Influence of small dams on the stream temperature in a protected area of southern Quebec.

Small dams represent 99% of the world's water impoundments, but little is known about their effect on river temperature. As stream temperature is an important variable in maintaining the aquatic ecosystems integrity, the study of the effect of small dams is necessary. This study purpose to understand the small dams effet on summer stream temperature in a protected area with low disturbance in southern Quebec, Canada. We compared four attributes of the thermal regime (magnitude, frequency and duration of warm events and rate of change) in streams i) upstream and downstream reservoir regulated by a small dam and ii) downstream reservoirs and natural lakes. with a generalized additive model, we also identified key determinants of August stream temperature. Compared to upstream reservoir conditions, we observed a 3.7°C warming in streams downstream of reservoirs regulated by small dams during August 2020. This warming wasn’t significantly different from that observed between upstream and downstream of natural lakes (3.4 °C). Proximity to an upstream waterbody, drainage area, and proportion of the watershed occupied by waterbodies were the principal determinants of water temperature in August, demonstrating the waterbodies importance on the thermal regime of streams.