4:00 PM - 4:15 PM
[AOS17-08] Assessing the distribution and source of dissolved organic matter in wetland-estuary-shallow coastal waters continuum
Keywords:Dissolved organic matter (DOM), Carbon cycle, Wetland river, Eelgrass, Aquaculture, Coastal shallow water ecosystem
The amount of carbon in the dissolved organic matter (DOM) in the ocean is considered to be comparable to the amount of atmospheric carbon dioxide and terrestrial biomass (Hansen et al., 2015). Therefore, its dynamics is important for understanding the carbon cycle on Earth. Labile DOM is biologically available for bacteria and then returned to the food chain through the microbial loop by bacteria–protozoa–zooplankton pathway. On the other hand, biologically refractory DOM is the major carbon pool in the ocean. Previous studies on DOM have been conducted separately in wetlands as a source of refractory DOM (mainly humic substances), in coastal areas and in aquaculture areas. However, little is known about the contribution and the proportion of various ecosystems such as wetlands, aquaculture organisms, and eelgrass to DOM in wetland-estuary-shallow coastal waters continuum.
Here, we investigated the distribution and sources of DOM in the water continuum in Akkeshi watershed, which is characterized by several distinct ecosystems; wetland river flowing through the Bekanbeushi Wetland (the second largest wetland in Japan), oyster and clam aquaculture, eelgrass meadow and shallow coastal area influenced by the Oyashio Current.
Water samples were collected in May, June, August, September, and October 2022 from the wetland river, the estuary of Akkeshi-ko, and the coastal shallow water area, to investigate spatio-temporal changes in absorption spectra of colored dissolved organic matter (CDOM), excitation-emission matrix (EEM) fluorescence spectra of fluorescent dissolved organic matter (FDOM), salinity, and water temperature.
The absorption spectra of CDOM were determined by a spectrophotometer, and the absorption coefficient was calculated following the method of Babin et al. (2003). FDOM was classified and identified as protein-like and humus-like fluorescent substances using EEM (Lawaetz and Stedmon, 2009). Salinity and water temperature at each sampling station were obtained by CTD sensor.
The relationships between the absorption coefficient of CDOM at 355 nm (aCDOM(355)) and salinity showed conservative mixing across all seasons, indicating that most of the CDOM stemmed from wetland. However, data obtained from aquaculture and eelgrass areas showed no apparent conservative mixing between aCDOM(355) and salinity in June, September and October, suggesting that aquaculture organisms and eelgrass contribute to the production of CDOM. Analysis of FDOM showed components such as humic substances, protein tyrosine, and tryptophan. The humic substances showed conservative mixing with salinity, and their sources were mainly wetlands. On the other hand, proteins were released from all ecosystems to the same extent, suggesting the contribution of aquaculture organisms and eelgrass to the production of protein-like FDOM.
Here, we investigated the distribution and sources of DOM in the water continuum in Akkeshi watershed, which is characterized by several distinct ecosystems; wetland river flowing through the Bekanbeushi Wetland (the second largest wetland in Japan), oyster and clam aquaculture, eelgrass meadow and shallow coastal area influenced by the Oyashio Current.
Water samples were collected in May, June, August, September, and October 2022 from the wetland river, the estuary of Akkeshi-ko, and the coastal shallow water area, to investigate spatio-temporal changes in absorption spectra of colored dissolved organic matter (CDOM), excitation-emission matrix (EEM) fluorescence spectra of fluorescent dissolved organic matter (FDOM), salinity, and water temperature.
The absorption spectra of CDOM were determined by a spectrophotometer, and the absorption coefficient was calculated following the method of Babin et al. (2003). FDOM was classified and identified as protein-like and humus-like fluorescent substances using EEM (Lawaetz and Stedmon, 2009). Salinity and water temperature at each sampling station were obtained by CTD sensor.
The relationships between the absorption coefficient of CDOM at 355 nm (aCDOM(355)) and salinity showed conservative mixing across all seasons, indicating that most of the CDOM stemmed from wetland. However, data obtained from aquaculture and eelgrass areas showed no apparent conservative mixing between aCDOM(355) and salinity in June, September and October, suggesting that aquaculture organisms and eelgrass contribute to the production of CDOM. Analysis of FDOM showed components such as humic substances, protein tyrosine, and tryptophan. The humic substances showed conservative mixing with salinity, and their sources were mainly wetlands. On the other hand, proteins were released from all ecosystems to the same extent, suggesting the contribution of aquaculture organisms and eelgrass to the production of protein-like FDOM.