Abstract
Dissolved organic matter (DOM) in rivers are an important factor in pollution management due to the abundance of stored carbon. Using fluorescent spectroscopy, we investigated the temporal and spatial dynamics of DOM compositions, as well as their properties, for two of the major four regulated rivers—Han River (HR) and Geum River (GR) in South Korea. We collected eight sampling sites, four from each of the two rivers (from close to the weirs) in order to observe the integrated effects of different land use (terrestrial input) during the monsoon (July) and post-monsoon periods (September). High integral values of DOM compositions (July: 30.81 ± 9.71 × 103 vs. September: 1.78 ± 0.66 × 103) were present in all eight sites after heavy rainfall during the monsoon period, which indicated that Asian monsoon climates occupy a potent role in the DOM compositions of the rivers. Regarding DOM compositions, tryptophan-like and fulvic acid-like components were predominant in HR and GR, especially in GR with high integral values of protein-like and humus components. However, the properties of terrestrial DOM between HR and GR are markedly different. These results considered due to the different land use, where the terrestrial DOM shows a low degree of humification due to a high percentage of agriculture and urban land use in GR. Furthermore, these two rivers are typical regulated rivers, due to their weir constructions. High values of DOM components were present in the downstream of the weirs; however, increasingly high patterns appeared in the HR because of heavy rainfall (511.01 mm in HR; 376.33 mm in GR). In addition, a lower increasing trend of humic-like component was present in the GR due to a low percentage of forest land use/cover. These results suggest that the effect of the weir on rivers can be highlighted by the different percentages of land use/cover under the conditions of the monsoon period. Hence, DOM fluorescence can serve as an effective indicator for providing an early signal for the complex impacts of the different land use and rainfall in the regulated river systems.
Highlights
Rivers occupy a paramount role in water supply and the strengthening of human activities [1,2,3]
The pH values found in the Han River (HR) ranged from 7.78 to 7.95 and all the sites were similar in July and September in this regard
The total nitrogen (TN) concentrations showed clear temporal change and had high values in July, which decreased in September in the HR
Summary
Rivers occupy a paramount role in water supply and the strengthening of human activities [1,2,3]. Rivers are important for sustainable water supply for human activities (e.g., urban runoff, agriculture, industry, and landscape), and for maintaining the biodiversity of local aquatic plants and animals [4]. Studies have shown that precipitation and terrestrial pollution sources (land use) are some of the paramount factors that determine the dynamics of the water quality of river systems [5,6,7]. In the unique Asian climate, heavy rainfall, caused by monsoons and/or typhoons produce heavy precipitation and impact the quality and quantity and change the flux of terrestrial pollution inputs from the surrounding catchment (land use) to the river ecosystems [3,6,8,9,10]. Studies have shown that the high rates of agricultural and urban land cover tend to increase the nutrient load of rivers, found to be higher there than in rivers with natural forest and wetland cover [11,12]
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