Integrating big data and a coordinated global field experiment, researchers have developed a model that can predict the decomposition rate of organic matter in rivers worldwide. The global model estimates decomposition rates in rivers across vast understudied areas of Earth, revealing rapid decomposition across continental-scale areas dominated by human activities. Earth's terrestrial ecosystems generate over 100 billion tons of plant detritus annually, with its fate – long-term storage, mineralization to greenhouse gasses, or incorporation into food webs – determined by decomposition rates. This organic material is continually added to rivers and streams. However, the factors that influence organic matter decomposition in rivers are poorly understood, particularly at large spatial scales and in tropical regions, where much of Earth's plant matter is produced. Accurate global carbon models require a mechanistic understanding of these processes to improve predictions and inform future environmental change scenarios.
To fill these knowledge gaps, Scott Tiegs and colleagues developed a predictive model for cellulose composition using global data from the CELLDEX experiment – a coordinated, distributed experiment on cellulose decomposition in rivers. The CELLDEX experiment investigated the decomposition of standard cotton fabric (as a proxy for plant detritus) in 514 sites across all 7 continents and each of Earth's major biomes. These findings were paired with detailed climate, soil, geology, vegetation, and physiochemical data to create a global, high-resolution predictive model of organic-matter decomposition in rivers. According to the authors, the model could accurately explain leaf-litter decomposition estimates from previously published studies. Tiegs et al. found that cellulose decomposition in rivers is significantly influenced by various environmental drivers, which are increasingly affected by human activities globally. Key human-influenced drivers of cellulose decomposition are temperature and nutrient loading, they say. As a result, ongoing environmental changes are likely to increase decomposition rates, leading to reduced short-term carbon storage in flowing waters and diminished carbon transport to long-term carbon storage sinks, such as reservoirs, floodplains, and oceans. "To further advance large-scale monitoring and assessment, we have made these modeling approaches accessible through an open-source online mapping tool," write the authors. "Application of the models to current and future environmental threats will enable scientists and natural-resource managers to forecast changes in the functioning of river networks at a planetary scale."
For reporters interested in trends, this study builds upon an October 2019 Science Advances study investigating the global patterns of carbon processing and ecosystem functioning in river ecosystems.
