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. The majority of the CO₂ degassed from freshwaters comes from the decomposition of allochthonous leaf litter inputs. Rates of decomposition, and thus CO₂ degassing, should increase with rising water temperature. 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 3000 records of leaf litter decomposition from 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 plant 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?