The effects of ultraviolet and visible radiation on dissolved organic carbon-iron interactions in south central Ontario streams: Particulate carbon and iron formation, spectrofluorometric signatures and iron lability.

摘要

This study examines the effects of solar radiation on dissolved organic carbon - iron interactions in South-Central Ontario streams. The goals of the study were threefold: (1) assess photo-chemical formation of colloidal and particulate organic carbon (COC and POC) in boreal streams and the role of iron in their formation, (2) evaluate differences in dissolved organic matter (DOM) spectrofluorometric signatures from streams draining a range of land use types and investigate the effects of irradiation on those signatures as well as degree of saturation of bound Fe, and (3) assess Fe lability in boreal streams.; Wet chemical analysis of carbon and iron as well as environmental scanning electron microscopy (ESEM) coupled with energy dispersive spectroscopy (EDS) were used to detect shifts of Fe and C from dissolved to particulate phases and to obtain POC/Fe ratios from artificially formed particulate matter. The ratios were comparable to Dorset lake mass balance ratios of retained POC/Fe, which suggests that the mechanism in the laboratory is similar to the dominant in situ mechanism in lakes. Furthermore, the addition of amorphous Fe post-irradiation resulted in greater POC-PFe ratios.; The spectrofluorometric signatures investigated included 3-D excitation-emission matrices (EEMs), peak intensities, peak wavelength shifts, a fluorescence index (FI) and fluorescence integrated over the 3-D matrix. Peak fluorescence excitation and emission wavelengths as well as Fl best distinguished DOM from the various sources. The results suggested that DOM from the boreal streams was of a higher molecular weight and more complex than that of urban streams. The greatest photolytic DOC losses occurred in the boreal streams, but were not correlated with integrated fluorescence losses. The addition of Fe resulted in significant fluorescence quenching while NaF amendments did not increase fluorescence, suggesting that Fe is tightly bound to stream DOM.; To assess Fe lability, dialysis experiments were used. Irradiation with UV-visible radiation resulted in increased Fe lability compared to the dark controls in the boreal stream. Significant Fe lability in stream water was demonstrated for visible wavelengths between 400 and 550 nm, but not above 550 nm, indicating that wavelengths greater than 400 nm play a significant role.