Autochthonous primary production in southern Amazon headwater streams: Novel indicators of altered environmental integrity

Abstract

The riparian forest reduces the amount of light entering streams, which limits autochthonous primary production. The aim of this study was to evaluate temporal variation of autochthonous primary production in pristine and altered streams, with the goal of identifying indicators of change in environmental integrity in the southern Brazilian Amazon. We evaluated free algal biomass in the water column, the presence of periphyton, and the richness and cover of aquatic herbaceous plants in 20 streams (10 pristine and 10 altered, i.e., with riparian deforestation) during the dry period, at the beginning of the rainy period, and at the end of the rainy period. In altered streams, we recorded the presence of macroscopic periphyton and the amount of algal biomass varied between the dry and flood seasons. Variations in hydrological periods did not contribute to changes in algal biomass in pristine streams; we did not observe the presence of macroscopic periphyton these streams. In altered streams, 23 aquatic herbaceous species were identified, versus only four in the pristine streams. Results showed that riparian deforestation contributes to increased autochthonous primary production, which is also influenced by different hydrological periods, with algae and aquatic herbaceous plants responding differently to dry and rainy periods. The responses of these primary producers confirm their role as important bioindicators of change in the environmental integrity of southern Amazonian streams.