Distribution of dissolved carbohydrates and uronic acids in a tropical estuary, India

Abstract

Carbohydrates including uronic acids are among the active components of dissolved organic carbon, and play an important role in biogeochemical cycling of organic carbon in marine environments. In order to understand their distribution, concentrations of total dissolved carbohydrate (TCHO), dissolved polysaccharide (PCHO), dissolved monosaccharide (MCHO), and dissolved uronic acid (URA) were measured in the Mandovi estuary, west coast of India during the monsoon and premonsoon seasons. The estuary experienced nearly fresh water condition during the monsoon season and marine condition during the pre-monsoon season. Concentrations of TCHO, MCHO and URA ranged from 17.7 to 67.3 µM C, 4.1 to 15.5 µM C and 2.3 to 10.8 µM C, and their contribution to dissolved organic carbon (DOC) varied from ∼ 11 to 60%, 2.5 to 9.7%, and 1.8 to 5.3%, respectively. PCHO accounted for ∼ 52 to 92% of the TCHO. Generally, concentrations and yields of TCHO species were greater during the monsoon season. Phytoplankton abundance and bacterial cell numbers influenced the distribution of TCHO in the pre-monsoon season but not during the monsoon season. Transport of TCHO rich (11 to 60%) dissolved organic matter from the Mandovi estuary to the coastal waters during the monsoon season may affect ecosystem function by fueling biological activity of heterotrophic micro-organisms.

Dynamics of dissolved organic carbon in eutrophic Lake Taihu and its tributaries and their implications for bacterial abundance during autumn and winter

“…The high proportion of PCHO to TCHO (92%À96%) in the tributaries was in contrast to that found in riverine environments (Hung et al 2005;Gu eguen et al 2006), suggesting that not all carbohydrates originate from the decomposition products of soil litter (Hedges et al 1994). The contribution of TCHO to DOC is defined as the carbohydrate yield (Khodse et al 2010;Wu & Yang 2013) and varied from 6% to 34% in the present study, close to the range (15%À30%) recorded for freshly derived organic matter from phytoplankton (Pakulski & Benner 1994). Thus, the high proportion of PCHO to TCHO may be due to the in situ production of high-molecular-weight PCHO compounds by phytoplankton or bacteria (Hung et al 2003;Guimarães et al 2013).…”

“…Chrost et al (1989) observed that the highest concentration of total dissolved carbohydrates (TCHO) occurred shortly after the peak of phytoplankton biomass. Furthermore, a significant negative correlation between bacterial abundance (BA) and the ratio of total dissolved carbohydrates to dissolved organic carbon (TCHO/DOC) was observed in the Mandovi estuary (Khodse et al 2010). Allochthonous DOC is composed extensively of humic substances, which can be measured by specific ultraviolet absorbance (SUVA 254 ); therefore, it has been considered recalcitrant (Moran & Hodson 1990).…”

“…The distribution of TCHO to DOC is useful for assessing the degradation state of organic substances (Hung et al 2005;Khodse et al 2010). Hung et al (2005) observed a negative linear relationship between WT and TCHO/DOC ratio, suggesting that microbial utilization of carbohydrates was strongly influenced by WT.…”

Origin and biochemical cycling of particulate nitrogen in the Mandovi estuary

“…D-amino acids are derived from bacterial cell wall, and bacterial macromolecules but are absent in phytoplankton or vascular plants (Kaiser and Benner, 2008). In the Mandovi estuary, a shift in the ecosystem production from net heterotrophy to net autotrophy occurs during the pre-moonsoon season (Khodse et al, 2010). The higher D-amino acid concentration observed during the pre-monsoon season (Table 2) indicate that accumulation of bacterial remnants due to diagenetic processes was not the reason for the observed higher D-amino acids concentrations in the Mandovi estuary.…”

Bacterial utilization of size-fractionated dissolved organic matter

“…TDCHO accounts for a significant fraction of the DOC pool in both oceanic waters (20 to 30%) (Pakulski & Benner 1992) and estuarine waters (9 to 60%) , Khodse et al 2010. Heterotrophic bacteria use TDCHO as a source of carbon and energy (Hanisch et al 1996, Amon et al 2001).…”