Significant positive relationships were found between the terrestrial humic-rich C2 and tryptophan-like C1 and chlorophyll-a and chemical oxygen demand, indicating that anthropogenic inputs and algal degradation contributed significantly to the CDOM pool in Lake Taihu. We further found a significant positive relationship between DOC concentration and Fmax of terrestrial humic-rich C2 (r2=0.58, P<0.001), suggesting that DOC in Lake Taihu was primarily derived from allochthonous input.

[Distribution and Burial Characteristics of Nitrogen Forms in Sediment of Dianchi Lake During Last Century].

In order to analyze the composition, distribution and burial characteristics of nitrogen in sediments of Dianchi Lake in the last hundred years, 6 sediment cores were sampled in July 2014 to determine the contents of different nitrogen species and sedimentary age sequence. The integrated results demonstrated a high content of total nitrogen in sediments ranging from 1263.68-7155.17 mg·kg-1. The contents of nitrate nitrogen and ammonium nitrogen were low, which were 10.00-144.00 mg·kg-1and 9.20-146.50 mg·kg-1, respectively. Organic nitrogen was the main component in the sediments, ranging from 255.80 to 5644.25 mg·kg-1, composing a large average percentage of 91.26%. In addition, the nitrogen pollution of sediment in Dianchi Lake has reached a high level and is becoming serious since 1970s, which surged in the late 1990s. The spatial difference of total nitrogen was obvious, with comparably the most in the south, less in the north and least in the center. The average deposition rate was changing from 0.092 g·(cm2·a)-1 to 0.187 g·(cm2·a)-1 in the last 100 years and increased first, then declined, finally showed a slight upward trend over time. The burial rate of total nitrogen in sediment increased over time and almost grew up straightly after 1990,which decreased from the south to the north of Dianchi Lake in space. It was estimated that the reserves of total nitrogen, organic nitrogen, nitrate nitrogen, ammonium nitrogen in the sediment were 92139.15 t, 86745.62 t, 2464.16 t, 2929.37 t, respectively, from 1900 to 2014.

[Sedimentary Characteristics and Sources of Organic Matter in Sediments of Dianchi Lake].

Sediment columns in the southeast and east of Dianchi Lake were taken as the object of the study to determine ages by 210 Pb dating method.The contents and sediment fluxes of total organic carbon (TOC) and n-alkanes of the sediments were investigated,and organic sources were tracked according to the relevant indexes of n-alkanes.The results indicated that TOC contents and sediment fluxes of two sampling sediments both presented an increasing trend on the whole;Sediment fluxes of n-alkanes varied as three stages:increasing period,decreasing period and re-increasing period.When the sediment fluxes of n-alkanes and TOC both went up,it showed that they had the same sources:sediments in the lake and carried by the rivers;From 1980s to the end of 20th century,sediment fluxes of n-alkanes were going down while those of TOC were going up.This result means there was a big difference in the sources of n-alkanes and TOC.The bacteria and algae in the lake made a great contribution to n-alkanes while TOC was mainly influenced by sediments in the lake and carried by the rivers.n-alkanes of the two sampling sites both ranged from C12 to C35.Based on the basic features and relevant indexes of n-alkanes,we proposed that emergent plants made big contributions to the sources of organic matter in the sediments of Dianchi Lake,simultaneously,bacteria and algae had significant contributions to the sources of organic matter in shallow depth of Dianchi Lake.

Analysis of the Antennal Transcriptome and Insights into Olfactory Genes in Hyphantria cunea (Drury).

Hyphantria cunea (Drury) (Lepidoptera: Arctiidae) is an invasive insect pest which, in China, causes unprecedented damage and economic losses due to its extreme fecundity and wide host range, including forest and shade trees, and even crops. Compared to the better known lepidopteran species which use Type-I pheromones, little is known at the molecular level about the olfactory mechanisms of host location and mate choice in H. cunea, a species using Type-II lepidopteran pheromones. In the present study, the H. cunea antennal transcriptome was constructed by Illumina Hiseq 2500TM sequencing, with the aim of discovering olfaction-related genes. We obtained 64,020,776 clean reads, and 59,243 unigenes from the analysis of the transcriptome, and the putative gene functions were annotated using gene ontology (GO) annotation. We further identified 124 putative chemosensory unigenes based on homology searches and phylogenetic analysis, including 30 odorant binding proteins (OBPs), 17 chemosensory proteins (CSPs), 52 odorant receptors (ORs), 14 ionotropic receptors (IRs), nine gustatory receptors (GRs) and two sensory neuron membrane proteins (SNMPs). We also found many conserved motif patterns of OBPs and CSPs using a MEME system. Moreover, we systematically analyzed expression patterns of OBPs and CSPs based on reverse transcription PCR and quantitative real time PCR (RT-qPCR) with RNA extracted from different tissues and life stages of both sexes in H. cunea. The antennae-biased expression may provide a deeper further understanding of olfactory processing in H. cunea. The first ever identification of olfactory genes in H. cunea may provide new leads for control of this major pest.

[Distribution Characteristics of n-alkanes in Sediment Core and Implication of Environment in Different Lakes of Dianchi].

In order to study the composition and environment significance of the organic matter in Lake Dianchi, samples from two sediment cores from the northern and southern parts of the lake were collected in July, 2014. Meanwhile, the vertical distributions of total organiccarbon (TOC), total nitrogen (TN), n-alkanes fractions were investigated. The results showed that ① the concentrations of TOC and TN had been clearly increasing since the 1970s, which implied that the primary productivity of Lake Dianchi was continuously enhanced; ② The values of the parameter n-C27/n-C31, Paqand CPI indicated the alternation between herbs and woody plants from the bottom up in Lake Dianchi sediments. Besides, the high carbon number of organic matter in sediments mainly originated from endogenous submerged floating and large plants; ③ The index of C/N and distribution characteristics of n-alkanes suggested differences in the various sources of organic matter in different lakes. In detail, organic matter came from terrigenous organic matter of anthropogenic sources and endogenous bacteria in the sediments of northern Dianchi, while organic matter was derived from endogenous aquatic and terrestrial higher plants mixed source in the sediments of southern Dianchi. Finally, it is worthwhile to emphasize further research on organic matter in different lakes of Lake Dianchi.

[Hyperspectral remote sensing of chlorophyll a concentrations in the Lake Taihu, based on water optical classification].

Four field investigations into the Lake Taihu were carried out for collecting in situ observed data in Nov., 2006, Nov., 2008, May and Aug. , 2010. On the basis of water optical classification, different retrieval algorithms were developed, specifically for different types of waters. The obtained optimal models were (1) the four-band model for Type 1 water; (2) the first-order differential model for Type 2 and Type 3 waters. Meanwhile, an optimal retrieval model was also established using the same aggregated calibration data. Some comparisons were done between the developed models for the classified and non-classified waters. The compared results showed that models for the classified waters had better performances than that for the non-classified water, in both retrieval accuracy and model stability. The findings of this study are significant for promoting the development of water color remote sensing for optically complex turbid inland waters.

[Elementary quantitative study on factors of phytoplankton bloom].

This study investigated the effect quantitatively on phytoplankton population by various factors such as sinking velocity, diffusivity, growth, mortality and water depth, through both numerically and theoretical methods, then proposed an initial judgment criterion for estimating phytoplankton population development. To the conventional simplification about even growth rate and vertical turbulent diffusivity, which is not consistent with the fact, this study investigated the influence by the asymmetric growth rate, as a result of light attenuation and nutrient limit, and uneven vertical turbulent diffusivity. It was shown that the 'shade effect' by light attenuation and nutrient flux limit both led. phytoplankton population from blooming or collapsing to quasi-steady condition. The uneven vertical turbulent diffusivity influenced the phytoplankton population by l/H which is upper euphotic layer depth by water depth. The influence is not apparent only if the water depth is large enough while l/H is small. Hence even vertical turbulent diffusivity can be utilized approximately in very shallow lakes.

[Study on influencing factors and universality of chlorophyll-a retrieval model in inland water body].

The semi-analytical three-and four-band model and bio-optical analytical model of chlorophyll-a were checked by the 'mh, constituents and optical properties with high spatio-temporal variation. The influencing factors and universality of the retrieval model were studied by the modeling checking results. The study results indicate that the unjversality of bio-optical analytical model is much higher than the three-and four-band model, and the accuracy of the retrieval model is acceptable, but the accuracy of the retrieval model was highly affected by the specific absorption coefficient of chlorophyll-a. The accuracy of the three-and four-band model higher than the bio-optical analytical model. However, the universality of the three-and four-band model is not very high, because of the optimal wavelength position of the retrieval factors and the greater variability of the retrieval model parameters. The spectral shape of particle backscattering coefficient and chlorophyll-a specific absorption coefficient are the dominant influencing factors of the three and four-band retrieval model.

Molecular biomarkers for sources of organic matter in lacustrine sediments in a subtropical lake in China.

N-alkanes distributions and stable isotopic compositions (δ(13)C and δ(15)N) in the lacustrine sediments of Shijiu lake were measured to assess whether biological source information was recorded in the molecular biomarker. Results showed regular unimodal n-alkanes distribution in range of C16-C33 with strong predominance of odd-numbered n-alkanes, maximizing at C29. The δ(15)N for SON were uniformly low, ranging from -6.7‰ to 3.8‰ and C/N ratios ranged from 6.6 to 10.0, suggesting that most of organic matter was influenced by terrestrial characteristics of the watershed. The δ(13)C for C27 to C31n-alkanes and for SOC varied from -32.9‰ to -26.6‰ and -23.4‰ to -21.6‰, respectively, falling within the range of corresponding n-alkanes in leaves mainly from C3 land plants. The values of C/N, CPI, OEP, ACL and C27/C31 exhibit similar temporal changes with the primary production, showing enhanced eutrophication resulted from increased anthropogenic activities in Shijiu lake from 1852 to 2010.

[Estimation and forecast of chlorophyll a concentration in Taihu Lake based on ensemble square root filters].

Chlorophyll a concentration is one of the important parameters for the characterization of water quality, which reflects the degree of eutrophication and algae content in the water body. It is also an important factor in determining water spectral reflectance. Chlorophyll a concentration is an important water quality parameter in water quality remote sensing. Remote sensing quantitative retrieval of chlorophyll a concentration can provide new ideas and methods for the monitoring and evaluation of lake water quality. In this work, we developed a data assimilation scheme based on ensemble square root filters and three-dimensional numerical modeling for wind-driven circulation and pollutant transport to assimilate the concentration of chlorophyll a. We also conducted some assimilation experiments using buoy observation data on May 20, 2010. We estimated the concentration of chlorophyll a in Taihu Lake, and then used this result to forecast the concentration of chlorophyll a. During the assimilation stage, the root mean square error reduced from 1.58, 1.025, and 2.76 to 0.465, 0.276, and 1.01, respectively, and the average relative error reduced from 0.2 to 0.05, 0.046, and 0.069, respectively. During the prediction stage, the root mean square error reduced from 1.486, 1.143, and 2.38 to 0.017, 0.147, and 0.23, respectively, and the average relative error reduced from 0.2 to 0.002, 0.025, and 0.019, respectively. The final results indicate that the method of data assimilation can significantly improve the accuracy in the estimation and prediction of chlorophyll a concentration in Taihu Lake.

[Depth profile of suspended particle scattering coefficient and its impact factors in Taihu Lake].

To acquire the depth profile of suspended particle scattering coefficient and the mechanism of surface reflection, three different depths of Taihu Lake scattering coefficient and backscattering coefficient are obtained in Nov. 2008, respectively. And their characteristic variation with depth is studied. Profiling distribution of the slope of particulate size distribution (PSD) is computed by the attenuation coefficient. Profiling distribution of the concentration and composition of suspended particle is computed according the relationship between the scattering coefficient and the suspended particle concentration. Impact dominant factors on scattering coefficient of the depth of water are divided according to the range of refractive index. At the three depths (0, 50, 100 cm), the particle scattering, with the percentage 14%, 17%, 12% of the samples are dominated by algae, respectively. 35%, 30%, 34% of the samples are dominated by inorganic particulate matter and Non-algal organic particulate matter,and 51%, 53%, 51% of the samples are dominated by the above all. The results can be concluded as: scattering and backscattering coefficient of Taihu Lake water body changes with depth slightly. The concentration of total suspended particles is of more diversity in different lake area, but there is less difference at different depths except those samples near the inflow rivers. The main factors of scattering coefficient of most aquatic scattering in Taihu Lake had little difference at different depths, except several samples beside the inflow rivers.

[Characteristics of the diffuse attenuation coefficient and its impact on aquatic ecology environment].

According to the optical property data measured in Taihu Lake at October and November 2006, the characteristics of the diffuse attenuation coeffcient (Kd), the contribution of each factor effecting on Kd and the effect of Kd on the aquatic ecology environment were analyzed. The results indicate that, the diffuse attenuation coefficient Kd of Taihu Lake has two main trends in the whole visible wavelength range (400-700 nm). The first type is that, Kd decreases with the wavelengths by exponential style in the range of less than 571 nm wavelengths, and the second type is that, Kd is in the form of fluctuations in the range of larger than 571 nm wavelengths. In the range of 400-700 nm wavelength, the absorption coefficient of pigment particles is the first contributors of diffuse attenuation coefficient. Non-pigment particles absorption and scattering coefficients is the second contributor, and the rate of contribution of yellow substance is the smallest. The Kd of Taihu Lake determines the light factor of the Taihu water ecosystem. The "water window" shaped by the Kd provides the light base for different kinds of ecosystem and the appearance of Microcystic aentginosa which is the preponderant algae in the "algal blooms" phenomenon.

[Differences of inherent optical properties of inland lake water body in typical seasons].

Inherent optical property is one of the important properties of water body, which lays the foundation for the establishment of water color analytical models. By using quantity filter technology (QFT) and BB9 backscattering meter, the absorption coefficients of chromophoric dissolved organic matter (CDOM) and total suspended matters (TSM) and the backscattering coefficient of TSM in the water body at Meiliang Bay of Taihu Lake were measured in summer and winter. Based on the spectral comparison of the absorption and backscattering coefficients, their differences between the two seasons were demonstrated, and the reasons that caused these differences were also explored in the context of their relations to the changes in water quality. Consequently, water environment condition could be revealed by using the inherent optical property. The relationship between the backscattering coefficient and the TSM concentration was established, which could provide supporting coefficients to the analytical models to be developed.

[Spatio-temporal distribution of chlorophyll a concentration and its estimation in Taihu Lake].

The temporal and spatial distribution of chlorophyll a concentration in Taihu Lake was analyzed using the data measured from January to October in 2005. Otherwise, chlorophyll a retrieval model was built using the synchronous spectrum data obtained in different season to evaluate the effect of chlorophyll a concentration temporal and spatial variation on the retrieval model. Firstly, temporal distribution of chlorophyll a concentration was analyzed. Then, chlorophyll a concentration was induced by Inverse Distance Weight method. Lastly, the chlorophyll a concentration estimation models based on spring, summer, autumn and different trophic states were built. An obvious spatial-temporal distribution was found for chlorophyll a concentration in Taihu. Chlorophyll a concentration had the maximal value in summer and the minimal value in winter,and the average chlorophyll a concentration was 56.29 microg/L, 13.61 microg/L respectively. Due to the effect of autumn, the average chlorophyll a concentration in autumn was higher than that in spring, and the average chlorophyll a concentration was 26.43 microg/L, 34.78 microg/L respectively. Marked spatial difference for chlorophyll a concentration was found in summer,while in winterthe spatial variation was ambiguous. The spatial variation in autumn was greater than that in spring as influenced by summer. Spatially, the variation in north area was greater than those in the other areas and the south area had less variation during the year. Because of the different chlorophyll a concentration, different season had different retrieval model. Band-ratio had better retrieval result in spring and autumn as there were lower concentration and less variation correspondingly. While in summer, because of the high chlorophyll a concentration and great spatial variation, among the arithmetic built in summer, the differential arithmetic was the optimal model, and the difference of Chl-a concentration retrieval model of different trophic state was minor.

[Scattering characteristics of Taihu Lake and its relationship models with suspended particle concentration].

Water scattering characteristics are closely related to water quality parameters, such as suspended particles and their concentrations. Through the observing system of water inherent optical properties, which were developed by WETlabs Inc, the backscattering and scattering coefficients of Lake Taihu had been obtained in Oct. 2006 and Nov. 2006. Based on analysis of data, the backscattering coefficient spectra model had been established. In addition, the water refraction indexes were computed by backscattering ratio. According to the change scopes of refraction index, the dominant factors of in-water particles were divided into three categories: (1) phytoplankton; (2) inorganic particles; (3) both of the above. By analyzing the correlations between scattering coefficients with inorganic particle, organic particle and total particle concentration, the relationship between scattering coefficient and inorganic particle concentration was simulated well by power function for three different categories respectively.