Linking CDOM patterns in Cayuga Lake, New York, USA, to terrigenous inputs

Lacustrine patterns of the light absorption of colored dissolved organic matter (aCDOM) and its composition proxies were resolved and linked to concurrent conditions of tributary inputs for Cayuga Lake, New York. We analyzed fixed-frequency samples of the lake at 3 sites and runoff event-based samples at the mouths of 3 gauged tributaries over a 7 month interval and measured dissolved organic carbon (DOC) and aCDOM over the visible wavelengths (400–700 nm) and at 254 nm. The tributaries are demonstrated to be enriched in aCDOM and DOC, with widely different proxy conditions compared to the lake, which further diverge during runoff events. DOC, aCDOM, and the composition proxies for the tributaries had significant, and mostly strong, dependencies on flow rate, described by power-law relationships. The differences in the composition proxies indicated lower contributions of CDOM to the DOC pool, reduced aromaticity, decreased molecular size of CDOM, and decreased amounts of humic versus fulvic acids in the lake compared to the tributaries, all accepted signatures of photobleaching. Dynamics of aCDOM in the upper waters of the lake depended primarily on composition (e.g., color quality) and secondarily on a quantity metric (DOC), as demonstrated in a 2-component linear least-squares regression format. Signatures of linkages between the terrestrial inputs and in-lake aCDOM patterns and the effects of photobleaching include (1) the preferential in-lake loss of aCDOM relative to DOC, estimated from budget calculations; (2) the intermediate characteristics resolved at a near-shore site adjoining multiple tributary inflows; and (3) the magnitude and character of the dynamics observed at the pelagic sites