Marine sediments represent a major carbon reservoir on Earth.Dissolved organic matter(DOM)in pore waters accumulates products and intermediates of carbon cycling in sediments.The application of excitation-emission mat...Marine sediments represent a major carbon reservoir on Earth.Dissolved organic matter(DOM)in pore waters accumulates products and intermediates of carbon cycling in sediments.The application of excitation-emission matrix spectroscopy(EEMs)in the analysis of subseafloor DOM samples is largely unexplored due to the redox-sensitive matrix of anoxic pore water.Therefore,this study aims to investigate the interference caused by the matrix on EEMs and propose a guideline to prepare pore water samples from anoxic marine sediments.The parameters determined by fluorescence spectra include 3D-index derived from EEMs after parallel factor analysis(PARAFAC),fluorescence index(FI)(contribution of terrigenous DOM),biological index(BIX)and humification index(HIX)derived from 2D emission spectra.First,we investigated the impacts of extensively-presented ions as typical electron acceptors,which are utilized by anaerobic microbes and stratified in marine sediments:Fe(II),Fe(III),Mn(II)and sulfide in anoxic pore water resulted in biases of fluorescent signals.We proposed threshold concentrations of these ions when the interference on EEMs occurred.Effective removal of sulfide from sulfide-rich samples could be achieved by flushing with N_(2)for 2 min.Second,the tests based on DOM standard were further verified using pristine samples from marine sediments.There was a significant change in the fluorescence spectra of DOM in anoxic sediments from the Rhône Delta.This study demonstrated that the change was caused by oxidation of the matrix rather than the intrinsic alteration of DOM.It was confirmed by extracted DOM via both EEMs analysis and Fourier transform ion cyclotron resonance mass spectrometry(FT-ICR-MS).Slight oxidation of sulfur-containing compounds(e.g.,sulfhydryl)and polyphenol-like compounds occurred.Finally,a sample preparation sequence is proposed for pore water from anoxic sediments.This method enables measurement with small volumes of the sample(e.g.,50µL in this study)and ensures reliable data without the interference of the redox-sensitive matrix.This study provides access to the rapid analysis of DOM composition in marine sediments and can potentially open a window into examining the carbon cycling of the marine deep biosphere.展开更多
Landscape urbanization broadly affects ecosystems in coastal watersheds, but, until now, the influence of nonpoint source urban inputs on dissolved organic matter (DOM) amount, composition, and source is poorly unders...Landscape urbanization broadly affects ecosystems in coastal watersheds, but, until now, the influence of nonpoint source urban inputs on dissolved organic matter (DOM) amount, composition, and source is poorly understood. To understand how DOM composition varied with urbanization, fluorescence excitation-emission matrices (EEMs) were determined for urban and non-urban waters from upstream to downstream sites along three adjacent coastal watersheds that flow into the Mediterranean Sea. Two humic DOM fluorescent components (humic-like and fulvic-like peaks) and two proteinic components (tyrosine-like and tryptophane-like peaks) were identified by EEM fluorescence. The results indicated that urbanization had an important influence on DOM concentration and composition, with urban waters having a high degree of DOM variation due to different land uses surrounding each body of water. Urban waters show a higher DOM fluorescence index (FI), the highest fluorescence intensity of protein-like manifested also by BIX values, and a lower value of the humification index (HIX) than non-urban waters which were dominated by allochthonous inputs. In addition, the EEM was compared in dry and wet season where higher DOM amounts and FI appeared in summer due to autochthonous production coming from algae growth compared to allochthonous input from rainfall dominated in wet season. The concentration of DOC increased from upstream to downstream for the three rivers, especially Beirut River. The increase in DOC values was observed in both dry and wet seasons by 39 and 19 times respectively compared to upstream (0.93 - 0.91 mgC/L).展开更多
基金The European Union’s Seventh Framework Programme—Ideas Specific Programme under contract No.247153(Advanced Grant DARCLIFEPrincipal Investigator,K.-U.)+2 种基金the Fund of the Deutsche Forschungsgemeinschaft through the Research Center/Excellence Cluster MARUM—Center for Marine Environmental Sciences,Project GB2the Fund of China Scholarship Councilthe Fund of Bremen International Graduate School for Marine Sciences.
文摘Marine sediments represent a major carbon reservoir on Earth.Dissolved organic matter(DOM)in pore waters accumulates products and intermediates of carbon cycling in sediments.The application of excitation-emission matrix spectroscopy(EEMs)in the analysis of subseafloor DOM samples is largely unexplored due to the redox-sensitive matrix of anoxic pore water.Therefore,this study aims to investigate the interference caused by the matrix on EEMs and propose a guideline to prepare pore water samples from anoxic marine sediments.The parameters determined by fluorescence spectra include 3D-index derived from EEMs after parallel factor analysis(PARAFAC),fluorescence index(FI)(contribution of terrigenous DOM),biological index(BIX)and humification index(HIX)derived from 2D emission spectra.First,we investigated the impacts of extensively-presented ions as typical electron acceptors,which are utilized by anaerobic microbes and stratified in marine sediments:Fe(II),Fe(III),Mn(II)and sulfide in anoxic pore water resulted in biases of fluorescent signals.We proposed threshold concentrations of these ions when the interference on EEMs occurred.Effective removal of sulfide from sulfide-rich samples could be achieved by flushing with N_(2)for 2 min.Second,the tests based on DOM standard were further verified using pristine samples from marine sediments.There was a significant change in the fluorescence spectra of DOM in anoxic sediments from the Rhône Delta.This study demonstrated that the change was caused by oxidation of the matrix rather than the intrinsic alteration of DOM.It was confirmed by extracted DOM via both EEMs analysis and Fourier transform ion cyclotron resonance mass spectrometry(FT-ICR-MS).Slight oxidation of sulfur-containing compounds(e.g.,sulfhydryl)and polyphenol-like compounds occurred.Finally,a sample preparation sequence is proposed for pore water from anoxic sediments.This method enables measurement with small volumes of the sample(e.g.,50µL in this study)and ensures reliable data without the interference of the redox-sensitive matrix.This study provides access to the rapid analysis of DOM composition in marine sediments and can potentially open a window into examining the carbon cycling of the marine deep biosphere.
文摘Landscape urbanization broadly affects ecosystems in coastal watersheds, but, until now, the influence of nonpoint source urban inputs on dissolved organic matter (DOM) amount, composition, and source is poorly understood. To understand how DOM composition varied with urbanization, fluorescence excitation-emission matrices (EEMs) were determined for urban and non-urban waters from upstream to downstream sites along three adjacent coastal watersheds that flow into the Mediterranean Sea. Two humic DOM fluorescent components (humic-like and fulvic-like peaks) and two proteinic components (tyrosine-like and tryptophane-like peaks) were identified by EEM fluorescence. The results indicated that urbanization had an important influence on DOM concentration and composition, with urban waters having a high degree of DOM variation due to different land uses surrounding each body of water. Urban waters show a higher DOM fluorescence index (FI), the highest fluorescence intensity of protein-like manifested also by BIX values, and a lower value of the humification index (HIX) than non-urban waters which were dominated by allochthonous inputs. In addition, the EEM was compared in dry and wet season where higher DOM amounts and FI appeared in summer due to autochthonous production coming from algae growth compared to allochthonous input from rainfall dominated in wet season. The concentration of DOC increased from upstream to downstream for the three rivers, especially Beirut River. The increase in DOC values was observed in both dry and wet seasons by 39 and 19 times respectively compared to upstream (0.93 - 0.91 mgC/L).
