[CDOM Optical Characteristics and Related Environmental Factors of High-turbidity Waters on the Loess Plateau].

Chromophoric dissolved organic matter (CDOM) optical absorption characteristics, CDOM spectral slopes (S275-295), contribution of each component to water absorption, and the effects of environmental factors on them were analyzed to determine the sources and composition of CDOM in high-turbidity waters on the Loess Plateau. Samples in rivers and lakes (saline and freshwater) in the Loess Plateau area of Shaanxi and Inner Mongolia were collected in May 2018. The results demonstrated significant differences in CDOM absorption optical characteristics between rivers and lakes. The average aCDOM(440) (CDOM concentration, 8.45 m-1) in lakes was higher than that of rivers (2.70 m-1), and the saline lakes showed a higher CDOM concentration (13.52 m-1) than the freshwater lakes (3.38 m-1). Moreover, the light utilization efficiency of freshwater lakes is higher than that of saline lakes and turbid rivers. Great differences in pH and dissolved organic carbon (DOC) were observed between different types of water (P<0.01). The differences in electrical conductivity (EC), turbidity (Tur), and total suspended matter concentration (TSM) were significant with no statistical significances (P>0.1). The chlorophyll a concentration (Chla) in saline lakes was close to the Chla concentration in freshwater lakes if extreme values were excluded. In addition, the CDOM molecular weights of lake water were lower than those in the rivers, while CDOM molecular weights in saline lakes were lower than those in freshwater lakes based on the S275-295. Analyses of specific ultraviolet absorbance (SUVA254) were also conducted to determine the sources of CDOM in different water types, and the results showed that the more terrigenous humus were brought into the rivers and saline lakes compared with the freshwater lakes. Redundancy analysis (RDA) indicated that river and lake water quality parameters of the cumulative variance explained rates were 35.2% for river samples and 61.4% for lake samples, and 100% for samples in the saline and freshwater lakes individually. The results of RDA showed that dissolved oxygen (DO), water temperature, and EC exerted significant effects on CDOM optical properties of the river (P<0.01), while DOC, TSM, and Tur had a great influence on the CDOM optical properties of lakes (P<0.01). There was a strong correlation between pH and CDOM in the saline lakes, while DOC was significantly correlated with CDOM in the freshwater lakes (P<0.05).

[Comparative Characteristics of Optical Absorption in Waters from Yiluo River and Huntai River in Spring].

The absorption characteristics, composition, spatial variability, and relative contribution of optically active constituents over the range of photosynthetically active radiation (PAR, 400-700 nm) were analyzed from samples collected in the Yiluo and Huntai Rivers in May 2017 and 2013, respectively. Results demonstrated that the absorption curves of total suspended particulates[ap(λ)] were similar to those of non-algae particles[ad(λ)]. Significant correlations between ap(λ) and ad(λ) were obtained, especially at 440 nm, with r=0.968 in the Yiluo River and r=0.899 in the Huntai River. Meanwhile, positive correlations between ap(λ) and the absorption of phytoplankton[aph(λ)] were observed at 675 nm. ap(λ) in the two basins was dominated by ad(λ). Moreover, the composition of auxiliary pigments and chloropyhll a concentration[Chla] showed more significant spatial variations based on aph(440)/aph(675) in the Yiluo River than in the Huntai River. In addition, CDOM absorption slopes (SCDOM) indicated that CDOM composition in the Yiluo River was dominated by exogenous substances; in comparison, the Huntai River had more endogenous substances. SCDOM in the Yiluo River was lower than in the Huntai River, indicating that the CDOM composition of the Yiluo River was inclined towards high molecular weights. Furthermore, Mr[aCDOM(250)/aCDOM(365)] showed greater ranges and lower mean values in the Yiluo River than in the Huntai River, confirming that CDOM molecular weight varied greatly in the former. CDOM molecular weight in the Huntai River was also lower than in the Yiluo River, in accordance with SCDOM results.

[Seasonal changes of optical absorption properties of river and lake in East Liaohe River basin, Northeast China]. / ä¸œè¾½æ²³æµåŸŸæ²³æ¹–å ‰å­¦å¸æ”¶ç‰¹æ€§çš„å­£èŠ‚å˜åŒ–.

The absorption characteristics of optically active constituents (OACs) in water column are important optical properties and basic parameters of establishing the inverse analysis model. Comparative analyses about seasonal variability of the optical absorption characteristics (phytoplankton, non-algal particles and chromophoric dissolved organic matter absorption characteristics) and water quality status of East Liaohe River basin were conducted based on the water samples in Erlong-hu Reservoir collected in June, September and October of 2011 and samples in East Liaohe River in October of 2012. The results demonstrated that the eutrophication status of Erlonghu Reservoir was lower in June, eutrophic in September and moderately eutrophic in October. Some of the sampling points of the East Liaohe River belonged to the middle trophic level and the other part belonged to the eutrophic level. The absorption coefficient of each component of water increased with increasing nutrient level. Besides, the absorption spectra of total suspended particulate of Erlonghu Reservoir in June and October were similar to that of non-algal particles, and chromophoric dissolved organic matter (CDOM) contributed most to the total absorption of water. The absorption spectra of total suspended particulate matter in September were similar to that of phytoplankton and phytoplankton was the dominant contributor to the total absorption. For samples of Erlonghu Reservoir in June and September, aph(440) and total phosphorus (TP) were correlated closely with each other. Significant correlation between aph(440) and dissolved organic carbon (DOC) of Erlonghu Reservoir in June was observed, while ad(440) was only correlated with Chla. There were positive correlations between aph(675) and Chla, Carlson index (TLI) in Erlonghu Reservoir (September) and East Liaohe River. Obvious differences of water optical properties were found between river and lake located in the East Liaohe River basin as follows: There were two types of phytoplankton spectra curves of East Liaohe River and the contribution rates of different components varied greatly from sites to sites; Phytoplankton dominated spectral absorption in waters with high nutrition level (Erlonghu Reservoir in September and the East Liaohe River) while CDOM and the particles were both the main components for Erlonghu Reservoir in June and October; CDOM was composed of large-size molecules in waters of Erlonghu Reservoir in June and in the East Liaohe River in October and mainly of small-size molecules in Erlonghu Reservoir in September and October.

[Seasonal Variability of Greenhouse Gas Emissions in the Urban Lakes in Changchun, China].

The partial pressures of carbon dioxide p(CO2) and methane p(CH4) in the surface water of seven urban lakes in Changchun city, China (Nan Lake, Bei Lake, Yanming Lake, Shengli, Dilisuo, Changchun, Tianjia) , have been studied in both summer and autumn related to the environment and water quality parameters. The results indicated that both in summer and autumn, CH4 of seven lakes was all supersaturated, and CO2 was all supersaturated except in Nan lake and Shengli lake. For either p( C02) or p( CH4), there was a significant difference among different urban lakes (P < 0.05), and there was almost no obvious difference in the same lake between summer and autumn. The gas flux also had a significant difference among different urban lakes (P <0. 05). Except for Nan Lake and Shengli, all other lakes were the sources of atmospheric CO2 and CH4 both in summer and fall, and the discharge of CO2 to atmosphere by lakes was more than that of CH4. According to the correlation analysis, there was a significant negative relationship between p(CO2, CH4) and sunshine duration in summer (r p(CO2) = -0.48, P <0. 05; rp(CH4) = -0.63, P < 0.01). The sunshine duration could affect the concentrations of CO2 and dissolved oxygen in the water by influencing the photosynthesis of aquatic plants. There was also a significant negative relationship between p(CH4) and precipitation in summer (r p(CH4) = 0.44, P < 0.05), and between p (CO2) and air temperature in autumn (r p(cO2) = -0.39, P < 0.05). The correlation analysis between water quality parameters and p(CO2, CH4) showed that both p(CO2) and p(CH4) were negatively correlated with pH (r(Co2) = -0.51, r P(C4) = -0.82, P < 0.01), while they were positively correlated with salinity (r p(CO2) = 0.38, P < 0.05; r p(CH4) = 0.75, P < 0.01). The results suggested that the levels of nutrients in these urban lakes, which were related to the phytoplankton biomass, were not the main influencing factors for p(CO2) in surface water, and sunshine duration, pH, and salinity all had a greater impact on p (CO2) and p(CH4) in summer and autumn.

[Absorption Characteristics of Particulates and CDOM in Waters of Chagan Lake and Xinlicheng Reservoir in Autumn].

Field surveys and laboratory analysis were carried out in Chagan Lake and Xinlicheng Reservoir under different salinity conditions in September 2012. In the laboratory, the absorption coefficients of particulates and chromophoric dissolved organic matter (CDOM) were measured, aiming to compare the absorption features, source of optical active substances and relative contribution of optical active constituents over the range of PAR (400-700 nm) in Chagan Lake and Xinlicheng Reservoir. The results showed that the Chagan Lake and Xinlicheng Reservoir were water bodies with medium eutrophication in autumn by TAL nutrient index and the absorption spectra of particulates matters were similar to those of phytoplankton. For the Chagan Lake with high salinity( EC = 988. 87 micro S x cm(-1)), the total particulate absorption was dominated by the nonalgal particles, and the contribution rate was in the order of nonalgal particles > phytoplankton > CDOM. For the Xinlicheng Reservoir with low salinity (EC = 311.67 microS x -cm(-1)), the total particulate absorption was dominated by the phytoplankton, and the contribution rate was ranked as phytoplankton > nonalgal particles > CDOM. Positive correlation was observed between a(p) (440), a(p) (675), a(d) (440) and total suspended matter (TSM), inorganic suspended matter (ISM), organic suspended matter (OSM) and Chl-a respectively in Chagan Lake, with correlation coefficients all above 0.55. Positive correlation was observed between a(p)(440), a(p) (675) and Chl-a (0.77 and 0.85, P < 0.05) , so did a(d) (440) and ISM (0.74, P < 0.01), while negative correlation was observed between a(p) (440) and OSM in the Xinlicheng Reservoir. In terms of Chagan Lake, negative correlation was merely observed between a(g) (440) and OSM (-0.54, P < 0.05) , but not in the Xinlicheng Reservoir. Both Sg, which was calculated by the fitting absorption curve from 250 to 400 nm, and relative molecular weight M showed that Sg[ (0.021 +/- 0.001) m(-1)] in Chagan Lake was greater than that in the Xinlicheng Reservoir [(0.0176 +/- 0.001) m(-1)], and Mr, in Chagan Lake was 11.44 +/- 2.00 (7.5-15.09), which was greater than that in Xinlicheng Reservoir 7.53 +/- 0.79 (6.17-8.89), indicating that the relative molecular weight of CDOM in the Chagan Lake was less than that in the Xinlicheng Reservoir. The Chagan Lake was greatly affected by wind speed and shore collapse to produce suspended mineral and sediment particles. Thereby the total particulate absorption was dominated by the nonalgal particles. The waters in the Xinlicheng Reservoir were greatly impacted by terrestrial inorganic matter, and the growth of phytoplankton was weakened and microbes activities were strengthened simultaneously, which led to the negative correlations between a(g)(lamda) and OSM.

[Spatial-temporal pattern and factor diagnoses of agroecosystem health in major grain producing areas of Northeast China: A case study in Jilin Province]. / ä¸œåŒ—ç²®é£Ÿä¸»äº§åŒºå†œä¸šç”Ÿæ€ç³»ç»Ÿå¥åº·æ ¼å±€ä¸Žå› å­è¯Šæ–­­­ä»¥å‰æž—省为例.

It is of great significance to study agroecosystem health in major grain producing areas based on the theory and method of ecosystem health. This paper selected Jilin Province as the study area, and an evaluation index system of agroecosystem health was built based on the SSI-VOR conceptual framework model. Using the optimal combined weights method, comprehensive evaluation assessment, GIS spatial analysis and grey slope similarity incidence models, the spatial-temporal pattern of agroecosystem health and influence factors were analyzed from 2000 to 2011 in Jilin Pro-vince. The results indicated that, temporally, the composite index of agroecosystem health showed a rising trend in Jilin Province from 1995 to 2011, and the agroecosystem health level changed from not healthy to relatively healthy; spatially, the spatial discrepancy of agroecosystem health level tended to become larger, which remained unchanged in central area, while was gradually improved in southeast and west. The main contributors which improved the agroecosystem health level were economic driving force, environmental management and social development, while the main 'dragging' factors were ecological pressure, organization structure and input capacity. Finally, relevant measures were put forward to improve the agroecosystem health condition.

[Quantification of crop residue burned areas based on burning indices using Landsat 8 image].

Crop residue burning leads to atmospheric pollution and is an enormous waste of crop residue resource. Crop residue burning can be monitored timely in large regions as the fire points can be recognized through remotely sensed image via thermal infrared bands. However, the area, the detailed distribution pattern and especially the severity of the burning areas cannot be derived only by the thermal remote sensing approach. The burning index, which was calculated with two or more spectral bands at where the burned and unburned areas have distinct spectral characteristics, is widely used in the forest fire investigation. However its potential application for crop residue burning evaluation has not been explored. With two Landsat 8 images that cover a part of the Songnen Plain, three burning indices, i.e., the normalized burned ratio (NBR), the normalized burned ratio incorporating the thermal band (NBRT), and the burned area index (BAI), were used to classify the crop residue burned and unburned areas. The overall classification accuracies were 91.9%, 92.3%, and 87.8%, respectively. The correlation analysis between the indices and the crop residue coverage indicated that the NBR and NBRT were positively correlated with the crop residue coverage (R2 = 0.73 and 0.64, respectively) with linear regression models, while the BAI was exponentially correlated with the crop residue coverage (R2 = 0.68). The results indicated that the use of burning indices in crop residue burning monitoring could quantify crop residue burning severity and provide valuable data for evaluating atmospheric pollution.

[Seasonal variation in the absorption and fluorescence characteristics of CDOM in downstream of Liaohe River].

Chromophoric dissolved organic matter (CDOM), which is an important part of dissolved organic matter (DOM), is considered as the largest storage of dissolved organic carbon in the aquatic environment. Liaohe River is the seventh largest river in China with annual runoff of 1.48 billion m3. As a result, studying on CDOM of Liaohe River is very important in estimating the organic carbon flux into sea. Seasonal optical characteristics of CDOM in the downstream of Liaohe River were investigated using absorbance spectroscopy and fluorescence excitation-emission matrices (EEMs). CDOM absorption coefficient at 355 nm [aCDOM (355)] in spring was lower than that in autumn and winter while low molecular weight substances were found in autumn and high molecular weight substances in spring based on the absorption coefficient and absorption slope (S) of CDOM. Samples in different seasons all exhibited fairly strong protein-like fluorophore (fluorophore B and fluorophore T) in the EEMs but the values showed apparent temporal variations. Based on the analysis of the relationships between different fluorophores, strong correlations (R2 > 0. 9) were observed between fluorophore A and C in spring, fluorophore B and T in autumn and winter, which illustrated that they had similar CDOM originalsources. However, a weak relationship (R2 = 0.21) was found between fluorophore B and T in spring, demonstrating the complexity and diversity of CDOM sources. Starting from autumn to winter and the subsequent spring, humic-like fluorophores exhibited enhanced fluorescent intensity, which could be ascribed to exogenous input. Furthermore, linear relationship between aCDOM (355) and Fn (355) in different seasons was examined in the study, and the strongest relationship was obtained in winter (R2 = 0.75), followed by autumn (R2 = 0.48) and spring (R2 = 0.01). This study indicated that fluorophore B in autumn and winter (R = 0.66; R = 0.89) as well as humic-like fluorophores (A and C, R = 0.74; R = 0.82) in spring were the main contributors to the CDOM optical characteristics.