Origin and fate of dissolved organic matter in the subsoil driven by dynamic exchange and remobilization processes

点击翻译按钮获取中文摘要

Results obtained so far from the subsoil observatories and sequential column experiments indicate a cascade of sorption-desorption processes of dissolved organic matter (DOM) on soil minerals while travelling to the subsoil. Further, results suggest that the sorption capacity of the subsoil is limited, possibly due to high C loading of the reactive minerals in the sandy soil. We assume that the microbial activity might depend on the C loading of the minerals controlling remobilization processes, in addition to the composition of organic matter (OM) on mineral surfaces. Consequently, in the second phase we will address the complex interplay of continuous sorption processes combined with microbial processes and subsequent remobilization depending on source and composition of OM and surface characteristics of the mineral phase. We hypothesize that (i) the composition of DOM entering the mineral soil affects exchange/remobilization processes stronger in the upper part of the soil than deeper subsoil due to an increased microbial processing with increasing soil depth, (ii) the exchange/remobilization of sorbed OM increases with increasing C loading of the minerals, and (iii) microbial transformation of mineral-associated OM is an important source of DOM in larger soil depths. We will approach these hypotheses by a set of experiments starting from complex field conditions to controlled laboratory approaches. The field approaches include a DO13C switch-off pulse in the Grinderwald observatories and a DO13C injection experiment at Grinderwald and two regional sites to study the fate of DOM of different source and composition in the subsoil depending on mineralogical properties and microbial activity. In a comparative way, sorption capacity, C loading, spatial C distribution, C exchange, and OM composition and decomposability (the latter determined by P6) on mineral surfaces will be related to source, composition, C exchange, and microbial stability of DOM. A similar analytical approach will be performed in flow cell experiments, where under defined boundary conditions transport, sorption, and mineralization of the applied DO13C will be assessed. Finally, in a laboratory column experiment with 13C-labeled DOM the effects of microbial activity, manipulated by different incubation temperatures, on the translocation of DOM by sorption and exchange/remobilization processes depending on the mineral surface properties will be studied. With that P5 focuses on the central hypothesis 3 of the frame proposal but also addresses hypotheses 2. P5 will deliver crucial data for the integrative modeling of OC in subsoils such as DOC and DO13C concentration and fluxes, DOM stability against microbial decay, sorption capacity and C loading of the soils and, therefore, for testing the central hypothesis 5.