Climate variability affects a vital ecosystem function: Long-term perspective on leaf decomposition in the Ogeechee River

Leaf-litter decomposition in stream ecosystems is an important component of the energy and nutrient cycle, representing a food source for aquatic organisms. As such, this process represents a tool for assessing long-term stream responses to disturbance that are brought about by changes in the assemblage of macroinvertebrates that colonize leaf packs. We used 5 y (2013–2017) of leaf-litter decomposition data at the Ogeechee River, Georgia, USA, following a 3-y drought period (2010–2012) to assess the effects of climatic variability, and the associated macroinvertebrate community, on the decomposition process. We predicted that climate variability, specifically drought and flood disturbances, would have an impact on the decomposition process and that stream temperature, stream discharge, and relative abundance of the shredder functional feeding group would drive these changes. Additionally, we predicted these disturbances would negatively affect macroinvertebrate abundance and richness. This study identified changes in the rate of decomposition in a post-drought year (2013) and the subsequent years that were explained by fluctuations in temperature, discharge, and potentially shredder abundance. Additionally, we detected a shift in species composition after the post-drought year into a more stable period, alluding to a lag effect in species richness. These results illustrate that we can predict an increase in decomposition rates during disturbance events, especially drought, as well as a decrease in both abundance and richness of colonizing macroinvertebrates. These findings underscore the vulnerability of key ecosystem processes to climate-driven disturbances, suggesting that shifts in decomposition dynamics and macroinvertebrate communities during drought may compromise nutrient cycling and biological integrity in freshwater systems. By linking long-term patterns to disturbance regimes, this work informs predictive frameworks for stream management under future climate scenarios and highlights the need for integrative monitoring approaches that capture both functional and biodiversity metrics.