On the other hand, Kim and Kim (2016) reported that anaerobic production in the bottom sediment of the deep East Sea (Japan Sea) accounted for approximately 10 % of the total production of FDOM H in the deep-water column. Rivers are known as the major source of the humic-like FDOM ( FDOM H) in the coastal ocean (Stedmon and Nelson, 2015 Kim and Kim, 2016), while aerobic microbial remineralization of sinking organic matter is the major source of FDOM H in the deep sea (Jørgensen et al., 2011 Catalá et al., 2015 Kim and Kim, 2016). The major fraction of CDOM, which emits fluorescence after absorbing light energy, is referred to as fluorescent DOM (FDOM) (Coble, 1996, 2007 Kim and Kim, 2016). In the coastal ocean, DOM sources include (1) in situ biological production (Carlson and Hansell, 2015), (2) terrestrial organic matter such as soils and plant matters (Opsahl and Benner, 1997 Bauer and Bianchi, 2011), and (3) anthropogenic sources such as industrial and agricultural wastewaters (Tedetti et al., 2010 Griffith and Raymond, 2011).Ī part of DOM is known as colored dissolved organic matter (CDOM), which is the light-absorbing fraction of organic matter (Coble, 2007 Kim and Kim, 2016, 2018). DOC plays a significant role in coastal carbon dynamics and biogeochemical cycles, and thus it is important to understand the sources and characteristics of DOC (Vetter et al., 2007 Carson and Hansell, 2015). Our study demonstrates that the combination of these biogeochemical tools can be a powerful tracer of DOM sources and characteristics in coastal environments.ĭissolved organic carbon (DOC), a major component of dissolved organic matter (DOM), is the largest reduced carbon pool in the ocean (Benner et al., 1992 Raymond and Spencer, 2015). This terrestrial DOM source observed in 2017 was likely associated with DOM on the reclaimed land, which experienced extended exposure to light and bacterial degradation as indicated by the higher spectral slope ratio ( S R) of light absorbance and no concurrent increases in the FDOM H and NH 4 + concentrations. However, the origins of the excess DOC observed in 2017 appear to be from two different sources: one mainly from marine sources such as biological production based on the DOC- δ 13C values ( −19.1 ‰ to −20.5 ‰) and the other mainly from terrestrial sources by land–seawater interactions based on its depleted DOC- δ 13C values ( −21.5 ‰ to −27.8 ‰). The excess DOC occurring in the lower-salinity waters originated mainly from marine sediments of tidal flats, based on the DOC- δ 13C values ( - 20.7 ± 1.2 ‰) and good correlations among the DOC, humic-like fluorescent DOM ( FDOM H), and NH 4 + concentrations. Here, the excess DOC represents any DOC concentrations higher than those in the incoming open-ocean seawater.
The DOC concentrations were generally higher in lower-salinity waters in both periods, and excess of DOC was also observed in 2017 in high-salinity waters. Sihwa Lake is enclosed by a dike along the western coast of South Korea, and the water is exchanged with the Yellow Sea twice a day through the sluice gates.
In order to determine the origins of dissolved organic matter (DOM) occurring in the seawater of Sihwa Lake, we measured the stable carbon isotope ratios of dissolved organic carbon (DOC- δ 13C) and the optical properties (absorbance and fluorescence) of DOM in two different seasons (March 2017 and September 2018).
0 kommentar(er)
