Bioavailability and size-fraction of dissolved organic carbon, nitrogen, and sulfur at the Arbutus Lake watershed, Adirondack Mountains, NY

The heterogeneity of DOM is closely linked with the various sources and the diversity of biogeochemical processes. We studied the spatial and temporal patterns of the quantity (bioavailable [B-] and refractory concentrations by laboratory incubations) and quality (delta C-13, aromaticity, and size-fraction by ultrafiltration [low molecular weight (LMW) < 1 kDa and high molecular weight (HMW) > 1 kDa]) of dissolved organic C (DOC), N (DON), and S (DOS) for surface waters (two upland streams, two wetland-affected streams, and lake outlet) over a 14-month period within the Arbutus Lake watershed in the Adirondack Mountains of New York State, USA. The % BDOC and % BDON of this watershed averages ranged from 6 to 18 % and from 12 to 43 %, respectively. The DOC and DON concentrations increased as water was transported through wetland areas of the Arbutus Lake watershed. DOC and DON constituents in the surface waters passing through a wetland were composed mostly of refractory HMW components (% HMWDOC: 55 %, % HMWDON: 60 %) with a higher level of aromaticity compared to upland streams (% HMWDOC: approximately 35 %, % HMWDON: approximately 30 %). DOS was dominated by the refractory (% BDOS range 6-13 %) and LMW (% LMWDOS range 62-96 %) form and we suggest that bacterial dissimilatory sulfate reduction might play an important role in generating this distinct DOS biogeochemistry. The aromaticity was positively related to total DOC concentration, but negatively to % BDOC. Arbutus Lake DOM was dominated by bioavailable and LMW characteristics, compared to wetland-affected streams where refractory and HMW DOM fractions were more prevalent. Our study suggests the different variability of DOM characteristics among elements (C, N, S) using a bioavailability-molecular size model showing a diagenetic perspective due to the relative refractoriness of the LMW DOS. This study also highlights the importance of multiple approaches for understanding DOM biogeochemistry with respect to molecular size, bioavailability, aromaticity, stoichiometry, isotopic values, and elemental concentrations.