Analysis of Hydrochemical Characteristics and Three-Dimensional Fluorescence Spectra in the Semi-Arid Ebinur Lake Watershed, Xinjiang, China
Hydrochemical characteristics and three-dimensional fluorescence spectra for Lake Ebinur and its major inflow tributaries have been analyzed. The results indicate that Jing and Bortala River ions differ very little. Anions are composed of HCO 3 − > SO 4 2− > Cl − , while cations have the following composition: Ca 2+ > Mg 2+ > Na + > K + . The Jing and Bortala Rivers include mainly SO 4 2− and HCO 3 − anions; these cations are primarily Ca 2+ . Hydrochemical components of the Jing and Bortala
... Jing and Bortala Rivers are of the HCO 3 − -Ca 2+ type. Ion compositions of the Jing and Bortala Rivers are derived primarily from the weathering of rocks. In addition, a parallel factor method (PARAFAC) analysis of three-dimensional fluorescence spectra (EEM) of the Jing and Bortala Rivers shows that all the sampled water bodies contain C1 (260/420 nm) humic organic matter, C2 (240, 240/490 nm), C3 (220/280, 300/450 nm) protein-like C4 (260, 270/530 nm), and humic substances. To further understand characteristics of dissolved organic matter (DOM) components, we base our research on regional standards related to water quality and fluorescence. A fluorescence regional integration (FRI) analysis of the Jing and Bortala Rivers shows that protein organic matter levels are the highest, whereas fulvic acid levels are the lowest. Of the correlation coefficients of hydrochemical factors and fluorescence indices, the biological index (BIX), TDS, HCO 3 − , and K + are stronger in major inflow tributaries of Ebinur Lake with correlation coefficients of 0.577, 0.708, and 0.764, respectively, at the p < 0.01 significance level; correlations between the humification index (HIX) and HCO 3 − concentrations amount to 0.568 at the p < 0.05 significance level. Hydrochemical factors and fluorescence indices show the presence of three fitting relationships. While the HIX and HCO 3 − fitting effect is strongest with a correlation coefficient of 0.789, the second strongest is that of BIX and K + with a correlation coefficient of 0.814. The results of this work offer scientific support for water quality monitoring and restoration in arid regions of Central Asia. Water 2018, 10, 426 2 of 17 by analyzing salt content and changes in anions and cations in river water. Hydrochemistry is the science of studying the chemical compositions and internal chemical changes of natural water bodies  . A river, as a channel that connects land to the sea, is an important source of material and energy cycling. A river's water chemistry composition characteristics are influenced by geological characteristics, climatic characteristics, human activities, biogeochemical behaviors of elements, etc.    . In turn, water chemistry characteristics can also affect the economic and social development of a basin through the water-environment-food-grain-health transfer chain  . Foreign scholars started to conduct systematic research on the chemical characteristics of surface water earlier on. In 1970, Gibbs  adopted total dissolved solids (TDS) and the relationship between cations and the cation concentration ratio. He also systematically described differences in water chemistry characteristics of the world's major watersheds resulting from precipitation, rock weathering, and evaporation-crystallization processes. Water fluorescence is also central to understanding water environments. Understanding the structure of dissolved organic matter (DOM) in water is central to understanding the water environment. At present, the fluorescence spectra of different rivers can be analyzed by fluorescence spectroscopy. Fluorescence spectrometry is efficient, is highly sensitive, offers a low detection limit, can be applied to small samples, and does not damage sample structures  . In recent years, with the development of fluorescence spectrum technologies, the synchronous rapid scanning of excitation and emission wavelengths has been discovered, and a three-dimensional excitation-emission fluorescence spectrum has been produced. Three-dimensional fluorescence spectroscopy presents potential applications for the water quality monitoring of large lakes and rivers. Related research was performed abroad early on and has undergone rapid development and application. The fluorescence spectrum technique can be used to quickly analyze water quality levels in a timely fashion. In addition, it can achieve good results, such as those of , revealing DOM characteristics of rivers, lakes, groundwater, seas and sewage and in evaluating and estimating surface water quality levels     . Several scholars have identified five fluorescence feature peaks for characterizing DOM structures in water bodies. In recent years, many researchers have used conventional methods such as regional integrals, parallel factors, and self-organizing neural networks to characterize the structure of DOM. However, hydrochemical characteristics of water directly reflect the water salinization; the salt cations are the main chemicals that characterize the salinization, and they lead to the salinization of water; thus, studying the anions and cations with fluorescence index is the novelty of this study. The Ebinur Lake Watershed is located at the lowest elevation point of the Junggar Basin of the Xinjiang Uyghur Autonomous Region in China. The lake is a terminal lake fed by the Bortala, Akeqisu, Jing, Tuotuo, and Daheyanzi Rivers, which present water ecological safety problems. The region is a typical arid area of Central Asia. The ecological environment has been extremely fragile in arid areas of Northwest China in recent years. With the increasing intensity and range of human activities, the discharge of anthropogenic pollutants has been increasing the pollution of oasis rivers and sediments  . Because of the water reduction of Boltara River, Jing River, and other rivers, the area of Ebinur Lake declined substantially, the water level decreased, the water became salty, the water quality was polluted, and the average mineralization degree was high, which significantly affected the ecological environment, water quality salinization, and lake degradation. However, the Bortala and Jing Rivers are the most important Major Inflow Tributaries of Ebinur Lake in the Ebinur Lake Watershed. The two rivers not only play an important role in the ecological environment of the Ebinur Lake National Nature Reserve but also provide agricultural water to surrounding areas such as the Bole and Jinghe counties, which play a decisive role in the development of oasis agricultural systems. Therefore, current and future conditions, surface river pollution identification, river water pollution monitoring, basic research, surface water resource regeneration, and sustainable resource use have important implications for the improvement of ecological river environments and for maintaining the structure and function of this ecosystem.