Toward a universal model of hyporheic exchange and nutrient cycling in streams

Transformation and removal of dissolved nutrients and pollutants in streams strongly depends on microbial processes in streambed sediments. The contact between these solutes and microbial communities is mediated by the physical transport from the bulk stream to, and through, the streambed, a process broadly referred to as hyporheic exchange. Even though multiple physical and biological processes influence the rate of hyporheic exchange, we here show that many hyporheic exchange mechanisms can be represented simply as a one‐dimensional diffusion process, where the diffusion coefficient decays exponentially with depth into the streambed. This framework is applied to a classic study of nitrate removal in 72 headwater streams across the United States, showing how the interplay among land‐use, stream physics, and stream biology collectively influence nutrient transformation in streambeds. The proposed modeling framework can help the upscaling of hyporheic exchange and promote better understanding of its role for processing and removal of contaminants in streams.