Concentration, Molecular Weight Distribution and Neutral Sugar Composition of DOC in Maritime Antarctic Lakes of Differing Trophic Status

The molecular weight distributions and hydrolysable neutral sugar composition of dissolved organic carbon (DOC) was investigated in four maritime Antarctic lakes on Signy Island of different trophic status; Heywood Lake (eutrophic), Light Lake (oligo-mesotrophic), Sombre Lake and Moss Lake (both oligotrophic). Tangential flow ultra-filtration (TFU) was used to separate DOC into high molecular weight (HMW; >1000 Da) and low molecular weight (LMW; < 1000 Da) size fractions. Pulsed amperometric detection-high performance liquid chromatography (PAD-HPLC) was used to determine the hydrolysable neutral sugar molecular composition of each size fraction. Total DOC concentrations defined the trophic trend in the four lakes and ranged from 8 to 303 μM. The <1000 Da fraction of all the lakes dominated the DOC distribution, comprising 76% in Light Lake which also had the highest chl-a concentrations. Heywood Lake was relatively enriched in >1000 Da total organic carbon and had extremely high concentrations of total hydrolysable neutral sugars (11 μM) corresponding to 43% of total DOC. However, no clear pattern was apparent with regard to lake trophic status and potential sources of DOC, and the measured variations in individual aldose concentration, composition and their various molecular weight fractions.