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Assessing anthropogenic effects on fungal decomposer communities along land use gradients of the Deschutes River system

  • Daniel Gilberts, The Evergreen State College 

  • 2022

Fungi initiate the breakdown of organic carbon in rivers and streams, but little work has been done to understand their responses to anthropogenic effects in freshwater environments. This study focuses on how fungal decomposers of leaf litter, specifically hyphomycetes, in the Deschutes River system in western Washington respond to differences in chemical inputs and proximity to human influence. Past work has focused on assessment of hyphomycetes in disturbed areas such as canals, urban water ways, and streams affected by mining tailings. The present study will directly compare relatively undisturbed areas to those with strong anthropogenic changes within the same watershed, represented by unique chemical inputs. In addition, profiles of hyphomycetes that have a direct relationship with the quality and palatability of leaf litter have not been analyzed in this system.

This project will compare fungal communities and identify which organisms and decompositional pathways are more resilient, and which are more directly impacted by various human activities. Twelve sites have been selected to represent four site types: 1) in forested areas with limited human influence, 2) near agricultural inputs of pesticides and nutrients (nitrogen and phosphorus), 3) along sections of urban stretches with industrial inputs of E.coli and coliform bacteria and the heavy metals zinc and copper, and 4) at lakes that are fed by the river and experience eutrophication. To determine variations in fungal populations and their response to disturbance, we propose to conduct conidia identification, colony isolation, metagenomic sequencing, and profiles of primary decomposers recruited onto leaf bait replicates of three species of plants (Salix, Alnus, and Quercus) that are found along the full stretch of the Deschutes River. Fungal profiles for each site and their relationship to river flow velocity, pH, conductivity, water temperature, dissolved oxygen, presence of E. coli or coliform bacteria, nitrogen levels, and phosphorus concentrations will also be analyzed. Our fungal community data will also dovetail with an invertebrate monitoring program by residents along the Deschutes River system, which was launched due to concern about the health of this habitat and contamination in and along its waters. Aquatic invertebrates are another indicator of healthy decomposition processes in riparian habitats.

The overarching goal of this study is to improve and inform our approaches to ecological restoration. By comparing site data that directly isolates anthropogenic inputs, the study will help determine if and how this anthropogenic disturbance affects fungal community structure and function. This in turn may impact decomposition rates and hinder carbon exchange within the system, impacting all biological processes downstream. Identification of these zones can be used to determine restoration goals for improving water quality parameters and enhancing hyphomycete decomposer biodiversity as part of a holistic approach to ecological restoration.