Simulated In-Stream CO₂ Production With Changing Precipitation and Urbanization

Abstract

Increasing urbanization coupled to changes in precipitation magnitude confound our understanding of the carbon (C) movement and transformation in streams. Precipitation drives organic C into waterways, while watershed urbanization can increase the lability of dissolved organic carbon (DOC). The uncertainty about how these disturbances interact and influence CO₂ production hinders predictions of the urban stream C cycle and strategies for reducing stream CO₂ efflux. To understand the effects of precipitation and urbanization on the C cycle in streams, we simulated CO₂ production across two Baltimore watersheds (Maryland, U.S.A.) that span an urbanization gradient using AquaMEND, a multipool C decomposition model coupled to stream geochemistry. We hypothesized that precipitation-driven C loading and urbanization-enhanced DOC lability boost in-stream CO₂ production more in urban streams than in exurban streams. Urban streams showed a greater shift in CO₂ production in response to precipitation-driven C loading, while CO₂ production in exurban streams responded more to urbanization-driven changes in DOC lability. Over all streams, increasing C loading due to precipitation had a stronger effect on CO₂ production than changes in DOC lability, and the highest CO₂ production resulted when these disturbances co-occurred. These results suggest a shift in primary drivers of stream metabolism as landscapes transition from exurban to urban, and highlight that urban streams have high CO₂ production potential. This study reveals how urbanization and precipitation-driven C dynamics interact to shape stream metabolic responses, and demonstrates the importance of incorporating precipitation variability and land use change into efforts to assess and mitigate stream CO₂ production.