Effects of vegetation types on water-extracted soil organic matter (WSOM) from riparian wetland and its impacts on riverine water quality: Implications for riparian wetland management

Abstract

Riparian wetlands play important roles in the enhancement of water quality by controlling nonpoint source pollution and protecting aquatic ecosystems. In the present study, we surveyed and identified vegetation types in riparian wetlands, evaluated how vegetation types influence spatial patterns of water-extracted soil organic matter (WSOM) from riparian wetland, and probed the impacts of riparian fluorescent WSOM on fluorescent dissolved organic matter (FDOM) and water trophic states in river ecosystems. We used absorption and excitation-emission-matrix (EEM) fluorescence spectroscopy to characterize the optical properties of riparian WSOM and riverine DOM from Chongming Island, China, the largest alluvial plain island in the world. Our results showed that fifty-eight spermatophytes in riparian wetland were clustered into five vegetation types, including warm coniferous forest (WCF), deciduous broad leaf forest (DBF), evergreen broad leaf forest (EBF), aquatic plants (AP) and herbaceous plants (HP). Absorption spectra revealed the effects of vegetation types on riparian chromophoric WSOM quantity. Although no difference in water-extracted soil organic carbon (WSOC) contents was observed, deciduous broad leaf forest (DBF) and evergreen broad leaf forest (EBF) fed more fluorescent WSOM quantity than did the other vegetation (AP, HP and WCF), and deciduous broad leaf forest (DBF) and aquatic plants (AP) provided more humic-like (RC.1 and RC.2) and fulvic-like (RC.3) substances into riparian wetland (P<0.05 or P<0.01). In addition, we noted that humic-like and protein-like substances (RC.4) transported from riparian wetland into a river water body, and riverine terrestrial-originated components (FC.1 and FC.2) were significantly related to the four riparian fluorescent WSOM components (P<0.05). Furthermore, the riverine trophic state was significantly higher when the fluvial DOM and its component quantity increased (P<0.05). We concluded that riparian wetland can control the quantity and quality of riparian WSOM and reshaped riverine DOM compositions and riverine water quality with important management implications.