Transport and humification of dissolved organic matter within a semi-arid floodplain
Wenming Dong , Jiamin Wan , Tetsu K. Tokunaga , Benjamin Gilbert , Kenneth H. Williams
DOI:10.1016/j.jes.2016.12.011
Received August 26, 2016,Revised November 16, 2016, Accepted December 06, 2016, Available online December 29, 2016
Volume 29,2017,Pages 24-32
In order to understand the transport and humification processes of dissolved organic matter (DOM) within sediments of a semi-arid floodplain at Rifle, Colorado, fluorescence excitation–emission matrix (EEM) spectroscopy, humification index (HIX) and specific UV absorbance (SUVA) at 254 nm were applied for characterizing depth and seasonal variations of DOM composition. Results revealed that late spring snowmelt leached relatively fresh DOM from plant residue and soil organic matter down into the deeper vadose zone (VZ).More humified DOM is preferentially adsorbed by upper VZ sediments, while non- or less-humified DOM was transported into the deeper VZ. Interestingly, DOM at all depths undergoes rapid biological humification process evidenced by the products of microbial by-product-like(i.e.,tyrosine-likeandtryptophan-like)matterinlatespringandearlysummer, particularly in the deeper VZ, resulting in more humified DOM (e.g., fulvic-acid-like and humic-acid-like substances) at the end of year. This indicates that DOM transport is dominatedbyspringsnowmelt,andDOMhumificationiscontrolledbymicrobialdegradation, with seasonal variations. It is expected that these relatively simple spectroscopic measure-ments (e.g., EEM spectroscopy, HIX and SUVA) applied to depth- and temporally-distributed pore-water samples can provide useful insights into transport and humification of DOM in other subsurface environments as well.
