Allometric scaling of hyporheic respiration across basins in the Pacific Northwest USA

Abstract

Hyporheic zones regulate biogeochemical processes in streams and rivers, but high spatiotemporal heterogeneity makes it difficult to predict how these processes scale from individual reaches to river basins. Recent work applying allometric scaling (i.e., power-law relationships between size and function) to river networks provides a new paradigm to develop a scalable understanding of hyporheic biogeochemical processes. We used reach-scale hyporheic aerobic respiration estimates to explore allometric scaling patterns across two basins, and related these patterns to watershed characteristics. We found consistent scaling behaviors at lowest and highest exchange flux (HEF) quantiles, and consistent but HEF-dependent relationships to watershed elevation, precipitation, and land-cover. Our results also suggest variability of hyporheic respiration allometry for middle exchange flux quantiles, and in relation to land-cover. Our findings provide initial evidence that allometric scaling may be useful for predicting hyporheic biogeochemical dynamics across watersheds from reach to basin scales. Scientific Significance Statement:The hyporheic zone is a biogeochemical control point in streams and rivers, and processes like hyporheic respiration are important determinants of how watersheds move and process carbon and nutrients. However, the hyporheic zone is also characterized by high spatial heterogeneity, which makes it difficult to predict how hyporheic functions like respiration change across watersheds from reach to basin scales. This study applies allometric scaling theory, which suggests that function scales in a predictable way with size, to determine if hyporheic respiration scales with watershed area in two basins with contrasting watershed characteristics. We found some consistent patterns between basins that suggest allometric scaling of hyporheic respiration may be a tool for transferable knowledge of hyporheic function between basins, but also note some site-specific relationships may constrain the generalizability of this method to other regions and watersheds.