Fluorescence characteristics and biodegradability of dissolved organic matter in forest and wetland soils from coastal temperate watersheds in southeast Alaska

Understanding how the concentration and chemical quality of dissolved organic matter (DOM) varies in soils is critical because DOM inXuences an array of biological, chemical, and physical processes. We used PARAFAC modeling of excitation–emission Xuorescence spectroscopy, speciWc UV absorbance (SUVA254) and biodegradable dissolved organic carbon (BDOC) incubations to investigate the chemical quality of DOM in soil water collected from 25 cm piezometers in four diVerent wetland and forest soils: bog, forested wetland, fen and upland forest. There were signiWcant diVerences in soil solution concentrations of dissolved organic C, N, and P, DOC:DON ratios, SUVA254 and BDOC among the four soil types. Throughout the sampling period, average DOC concentrations in the four soil types ranged from 9–32 mg C l¡1 and between 23–42% of the DOC was biodegradable. Seasonal patterns in dissolved nutrient concentrations and BDOC were observed in the three wetland types suggesting strong biotic controls over DOM concentrations in wetland soils. PARAFAC modeling of excitation–emission Xuorescence spectroscopy showed that protein-like Xuorescence was positively correlated (r = 0.82; P < 0.001) with BDOC for all soil types taken together. This Wnding indicates that PARAFAC modeling may substantially improve the ability to predict BDOC in natural environments. Coincident measurements of DOM concentrations, BDOC and PARAFAC modeling conWrmed that the four soil types contain DOM with distinct chemical properties and have unique Xuorescent Wngerprints. DOM inputs to streams from the four soil types therefore have the potential to alter stream biogeochemical processes diVerently by inXuencing temporal patterns in stream heterotrophic productivity.