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

Sediment respiration in streams/rivers impacts global biogeochemical cycles, yet is mostly studied under perennially-inundated conditions despite all river corridors having variably inundated areas and most streams going dry each year. Previous experiments observed sediment rewetting to cause elevated or suppressed aerobic respiration, indicating variation across studies. To deepen understanding, we conducted 21-day wet/dry experiments with sediments from 64 streams spread across the contiguous United States. Here we show that drying and rewetting sediments from perennial and non-perennial streams had near-neutral effects or suppressed O 2 consumption rates. These biogeochemical cold moments contrast previous studies that observed hot moments. Sediment texture and microbial activity explained variation in responses to rewetting, but this did not reveal why some studies observed cold moments while others observed hot moments. To solve this we propose a unifying conceptual model whereby hot and cold moments exist simultaneously upon rewetting by considering both dry-state and perennially-inundated reference points.