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

Abstract

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. © 2022. The Authors.