Drying and Rewetting of Riverbed Sediments Cools Rather Than Boosts Respiration

Riverbed sediments that dry out and are rewetted generally show neutral or suppressed oxygen consumption rather than the respiration surges reported in many earlier experiments, according to a study published in Communications Earth & Environment. The finding, drawn from sediments collected at 64 streams across the contiguous United States, challenges the assumption that rewetting reliably triggers a burst of microbial carbon processing in stream and river beds.

Sediment respiration in streams and rivers is a key component of global biogeochemical cycles, yet most research has been conducted under perennially inundated conditions. In reality, every river corridor contains areas that are variably inundated, and most streams go dry at some point each year. How these drying sediments behave when water returns therefore matters for understanding carbon and nutrient fluxes at broad scales.

The research team, led by Vanessa Garayburu-Caruso of Pacific Northwest National Laboratory and colleagues, carried out 21-day wet/dry experiments with sediments from both perennial and non-perennial streams. The design allowed them to measure aerobic respiration, indexed by O2 consumption rates, across controlled drying and rewetting cycles under standardized laboratory conditions.

The results showed that drying and rewetting sediments from both stream types had near-neutral effects or suppressed O2 consumption. The authors describe these responses as biogeochemical cold moments, in contrast to the hot moments of elevated respiration that previous studies had observed after rewetting. Earlier experiments had variously found that rewetting caused either elevated or suppressed aerobic respiration, indicating substantial variation across studies.

To explain that variation, the team examined sediment properties and microbial activity. Sediment texture and microbial activity explained some of the differences in how sediments responded to rewetting, but this alone did not reveal why some studies had recorded hot moments while others recorded cold moments.

To resolve the discrepancy, the authors propose a unifying conceptual model in which hot and cold moments exist simultaneously upon rewetting. The key insight is a matter of reference points: comparing post-rewetting respiration against the dry state can indicate a hot moment, while the same rates measured against a perennially inundated baseline can indicate a cold or neutral response. The apparent contradictions among studies may therefore reflect differences in what each experiment treats as its starting condition, rather than fundamentally different sediment behavior.

The study’s scope is deliberately broad, spanning 64 streams across the contiguous United States and encompassing both perennial and non-perennial systems, which strengthens its representativeness compared with single-site experiments. The experiments were conducted over 21-day laboratory cycles, so they capture controlled drying and rewetting responses rather than the full complexity of natural stream corridors.

The authors caution that while texture and microbial activity account for variation in rewetting responses within their experiments, the mechanisms determining when a given sediment will show suppression versus neutral response remain unresolved. The proposed conceptual model is presented as a framework for reconciling conflicting results across the literature and for guiding future tests of when rewetting events accelerate or dampen sediment respiration in drying river networks.

Subject of Research: Biogeochemical responses of streambed sediments to drying and rewetting

Article Title: Drying and rewetting of riverbed sediments results in cold to neutral biogeochemical moments

Article References: Garayburu-Caruso, V., Laan, M., Coulson, L., Delgado, D., Forbes, B., Goldman, A., McKever, S., Renteria, L., Rod, K., Veach, A., Vergara, M., & Stegen, J. (2026). Drying and rewetting of riverbed sediments results in cold to neutral biogeochemical moments. Communications Earth & Environment. https://doi.org/10.1038/s43247-026-04081-y

Image Credits: AI Generated

DOI: 10.1038/s43247-026-04081-y

Keywords: riverbed sediments, rewetting, biogeochemistry, sediment respiration, non-perennial streams, aerobic respiration, microbial activity, hot moments, cold moments, oxygen consumption, Drying, riverbed