Drivers of metabolism and decomposition in forested Lake Superior tributary streams

Document Type

Article

Publication Date

1-1-2025

Abstract

Ecosystem respiration (ER) and decomposition are fundamental carbon cycling processes in streams. Decomposition and ER may be controlled by similar environmental factors, as decomposition is carried out by heterotrophic bacteria, fungi, and macroinvertebrates, whose metabolic activity is a major contributor to ER. However, ER also includes respiration by autotrophs, and their respiration will be affected by factors that influence gross primary production (GPP). We quantified decomposition, GPP, and ER and estimated autotrophic respiration (AR) and heterotrophic respiration (HR) at eight sites in four forested streams in the Upper Peninsula of Michigan. These streams spanned gradients of canopy cover and dissolved organic carbon (DOC) concentrations, which we predicted would differentially affect activity due to changes in light and carbon availability. We also explored relationships between ER, AR, HR, and decomposition with other environmental drivers like temperature and nutrient availability. ER was related to TP concentrations but not DOC or canopy cover, and AR and HR were not related to any environmental drivers. Decomposition was related to canopy cover and dissolved nutrient concentrations, but not DOC. While our results did not demonstrate direct relationships between canopy cover or DOC concentration and respiration rates, we did find a wide variation in the fraction of respiration carried out by autotrophs relative to other studies, and that decomposition rates were comparable across study sites despite differences in GPP and ER. Together, these results suggest a need to improve methods and estimates of AR and HR in forested streams to integrate these important aquatic ecosystems into global climate models.

Publication Title

Hydrobiologia

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