1. Simulation of climate change (summer drought) stimulated autotrophy in a stream draining a Welsh peatland. Biofilm autotrophic biomass (chlorophyll) increased by 145% and was correlated with an increased overall metabolic activity (r = 0.75, P<0.05). Bacterial population densities were not significantly affected.

2. The increased autotrophy was probably related to a decrease in the organic:inorganic ratio of nutrients released from the wetland to the stream.

3. Bacterial reserves of poly-β-hydroxyalkanoate (PHA) fell by 51%. Increased nitrate concentrations were inversely correlated with autotrophic diversity (r=−0.88, P < 0.001).

4. The increased autotrophic biomass represents an increased nutrient supply for the higher trophic levels which could promote higher productivity within the stream ecosystem as a whole.

5. The simulation also caused a cooler (11%, P<0.01) streamflow from the drought-impacted wetland, which could mitigate against any adverse temperature-dependent effects of future climatic change.