The root of the problem: Direct influence of riparian vegetation on estimation of stream ecosystem metabolic rates

Abstract

Abstract Abundant living roots can be found in some streams and other shallow marine and freshwater habitats. A reach of a small Brazilian forested stream had 28% cover by live roots and exhibited diurnal trends in dissolved oxygen that could be attributed to gross primary production, but we hypothesized that activity of riparian tree roots in the channel caused this pattern. During sunny periods, trees transpire deoxygenated water from roots to the canopy but not in the dark, resulting in diurnal cycles of dissolved oxygen. Whole‐stream shading experiments showed that photosynthesis in the stream is not responsible for the pattern. Sealed chamber measurements showed living roots of riparian vegetation had substantial respiratory activity and ammonium and nitrate uptake, and rates per unit area were greater than sand and less than silt (the other two dominant substrata), indicating roots can substantially alter in‐stream biogeochemistry.