Effects of Soil Composition on Leaf Tannins in Water

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Tannins are polyphenolic biomolecules found in the leaves of most plants and play a role in protecting them from herbivory and pathogens. When tree leaves fall into water, tannins leach out of the leaves into the water. This can negatively affect aquatic organisms. While there has been some research on the effects of tannins on living organisms, its interaction with soil in aquatic ecosystems is poorly understood. In our research, our goal was to determine whether wetland soils affect tannin concentration in water over time and what components of soil are most important. To answer this, we performed two experiments by placing different soil types into jars with water containing dissolved tannins. We used two wetland soils in the first experiment and used clay, silt, and fine and coarse sand in the second. After taking water samples through time and analyzing tannin concentrations, we found tannins decreased the most with the wetland, silt, and clay soils. In the jars with fine and coarse sand, the decrease did not significantly differ from the control, which had no soil. Because the presence of soil with clay or silt led to a greater decrease in tannins than without, tannins are likely binding to the soil particles. Since most ponds have these soils, these areas are likely to have lower concentrations of tannins. This research tells us that aquatic organisms may be less affected by tannins in water with clay and silt soils.