Thermal regime alterations caused by dams

Thermal changes in streams/rivers have a wide effect on different trophic levels which may shift the type of macroinvertebrates that prosper in the environment, fish species richness, and brook trout populations (Lessard and Hayes 2003). Increased temperatures will negatively affect brook trout metabolism and cause stress responses that affect their growth rate and reproduction (Lessard and Hayes 2003; Chadwick 2012).

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A Massachusetts study has shown the installation of small dams has led to an increased thermal effect on downstream ecosystems. However, its significance depends on the width of the sediment impoundment, upstream reach length, and upstream temperature (Zaidel et al., 2021). Within Massachusetts, thermal regime changes affected 67% of the dams studied (Zaidel et al. 2021). During the warmer months, these thermal effects can affect ecosystems 2-3 km downstream (Lessard and Hayes 2003).

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In New England, we predict dams to impact the magnitude, duration, rate, frequency, and timing of annual stream temperatures. Preliminary data from one dam study shows that the mean annual temperature downstream of dams is significantly higher in dammed rivers versus reference rivers (Hare and Moore, unpublished). The number of warm events during the year was also higher in dammed rivers. Many aquatic ecosystems use temperature as an indicator for many life events such as spawning and reproduction. The increase in annual temperature downstream of dams may disrupt the receiving aquatic community.