Resiliency of Silica Export Signatures When Low Order Streams Are Subject to Storm Events

Silicon stable isotope ratios ((Formula presented.) ³⁰Si) of over 150 stream water samples were measured during seven storm events in six small critical zone observatory (CZO) catchments spanning a wide range in climate (sub-humid to wet, tropical) and lithology (granite, volcanic, and mixed sedimentary). Here we report a cross-site analysis of this dataset to gain insight into stream (Formula presented.) ³⁰Si variability across low-order catchments and to identify potential climate (i.e., runoff), hydrologic, lithologic, and biogeochemical controls on observed stream Si chemical and isotopic signatures. Event-based (Formula presented.) ³⁰Si exhibit variability both within and across sites (−0.22‰ to +2.27‰) on the scale of what is observed globally in both small catchments and large rivers. Notably, each site shows distinct (Formula presented.) ³⁰Si signatures that are preserved even after normalization for bedrock composition. Successful characterization of observed cross-site behavior requires the merging of two distinct frameworks in a novel combined model describing both non-uniform fluid transit time distributions and multiple fractionating pathways in application to low-order catchments. The combined model reveals that site-specific architecture (i.e., biogeochemical reaction pathways and hydrologic routing) regulates stream silicon export signatures even when subject to extreme precipitation events.