Abstract
The dissolved organic matter (DOM) is one of the important factors for controlling water quality. The behavior and constitutions of DOM is related to the risk of human health because it is able to directly or indirectly affect the behavior, speciation and toxicity of various environmental pollutants. However, it is not easy to know the contents of DOM components without using various complicated and time consuming analytical methods because DOM is a complex mixture and usually exists at low concentration. Here, we describe the fluorescence properties of DOM components in water samples collected from four rivers in Toyama, Japan by means of the three-dimensional excitation-emission matrix (3DEEM) fluorescence spectroscopy. In order to evaluate the alterations of DOM components in each of the river during the flow from upstream to downstream, the patterns of relative fluorescence intensity (RFI) at six peaks which are originated from fluorophores including humic-like and protein-like components were investigated. The changes in the patterns of RFI values at each of the peak and the concentration of dissolved organic carbon (DOC) for each river water sample were discussed in connection with the differences of land use managements and basic water quality parameters, such as pH, EC, turbidity, Fe3+, T-N, NO3-N, T-P, PO4-P, chlorophyll a, DOC and N/P ratio. The DOC concentrations in the water samples collected from these rivers were relatively low (0.63–1.16 mg/L). Two main peaks which have a strong RFI value expressed a positive correlation with the DOC concentration (r = 0.557, 0.535). However, the correlations between the RFI values for other four peaks and the DOC concentration were below 0.287. The alterations of DOM components during the flow of a river from upstream to downstream were investigated from the changes in the patterns of RFI values for six fluorescent peaks. It was clarified that the great increase of RFI values in peak A and peak T from river water located in urban area showed high concentration of PO4-P and Fe3+, and low N/P ratio due to the high biological activities. The values of fluorescence index (FIX) and biological index (BIX) were as high as 1.60 and 0.72, respectively.
Highlights
There are many human activities that emit a wide variety of chemicals into the environment
The results obtained in this study showed that the 3DEEM method is able to evaluate the alterations of dissolved organic matter (DOM) components during the flow of a river from upstream to downstream
The changes in the patterns of relative fluorescence intensity (RFI) values at six different fluorescence peaks obtained from the 3DEEM spectra for each of the river water sample were investigated
Summary
There are many human activities that emit a wide variety of chemicals into the environment. The behavior and constituents of DOM is very important in assessing the water quality and its potential risk to human health. DOM consists of a complex mixture of organic components with a wide variety of chemical structures and molecular weights, which is operationally defined as the fraction of organic matter that can pass through a membrane filter with 0.45 μm pore diameter [3]. The DOM in aquatic environment represents one of the largest active organic carbon reservoirs in the biosphere [4] and originates from three different sources as follows: (1) Natural sources which include the production of humic substances in soil environment by biochemical and chemical reactions during the decay and transformation of plant and microbial remains. The quantitative and qualitative analysis for DOM which has a strong effect directly and indirectly to water quality is critically important for evaluating aquatic environment
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