Organic matter transformations are disconnected between surface water and the hyporheic zone

[摘要] Biochemical transformations of organic matter (OM) are a primary driver of river corridor biogeochemistry, thereby modulating ecosystem processes atlocal to global scales. OM transformations are driven by diverse biotic and abiotic processes, but we lack knowledge of how the diversity of thoseprocesses varies across river corridors and across surface and subsurface components of river corridors. To fill this gap we quantified the numberof putative biotic and abiotic transformations of organic molecules across diverse river corridors using ultra-high-resolution massspectrometry. The number of unique transformations is used here as a proxy for the diversity of biochemical processes underlying observed profilesof organic molecules. For this, we use public data spanning the contiguous United States (ConUS) from the Worldwide Hydrobiogeochemical ObservationNetwork for Dynamic River Systems (WHONDRS) consortium. Our results show that surface water OM had more biotic and abiotic transformations than OMfrom shallow hyporheic zone sediments (1–3  cm depth). We observed substantially more biotic than abiotic transformations, and the numbers of bioticand abiotic transformations were highly correlated with each other. We found no relationship between the number of transformations in surface waterand sediments and no meaningful relationships with latitude, longitude, or climate. We also found that the composition of transformations insediments was not linked with transformation composition in adjacent surface waters. We infer that OM transformations represented in surface waterare an integrated signal of diverse processes occurring throughout the upstream catchment. In contrast, OM transformations in sediments likelyreflect a narrower range of processes within the sampled volume. This indicates decoupling between the processes influencing surface water andsediment OM, despite the potential for hydrologic exchange to homogenize OM. We infer that the processes influencing OM transformations and thescales at which they operate diverge between surface water and sediments.

[学科分类] 大气科学