Dynamics and Characteristics of Fluorescent Dissolved Organic Matter in the Groundwater, River and Lake Water

Abstract

Fluorescent dissolved organic matters (FDOM) in the groundwater-river-lake environments were investigated using three-dimensional excitation-emission matrix (EEM) and measuring the dissolved organic carbon (DOC), inorganic anions and electric conductivity (EC) in shallow groundwater, river and lake waters. DOC concentrations were high and largely varied in groundwater, 16–328 μM C (mean 109 ± 88 μM C), and in river waters, 43–271 μM C (mean 158 ± 62 μM C) and were very low in the lake Biwa waters, 89–97 μM C (mean 93 ± 2 μM C). The fluorescence properties of EEM showed that the fulvic-like components (peak C, peak A and peak M) were dominated in groundwater and river waters, but protein-like components (peak T) was in lake waters. The peak C was observed at $$ {{\text{Ex}}} \mathord{\left/ {\vphantom {{{\text{Ex}}} {{\text{Em}}}}} \right. \kern-\nulldelimiterspace} {{\text{Em}}} = {320 \pm 9} \mathord{\left/ {\vphantom {{320 \pm 9} {424 \pm 5}}} \right. \kern-\nulldelimiterspace} {424 \pm 5}\;{\text{nm}} $$ in groundwater, and 340 ± 5/432 ± 4 nm in river waters, but the lake waters detected the two peaks, 347 ± 7/441 ± 11 nm (peak C) as a minor peak and 304 ± 2/421 ± 8 nm (peak M) as a major peak. Emission wavelength of peak T was observed to shorten in wavelengths from groundwater to river and then lake waters. Peak T in lake waters showed at shorter in wavelengths (279 ± 2/338 ± 11 nm) at the middle point of Lake Biwa compared to those of lake shore site (283 ± 3/350 ± 7 nm). Photo-irradiation experiment on upstream waters suggested the changes in the fluorescence peaks of fulvic acid-like substances in lake waters, which might be caused by photo-degradation. DOC concentration was significantly correlated with inorganic anions and EC in river waters. However, such correlations were not observed in groundwater. Anion concentrations in lake waters were low with respect to DOC concentration. These results showed that the optical and chemical properties of FDOM are characteristically varied among groundwater, river and lake waters, indicating the impacts of environments to various FDOM at the same watershed level.