Optical And Molecular-level Changes In The DOM In Cow Dung And Soil In Tianjin

Fluorescence?excitation-emission matrix,EEM?spectroscopy in combination with parallel factor?PARAFAC?i.e.EEM-PARAFAC modelling and FTIR were applied to characterize and isolate the DOM in raw cow dung along with degraded cow dung under the sunlight and dark conditions,as well as different types of soil.FTIR was applied to identify the function groups in the DOM in cow dung,processed cow dung and soil.EEM-PARAFAC modelling along with FTIR spectra suggested that tyrosine was the only key DOM component detected in the raw cow dung.Relatively high contents of NH₄⁺compared to those of NO₃^–are susceptible to subsequent production of NO₃^–from NH₄⁺through nitrification whilst NH₄⁺may originate from microbial degradation of organic nitrogen in tyrosine.EEM-PARAFAC modelling also demonstrated that extracellular polymeric substances were produced in cow dung upon exposure to sunlight and dark incubation,which subsequently produce humic-like substances in water.Based on the results obtained in this study,humification mechanism was extensively discussed with providing a conceptual model.From the results of different types of soil analyses,it was shown that humic acids were completely decomposed in drying affected soils compared to other types of soils.This study therefore indicates that high contents of tyrosine in cow dung and its humification processes could be useful information for better understanding of various applications of cow dung.This study also indicates that drying effects on soil DOM in Tianjin is taken place in different types of soil.