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Contributed Talk

Session: : Biogeochemistry: Biogeo Patterns Along Environmental Gradients 1

COS 207-4 - Decomposition rates across the Yakima River Basin co-vary with site characteristics

Wednesday, August 9, 2023
4:15 PM – 4:30 PM PDT
Location: B115
Abstract: Decomposition is a fundamental ecosystem process that drives nutrient cycling, impacts global climate, and informs stream functioning, yet is susceptible to physical and chemical perturbations and is therefore considered an ecological indicator. Previous research has found positive relationships between decomposition and site variables such as temperature and land use, although these are system-dependent, and there is a lack of understanding between decomposition and other metrics used to study ecosystem metabolism. Considering the current knowledge gap, our objectives were to 1) identify the spatial distribution of decomposition rates within a diverse basin and compare these to global rates; 2) compare decomposition rates to other metrics of ecosystem metabolism to determine if they are under similar controlling mechanisms; and 3) determine what site characteristics co-vary with decomposition. We conducted a field study in the summer of 2022 across the Yakima River Basin (YRB; Washington, USA); the YRB encompasses a diversity of stream orders (2-7) and climates (mesic, xeric, and hydric). To determine decomposition rates, we deployed replicate cotton strips (inside stainless-steel tea infusers to avoid invertebrate interference) at the interface of the water column and riverbed sediment at 48 streams and over 28 days. Cotton strips are composed of cellulose, a major component of terrestrial litter, and allow for a standardized assay to compare across sites and studies. The tensile strength of the cotton strips was measured and converted into mean decay per day (kD) for each site. Across the YRB, kD ranged from 0.003 to 0.206, which is similar to the range in rates observed from global studies (kD = 0.0013 to 0.2023) and indicates the YRB experiences heterogeneity in decomposition. We found greater decomposition in locations with higher fine-sediment respiration but with lower whole-river respiration, likely due to the contribution of invertebrates and autotrophs to whole-river respiration and are not captured in decomposition measurements. Decomposition rates were greater in larger streams (i.e., higher stream order), where carbon and nitrogen concentrations were elevated, temperatures were greater, and land use was dominated by agriculture. As we make more connections between decomposition and potential controls, we can better understand river ecosystems and predict how ecosystem metabolism varies depending on location and scale.