Warming up a stream reach: design of a hydraulic and heating system

Changes in land use, thermal pollution, and global warming are affecting the thermal regimes of streams. Laboratory experiments and field correlative studies suggest that important impacts on streams ecological integrity may occur from increases in temperature. However, there is a lack of ecosystem-level manipulative approaches in small detritus-based streams, hotspots of diversity on the fluvial net. Here we describe a hydraulic setup associated with a heating system to simulate an increase in whole-stream water temperature. A second-order stream reach (similar to 22 m long; similar to 1 m width) was divided longitudinally in half. A water temperature increase of 3.24 degrees C (+/- 0.81 degrees C SD) was implemented and operated with a continuous electricity supply. The system was composed of two tanks that received water by gravity, from the stream. One tank was equipped with resistors. One half of the stream reach received the water from the heating tank (mean flow: 2.13 +/- 0.50 SD L/s) whereas the other half received water from the unheated tank (mean flow: 2.17 +/- 0.54 SD L/s). Flow was controlled with valves and weirs. The system allowed natural daily and seasonal patterns of variation in abiotic factors (with 2 levels of temperature). This system was successfully used to evaluate the effects of warming on stream structure and functioning at several levels of biological resolution. This system allows easy replication, can be used in a variety of streams, and is easily adjusted to various combinations of flow and temperature. Regular cleaning and technical monitoring is nevertheless needed to keep the system operating.