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Tropical streams are one of the most endangered ecosystems in the world
due to the constant pressures from human activities. Among these
activities, agriculture represents a land use that is crucial for human
development but also a key driver of stream degradation and biodiversity
decline in the tropics. Against this background, we investigated indirect
effects of agriculture (alterations in stream flow and nutrient
availability) and climate characteristics (water temperature) on benthic
biofilm communities in tropical streams (São Paulo State, Brazil). Three
first-order streams draining catchments dominated by agricultural land use
(sugarcane for bioenergy production, pasture) with some remaining riparian
forest were studied for one year. We focused on the relationships of
benthic biofilm biomass, algal biomass, diatom community and functional
structure with streamflow dynamics, nitrate concentrations and water
temperature. Our results indicate that these biological responses were
mainly mediated by flow and water temperature and not by resource
availability in the studied headwater streams. This result could be
explained by the heavy rains and elevated runoff generation in these
tropical catchments under agricultural influence, which might override the
known effects of nutrient enrichment on benthic biofilm communities.
Considering forecast climate and land-use changes in tropical streams, our
findings may suggest potential shifts in benthic biofilm communities, with
functional consequences for aquatic food webs in these environments.
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