Scaling of Riverine Biogeochemical Function with Watershed Size

This research first published in Nature Communications.

Researchers: W. Wollheim, T. harms, A. Robison, L. Koenig, A. Helton, C. Song, W. Bowden, J. Finlay

A recent study has revealed that the size of a watershed significantly influences a river network's pollution-filtering capabilities, shedding light on coastal areas affected by human development and providing insights into the intricate global carbon cycle.

Much like the circulatory system in the human body facilitates the movement of blood and the filtration of waste, Earth's river networks serve as vital conduits that help sustain the planet. A key function of rivers is to mitigate pollution from various sources such as roads, agriculture, and sewage systems before these contaminants reach ecologically sensitive downstream areas like estuaries and oceans.

Using a comprehensive model based on existing knowledge of stream and river dynamics, a team of researchers discovered that as the land area draining into an aquatic system expands, the rate of pollution filtration by rivers doesn't simply increase linearly—it accelerates even more due to the prevalence of larger rivers often associated with bigger watersheds. This phenomenon, termed "superlinear scaling," demonstrates that larger rivers disproportionately contribute to the pollution-filtering function of entire aquatic ecosystems, encompassing wetlands, rivers, streams, and lakes. This research, led by Wilfred Wollheim, professor of natural resources and the environment at UNH, provides valuable insights into the role of rivers in both pollution management and the global carbon cycle.

The study emphasizes the importance of managing land use and addressing non-point source pollution, such as agricultural runoff carrying harmful chemicals, in smaller watersheds. This focus aims to reduce pollution reaching estuaries and coastal areas, where the opportunity for filtration is limited. The findings also illuminate the role of rivers in the carbon cycle, suggesting that larger watersheds may release carbon back into the atmosphere, in contrast to smaller watersheds where this process is less evident. The research team hopes that their insights into aquatic ecosystem behavior and river dynamics will inform effective pollution management strategies and contribute to a better understanding of the intricate relationship between Earth's ecosystems, the atmosphere, and the rate of climate change.

This work was supported by the National Science Foundation. Partial support was provided by the New Hampshire Agricultural Experiment Station through USDA National Institute of Food and Agriculture Hatch Project 0225006.

Key Findings

Recent research shows that the pollution-filtering efficiency of river networks is heavily tied to the size of their watersheds, revealing implications for estuaries and coastal areas impacted by human development and enhancing our grasp of the global carbon cycle.