Mass Loss: A Quantitative Synthesis of Leaf Decomposition in Streams and Rivers

Freshwater ecosystems play a significant role in the global carbon (C) cycle, emitting roughly 1.2 Pg C y/-1 to the atmosphere. Results from recent studies in freshwaters show that ecosystem respiration increases with elevated temperature faster than primary production. Hence, CO2 evasion is predicted to increase as global temperature rises. The majority of the CO2 degassed from heterotrophic streams and rivers comes from the decomposition of allochthonous leaf litter inputs. However, temperature is one of myriad intrinsic and extrinsic factors controlling decomposition. Through the Meta-Analysis and SynthesiS of Leaf decOmposition in StreamS (MASS LOSS) project, we have compiled over 1200 records of leaf litter decomposition from control treatments in streams and rivers located on 5 continents. With the goal of improved prediction of decomposition rate response to global change in mind, we are using this database to answer the following questions: What is the apparent activation energy of decomposition? Does it vary based on leaf bag mesh size or taxonomy? How much variation in decomposition is explained by temperature vs. other intrinsic (e.g., leaf chemistry) and extrinsic (e.g., stream order, macroinvertebrate density) factors? Do interactions exist? Are these patterns similar to those observed for terrestrial ecosystems