Impacts of land use patterns and typhoon-induced heavy rainfall event on dissolved organic matter properties in the South Tiaoxi River, China

Stream samples were collected from 16 subcatchments of the South Tiaoxi River, East China, before and after incidence of Typhoon Fitow in October 2013. Dissolved organic carbon (DOC) and dissolved organic nitrogen (DON), spectroscopic indices (i.e., specific ultraviolet absorbance at 254 nm, SUVA254; spectral slope ratio, SR; fluorescence index, FI; humification index, HIX), fluorescence excitation emission matrix spectroscopy in combination with parallel factor analysis (EEMs-PAR-AFAC) were applied to assess how extreme storm altered the amount and composition of dissolved organic matter (DOM). DOM properties between pre- and post-storm were significantly distinguished. The torm promoted increased DOC and DON concentrations respectively by 15 and 76 %. The humic-like fluorescence intensities increased by 10 %, and the fluorescence intensities of tyrosine-like substances increased while these of tryptophan-like substances decreased. Moreover, the DOM quality in streams shifted to higher HIX and SUVA254 but lower SR and FI. In addition, 16 subcatchments were clustered into four groups according to the dominated land use types. Principal component analysis (PCA) revealed that the differences in DOM properties among subcatchments were associated with the dominated land use types during storm. Our findings suggested that elevated DOC and DON concentration were associated with the proportion of residential area and planted forest land (Phyllostachys praecox), respectively. Humic-like materials were related to the proportion of native forest land and cropland, while protein-like components were associated with planted forest land. Extreme storm events will strengthen the linkage between terrestrial and aquatic ecosystems and further alter DOM in both quantity and quality in headwater streams, which is also associated with land use types in the watershed.