Dynamics and characteristics of dissolved organic carbon, nitrogen, and sulfur in the Arbutus Lake Watershed in the Adirondack Mountains of New York State

To investigate how biogeochemical processes affect the concentrations and fluxes of dissolved organic matter (DOM) in forested watersheds, I studied the quantity and quality of DOM at the Arbutus Lake Watershed, Adirondack Park (NY, USA). First, to understand the biogeochemical changes of DOM for surface waters in the watershed, I studied spatial and temporal patterns of the quantity (bioavailable/refractory concentrations) and quality (δ13C, aromaticity, and low (LMW; 1kDa) of dissolved organic carbon (DOC), nitrogen (DON), and sulfur (DOS). DOC and DON constituents passing through a wetland were composed of highly refractory, aromatic HMW components compared to upland streams. DOS was dominated by the refractory, LMW form. I developed a “bioavailability-molecular size model” showing the refractoriness of the LMW DOS compared to the HMW DOC and DON. Second, to evaluate how a lake nested in a forested watershed affects the dynamics of DOC and DON, I analyzed a mass balance of DOC, DON and dissolved inorganic nitrogen (DIN) from 2000 to 2009. Annual DOC and DON mass balances were strikingly uncoupled, and Arbutus Lake generally acted as a sink for DOC. But a periodic source for DON was observed, indicating that internal recycling between DIN and DON might be important in affecting DON concentrations in this oligo-mesotrophic lake. Third, isotopic signatures of DOS in the inlet catchment of the Watershed revealed that the incorporation of reduced S (e.g., SH-) derived from bacterial dissimilatory sulfate reduction contributed to generating DOS in ground and surface waters. These results provide new information on mechanisms for geochemical DOS formation in forested catchments. Last, to better understand isotopic changes in DOS, three isotopic pretreatment methods for sulfate widely used were compared. I found an excellent agreement of the δ34S-sulfate values among the three methods. However, some differences were observed in the δ18O-sulfate values associated with possible O contamination before isotopic measurements. Overall, my studies highlighted novel approaches comparing sources and transformation of three elemental DOM fractions of DOC, DON, and DOS along various watershed components and a lake nested forested watersheds