Abstract
Carbon cycling in rivers is altered by the creation of impoundments through dam construction. This paper seeks to identify the source and composition of dissolved organic matter (DOM) in both water and sediment in Lake Longjing by contrasting the optical characterization of DOM. By comparing the dissolved organic carbon (DOC) concentrations, we show that the sediment (53.7 ± 16.6 mg/L) acts as a DOC source to the overlying water (23.1 ± 1.4 mg/L). The estimated DOC flux in the original reservoir region (88.3 mg m−2 d−1) is higher than that in the newly submerged region (26 mg m−2 d−1), whereas the latter has larger contribution to the DOC annual load because of its larger sediment area. Spectroscopic analysis suggested that pore waters had higher aromaticity and lower proportion of fresh DOM than those in surface waters and benthic overlying waters. Through Parallel Factor Analysis, four fluorescent components were identified, i.e., two terrestrial humic-like components, one protein-like, and one microbial humic-like. Spearman correlation and Non-Metric-Multidimensional Scaling (NMDS) analysis manifested that fluorescent DOM in surface sediments is mainly contributed by autochthonous source, the others by allochthonous source. Due to the high sensitivity of the fluorescent intensity of the protein-like component, it is a useful indicator to reveal the changes of source of DOM.
Highlights
Worldwide construction in dams has occurred at a rapid pace over the past several decades such that approximately 50% of river water is directly or indirectly controlled by reservoirs before reaching an ocean [1,2]
The optical properties of dissolved organic matter (DOM) in SWs, OWs and PWs of a nascent river-type lake were explored through five optical indicators and four fluorescence components
Fluxes in original reservoir were higher than that in newly submerged region, while newly submerged region contributes the main portion of dissolved organic carbon (DOC) release, accounting for 74% of the DOC annual load
Summary
Worldwide construction in dams has occurred at a rapid pace over the past several decades such that approximately 50% of river water is directly or indirectly controlled by reservoirs before reaching an ocean [1,2]. Dam reservoirs inevitably break the connectivity of rivers and become an increasingly important component of inland waters [3]. Compared with natural fluvial ecosystem, the aquatic habitat of reservoirs has changed, characterized by longer water retention time, slower flow rate and stronger sediment retention ability. This leads to alterations of the source and composition of organic matters in water bodies [4]. As a central constituent of carbon cycle, dissolved organic matter (DOM) in sediments plays a key role in the transport and transformation of xenobiotics [5,6,7]. Changes in DOM quality and origin affect sediment microbial communities along the river continuum [8]
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