New Insights in Soil Hydrology of Forests

(ETH Zurich, May 29, 2025)

Researchers at ETH Zurich, led by Dr. Marius G. Floriancic, have discovered that two-thirds of the water stored in forest soils at a depth of just ten centimeters is over three weeks old, challenging previous beliefs about forest water turnover. This finding reveals that soils mainly hold water for months or years, not just the "new water" from recent rainfall, highlighting the "old water's" crucial role in supporting forests and affecting water cycles. The team set up an outdoor lab in a forest near the ETH Hönggerberg campus and used custom equipment to track water dynamics. By placing sensors in trees, soil, and a stream and analyzing samples of stable isotopes in soil water weekly for five years, they uncovered new details about the age, source, and path of the water samples. This work not only proves "old water" exists in soil but also deepens our understanding of the soil-plant-atmosphere relationship. ETH Zurich's innovative approach lays the groundwork for further studies on water movement, providing essential information for environmental science and forest management.