How multiple stressors interact and affect leaf decomposition in freshwaters.

Graciela Medina Madariaga, Verónica Ferreira, Roshni Arora, India Mansour, Gwendoline M. David, Sonja C. Jähnig, Fengzhi He

This is a plain language summary of a Functional Ecology research article which can be found here.

Different stressors can affect ecological functions in freshwater ecosystems, such as the rate at which leaves decompose after falling into the water. The effects of individual stressors on leaf decomposition have been well investigated. For example, increased temperature tends to accelerate the decomposition of leaves in freshwaters. Other stressors, such as insecticides or fungicides, might slow down leaf decomposition in freshwaters because they negatively affect organisms that facilitate leaf decomposition. Despite an increase in research efforts, there is still much to uncover regarding how different stressors interact and affect leaf decomposition in freshwaters. Leaf decomposition processes are not only influenced by different stressor combinations, but also by other elements, such as types of leaves, the involvement of aquatic invertebrates that feed on leaves, and the type of water bodies (running or standing waters) where the decomposition occurs.

Conceptual overview of factors affecting the process of leaf decomposition in freshwaters. The central inner circle represents the organisms that could affect the process of leaf litter decomposition, while the outer semicircle shows examples of stressors that can affect the decomposition of leaves. Note that leaf litter can originate from plants that may have different properties and affect the process too (Credit: the authors)

We investigated the data from 27 different experiments where researchers deliberately introduced two different stressors simultaneously to observe their combined effects on decomposition processes of leaves in freshwaters. These stressors include increased temperature, elevated concentrations of nutrients and fine sediment in water, altered flow velocity, and the addition of pollutants. What we found was intriguing. In individual observations, the combined effects of both stressors were often equal to the sum of individual stressor effects. However, when combining data from all observations, the overall effect of multiple stressors turned out to be less severe than simply adding up the individual effects. In addition, the interactions between different stressors were influenced by the involvement of aquatic invertebrates in leaf decomposition processes and the type of water bodies. For example, the combined effect of multiple stressors was more likely to be less severe than the sum of the individual stressor effects in running waters or when aquatic invertebrates participated in leaf decomposition. Our findings highlight the importance of considering interactions between different stressors when designing and implementing conservation and restoration actions. More studies are needed to investigate the influence of biotic interactions on multiple-stressor effects, which could facilitate the development of effective management strategies for freshwater ecosystems.