Rapid Modeling Eutrophication Techniquesusing Optical Parameters Of CDOM In The Coastal Waters

Eutrophication has become a complex and serious problem because of consequences of anthropogenic nutrient over-enrichment from local sources, including agriculture, energy production, industrial activities, transport, tourism and fishing.Eutrophication has been the most serious threat because of the spreading of hypoxia, increased harmful or toxic algal blooms, poorer conditions for zoobenthos and reduced fishery.Eutrophication in the Bohai Sea, the Yellow Sea and the East China Sea is a complex problem with serious effects on the state and health of the ecosystem.Because of their characteristics, the Bohai Sea, the Yellow Sea and the East China Sea are highly sensitive to all types of environmental damages. Currently, triditional methods for assessing the trophic status required the loadings of the nutrients and some other water quality parameters. Among these variables, determining the nutrients always needed to be performed in a lab and was often time consuming, costly and laborious. Tools for the in situ monitoring of eutrophication have been urgently needed by decision-makers and the scientific community because they can help to better understand the causes, status and trends of eutrophication.Optical techniques as monitoring tools are popular because of the simple sample preparation requirements, the quick data acquisition time, and the large amount of information that might be obtained from a single matrix. In situ fluorescence spectroscopy and ultraviolet-visual (UV-Vis) spectrometers make possible the long term collection of the absorption spectra multiple times per hour compared to the laboratory analysis. Fluorescence spectroscopy and UV-Vis absorbance have proven to be useful techniques for water resource management. Thus, the main objective of this study is to develop a rapid and low-cost eutrophic status assessment approach for the Bohai Sea, the Yellow Sea and East China Sea in spring using CDOM excitation-emission matrix spectroscopy, UV-Vis absorbance spectroscopy and other easy-to-measure parameters including temperature, salinity, dissolved oxygen, chlorophyll a, turbidityby parallel factor analysis, partial least squares regression and support vector machine.The main research contents and results are as follows:(1) The average values of TRIX are 5.62,5.68 and 5.39 for the three vorages of the Bohai Sea and Yellow Sea in spring of 2013, the Yellow Sea and East China Sea and the East China Sea, respectively. The most stations of the Bohai Sea are characterized as moderate water quality, except for the Yellow River estuary and surrounding waters characterized as poor water quality. The most areas of the Yellow Sea are characterized as good water quality and moderate water quality. The stations near to Yangtze eatuary under the influence of Yangtze runoff are characterized as poor water quality, however, the other areas of the East China Sea located in open sea areas which are free from major point and non-point pollution sources are characterized as good water quality.(2) Three fluorescent components (C1, C2 and C3) are identified by PARAFAC using EEMs from the Bohai Sea, the Yellow Sea and East China Sea water samples: two humic-like C1(340/435 nm) and C2 (270(390)/500 nm) and one protein-like C3(280/350 nm).C1 and C2 have similar characteristics affected by terrestrial inputs. However, C3 is affected by microbial activities.(3) Correlations between the TP, the TN and three fluorescence components (C1, C2 and C3), the UV-Vis absorption coefficients (a220,a254,a270,a350) and some other easy-to-measure water quality parameters (temperature, salinity, dissolved oxygen, turbidity and chlorophyll a)show different significance in the three voyages. Generally speaking, there is also a significant correlation betweena220 and the TP and TN. The TP and TN are also correlated with other optical parameters. Among the three voyages, the TP has a close correlation with turbidity. Therefore, CDOM fluorescence, UV-Vis absorbance, temperature, salinity, Chl-a, DO, and turbidity could be used to assess the eutrophic status instead of the nutrient parameters.(4) The classification accuracy of SVM modelsare 100%,85.0% and 90.5% for the validation data of the Bohai Sea, the Yellow Sea and the East China Sea, respectively. The classification accuracy of PLSR modelsare 100%,87.8% and 88.9% for the validation data of the Bohai Sea, the Yellow Sea and the East China Sea, respectively. It is evident that support vector machine and partial least square regression are useful tools to develop a rapid and low-cost eutrophication assessment model.SVM models are suitable for the Bohai Sea and the East China Sea, and PLSR models are are suitable for the Bohai Sea, the Yellow Sea and the East China Sea.That means that the models will be able to predict accurately the risk of eutrophication. In the study, we investigate the effect of temperature and salinity on the development of trophic model. Temperature is the influential variable for PLSR model of the Bohai Sea,Our results suggested that those easy-to-measure parameters could be used todevelop a simple approach for rapidly assessing and monitoring the eutrophication of estuary and offshore areas in situ. In conclusion, it would be more reasonable using above easy-to-measure parameters to evaluate eutrophic status in marine and coastal environments rather than model eutrophication using nutrient parameters.